Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    The Sphagnome Project : enabling ecological and evolutionary insights through a genus-level sequencing project
    Weston, David J. ; Turetsky, Merritt R. ; Johnson, Matthew G. ; Granath, Gustaf ; Lindo, Zoë ; Belyea, Lisa R. ; Rice, Steven K. ; Hanson, David T. ; Engelhardt, Katharina A.M. ; Schmutz, Jeremy ; Dorrepaal, Ellen ; Euskirchen, Eugénie S. ; Stenøien, Hans K. ; Szövényi, Péter ; Jackson, Michelle ; Piatkowski, Bryan T. ; Muchero, Wellington ; Norby, Richard J. ; Kostka, Joel E. ; Glass, Jennifer B. ; Rydin, Håkan ; Limpens, Juul ; Tuittila, Eeva Stiina ; Ullrich, Kristian K. ; Carrell, Alyssa ; Benscoter, Brian W. ; Chen, Jin Gui ; Oke, Tobi A. ; Nilsson, Mats B. ; Ranjan, Priya ; Jacobson, Daniel ; Lilleskov, Erik A. ; Clymo, R.S. ; Shaw, A.J. - \ 2018
    New Phytologist 217 (2018)1. - ISSN 0028-646X - p. 16 - 25.
    ecological genomics - ecosystem engineering - evolutionary genetics - genome sequencing - niche construction - peatlands - Sphagnome - Sphagnum
    Considerable progress has been made in ecological and evolutionary genetics with studies demonstrating how genes underlying plant and microbial traits can influence adaptation and even ‘extend’ to influence community structure and ecosystem level processes. Progress in this area is limited to model systems with deep genetic and genomic resources that often have negligible ecological impact or interest. Thus, important linkages between genetic adaptations and their consequences at organismal and ecological scales are often lacking. Here we introduce the Sphagnome Project, which incorporates genomics into a long-running history of Sphagnum research that has documented unparalleled contributions to peatland ecology, carbon sequestration, biogeochemistry, microbiome research, niche construction, and ecosystem engineering. The Sphagnome Project encompasses a genus-level sequencing effort that represents a new type of model system driven not only by genetic tractability, but by ecologically relevant questions and hypotheses.
    On the evolution of azole resistance in Aspergillus fumigatus
    Zhang, J. - \ 2016
    Wageningen University. Promotor(en): Bas Zwaan; P.E. Verweij, co-promotor(en): Fons Debets; Sijmen Schoustra. - Wageningen : Wageningen University - ISBN 9789462578555 - 183
    aspergillus fumigatus - azoles - triazoles - aspergillosis - resistance - life cycle - asexual reproduction - sexual reproduction - experimental evolution - evolutionary genetics - agriculture - composting - medicine - aspergillus fumigatus - azolen - triazolen - aspergillose - weerstand - levenscyclus - ongeslachtelijke voortplanting - geslachtelijke voortplanting - experimentele evolutie - evolutionaire genetica - landbouw - compostering - geneeskunde

    During the last decade azole resistance has increasingly been reported in Aspergillus fumigatus, which is a fungal pathogen involved in the vast majority of invasive aspergillosis infections in humans, and is now a global public health concern. Antifungal azoles, especially triazoles, are the drugs of choice for medical treatment. However, this treatment is hampered by the emergence of multi-azole resistant A. fumigatus isolates, especially the highly resistant variants TR34/L98H and TR46 /Y121F/T289A. Therefore, to control this disease, it is essential to elucidate by what mechanisms resistance emerges, how resistance spreads and how resistant genotypes persist in environments without azoles. The presented thesis shows the relevance of the life cycle of A. fumigatus to the development of azole resistance and possible evolutionary routes that lead to it. The work highlights the importance of fungal biology and evolution towards understanding the development of azole resistance in fungi. We conclude that azole resistance in A. fumigatus is a consequence of selection pressure by azole in the environment on the genetic variation generated via various aspects in the A. fumigatus life cycle. This thesis also introduces an experimental evolution approach to study the dynamics and mechanisms of the evolution of azole resistance. In addition, we investigate what condition can lead an environment to be a possible hotspot for the development of resistance. Finally, we link this to the potential conditions under which resistance can emerge and spread in the lungs of humans and how this depends on the specific azole used.

