Experimental demonstration of the benefits of somatic fusion and the consequences for allorecognition
Bastiaans, E. ; Debets, A.J.M. ; Aanen, D.K. - \ 2015
Evolution 69 (2015)4. - ISSN 0014-3820 - p. 1091 - 1099.
vegetative incompatibility - neurospora-crassa - heterokaryon incompatibility - natural-populations - filamentous fungi - recognition - evolution - selection - genetics - cooperation
Allorecognition, the ability to distinguish “self” from “nonself” based on allelic differences at allorecognition loci, is common in all domains of life. Allorecognition restricts the opportunities for social parasitism, and is therefore crucial for the evolution of cooperation. However, the maintenance of allorecognition diversity provides a paradox. If allorecognition is costly relative to cooperation, common alleles will be favored. Thus, the cost of allorecognition may reduce the genetic variation upon which allorecognition crucially relies, a prediction now known as “Crozier's paradox.” We establish the relative costs of allorecognition, and their consequences for the short-term evolution of recognition labels theoretically predicted by Crozier. We use fusion among colonies of the fungus Neurospora crassa, regulated by highly variable allorecognition genes, as an experimental model system. We demonstrate that fusion among colonies is mutually beneficial, relative to absence of fusion upon allorecognition. This benefit is due not only to absence of mutual antagonism, which occurs upon allorecognition, but also to an increase in colony size per se. We then experimentally demonstrate that the benefit of fusion selects against allorecognition diversity, as predicted by Crozier. We discuss what maintains allorecognition diversity
Heritable Environmental Variance Causes Nonlinear Relationships Between Traits: Application to Birth Weight and Stillbirth of Pigs
Mulder, H.A. ; Hill, W.G. ; Knol, E.F. - \ 2015
Genetics 199 (2015)4. - ISSN 0016-6731 - p. 1255 - 1269.
generalized linear-models - phenotypic variability - genetic-heterogeneity - residual variance - natural-populations - breeding values - litter size - body-size - selection - uniformity
There is recent evidence from laboratory experiments and analysis of livestock populations that not only the phenotype itself, but also its environmental variance, is under genetic control. Little is known about the relationships between the environmental variance of one trait and mean levels of other traits, however. A genetic covariance between these is expected to lead to nonlinearity between them, for example between birth weight and survival of piglets, where animals of extreme weights have lower survival. The objectives were to derive this nonlinear relationship analytically using multiple regression and apply it to data on piglet birth weight and survival. This study provides a framework to study such nonlinear relationships caused by genetic covariance of environmental variance of one trait and the mean of the other. It is shown that positions of phenotypic and genetic optima may differ and that genetic relationships are likely to be more curvilinear than phenotypic relationships, dependent mainly on the environmental correlation between these traits. Genetic correlations may change if the population means change relative to the optimal phenotypes. Data of piglet birth weight and survival show that the presence of nonlinearity can be partly explained by the genetic covariance between environmental variance of birth weight and survival. The framework developed can be used to assess effects of artificial and natural selection on means and variances of traits and the statistical method presented can be used to estimate trade-offs between environmental variance of one trait and mean levels of others.
Sex-biased inbreeding effects on reproductive success and home range size of the critically endangered black rhinoceros
Cain, W.S. ; Wandera, A.B. ; Shawcross, S.G. ; Ouma, B.O. ; Watts, P.C. - \ 2014
Conservation Biology 28 (2014)2. - ISSN 0888-8892 - p. 594 - 603.
heterozygosity-fitness correlations - wide genetic diversity - natural-populations - diceros-bicornis - multilocus heterozygosity - microsatellite markers - wild populations - south-africa - depression - reserve
A central premise of conservation biology is that small populations suffer reduced viability through loss of genetic diversity and inbreeding. However, there is little evidence that variation in inbreeding impacts individual reproductive success within remnant populations of threatened taxa, largely due to problems associated with obtaining comprehensive pedigree information to estimate inbreeding. In the critically endangered black rhinoceros, a species that experienced severe demographic reductions, we used model selection to identify factors associated with variation in reproductive success (number of offspring). Factors examined as predictors of reproductive success were age, home range size, number of nearby mates, reserve location, and multilocus heterozygosity (a proxy for inbreeding). Multilocus heterozygosity predicted male reproductive success (p<0.001, explained deviance >58%) and correlated with male home range size (p <0.01, r2 > 44%). Such effects were not apparent in females, where reproductive success was determined by age (p <0.01, explained deviance 34%) as females raise calves alone and choose between, rather than compete for, mates. This first report of a 3-way association between an individual male's heterozygosity, reproductive output, and territory size in a large vertebrate is consistent with an asymmetry in the level of intrasexual competition and highlights the relevance of sex-biased inbreeding for the management of many conservation-priority species. Our results contrast with the idea that wild populations of threatened taxa may possess some inherent difference from most nonthreatened populations that necessitates the use of detailed pedigrees to study inbreeding effects. Despite substantial variance in male reproductive success, the increased fitness of more heterozygous males limits the loss of heterozygosity. Understanding how individual differences in genetic diversity mediate the outcome of intrasexual competition will be essential for effective management, particularly in enclosed populations, where individuals have restricted choice about home range location and where the reproductive impact of translocated animals will depend upon the background distribution in individual heterozygosity. © 2013 Society for Conservation Biology.
Epigenetic variation in asexually reproducing organisms
Verhoeven, K.J.F. ; Preite, V. - \ 2014
Evolution 68 (2014)3. - ISSN 0014-3820 - p. 644 - 655.
dna methylation - arabidopsis-thaliana - japanese knotweed - transgenerational plasticity - phenotypic plasticity - transposable elements - natural-populations - fallopia-japonica - mutation-rates - clonal plants
The role that epigenetic inheritance can play in adaptation may differ between sexuals and asexuals because (1) the dynamics of adaptation differ under sexual and asexual reproduction and the opportunities offered by epigenetic inheritance may affect these dynamics differently; and (2) in asexual reproduction epigenetic reprogramming mechanisms that are associated with meiosis can be bypassed, which could promote the buildup of epigenetic variation in asexuals. Here, we evaluate current evidence for an epigenetic contribution to adaptation in asexuals. We argue that two aspects of epigenetic variation should have particular relevance for asexuals, namely epigenetics-mediated phenotypic plasticity within and between generations, and heritable variation via stochastic epimutations. An evaluation of epigenetic reprogramming mechanisms suggests that some, but not all, forms of asexual reproduction enhance the likelihood of stable transmission of epigenetic marks across generations compared to sexual reproduction. However, direct tests of these predicted sexual–asexual differences are virtually lacking. Stable transmission of DNA methylation, transcriptomes, and phenotypes from parent to clonal offspring are demonstrated in various asexual species, and clonal genotypes from natural populations show habitat-specific DNA methylation. We discuss how these initial observations can be extended to demonstrate an epigenetic contribution to adaptation.
