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Variation in foraging strategies over a large spatial scale reduces parent–offspring conflict in Manx shearwaters
Wischnewski, Saskia ; Arneill, Gavin E. ; Bennison, Ashley W. ; Dillane, Eileen ; Poupart, Timothée A. ; Hinde, Camilla A. ; Jessopp, Mark J. ; Quinn, John L. - \ 2019
Animal Behaviour 151 (2019). - ISSN 0003-3472 - p. 165 - 176.
dual foraging - Mid-Altlantic Ridge - parental care - parent–offspring conflict - Procellariiformes - spatial ecology - trade-off - tubenoses
Parental care can lead to a conflict of interest between parents and offspring. For central place foragers, conflict is expected to be particularly intensive in species that feed on relatively inaccessible, distant food resources. Some pelagic seabirds use distinct foraging strategies when provisioning young versus self-feeding: short trips near the colony versus long trips far away. Limited empirical evidence suggests that the strategy used by parents depends on their own state and that of their young, suggesting that dynamic optimization may help reduce conflict. Tests of this hypothesis, however, are scarce. Using a combination of GPS tracking and nest monitoring, we examined whether foraging strategy choice by Manx shearwaters, Puffinus puffinus, is explained by the body condition of parents and offspring before trip departure, and whether choice affects condition upon return. When chick body condition was poor prior to departure, subsequent foraging trips by adults were significantly shorter and faster, and chick condition upon return improved. When chick condition was good prior to departure, the reverse happened. There was no evidence that adult condition affected subsequent trip choice, but adults returning from slow, long-duration trips were in comparatively better condition. Thus, although the trips that were good for offspring were different to those that were favourable for adults, trip choice was only dependent on chick condition, which may explain why there was no evidence for a trade-off between adult and chick condition during individual trips. Our results suggest that spatiotemporal variation in foraging strategies is driven by the conflicting needs of parents and offspring, but that the parents can reduce the conflict, resulting in no detectable trade-off under these conditions. This link between parental care and space use is likely to be widespread in central place foragers but remains largely unexplored in most systems.
Data from: Simulated moult reduces flight performance but overlap with breeding does not affect breeding success in a long-distance migrant
Mizumo Tomotani, Barbara ; Muijres, F.T. ; Koelman, Julia ; Casagrande, Stefania ; Visser, Marcel E. - \ 2017
trade-off - pied flycatcher - high-speed camera - parental care - PIT-TAG - oxidative stress - plumage - Ficedula hypoleuca
1. Long-distance migrants are time-constrained as they need to incorporate many annual cycle stages within a year. Migratory passerines moult in the short interval between breeding and migration. To widen this interval, moult may start while still breeding, but this results in flying with moulting wings when food provisioning. 2. We experimentally simulated wing gaps in breeding male pied flycatchers by plucking 2 primary feathers from both wings. We quantified the nest visitations of both parents, proportion of high-quality food brought to the nestlings and adults and nestlings condition. Differences in oxidative damage caused by a possible reduction in flight efficiency were measured in amounts of ROMs and OXY in the blood. We also measured how flight performance was affected with recordings of the male`s escape flight using high-speed cameras. Finally, we collected data on adult survival, clutch size and laying date in the following year. 3. “Plucked” males travelled a 5% shorter distance per wingbeat, showing that our treatment reduced flight performance. In line with this, “plucked” males visited their nests less often. Females of “plucked” males, however, visited the nest more often than controls, and fully compensated their partner’s reduced visitation rate. As a result, there were no differences between treatments in food quality brought to the nest, adult or chick mass or number of successfully fledged chicks. Males did not differ in their oxidative damage or local survival to the following year. In contrast, females paired with plucked males tended to return less often to breed in the next year in comparison to controls, but this difference was not significant. For the birds that did return there were no effects on breeding. 5. Our results reveal that wing gaps in male pied flycatchers reduce their flight performance, but when it occurs during breeding they prioritise their future reproduction by reducing parental care. As a result, there is no apparent detriment to their condition during breeding. Because non-moulting females are able to compensate their partner’s reduced care, there is also no immediate costs to the offspring, but females may pay the cost suffering from a reduced survival.
Cell kinetics during regeneration in the sponge Halisarca caerulea: how local is the response to tissue damage?