    The butterfly plant arms-race escalated by gene and genome duplications
    Edger, P.P. ; Heidel-Fischer, H.M. ; Bekaert, K.M. ; Rota, J. ; Glockner, G. ; Platts, A.E. ; Heckel, D.G. ; Der, J.P. ; Wafula, E.K. ; Tang, M. ; Hofberger, J.A. ; Smithson, A. ; Hall, J.C. ; Blanchette, M. ; Bureau, T.E. ; Wright, S.I. ; dePamphilis, C.W. ; Schranz, M.E. ; Conant, G.C. ; Barker, M.S. ; Wahlberg, N. ; Vogel, H. ; Pires, J.C. ; Wheat, C.W. - \ 2015
    Proceedings of the National Academy of Sciences of the United States of America 112 (2015)27. - ISSN 0027-8424 - p. 8362 - 8366.
    evolutionaire genetica - co-evolutie - diversificatie - brassica - pieridae - papilionidae - glucosinolaten - fylogenie - evolutionary genetics - coevolution - diversification - brassica - pieridae - papilionidae - glucosinolates - phylogeny - diversity - defense - cytochrome-p450 - polymorphism - arabidopsis - metabolism - expression - speciation
    Coevolutionary interactions are thought to have spurred the evolution of key innovations and driven the diversification of much of life on Earth. However, the genetic and evolutionary basis of the innovations that facilitate such interactions remains poorly understood. We examined the coevolutionary interactions between plants (Brassicales) and butterflies (Pieridae), and uncovered evidence for an escalating evolutionary arms-race. Although gradual changes in trait complexity appear to have been facilitated by allelic turnover, key innovations are associated with gene and genome duplications. Furthermore, we show that the origins of both chemical defenses and of molecular counter adaptations were associated with shifts in diversification rates during the arms-race. These findings provide an important connection between the origins of biodiversity, coevolution, and the role of gene and genome duplications as a substrate for novel traits.
    Sexual selection in Fungi
    Nieuwenhuis, B.P.S. - \ 2012
    Wageningen University. Promotor(en): Rolf Hoekstra, co-promotor(en): Duur Aanen. - S.l. : s.n. - ISBN 9789461733580 - 156
    schimmels - geslachtsselectie - genetica - geslachtelijke voortplanting - evolutionaire genetica - evolutie - fungi - sexual selection - genetics - sexual reproduction - evolutionary genetics - evolution

    Sexual selection is an important factor that drives evolution, in which fitness is increased, not by increasing survival or viability, but by acquiring more or better mates. Sexual selection favours traits that increase the ability of an individual to obtain more matings than other individuals that it is in competition with. For many sexually reproducing organisms, obtaining mates is an essential part of the lifecycle, sexual selection can therefore be very strong. A trait that leads to more matings can be selected, even if it strongly reduces other components of fitness, for instance predator escape. Often sexual selection leads to sex specific traits, which can become very extravagant. In animals and plants, it has been well established that this form of selection is an important evolutionary force, but it has not been considered for fungi. This thesis revolves around the idea that in this aspect, fungi are not fundamentally different from animals and plants and that also for species from this kingdom sexual selection influences evolution. Many fungi reproduce sexually and need to find a partner before reproduction can proceed. Furthermore, it is likely that not all individuals that benefit from mating can perform mating, hence a struggle for mate acquisition will occur.
    In my research I have investigated how likely it is that in fungi such struggles occur and which mechanisms might act during competitions. For these studies I used the mushroom forming basidiomycete fungus Schizophyllum commune as a model organism. I studied the potential for mate competition in natural populations, performed laboratory mating essays to test competition and preference, and experimentally tested if sexual selection can increase competitive ability.
    Sexual reproduction in fungi is highly regulated. Many molecular mechanisms are known that modulate each step, from meiosis to gamete production and from mate finding to gamete fusion. In most fungi these characteristics are regulated by genes located on the mating type locus or loci. These genes do not only regulate mating, but also define compatibility between the gametes: gametes with the same alleles at a mating type locus cannot fuse. Because of this double function, fungal mating types are potentially very important for sexual selection. Besides that mating types are a target for sexual selection because they affect traits that might increase competitive ability, since the mating types determine compatibility, they also define who competes with whom. Sexual selection describes how within one sex mating occurs for individuals of the other sex and is therefore always intra-sexual. Fungi do not have different sexes, but do have sex roles. Sexual selection will therefore act if there is competition for mating in the male or female role. Compatibility between sex roles is different from compatibility between mating types. The first is defined by the size of the mycelium, and the second by a genetic recognition mechanism. This difference is of importance to understand how sexual selection can act in fungi and is explained in Chapter 2.