Development of a Nasonia vitripennis outbred laboratory population for genetic analysis
Zande, L. van de; Ferber, S. ; Haan, A. de; Beukeboom, L.W. ; Heerwaarden, J. van; Pannebakker, B.A. - \ 2014
Molecular Ecology Resources 14 (2014)3. - ISSN 1755-098X - p. 578 - 587.
parasitoid wasp nasonia - local mate competition - sex-ratio - drosophila-melanogaster - natural-populations - ectoparasitic wasp - hymenoptera - genome - evolution - recombination
The parasitoid wasp genus Nasonia has rapidly become a genetic model system for developmental and evolutionary biology. The release of its genome sequence led to the development of high-resolution genomic tools, for both interspecific and intraspecific research, which has resulted in great advances in understanding Nasonia biology. To further advance the utility of Nasonia vitripennis as a genetic model system and to be able to fully exploit the advantages of its fully sequenced and annotated genome, we developed a genetically variable and well-characterized experimental population. In this study, we describe the establishment of the genetically diverse HVRx laboratory population from strains collected from the field in the Netherlands. We established a maintenance method that retains genetic variation over generations of culturing in the laboratory. As a characterization of its genetic composition, we provide data on the standing genetic variation and estimate the effective population size (Ne ) by microsatellite analysis. A genome-wide description of polymorphism is provided through pooled resequencing, which yielded 417 331 high-quality SNPs spanning all five Nasonia chromosomes. The HVRx population and its characterization are freely available as a community resource for investigators seeking to elucidate the genetic basis of complex trait variation using the Nasonia model system
A comparison of microsatellites and SNPs in parental assignment in the GIFT strain of Nile tilapia (Oreochromis niloticus): The power of exclusion
Trong, T.Q. ; Bers, N.E.M. van; Crooijmans, R.P.M.A. ; Dibbits, B.W. ; Komen, J. - \ 2013
Aquaculture 388-391 (2013). - ISSN 0044-8486 - p. 14 - 23.
genotyping errors - computer-program - empirical-evaluation - natural-populations - markers - wild - inference - paternity - sibship - salmon
In this study, parental assignment was studied in the 10th generation of a pedigreed selected Nile tilapia (Oreochromis niloticus) population (GIFT) and their offspring, by comparing two types of molecular markers, microsatellites and SNPs, using an exclusion-based (Vitassign) and a likelihood-based (Cervus) method. For the experiment, G10 parents were divided in 4 groups (cohorts) and allowed to produce offspring by natural group mating. In total 173 offspring were tested against 238 parents, using either 12 microsatellites (PIC = 0.639; exclusion power 68.0%) or 122 SNPs (PIC = 0.341; exclusion power 99.9%). In this study, more than half of the candidate parents were either full- or half-sibs with other parents. Furthermore, 13.8% of the parents died before being sampled for DNA. When offspring were assigned to parents in the same cohort, using Vitassign, for microsatellites, allowing up to 2 mismatches, 37.6% offspring got unique assignments, 45.1% got multiple assignments, and 17.3% were not assigned; for SNPs with up to 15 mismatches allowed, 83.8% offspring got unique assignments while 13.9% got multiple assignments. Only 2.3% were not assigned. Using Cervus, for microsatellites, the mean ‘strict’ (> 95% CF) assignment rate across the 4 cohorts was 18%, the ‘relax’ (80–95% CF) assignment rate was 43%, and 39% were not assigned; for SNPs, 39% ‘strict’ assignments were obtained (mean across 4 cohorts); the remaining offspring were not assigned. In general assignment rates were higher when cohort offspring were assigned to all parents combined, irrespective of method (Vitassign or Cervus) or marker used. However, consistency of assignments between microsatellites and SNPs was low: 28% with Vitassign and 16% with Cervus. Consistency of assignments between Cervus and Vitassign was high with SNPs (65%), but was low with microsatellites (31%). We conclude that missing parents and relatedness among candidate parents resulted in low assignment rates. Furthermore, low exclusion power of the microsatellite set resulted in low assignment rates and multiple parent pair assignments irrespective of method used. Exclusion methods and likelihood-based methods can be equally good for parental assignments, providing that good marker sets with high exclusion power are available.
Within-population genetic structure in beech (Fagus sylvatica L.) stands characterized by different disturbance histories: does forest management simplify population substructure?
Piotti, A. ; Leonardi, S. ; Heuertz, M. ; Buiteveld, J. ; Geburek, T. ; Gerber, S. ; Kramer, K. ; Vettori, C. ; Vendramin, G.G. - \ 2013
PLoS ONE 8 (2013)9. - ISSN 1932-6203 - 9 p.
european beech - populus-trichocarpa - natural-populations - plant-populations - pollen dispersal - estimating seed - f-statistics - null alleles - douglas-fir - white-pine
The fine-scale assessment of both spatially and non-spatially distributed genetic variation is crucial to preserve forest genetic resources through appropriate forest management. Cryptic within-population genetic structure may be more common than previously thought in forest tree populations, which has strong implications for the potential of forests to adapt to environmental change. The present study was aimed at comparing within-population genetic structure in European beech (Fagus sylvatica L.) plots experiencing different disturbance levels. Five plot pairs made up by disturbed and undisturbed plots having the same biogeographic history were sampled throughout Europe. Overall, 1298 individuals were analyzed using four highly polymorphic nuclear microsatellite markers (SSRs). Bayesian clustering within plots identified 3 to 11 genetic clusters (within-plot hST ranged from 0.025 to 0.124). The proportion of within-population genetic variation due to genetic substructuring (FCluPlot = 0.067) was higher than the differentiation among the 10 plots (FPlotTot = 0.045). Focusing on the comparison between managed and unmanaged plots, disturbance mostly explains differences in the complexity of within-population genetic structure, determining a reduction of the number of genetic clusters present in a standardized area. Our results show that: i) genetic substructuring needs to be investigated when studying the within-population genetic structure in forest tree populations, and ii) indices describing subtle characteristics of the within-population genetic structure are good candidates for providing early signals of the consequences of forest management, and of disturbance events in general.
A genetic linkage map for the South African angora goat
Visser, C. ; Crooijmans, R.P.M.A. ; Marle Koster, E. Van - \ 2010
Small Ruminant Research 93 (2010)2-3. - ISSN 0921-4488 - p. 171 - 179.
natural-populations - sheep - genome - animals - breeds - locus
Despite their economical importance, relatively few molecular studies have been made on goats compared to other livestock species. The most recent goat map was published in 1998, and lacks complete genome coverage. A large number of discrepancies and especially inter-chromosomal re-assignments were reported between the 1998 goat linkage map and the sheep map. In this study 94 microsatellite markers were amplified in 12 half-sib South African Angora goat families for compilation of a genetic map, aiming to confirm or reject previously reported rearrangements and to improve the alignment between the ovine and caprine maps. The number of informative meiosis per marker ranged from 69 to 836, with an average of 518. The microsatellites were mapped to 23 chromosomes, spanning 1352 cM and resulting in an average marker interval of 23.0 cM. Marker orders were compared to the previously published goat maps, as well as to the ovine map. Six chromosomes (CHI 2, 4, 5, 11, 13 and 19) showed rearrangements in marker order compared to the 1998 Schibler et al. goat map, while nine previously unmapped markers were conclusively assigned to eight chromosomes. Four of the previously reported intra-chromosomal rearrangements between the goat and sheep maps were confirmed to be either population specific or mapping errors. The verification of rearrangements in loci order will lead to improved alignment between the two maps, as well as improved efficiency of genome and fine mapping efforts in goats
Genome-wide SNP detection in the great tit Parus major using high throughput sequencing
Bers, N.E.M. van; Oers, K. van; Dibbits, B.W. ; Groenen, M.A.M. ; Crooijmans, R.P.M.A. - \ 2010
Molecular Ecology 19 (2010)Suppl. s1. - ISSN 0962-1083 - p. 89 - 99.
wild bird population - natural-populations - climate-change - linkage map - phenotypic plasticity - future-directions - genotyping assay - passerine bird - dna-sequences - evolution
Identifying genes that underlie ecological traits will open exiting possibilities to study gene–environment interactions in shaping phenotypes and in measuring natural selection on genes. Evolutionary ecology has been pursuing these objectives for decades, but they come into reach now that next generation sequencing technologies have dramatically lowered the costs to obtain the genomic sequence information that is currently lacking for most ecologically important species. Here we describe how we generated over 2 billion basepairs of novel sequence information for an ecological model species, the great tit Parus major. We used over 16 million short sequence reads for the de novo assembly of a reference sequence consisting of 550 000 contigs, covering 2.5% of the genome of the great tit. This reference sequence was used as the scaffold for mapping of the sequence reads, which allowed for the detection of over 20 000 novel single nucleotide polymorphisms. Contigs harbouring 4272 of the single nucleotide polymorphisms could be mapped to a unique location on the recently sequenced zebra finch genome. Of all the great tit contigs, significantly more were mapped to the microchromosomes than to the intermediate and the macrochromosomes of the zebra finch, indicating a higher overall level of sequence conservation on the microchromosomes than on the other types of chromosomes. The large number of great tit contigs that can be aligned to the zebra finch genome shows that this genome provides a valuable framework for large scale genetics, e.g. QTL mapping or whole genome association studies, in passerines.