    Mating in mushroom fungi occurs by reciprocal exchange of nuclei. In the female role nuclei from a compatible mate are incorporated into the haploid mycelium. These nuclei migrate though the mycelium until in each cell of the mycelium two haploid nuclei are present; it becomes a so called dikaryon. Only a dikaryon can produce mushrooms that produce spores. In the male role, a mycelium can donate nuclei to a haploid mycelium. A mycelium can thus be considered hermaphroditic. After fertilize, the dikaryon can still act as a nucleus donor, but not incorporate more nuclei – this type of mating is known as the Buller phenomenon. Also spores can act as male, but as they have no mycelium, not as a female. Due to the presence of more individuals that can mate in the male role than there are female mycelia (monokaryons), competition over fertilizations is expected.
    Competition can only occur when there are multiple individuals. Fungi are sessile organisms that can only meet other individuals when they are in the same locality. To test whether there is potential for sexual selection in nature, the number of individuals that meet each other needs to be defined. Not much knowledge on numbers of individuals is known, because mushroom fungi generally grow by mycelium expansion inside a substratum and each part of the mycelium can produce mushrooms. Therefore, all mushrooms on a tree can be one genetic individual, but it is also possible that each mushroom is a separate individual. We sampled 24, 12 and 24 mushrooms from the same substrate of three natural populations to analyse how mating occurred (Chapter 3). We determined the identity of the two different nuclei in each mushroom, as well as the mitochondria. Because mitochondria do not migrate during mating, they are specific for each female mycelium. We found that multiple genetic individuals (3, 3 and 8) are present in a small area, and that many matings must have occurred. Even though it is generally assumed that matings occur between two monokaryons, none such matings were found. The data suggest that mating in nature occurs between a monokaryon and a spore, or a monokaryon and a dikaryon.
    During a dikaryon-monokaryon (di-mon) mating only one of the two nucleus types from the dikaryon is successful in fertilizing the monokaryon. The nucleus type that is successful will likely increase its fitness considerably, as the entire female mycelium becomes colonized. Sexual selection is expected to select for nuclei that are better in performing this fertilization. Furthermore, during mating the receiving monokaryon meets two different nuclei, and might be able to choose between them. We performed crosses between 15 dikaryons and six different monokaryons to test if selection occurs, and whether selection occurs by male-male competition, or by female choice (Chapter 4). When confronting the same dikaryon with different monokaryon, in some of the cases the female mycelium decided which of the two nuclei won. In most cases however, the same nucleus always fertilized the monokaryon, irrespective of which monokaryon. This suggests that nuclei are able to either manipulate the monokaryon in incorporating them into the mycelium and not the other type, or that the nuclei of one type can directly suppress mating by the other nuclei in the dikaryon.
    Nuclei in a dikaryon have a strict way of cell division in which the different types divide in synchrony. Probably the two nuclei keep each other in check to assure this synchrony. Experiments in which the two nuclei in a dikaryon are separated into monokaryons suggest that the two nuclei suppress each other’s mitotic division, and that one of the two nuclei is better in suppression than the other. Consequently, after de-dikaryotisation more monokaryons of one type are recovered than of the other. We tested if this mechanism of suppression might be responsible for the dominant nuclei in the di-mon matings (Chapter 5). Separating the two nuclei confirmed earlier findings that always one of the two nuclei is dominant and that a hierarchy in dominance exists. This pecking order did not correspond with the results from the winner in the di-mon matings, which suggests that the mechanism of suppressed mitotic division is not responsible for dominance in di-mon matings. Nevertheless, we argue that the hypothesis that a link between the two mechanisms exists should not be completely written off. Because the interactions that take place during di-mon matings are very complex, the functioning of this mechanism might be obscured during mating.
    The observed variance in mating success described above might lead to sexual selection, however, it does not show that sexual selection actually led to traits that improve increased mate acquisition. To show that traits can evolve that increase fitness by higher mating success, we performed an evolution experiment (Chapter 6). An evolving population of nuclei was continuously mated with a non-evolving monokaryon. This setup selected for novel traits that increase competitive ability over matings. After 20 transfers, four out of twelve evolved lines had increased in competitive fitness and one line had decreased. Different fitness components were measured to investigate which traits had resulted in changed fitness. Fertilization success was mainly determined at the moment of fusion with and in initial migration into the receiving monokaryon. Two strains showed increased spores production, but this did not add to the increased fitness caused by fusion and initial migration. Little fitness change occurred during migration or in the dikaryon phase. We observed no clear trade-offs between the competitive ability of fertilizing in the male role, and female characteristics. This experiment showed that sexual selection can act in mushroom fungi.
    Sexual selection can also play a role in other groups of fungi than the mushroom forming fungi. So far this has not been considered, and little research has been done to show how mate competition might influence evolution. We reinterpreted the current knowledge on mating in fungi and assessed whether and when sexual selection might play a role (Chapter 7). Sexual selection is most likely to occur when sex roles can be observed during mating, as this can lead to skewed sex ratios. Also when there is large difference in quality between potential mates sexual selection might lead to evolution of choice. Directions are given where sexual selection is expected to function in fungal mating. Examples are given of how sexual selection might have led to for instance the evolution of micro-conidia in ascomycetes and pheromone redundancy in basidiomycetes. Furthermore, the existence of different sex roles in fungi, can lead to sexual conflict between the genomes derived from the paternal and the maternal gametes of which examples are given. The realization that sexual selection can also act in fungi gives great opportunity to test how universal general theories of sexual selection are in another important group of organisms. Additionally, because fungi are easy to manipulate, predictions on sexual selection can be tested experimentally using fungi.
    Mushroom forming fungi have a life history which differs from animals and plants. Sexual selection will therefore affect mushroom fungi in a different manner than it would animals and plants. In the general discussion of this thesis (Chapter 8) I will assess how mating influences fungal fitness, teasing apart the benefits and costs of mating in the male and female roles. I give directions for future research and discuss a setup to directly measure the effect of pheromones on female choice in mushroom fungi.
    There are still many unanswered fundamental questions about sexual selection. Adding knowledge from a third important kingdom can help increase the understanding of the principles that drive evolution by sexual selection. Furthermore, applying sexual selection theory to fungi might elucidate the functioning of the sometimes very complex mechanisms that have evolved for fungal mating.

    The role of Mallard (Anas platyrhynchos) in the spread of avian influenza: genomics, population genetics, and flyways
    Kraus, R.H.S. - \ 2011
    Wageningen University. Promotor(en): Herbert Prins; Ron Ydenberg, co-promotor(en): Pim van Hooft. - [S.l.] : S.n. - ISBN 9789461730282 - 143
    aviaire influenzavirussen - aviaire influenza - anas platyrhynchos - ziekteoverdracht - vogeltrek - genomica - populatiegenetica - evolutionaire genetica - zoögeografie - bioveiligheid - ziekteoverzichten - epidemiologie - avian influenza viruses - avian influenza - anas platyrhynchos - disease transmission - bird migration - genomics - population genetics - evolutionary genetics - zoogeography - biosafety - disease surveys - epidemiology

    Birds, in particular poultry and ducks, are a source of many infectious diseases, such as those caused by influenza viruses. These viruses are a threat not only to the birds themselves but also to poultry farming and human health, as forms that can infect humans are known to have evolved. It is believed that migratory birds in general play an important role in the global spread of avian influenza (AI). However, it is still debated how large this role precisely is and whether other modes of spread may be more important. The mallard (Anas platyrhynchos) is the world’s most abundant and well-studied waterfowl species. Besides being an important game and agricultural species, it is also a flagship species in wetland conservation and restoration. Waterfowl (Anseriformes: Anatidae) and especially ducks currently are the focal bird group in long distance dispersal of Avian Influenza in the wild, and the mallard has been identified as the most likely species to transport this virus.

    In my thesis I report aspects of the biology of this important host species of AI by molecular ecological means. As molecular marker system I established a genome-wide set of more than 100,000 SNPs of which I developed a subset of 384 SNPs into an assay to genotype about 1,000 ducks. This subset was employed to study the evolutionary history and speciation processes in the Anas genus. Further investigations into the world-wide mallard population structure on a species level were based not only on this set of 384 SNPs but also on mitochondrial DNA sequences. Last but not last, I investigated an option of AI sampling and detection from duck faeces by technology that is safe from a biohazard perspective, and solves transportation issues related to cold chains.