Rainfall-driven sex-ratio genes in African buffalo suggested by correlations between Y-chromosomal haplotype frequencies and foetal sex ratio
Hooft, W.F. van; Prins, H.H.T. ; Getz, W.M. ; Jolles, A.E. ; Wieren, S.E. van; Greyling, B.J. ; Helden, P.D. ; Bastos, A.D.S. - \ 2010
BMC Evolutionary Biology 10 (2010). - ISSN 1471-2148 - 11 p.
cattle bos-taurus - syncerus-caffer - male-fertility - meiotic drive - bovine tuberculosis - drosophila-melanogaster - microsatellite analysis - natural-populations - sperm - selection
Background - The Y-chromosomal diversity in the African buffalo (Syncerus caffer) population of Kruger National Park (KNP) is characterized by rainfall-driven haplotype frequency shifts between year cohorts. Stable Y-chromosomal polymorphism is difficult to reconcile with haplotype frequency variations without assuming frequency-dependent selection or specific interactions in the population dynamics of X- and Y-chromosomal genes, since otherwise the fittest haplotype would inevitably sweep to fixation. Stable Y-chromosomal polymorphism due one of these factors only seems possible when there are Y-chromosomal distorters of an equal sex ratio, which act by negatively affecting X-gametes, or Y-chromosomal suppressors of a female-biased sex ratio. These sex-ratio (SR) genes modify (suppress) gamete transmission in their own favour at a fitness cost, allowing for stable polymorphism. Results - Here we show temporal correlations between Y-chromosomal haplotype frequencies and foetal sex ratios in the KNP buffalo population, suggesting SR genes. Frequencies varied by a factor of five; too high to be alternatively explained by Y-chromosomal effects on pregnancy loss. Sex ratios were male-biased during wet and female-biased during dry periods (male proportion: 0.47-0.53), seasonally and annually. Both wet and dry periods were associated with a specific haplotype indicating a SR distorter and SR suppressor, respectively. Conclusions - The distinctive properties suggested for explaining Y-chromosomal polymorphism in African buffalo may not be restricted to this species alone. SR genes may play a broader and largely overlooked role in mammalian sex-ratio variation
The reintroduction of the Eurasian otter (Lutra lutra) into the Netherlands: hidden life revealed by noninvasive genetic monitoring
Koelewijn, H.P. ; Pérez-Haro, M. ; Jansman, H.A.H. ; Boerwinkel, M.C. ; Bovenschen, J. ; Lammertsma, D.R. ; Niewold, F.J.J. ; Kuiters, A.T. - \ 2010
Conservation Genetics 11 (2010)2. - ISSN 1566-0621 - p. 601 - 614.
natural-populations - individual identification - conservation genetics - spatial-organization - microsatellite loci - genotyping feces - eastern germany - dna - size - biology
The last recorded presence of the Eurasian otter (Lutra lutra) in the Netherlands dates from 1989 and concerned a dead individual. In 2002 a reintroduction programme was started, and between June 2002 and April 2008 a total of 30 individuals (10 males and 20 females) were released into a lowland peat marsh in the north of the Netherlands. Noninvasive genetic monitoring based on the genetic profiles obtained from DNA extracted from otter faeces (spraints) was chosen for the post-release monitoring of the population. To this end, the founding individuals were genotyped before release and spraints were collected in the release area each winter from 2002 to 2008. From June 2002 to April 2008 we analysed the genetic profile of 1,265 spraints on the basis of 7–15 microsatellite loci, 582 of which (46%) were successfully assigned to either released or newly identified genotypes. We identified 54 offspring (23 females and 31 males): the females started to reproduce after 2 years and the males after 4 years. The mating and reproductive success among males was strongly skewed, with a few dominant males fathering two-thirds of the offspring, but the females had a more even distribution. The effective population size (Ne) was only about 30% of the observed density (N), mainly because of the large variance in reproductive success among males. Most juvenile males dispersed to surrounding areas on maturity, whereas juvenile females stayed inside the area next to the mother’s territory. The main cause of mortality was traffic accidents. Males had a higher mortality rate (22 out of 41 males (54%) vs. 9 out of 43 females (21%)). During winter 2007/08 we identified 47 individuals, 41 of which originated from mating within the release area. This study demonstrates that noninvasive molecular methods can be used efficiently in post-release monitoring studies of elusive species to reveal a comprehensive picture of the state of the population
Phylogenetic and biological species diversity within the Neurospora tetrasperma complex
Menkis, A. ; Bastiaans, E. ; Jacobson, D.J. ; Johannesson, H. - \ 2009
Journal of Evolutionary Biology 22 (2009)9. - ISSN 1010-061X - p. 1923 - 1936.
mating-type chromosome - het-c locus - natural-populations - sexual dysfunction - model eukaryote - fungi - recognition - evolution - strains - heterothallism
The objective of this study was to explore the evolutionary history of the morphologically recognized filamentous ascomycete Neurospora tetrasperma, and to reveal the genetic and reproductive relationships among its individuals and populations. We applied both phylogenetic and biological species recognition to a collection of strains representing the geographic and genetic diversity of N. tetrasperma. First, we were able to confirm a monophyletic origin of N. tetrasperma. Furthermore, we found nine phylogenetic species within the morphospecies. When using the traditional broad biological species recognition all investigated strains of N. tetrasperma constituted a single biological species. In contrast, when using a quantitative measurement of the reproductive success, incorporating characters such as viability and fertility of offspring, we found a high congruence between the phylogenetic and biological species recognition. Taken together, phylogenetically and biologically defined groups of individuals exist in N. tetrasperma, and these should be taken into account in future studies of its life history traits.
The effect of sheltered load on reproduction in Solanum carolinense, a species with variable self-incompatibility
Mena-Ali, J.I. ; Keser, L.H. ; Stephenson, A.G. - \ 2009
Sexual Plant Reproduction 22 (2009)2. - ISSN 0934-0882 - p. 63 - 71.
pollen-tube growth - inbreeding depression - flowering plants - natural-populations - nicotiana-alata - s-alleles - evolution - solanaceae - model - fertilization
In previous studies, we have investigated the strength of self-incompatibility (SI) in Solanum carolinense, a highly successful weed with a fully functional SI system that inhabits early successional and other disturbed habitats. We have found that the SI response in S. carolinense is a plastic trait—its strength being affected by the age of the flowers, and the presence of developing fruits and that there are genetic differences among families in their self-fertility. However, in species with a fully functional SI response, selfing would not be that common. As a result, deleterious recessives scattered though the genome of horsenettle are only occasionally exposed to selection. It has been suggested that deleterious recessives accumulate near S-alleles in strong SI species because the S-locus is located in a non-recombining region of the genome and because strong S-alleles are never in the homozygous state, thus sheltering some of the genetic load near the S-locus from selection. We performed a series of laboratory and greenhouse experiments to determine the extent to which sheltered load adds to the overall magnitude of inbreeding depression in horsenettle. Specifically, we amplified and sequenced the S-alleles from 16 genets collected from a large population in Pennsylvania and performed a series of controlled self-pollinations. We then grew the selfed progeny in the greenhouse; recorded various measures of growth and reproductive output; and amplified and sequenced their S-allele(s). We found that the heterozygous progeny of self-pollinations produce more flowers and have a greater ability to set both self and cross seed than S-homozygous progeny. We also found evidence of variation in the magnitude of load among S-alleles. These results suggest that sheltered load might slow the fixation of weak (partially compatible) S-alleles in this population, thus adding to the maintenance of a mixed mating system rather than leading to the fixation of the selfing alleles
Comparison of marker-based pairwise relatedness estimators on a pedigreed plant population.
Bink, M.C.A.M. ; Anderson, A.D. ; Weg, W.E. van de; Thompson, E.A. - \ 2008
Theoretical and Applied Genetics 117 (2008)6. - ISSN 0040-5752 - p. 843 - 855.
maximum-likelihood - molecular markers - natural-populations - heritability - coefficients - individuals - information
Several estimators have been proposed that use molecular marker data to infer the degree of relatedness for pairs of individuals. The objective of this study was to evaluate the performance of seven estimators when applied to marker data of a set of 33 key individuals from a large complex apple pedigree. The evaluation considered different scenarios of allele frequencies and different numbers of marker loci. The method of moments estimators were Similarity, Queller-Goodknight, Lynch-Ritland and Wang. The maximum likelihood estimators were Thompson, Anderson-Weir and Jacquard. The pedigree-based coancestry coefficients were taken as the point of reference in calculating correlations and root mean square error (RMSE). The marker data comprised 86 multi-allelic SSR markers on 17 linkage groups, covering 11 Morgans. Additionally, we simulated 10 datasets conditional on the real pedigree to support the results on the real dataset. None of the estimators outperformed the others. Knowledge of allele frequencies appeared to be the most influential, i.e., the highest correlations and lowest RMSE were found when frequencies from the founder population were available. When equal allele frequencies were used, all estimators resulted in very similar, but on average lower, correlations. The use of allele frequencies estimated from the set of 33 individuals gave, on average, the poorest results. The maximum likelihood estimators and the Lynch-Ritland estimator were the most sensitive to allele frequencies. The results from the simulation study fully supported the trends in results of the real dataset. This study indicated that high correlations (up to 0.90) and small RMSE (below 0.03), may be obtained when population allelic frequencies are available. In this scenario, the performances of the various estimators were similar, but seemed to favor the maximum likelihood estimators. In the absence of reliable allele frequencies the method of moments estimators were shown to be more robust. The number of marker loci influenced the average performance of the estimators; however, the ranking was not affected. Correlations up to 0.80 were obtained when two markers per chromosome and appropriate allele frequencies were available. Adding more markers to the current dataset may lead to marginal improvements.
The Contribution of Social Effects to Heritable Variation in Finishing Traits of Domestic Pigs (Sus scrofa)
Bergsma, R. ; Kanis, E. ; Knol, E.F. - \ 2008
Genetics 178 (2008)3. - ISSN 0016-6731 - p. 1559 - 1570.
multiple-hen cages - group selection - kin selection - genetic-parameters - multilevel selection - natural-populations - variance-components - molecular markers - biological groups - model
Social interactions among individuals are ubiquitous both in animals and in plants, and in natural as well as domestic populations. These interactions affect both the direction and the magnitude of responses to selection and are a key factor in evolutionary success of species and in the design of breeding schemes in agriculture. At present, however, very little is known of the contribution of social effects to heritable variance in trait values. Here we present estimates of the direct and social genetic variance in growth rate, feed intake, back fat thickness, and muscle depth in a population of 14,032 domestic pigs with known pedigree. Results show that social effects contribute the vast majority of heritable variance in growth rate and feed intake in this population. Total heritable variance expressed relative to phenotypic variance was 71% for growth rate and 70% for feed intake. These values clearly exceed the usual range of heritability for those traits. Back fat thickness and muscle depth showed no heritable variance due to social effects. Our results suggest that genetic improvement in agriculture can be substantially advanced by redirecting breeding schemes, so as to capture heritable variance due to social effects.
Bridging the gap between ecophysiological and genetic knowledge to assess the adaptive potential of European beech
Kramer, K. ; Buiteveld, J. ; Forstreuter, M. ; Geburek, T. ; Leonardi, S. ; Menozzi, P. ; Povillon, F. ; Schelhaas, M.J. ; Teissier du Cros, E. ; Vendramin, G.G. ; Werf, D.C. van der - \ 2008
Ecological Modelling 216 (2008)3-4. - ISSN 0304-3800 - p. 333 - 353.
fagus-sylvatica l. - mating system parameters - natural-populations - shade tolerance - climate-change - postglacial recolonization - species distribution - british beechwoods - field-measurements - ecological theory
In this study we aimed to combine knowledge of the ecophysiology and genetics of European beech to assess the potential of this species to adapt to environmental change. Therefore, we performed field and experimental studies on the genetic and ecophysiological functioning of beech. This information was integrated through a coupled genetic¿ecophysiological model for individual trees that was parameterized with information derived from our own studies or from the literature. Using the model, we evaluated the adaptive response of beech stands in two ways: firstly, through sensitivity analyses (of initial genetic diversity, pollen dispersal distance, heritability of selected phenotypic traits, and forest management, representing disturbances) and secondly, through the evaluation of the responses of phenotypic traits and their genetic diversity to four management regimes applied to 10 study plots distributed over Western Europe. The model results indicate that the interval between recruitment events strongly affects the rate of adaptive response, because selection is most severe during the early stages of forest development. Forest management regimes largely determine recruitment intervals and thereby the potential for adaptive responses. Forest management regimes also determine the number of mother trees that contribute to the next generation and thereby the genetic variation that is maintained. Consequently, undisturbed forests maintain the largest amount of genetic variation, as recruitment intervals approach the longevity of trees and many mother trees contribute to the next generation. However, undisturbed forests have the slowest adaptive response, for the same reasons. Gene flow through pollen dispersal may compensate for the loss in genetic diversity brought about by selection. The sensitivity analysis showed that the total genetic diversity of a 2 ha stand is not affected by gene flow if the pollen distance distribution is varied from highly left-skewed to almost flat. However, a stand with a prevailing short-distance gene flow has a more pronounced spatial genetic structure than stands with equal short- and long-distance gene flows. The build-up of a spatial genetic structure is also strongly determined by the recruitment interval. Overall, the modelling results indicate that European beech has high adaptive potential to environmental change if recruitment intervals are short and many mother trees contribute to the next generation. The findings have two implications for modelling studies on the impacts of climate change on forests. Firstly: it cannot be taken for granted that parameter values remain constant over a time horizon of even a few generations ¿ this is particularly important for threshold values subject to strong selection, like budburst, frost hardiness, drought tolerance, as used in species area models. Secondly: forest management should be taken into account in future assessments, as management affects the rate of adaptive response and thereby the response on trees and forests to environmental change, and because few forests are unmanaged. We conclude that a coupled ecophysiological and quantitative genetic tree model is a useful tool for such studies
Genetic diversity of maize (Zea mays L. ssp. mays) in communities of the western highlands of Guatemala: geographical patterns and processes.
Etten, J. van; Fuentes, M.R. ; Molina, L.G. ; Ponciano, K.M. - \ 2008
Genetic Resources and Crop Evolution 55 (2008)2. - ISSN 0925-9864 - p. 303 - 317.
natural-populations - similarity - markers - mexico - flow
This study concerns spatial genetic patterning, seed flow and the impact of modern varieties in maize populations in Chimaltenango, Guatemala. It uses a collection of 79 maize seed samples from farmers in the area and five samples derived from modern varieties. Bulked SSR markers employed with bulked samples (ten plants) were used. Genetic distances between populations based on these SSR data were used as a measure of co-ancestry. The study describes the genetic variation in space, assesses the association of maize diversity with spatial and environmental descriptors and quantitative traits, and provides a test of the impact of improved varieties. Maize diversity showed significant isolation-by-distance locally, but not regionally. This was interpreted as evidence for a difference between local and regional mechanisms of seed exchange; regional exchange is more related to innovation. There was also a significant association with altitude and ear/grain characteristics (related to racial classifications). Also, consistent evidence for the influence of modern varieties of maize was found, although its impact was limited spatially. It is argued that the spatial distributions of maize diversity are important to consider for germplasm collection, but should be seen as a recent outcome of dynamic processes.