    The main results of my thesis include the development of a generally applicable improved analysis pipeline to develop genome-wide SNP sets for non-model organisms. Further, my results show that, from a migration system perspective, mallard flyways/populations can hardly be delineated from a biological point of view. Detailed phylogenetic, population genetic and coalescent analyses of a data set of samples spanning the whole northern hemisphere leads me to conclude that the only firm population boundaries that I can draw are between Eurasia and North America, within which panmixia is almost achieved. Mallards’ and other Anas-ducks’ whole continental to global distribution brings them together in sympatry. I can show that a combination of sympatric distribution, conflicting genetically determined and learned mate recognition mechanisms, and genomic compatibility between species helps to explain the long-standing puzzle of waterfowl hybridisation and introgression of genes from one duck species into another. Besides obvious management implications I propose that this fact can be part of the explanation why ducks are so well adaptable and successful, as well as why they show extraordinary abilities to withstand AI infections, or its consequences for health status.

    Temperature-induced plasticity in egg size and resistance of eggs to temperature stress in a soil arthropod
    Liefting, M. ; Weerenbeck, M. ; Dooremalen, C. van; Ellers, J. - \ 2010
    Functional Ecology 24 (2010)6. - ISSN 0269-8463 - p. 1291 - 1298.
    guttata-guttata lepidoptera - drosophila-melanogaster - orchesella-cincta - evolutionary genetics - adaptive significance - fitness consequences - thermal evolution - migrant skipper - reaction norms - seed beetle
    Keywords:acclimation;cold shock;development rate;egg hatching;heat shock;phenotypic plasticity;Orchesella cincta;oviposition temperature Summary 1. Temperature is considered one of the most important mediators of phenotypic plasticity in ectotherms, resulting in predictable changes in egg size. However, the fitness consequences of temperature-induced plasticity in egg size are not well understood and are often assessed at mild temperatures, whereas in the field, extreme temperatures will occur. 2. In this study we investigated egg size plasticity and fitness-linked traits of eggs in response to temperature in the springtail Orchesella cincta. Eggs were oviposited at two temperatures (16 and 20 °C), and transplanted to 10, 15 and 20 °C for rearing, or exposed to temperature shock (-6 and 38 °C) to measure survival, development rate and growth. 3. Eggs oviposited at 16 °C had a greater volume and dry weight than eggs oviposited at 20 °C but had similar lipid content. Eggs oviposited at 16 °C had high survival at all rearing temperatures, whereas survival of eggs oviposited at 20 °C declined at lower rearing temperatures and was significantly lower than survival of large eggs when reared at 10 and 15 °C. No difference in egg development rate was found between oviposition temperatures, although development rate increased with rearing temperature. Juveniles were 5–10% larger when hatching from eggs oviposited at 16 °C, independent of the temperature at which the eggs were reared. 4. Eggs oviposited at 16 °C were more resistant to thermal stress, as their survival after exposure to cold or heat shock was higher than survival of eggs oviposited at 20 °C. However, egg development rate of the eggs that survived temperature shock was not different from the control, independent of egg oviposition temperature. 5. Our results show that temperature-induced plasticity in O. cincta affects fitness-linked traits of offspring through increased hatchling size and increased thermal tolerance of eggs produced at lower temperatures. 6. The increased resistance to thermal stress of O. cincta eggs oviposited at lower temperatures may provide a protective strategy in uncertain thermal environments.