Evolution and genetic population structure of prickly lettuce (Lactuca serriola) and its RGC2 resistance gene cluster
Kuang, H. ; Eck, H.J. van; Sicard, D. ; Michelmore, R. ; Nevo, E. - \ 2008
Genetics 178 (2008)3. - ISSN 0016-6731 - p. 1547 - 1558.
mildew bremia-lactucae - arabidopsis-thaliana - natural-populations - wild lactuca - cultivated lettuce - molecular evolution - statistical tests - encoding genes - major cluster - diversity
Genetic structure and diversity of natural populations of prickly lettuce (Lactuca serriola) were studied using AFLP markers and then compared with the diversity of the RGC2 disease resistance gene cluster. Screening of 696 accessions from 41 populations using 319 AFLP markers showed that eastern Turkish and Armenian populations were the most diverse populations and might be located in the origin and center of diversity of L. serriola. Screening 709 accessions using the microsatellite MSATE6 that is located in the coding region of most RGC2 homologs detected 366 different haplotypes. Again, the eastern Turkish and Armenian populations had the highest diversities at the RGC2 cluster. The diversities at the RGC2 cluster in different populations were significantly correlated with their genomewide diversities. There was significant variation of copy number of RGC2 homologs in different populations, ranging from 12 to 22 copies per genome. The nucleotide diversities of two conserved lineages (type II) of RGC2 genes (K and L) were not correlated with diversities calculated using the MSATE6 or AFLP data. We hypothesize that the high genomewide diversity and diversity of the RGC2 cluster in eastern Turkish and Armenian populations resulted from high abiotic and biotic stresses in the regions of origin of L. serriola.
Structure of the genetic diversity in Black poplar (Populus nigra L.) populations across European river systems: consequences for conservation and restoration
Smulders, M.J.M. ; Cottrell, J.E. ; Lefevre, F. ; Schoot, J. van der; Arens, P.F.P. ; Vosman, B. ; Tabbener, H.E. ; Grassi, F. ; Fossati, T. ; Castiglione, S. ; Krystufek, V. ; Fluch, S. ; Burg, K. ; Vornam, B. ; Pohl, A. ; Gebhardt, K. ; Alba, N. ; Agúndez, D. ; Maestro, C. ; Notivol, E. ; Volosyanchuck, R. ; Pospiskova, M. ; Bordacs, S. ; Bovenschen, J. ; Dam, B.C. van; Koelewijn, H.P. ; Halfmaerten, D. ; Ivens, B. ; Slycken, J. Van; Vanden Broeck, A. ; Storme, V. ; Boerjan, W. - \ 2008
Forest Ecology and Management 255 (2008)5-6. - ISSN 0378-1127 - p. 1388 - 1399.
fragment length polymorphism - microsatellite markers - natural-populations - aflp markers - linkage maps - dispersal - stands - reproduction - tremuloides - salicaceae
Black poplar (Populus nigra L.) is a keystone species for riparian ecosystems in Europe. We analysed the structure of genetic diversity of 17 populations from 11 river valleys that are part of seven catchment systems (Danube, Ebro, Elbe, Po, Rhine, Rhone, and Usk) in Europe, in relation to geography and river management. In total, 1069 trees were genotyped using AFLP and microsatellite markers. The trees had an observed heterozygosity of 0.74 (range 0.59¿0.82 across microsatellite loci). The majority (72.6¿90.8%, depending on the marker system) of the genetic variation was present within populations. Most pairs of populations along a river were relatively similar (pairwise Fst 0.042¿0.135 based on AFLP, 0.002¿0.037 based on microsatellites). Overall population differentiation among rivers was considerable (Fst among populations was 0.268 based on AFLP, and 0.081 based on microsatellites). An analysis using the program Structure indicated that all populations recruited plants from several clusters. Geographically close populations tended to draw from the same Structure clusters, including populations from adjacent catchments. The Danube and Inn populations in Austria were genetically more similar to the Vltava population (Elbe catchment) in Czech Republic than the geographically more distant populations along the Tisa and Prut rivers of the Danube catchment in Ukraine. This indicates that gene flow and dispersal takes place across fairly large distances and between river catchments. Consistent with this result, a principal coordinate analysis of genetic distances among individual trees based on AFLP bands showed large overlap of populations, although the French and Spanish samples formed distinct clusters, and the samples from the Ticino (Italy) were at an intermediate position. The extent of clonal duplication was highest along regulated rivers, with e.g., 41% clonal duplication along the Rhine in The Netherlands (up to 32 trees for one genet). The Usk contained a man-made population (two genotypes along the entire river, one genet present as 70 trees out of 72 trees sampled). No clonal duplication was found along dynamic rivers, such as the Ebro (Spain), the Drome (France), and the Tisa and Prut (Ukraine).
Acquisition and ecological characterization of Lactuca serriola L. germplasm collected in the Czech Republic, , Germany, the Netherlands and United Kingdom
Lebeda, A. ; Dolezalova, I. ; Kristkova, E. ; Dehmer, K.J. ; Astley, D. ; Wiel, C.C.M. van de; Treuren, R. van - \ 2007
Genetic Resources and Crop Evolution 54 (2007)3. - ISSN 0925-9864 - p. 555 - 562.
natural-populations - bremia-lactucae - asteraceae - spp.
Expeditions were conducted in the Czech Republic, Germany, the Netherlands and United Kingdom in 2001 (partly 1998) to study Lactuca serriola L. (prickly lettuce, compass plant) geographic distribution, ecology, habitat characteristics and occurrence of diseases and pests on this species. During these missions the seed material of L. serriola L. was collected in an east¿west transect of these four countries. The European transect where seeds were collected and field observations were made represents a relatively large area between 2°34¿50¿¿ W¿17°32¿46¿¿ E and 47°40¿42¿¿¿54°04¿19¿¿ N. The seed material was used for regeneration, inclusion in the national genetic resources collections of individual countries and for research purposes in follow-up studies. During the missions, 50 locations with occurrence of L. serriola L. were visited (16 in Czech Republic and Germany, 10 in UK and 8 in the Netherlands). Individual seed lots of sixteen different plants were collected at each location (L. serriola L. population). Thus, in total 800 seed samples were collected. In Czech Republic and Germany L. serriola L. f. serriola dominated in all observed populations, in the Netherlands both f. serriola and f. integrifolia occurred in pure or mixed stands, whereas in the United Kingdom L. serriola L. f. integrifolia (S.F. Gray) S.D. Prince et R.N. Carter was dominant. L. serriola L. was recorded at various altitudes (¿4 to 410 m), different habitats (ditches, along roads, fields and field margins, ruderal places, pavements and parking sites, fallow fields), individual populations varied substantially in size (20 to >1000 plants), area covered (25¿10,000 m2), and the structure and character of associated plant communities. Natural infections by downy mildew (Bremia lactucae Regel) and powdery mildew (Golovinomyces cichoracearum (DC.) V.P. Gelyuta) were observed in some populations. B. lactucae Regel was recorded only in Czech Republic, G. cichoracearum (DC.) V.P. Gelyuta was more common in continental Europe. General and specific aspects of L. serriola L. geographic distribution and ecology are discussed.
Fisheries-induced evolutionary changes in maturation reaction norms in North Sea sole Solea solea
Mollet, F.M. ; Kraak, S.B.M. ; Rijnsdorp, A.D. - \ 2007
Marine Ecology Progress Series 351 (2007). - ISSN 0171-8630 - p. 189 - 199.
pleuronectes-platessa l - life-history evolution - long-term changes - cod gadus-morhua - coral-reef fish - phenotypic plasticity - natural-populations - social inhibition - sexual maturity - egg size
Age and size at maturation decreased in several commercially exploited fish stocks, which, according to life history theory, may be due to fisheries-induced evolutionary change. However, the observed changes may also represent a plastic response to environmental variability. To disentangle phenotypic plasticity from evolutionary change, the probabilistic reaction norm approach was applied to 43 cohorts (1960 to 2002) of female sole Solea solea from market samples. The reaction norm for age and size at first maturation has significantly shifted towards younger age and smaller size. Size at 50% probability of maturation at Age 3 decreased from 28.6 cm (251 g) to 24.6 cm (128 g). This change was even stronger when condition was included as a third dimension in the reaction norm estimation. The influence of alternative factors was tested on the population level by regression of reaction norm midpoints on annual estimates of condition, temperature and competitive biomass. Although effects of temperature and competitive biomass were significant, the variation in the midpoints was best explained by the decreasing time trend. Therefore, the results provide strong evidence for a fisheries-induced evolutionary change in the onset of sexual maturity.
Genetic diversity and differentiation in European beech (Fagus sylvatica L.) stands varying in management history
Buiteveld, J. ; Vendramin, G.G. ; Leonardi, S. ; Kramer, K. ; Geburek, T. - \ 2007
Forest Ecology and Management 247 (2007)1-3. - ISSN 0378-1127 - p. 98 - 106.
microsatellite markers - natural-populations - spatial differentiation - f-statistics - douglas-fir - regeneration - crenata - consequences - silviculture - variability
The impact of forest management on genetic diversity and mating was examined in European beech (Fagus sylvatica L.). Ten beech stands located in Europe were studied in pair-wise plots, differing in management intensity. The stands were genotyped with four highly polymorphic microsatellite loci. Comparison for genetic diversity measures between the stands with limited management and the high management-intensity stands (mostly shelter wood system) revealed no significant differences for allelic richness (A), effective number of alleles (Ae), number of rare alleles (Arare), neither for observed (Ho) nor expected heterozygosity (He). In all stands a significant excess of homozygotes was found, which is in agreement with previous isozyme publications. However, the increase in the inbreeding coefficient (Fis) in the stands with limited management was significantly higher than in the highly managed stands. Expectedly a low, but significant, differentiation among all stands was found (Fst = 0.058) which still reveals a clear geographic structure. The results indicate that the shelter wood system has no or minimum impact on the genetic diversity in European beech.
Microarray challenges in ecology
Kammenga, J.E. ; Herman, M.A. ; Ouborg, N.J. ; Johnson, L. ; Breitling, R. - \ 2007
Trends in Ecology and Evolution 22 (2007)5. - ISSN 0169-5347 - p. 273 - 279.
gene-expression profiles - drosophila-melanogaster - ectomycorrhizal fungus - nicotiana-attenuata - natural-populations - cdna microarrays - evolution - arabidopsis - genomics - patterns
Microarrays are used to measure simultaneously the amount of mRNAs transcribed from many genes. They were originally designed for gene expression profiling in relatively simple biological systems, such as cell lines and model systems under constant laboratory conditions. This poses a challenge to ecologists who increasingly want to use microarrays to unravel the genetic mechanisms underlying complex interactions among organisms and between organisms and their environment. Here, we discuss typical experimental and statistical problems that arise when analyzing genome-wide expression profiles in an ecological context. We show that experimental design and environmental confounders greatly influence the identification of candidate genes in ecological microarray studies, and that following several simple recommendations could facilitate the analysis of microarray data in ecological settings.
Sampling effects on the assessment of genetic diversity of rhizobia associated with soybean and common bean
Alberton, O. ; Kaschuk, G. ; Hungria, M. - \ 2006
Soil Biology and Biochemistry 38 (2006)6. - ISSN 0038-0717 - p. 1298 - 1307.
phaseolus-vulgaris l. - 16s ribosomal-rna - length polymorphism analysis - biovar viciae populations - polymerase chain-reaction - genotypic characterization - bacterial diversity - natural-populations - nitrogen-fixation - tropici strains
Biological nitrogen fixation plays a key role in agriculture sustainability, and assessment of rhizobial diversity contributes to worldwide knowledge of biodiversity of soil microorganisms, to the usefulness of rhizobial collections and to the establishment of long-term strategies aimed at increasing contributions of legume-fixed N to agriculture. Although in recent decades the use of molecular techniques has contributed greatly to enhancing knowledge of rhizobial diversity, concerns remain over simple issues such as the effects of sampling on estimates of diversity. In this study, rhizobia were isolated from nodules of plants grown under field conditions, in pots containing soil, or in Leonard jars receiving a 10¿2 or a 10¿4 serially-diluted soil inoculum, using one exotic (soybean, Glycine max) and one indigenous (common bean, Phaseolus vulgaris) legume species. The experiments were performed using an oxisol with a high population (105 cells g¿1 soil) of both soybean rhizobia, composed of naturalized strains introduced in inoculants and of indigenous common-bean rhizobia. BOX-PCR was used to evaluate strain diversity, while RFLP-PCR of the ITS (internally transcribed spacer) region with five restriction enzymes aimed at discriminating rhizobial species. In both analyses the genetic diversity of common-bean rhizobia was greater than that of soybean. For the common bean, diversity was greatly enhanced at the 10¿4 dilution, while for the soybean dilution decreased diversity. Qualitative differences were also observed, as the DNA profiles differed for each treatment in both host plants. Differences obtained can be attributed to dissimilarity in the history of the introduction of both the host plant and the rhizobia (exotic vs. indigenous), to host-plant specificity, rhizobial competitiveness, and population structure, including ease with which some types are released from microcolonies in soil. Therefore, sampling method should be considered both in the interpretation and comparison of the results obtained in different studies, and in the setting of the goals of any study, e.g. selection of competitive strains, or collection of a larger spectrum of rhizobia. Furthermore, effects of sampling should be investigated for each symbiosis.
Biogeographic distribution of polyploidy and B chromosomes in the apomictic Boechera holboellii complex
Sharbel, T.F. ; Mitchell-Olds, T. ; Dobes, C. ; Kantama, L. ; Jong, J.H.S.G.M. de - \ 2005
Cytogenetic and Genome Research 109 (2005)1-3. - ISSN 1424-8581 - p. 283 - 292.
arabis-holboellii - molecular systematics - natural-populations - rust infection - brassicaceae - evolution - plants - arabidopsis - mechanisms - apomixis
The Boechera holboellii complex comprises B. holboellii and B. drummondii, both of which can reproduce through sex or apomixis. Sexuality is associated with diploid individuals, whereas apomictic individuals are diploid or triploid and may additionally have B chromosomes. Using flow cytometry and karyotype analysis, we have shown that B chromosomes (a) occur in both diploid and triploid apomictic B. holboellii, (b) may occur in triploid B. drummondii, and (c) are dispensable for the plant. Both diploid and triploid karyotypes are found in multiple chloroplast haplotypes of both species, suggesting that triploid forms have originated multiple times during the evolution of this complex. B chromosome carriers are found in geographically and genetically distinct popu-lations, but it is unknown whether the extra chromosomes are shared by common descent (single origin) or have originated via introgressive hybridization and repeated transitions from diploidy to triploidy. Diploid plants containing the Bs reproduce apomictically, suggesting that the supernumerary elements are associated with apomixis. Finally, our analyses of pollen size and viability suggest that irregular chromosome segregation in some triploid lineages may lead to the generation of diploid individuals which carry the B chromosomes.