    De evolutionaire dimensie van duurzaam visserijbeheer
    Rijnsdorp, A.D. - \ 2008
    IJmuiden : IMARES (Rapport / Wageningen IMARES C105/08) - 19
    visserij - visserijbeheer - evolutionaire genetica - adaptatiefysiologie - soortvorming - duurzaamheid (sustainability) - fisheries - fishery management - evolutionary genetics - adaptation physiology - speciation - sustainability
    Dit rapport behandelt de evolutionaire consequenties van visserij en de implicaties hiervan voor het duurzaam beheer. Visserij verhoogt de kans dat vissen worden weggevangen voordat ze volwassen worden en zich kunnen voortplanten. Dit betekent dat de dieren die genetisch geprogrammeerd zijn om op jongere leeftijd volwassen te meer nakomelingen zullen produceren dan dieren die pas op latere leeftijd volwassen worden. Een andere eigenschap die beïnvloed kan worden is de voortplantingsinspanning (aantal eieren) en de groeisnelheid. Dieren die meer eieren produceren zijn in het voordeel. Een verlaging van de geslachtsrijpe leeftijd en een verhoging van de voortplantingsinspanning resulteert in een afname van de groeisnelheid. Visserij leidt dus tot verschuivingen in de genetische eigenschappen (evolutionaire veranderingen) van de geëxploiteerde bestanden. In dit rapport wordt een overzicht gegevens van de huidige wetenschappelijk inzichten in de door de visserijgeïnduceerde evolutie en de implicaties die dit heeft voor het visserijbeheer. Speciale aandacht wordt gegeven aan de beschikbare kennis over Noordzee platvis en de mogelijkheden die er zijn om op basis van deze kennis tot een Evolutionair Impact Assessment voor deze bestanden te komen.
    Genetic analysis of larval host-plant preference in two sibling species of Helicoverpa
    Tang, Q.B. ; Jiang, J.W. ; Yan, Y.H. ; Loon, J.J.A. van; Wang, C.Z. - \ 2006
    Entomologia Experimentalis et Applicata 118 (2006)3. - ISSN 0013-8703 - p. 221 - 228.
    phytophagous insects - drosophila-melanogaster - swallowtail butterflies - oviposition preference - evolutionary genetics - heliothis-virescens - foraging behavior - food preference - h-assulta - lepidoptera
    The genetic basis of larval host-plant preference was investigated in reciprocal F1, F2, and backcrossed generations derived from hybrid crosses between the generalist species Helicoverpa armigera (Hu¿bner) and the closely related specialist species Helicoverpa assulta (Guene¿e) (Lepidoptera: Noctuidae). Host-plant preference for cotton [Gossypium arboreum L. (Malvaceae)] and pepper [Capsicum frutescens L. (Solanaceae)] of fifth-instar caterpillars was tested by using a two-choice leaf-disk assay. Helicoverpa armigera and H. assulta were significantly different in their feeding preferences, but the difference was not significant in the reciprocal hybrids, which showed there were no maternal/cytoplasmic effects. Comparisons of feeding preference between different groups of females or males demonstrated that the trait was not controlled by sex-linked loci. The distributions of feeding preference index values for crosses that carried similar complements of autosomal genes were not significantly different, whereas crosses with different complements of autosomal genes were associated with significantly different feeding preferences, indicating that feeding preference of the two species for cotton and pepper, respectively, is controlled by autosomal genes. It was found that one major autosomal locus affected this feeding preference, with the H. armigera-derived alleles being partially dominant to those carried by H. assulta. The genetic analysis of hybrids contributes to understand the evolution of feeding preference in these closely related species
    Quantitative genetic variation in an island population of the speckled wood butterfly (Pararge aegeria)
    Windig, J.J. ; Veerkamp, R.F. ; Nylin, S. - \ 2004
    Heredity 93 (2004)5. - ISSN 0018-067X - p. 450 - 454.
    sexual size dimorphism - bicyclus-anynana - fluctuating asymmetry - inbreeding depression - evolutionary genetics - natural-selection - reaction norms - wing pattern - trade-offs - inachis-io
    Evidence of changes in levels of genetic variation in the field is scarce. Theoretically, selection and a bottleneck may lead to the depletion of additive genetic variance (VA) but not of nonadditive, dominance variance (VD), although a bottleneck may converse VD to V A. Here we analyse quantitative genetic variation for the Speckled Wood butterfly Pararge aegeria on the island of Madeira about 120 generations after first colonisation. Colonisation of the island involved both a bottleneck and strong natural selection, changing the average value of traits. Several life history and morphological traits with varying levels of change since colonisation were analysed. In accordance with expectations, all traits except one showed relatively low levels of VA, with an average heritability (h2) of 0.078. Levels of VD for these traits were relatively high, 20-94% of total variance and on average 80% of VG. The exception was a morphological trait that probably had not experienced strong natural selection after colonisation, for which a h2 of 0.27 was found. Another interesting observation is that the population seems resistant to inbreeding effects, which may be the result of purging of deleterious alleles.
    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.
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