Polymorphism for pKALILO based senescence in Hawaiian populations of Neurospora intermedia and Neurospora tetrasperma.
Maas, M.F.P.M. ; Mourik, A. van; Hoekstra, R.F. ; Debets, A.J.M. - \ 2005
Fungal Genetics and Biology 42 (2005)3. - ISSN 1087-1845 - p. 224 - 232.
mitochondrial plasmids - vegetative incompatibility - natural-populations - nucleotide-sequence - fungus neurospora - kalilo plasmids - linear plasmids - dna - strains - crassa
The natural population of Neurospora intermedia from Hawaii is polymorphic for the presence of the linear mitochondrial plasmid pKALILO that is associated with an infectious senescence syndrome. Although inter-specific horizontal transmission is experimentally possible, thus far pKALILO associated senescence has never been found outside N. intermedia in nature. Here, we demonstrate that it is not limited to the natural population of the heterothallic species N. intermedia, but also present in the sympatric population of its close relative, the pseudo-homothallic species Neurospora tetrasperma. We did a comparative analysis of the hallmarks of senescence in both species and show that: (1) Senescence is contagious in both species: the senescent state is efficiently transmitted between vegetatively compatible isolates. (2) All senescent isolates from both species contain the autonomously replicating linear mitochondrial senescence plasmid pKALILO. (3) In both species, senescent cultures contained copies of pKALILO inserted into the mitochondrial genome. Two of these inserts were characterized using semi-random two-step PCR, and were located within the large subunit mitochondrial rRNA gene. (4) However, pKALILO was less frequent in N. tetrasperma than in N. intermedia. (5) Also, the onset of senescence was significantly delayed in N. tetrasperma, compared to that in N. intermedia. We hypothesize how these differences in frequency and effect of pKALILO are connected to the respective life histories of their hosts.
Studying genetics of adaptive variation in model organisms: flowering time variation in Arabidopsis lyrata
Riihimäki, M. ; Podolsky, R. ; Kuittinen, H. ; Koelewijn, H.P. ; Savolainen, O. - \ 2005
Genetica 123 (2005)1-2. - ISSN 0016-6707 - p. 63 - 74.
thaliana brassicaceae ecotypes - alcohol-dehydrogenase locus - linkage disequilibrium - natural-populations - arabis-petraea - environment interaction - molecular systematics - sequence variation - breeding system - diversity
Arabidopsis thaliana has emerged as a model organism for plant developmental genetics, but it is also now being widely used for population genetic studies. Outcrossing relatives of A. thaliana are likely to provide suitable additional or alternative species for studies of evolutionary and population genetics. We have examined patterns of adaptive flowering time variation in the outcrossing, perennial A. lyrata. In addition, we examine the distribution of variation at marker genes in populations form North America and Europe. The probability of flowering in this species differs between southern and northern populations. Northern populations are much less likely to flower in short than in long days. A significant daylength by region interaction shows that the northern and southern populations respond differently to the daylength. The timing of flowering also differs between populations, and is made shorter by long days, and in some populations, by vernalization. North American and European populations show consistent genetic differentiation over microsatellite and isozyme loci and alcohol dehydrogenase sequences. Thus, the patterns of variation are quite different from those in A. thaliana, where flowering time differences show little relationship to latitude of origin and the genealogical trees of accessions vary depending on the genomic region studied. The genetic architecture of adaptation can be compared in these species with different life histories
Effects of seed size, inbreeding and maternal sex on offspring fitness in gynodioecious Plantago coronopus
Koelewijn, H.P. ; Damme, J.M.M. van - \ 2005
Journal of Ecology 93 (2005)2. - ISSN 0022-0477 - p. 373 - 383.
phacelia-linearis hydrophyllaceae - silene-acaulis caryophyllaceae - relative growth-rate - oregana ssp spicata - male-sterility - thymus-vulgaris - reproductive allocation - desmodium-paniculatum - resource compensation - natural-populations
1 Male steriles (MS) must have a fitness advantage relative to hermaphrodites (H) if they are to be maintained in gynodioecious species. We report experiments in which we disentangle the relative contributions of seed size, inbreeding and maternal sex to the fitness advantage of male steriles in Plantago coronopus L. 2 Seed size effects were observed throughout growth experiments in the glasshouse and were reflected in all biomass measurements. In the field, seed size effects resulted in a fourfold increase in standardized seed production per initial buried seed after 2 years between small (mean weight = 0.13 mg) and large (0.20 mg) seeds. 3 Inbreeding depression, calculated from seed to seed was = 0.37 after one generation of selfing and = 0.93 after the second generation of selfing. Regression of log(1 ) on inbreeding level suggested synergistic epistasis in fitness. 4 Even after taking into account the effects of seed size and inbreeding level, the offspring of a male sterile mother had a 16% advantage over a hermaphrodite, but this disappeared when the progeny sex ratio (the ratio of MS : H individuals among the offspring) was taken into account. 5 In the field, offspring of large seeds had both a higher overall incidence of flowering, and a higher probability of flowering in their first year, thus generating an extra cohort of individuals. The high inbreeding depression in fitness after two generations of selfing was also due to a very low incidence of flowering among the S2 individuals. Flowering probability therefore appears to be a critical trait in this system. 6 In the field, the contributions of seed size variation (15%) and inbreeding (9%) combine with 48% higher seed production to give a total fitness advantage of 70% of male steriles relative to hermaphrodites. This is probably sufficient for maintenance of gynodioecy under nuclear-cytoplasmic inheritance of male sterility. 7 Both inbreeding effects (as a consequence of the sexual system) and pleiotropic effects (of the genes coding for male sterility) play a role in the maintenance of gynodioecy in this species, with an apparently greater role for the latter
The genetic basis of adaptive population differentiation: A quantitative trait locus analysis of fitness traits in two wild barley populations from contrasting habitats
Verhoeven, K.J.F. ; Vanhala, T.K. ; Biere, A. ; Nevo, E. ; Damme, J.M.M. van - \ 2004
Evolution 58 (2004)2. - ISSN 0014-3820 - p. 270 - 283.
local adaptation - hordeum-spontaneum - agronomic traits - heterogeneous environments - drosophila-melanogaster - inbreeding depression - host specialization - natural-populations - molecular markers - annual plant
We used a quantitative trait locus (QTL) approach to study the genetic basis of population differentiation in wild barley, Hordeum spontaneum. Several ecotypes are recognized in this model species, and population genetic studies and reciprocal transplant experiments have indicated the role of local adaptation in shaping population differences. We derived a mapping population from a cross between a coastal Mediterranean population and a steppe inland population from Israel and assessed F-3 Progeny fitness in the natural growing environments of the two parental populations. Dilution of the local gene pool, estimated as the proportion of native alleles at 96 marker loci in the recombinant lines, negatively affected fitness traits at both sites. QTLs for fitness traits tended to differ in the magnitude but not in the direction of their effects across sites, with beneficial alleles generally conferring a greater fitness advantage at their native site. Several QTLs showed fitness effects at one site only, but no opposite selection on individual QTLs was observed across the sites. In a common-garden experiment, we explored the hypothesis that the two populations have adapted to divergent nutrient availabilities. In the different nutrient environments of this experiment, but not under field conditions, fitness of the F-3 progeny lines increased with the number of heterozygous marker loci. Comparison of QTL-effects that underlie genotype X nutrient interaction in the common-garden experiment and genotype X site interaction in the field suggested that population differentiation at the field sites may have been driven by divergent nutrient availabilities to a limited extent. Also in this experiment no QTLs were observed with opposite fitness effects in contrasting environments. Our data are consistent with the view that adaptive differentiation can be based on selection on multiple traits changing gradually along ecological gradients. This can occur without QTLs showing opposite fitness effects in the different environments, that is, in the absence of genetic trade-offs in performance between environments.
Is the aneuploid chromosome in an apomictic Boechera holboellii a genuine B chromosome?
Sharbel, T.F. ; Voigt, M.L. ; Mitchell-Olds, T. ; Kantama, L. ; Jong, J.H.S.G.M. de - \ 2004
Cytogenetic and Genome Research 106 (2004)2-4. - ISSN 1424-8581 - p. 173 - 183.
arabis-holboellii - evolutionary genetics - molecular systematics - natural-populations - rust infection - brassicaceae - apomixis - arabidopsis - plants - parthenogenesis
The Boechera holboellii complex comprises B. holboellii and B. drummondii, both of which can reproduce through sex or apomixis. Sexuality is associated with diploidy, whereas apomictic individuals can either be diploid, aneuploid or triploid. Aneuploid individuals are found in geographically and genetically distinct populations and contain a single extra chromosome. It is unknown whether the supernumerary chromosomes are shared by common descent (single origin) or have originated via introgressive hybridizations associated with the repeated transition from diploidy to triploidy. Diploid plants containing the extra chromosome(s) reproduce apomictically, suggesting that the supernumerary elements are associated with apomixis. In this study we compared flow cytometry data, chromosome morphology, and DNA sequences of sexual diploid and apomictic aneuploids in order to establish whether the extra chromosome fits the classical concept of a B chromosome. Karyotype analyses revealed that the supernumerary chromosome in the metaphase complement is heterochromatic and often smaller than the A chromosomes, and differs in length between apomictic plants from different populations. DNA sequence analyses furthermore demonstrated elevated levels of non-synonymous substitutions in one of the alleles, likely that on the aneuploid chromosome. Although the extra chromosome in apomictic Boechera does not go through normal reductional meiosis, in which it may get eliminated or accumulated by a B-chromosome-specific process, its variable size and heterochromatic nature does meet the remaining criteria for a genuine B chromosome in other species. Its prevalence and conserved genetic composition nonetheless implies that this chromosome, if truly a B, may be atypical with respect to its influence on its carriers. Copyright (C) 2004 S. Karger AG, Basel.
Multiple CMS-restorer gene polymorphism in gynodioecious Plantago coronopus
Damme, J.M.M. van; Hundscheid, M.P.J. ; Ivanovic, S. ; Koelewijn, H.P. - \ 2004
Heredity 93 (2004)2. - ISSN 0018-067X - p. 175 - 181.
cytoplasmic male-sterility - thymus-vulgaris l - mitochondrial genome - natural-populations - lanceolata l - evolution - maize - dioecy
The mode of inheritance of the male sterility trait is crucial for understanding the evolutionary dynamics of the sexual system gynodioecy, which is the co-occurrence of female and hermaphrodite plants in natural populations. Both cytoplasmic (CMS) and nuclear (restorer) genes are known to be involved. Theoretical models usually assume a limited number of CMS genes with each a single restorer gene, while reality is more complex. In this study, it is shown that in the gynodioecious species Plantago coronopus two new CMS-restorer polymorphisms exist in addition to the two that were already known, which means four CMS-restorer systems at the species level. Furthermore, three CMS types were shown to co-occur within a single population. All new CMS types showed a multilocus system for male fertility restoration, in which both recessive and dominant restorer alleles occur. Our finding of more than two co-occurring CMS-restorer systems each with multiple restorer genes raises the question how this complex of male sterility systems is maintained in natural populations.
Spore killing in the fungus Podospora anserina: a possible connection between meiotic drive and vegetative incompatibility
Gaag, M. van der; Debets, A.J.M. ; Hoekstra, R.F. - \ 2003
Genetica 117 (2003)1. - ISSN 0016-6707 - p. 59 - 65.
heterokaryon incompatibility - natural-populations - neurospora - plasmids - dynamics
Fungi in which the haploid nuclei resulting from meiosis are linearly arranged in asci provide unique opportunities to analyse abnormal segregation. Any meiotic drive system in such fungi will be observed in a cross between a driving and a sensitive strain as spore killing: the degeneration of half the ascospores in a certain proportion of the asci. In a sample of some 100 strains isolated from a single natural population we have discovered at least six different meiotic drive elements (van der Gaag et al., 2000). Here we report results of research that was aimed at elucidating a possible correlation between meiotic drive and vegetative incompatibility in eight different Spore killer strains from this population. We show that there is a strong correlation between these two phenotypes, although the precise genetic nature of the correlation is not yet clear. We discuss the implications of our results for the understanding of the population genetics of meiotic drive in Podospora
Distribution and diversity of rhizobia nodulating agroforestry legumes in soils from three continents in the tropics
Bala, A. ; Murphy, P. ; Giller, K.E. - \ 2003
Molecular Ecology 12 (2003)4. - ISSN 0962-1083 - p. 917 - 929.
genetic diversity - natural-populations - kenyan conditions - specificity - phylogeny - evolution - spacer - host
The natural rhizobial populations of Calliandra calothyrsus, Gliricidia sepium, Leucaena leucocephala and Sesbania sesban were assessed in soils from nine sites across tropical areas of three continents. The rhizobial population size varied from undetectable numbers to 1.8 x 104 cells/g of soil depending on the trap host and the soil. Calliandra calothyrsus was the most promiscuous legume, nodulating in eight soils, while S. sesban nodulated in only one of the soils. Polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analyses of the 16S rRNA gene and the internally transcribed spacer (ITS) region between the 16S and 23S rRNA genes were used to assess the diversity and relative abundance of rhizobia trapped from seven of the soils by C. calothyrsus, G. sepium and L. leucocephala. Representatives of the 16S rRNA RFLP groups were also subjected to sequence analysis of the first 950 base pairs of the 16S rRNA gene. Eighty ITS groups were obtained, with none of the ITS types being sampled in more than one soil. RFLP analysis of the 16S rRNA yielded 23 'species' groups distributed among the Rhizobium, Mesorhizobium, Sinorhizobium and Agrobacterium branches of the rhizobial phylogenetic tree. The phylogeny of the isolates was independent of the site or host of isolation, with different rhizobial groups associated with each host across the soils from widely separated geographical regions. Although rhizobial populations in soils sampled from the centre of diversity of the host legumes were the most genetically diverse, soil acidity was highly correlated with the diversity of ITS types. Our results support the hypothesis that the success of these tree legumes in soils throughout the tropics is the result of their relative promiscuity (permissiveness) allowing nodulation with diverse indigenous rhizobial types.
Distribution of mating type alleles in the wheat pathogen Mycosphaerella graminicola over spatial scales from lesions to continents
Zhan, J. ; Kema, G.H.J. ; Waalwijk, C. ; McDonald, B.A. - \ 2002
Fungal Genetics and Biology 36 (2002)2. - ISSN 1087-1845 - p. 128 - 136.
fragment-length-polymorphisms - anamorph-septoria-tritici - in-field populations - natural-populations - sexual development - filamentous fungi - genetic-structure - high-frequency - winter-wheat - epidemics
A total of 2035 Mycosphaerella graminicola strains collected from 16 geographic locations on four continents were assayed for the mating type locus. RFLP fingerprints were used to identify clones in each population. At the smallest spatial scale analyzed, both mating types were found among fungal strains sampled from different lesions of the same leaf as well as from different pycnidia in the same lesion. At larger spatial scales, the two mating types were found at equal frequencies across spatial scales ranging from several square meters to several thousand square kilometers. Though the absolute frequencies of the two mating types sometimes varied for different sampling units within the same spatial scale in the hierarchy (plots within a field, fields within a country, or different continents of the world), none of the differences were statistically significant from the null hypothesis of equal frequencies for the two mating types. The evolutionary forces likely to maintain the even distribution of the two mating types in this pathogen were discussed