Alexander, B.E. ; Achlatis, M. ; Osinga, R. ; Geest, H.G. van der; Cleutjens, J.P.M. ; Schutte, B. ; Goeij, J.M. de - \ 2015
PeerJ 3 (2015). - ISSN 2167-8359
coral-reef sponges - morphological strategies - sublittoral demosponge - chemical defenses - cycle checkpoints - gene-expression - life-history - trade-off - growth - population
Sponges have a remarkable capacity to rapidly regenerate in response to wound infliction. In addition, sponges rapidly renew their filter systems (choanocytes) to maintain a healthy population of cells. This study describes the cell kinetics of choanocytes in the encrusting reef sponge Halisarca caerulea during early regeneration (0–8 h) following experimental wound infliction. Subsequently, we investigated the spatial relationship between regeneration and cell proliferation over a six-day period directly adjacent to the wound, 1 cm, and 3 cm from the wound. Cell proliferation was determined by the incorporation of 5-bromo-2'-deoxyuridine (BrdU). We demonstrate that during early regeneration, the growth fraction of the choanocytes (i.e., the percentage of proliferative cells) adjacent to the wound is reduced (7.0 ± 2.5%) compared to steady-state, undamaged tissue (46.6 ± 2.6%), while the length of the cell cycle remained short (5.6 ± 3.4 h). The percentage of proliferative choanocytes increased over time in all areas and after six days of regeneration choanocyte proliferation rates were comparable to steady-state tissue. Tissue areas farther from the wound had higher rates of choanocyte proliferation than areas closer to the wound, indicating that more resources are demanded from tissue in the immediate vicinity of the wound. There was no difference in the number of proliferative mesohyl cells in regenerative sponges compared to steady-state sponges. Our data suggest that the production of collagen-rich wound tissue is a key process in tissue regeneration for H. caerulea, and helps to rapidly occupy the bare substratum exposed by the wound. Regeneration and choanocyte renewal are competing and negatively correlated life-history traits, both essential to the survival of sponges. The efficient allocation of limited resources to these life-history traits has enabled the ecological success and diversification of sponges.
Maternal allocation in cooperative breeders: Should mothers match or compensate for expected helper contributions?
Savage, J.L. ; Russell, A.F. ; Johnstone, R.A. - \ 2015
Animal Behaviour 102 (2015). - ISSN 0003-3472 - p. 189 - 197.
egg size - clutch size - trade-off - parental investment - male attractiveness - offspring quality - breeding birds - body-size - number - growth
Among species with variable numbers of individuals contributing to offspring care, an individual's investment strategy should depend upon both the size of the breeding group and the relative contributions of each carer. Existing theoretical work on carer investment rules has, however, largely focused on biparental care, and on modelling offspring provisioning in isolation from other stages of investment. Consequently, there has been little exploration of how maternal investment prior to birth might be expected to influence carer provisioning decisions after birth, and how these should be modified by the number of carers present. In particular, it is unclear whether mothers should increase or decrease their investment in each offspring under favourable rearing conditions, and whether this differs under alternative assumptions about the consequences of being ‘high quality’ at birth. We develop a game-theoretical model of cooperative care that incorporates female control of prebirth investment, and allow increased maternal investment to either substitute for later investment (giving offspring a ‘head start’) or raise the value of later investment (a ‘silver spoon’). We show that mothers reduce prebirth investment under better rearing conditions (more helpers) when investment is substitutable, leading to concealed helper effects. In contrast, when maternal prebirth investment primes offspring to benefit more from postbirth care, mothers should take advantage of good care environments by investing more in offspring both before and after birth. These results provide novel mechanisms to explain contrasting patterns of maternal investment across cooperative breeders.
Explaining biomass growth of tropical canopy trees: the importance of sapwood
Sande, M.T. van der; Zuidema, P.A. ; Sterck, F.J. - \ 2015
Oecologia 177 (2015)4. - ISSN 0029-8549 - p. 1145 - 1155.
woody-tissue respiration - lowland rain-forest - stem water storage - functional traits - leaf traits - good predictors - light gradient - trade-off - ecology - area
Tropical forests are important in worldwide carbon (C) storage and sequestration. C sequestration of these forests may especially be determined by the growth of canopy trees. However, the factors driving variation in growth among such large individuals remain largely unclear. We evaluate how crown traits [total leaf area, specific leaf area and leaf nitrogen (N) concentration] and stem traits [sapwood area (SA) and sapwood N concentration] measured for individual trees affect absolute biomass growth for 43 tropical canopy trees belonging to four species, in a moist forest in Bolivia. Biomass growth varied strongly among trees, between 17.3 and 367.3 kg year-1, with an average of 105.4 kg year-1. We found that variation in biomass growth was chiefly explained by a positive effect of SA, and not by tree size or other traits examined. SA itself was positively associated with sapwood growth, sapwood lifespan and basal area. We speculate that SA positively affects the growth of individual trees mainly by increasing water storage, thus securing water supply to the crown. These positive roles of sapwood on growth apparently offset the increased respiration costs incurred by more sapwood. This is one of the first individual-based studies to show that variation in sapwood traits—and not crown traits—explains variation in growth among tropical canopy trees. Accurate predictions of C dynamics in tropical forests require similar studies on biomass growth of individual trees as well as studies evaluating the dual effect of sapwood (water provision vs. respiratory costs) on tropical tree growth.
Functional Trait Strategies of Trees in Dry and Wet Tropical Forests Are Similar but Differ in Their Consequences for Succession
Lohbeck, M.W.M. ; Lebrija-Trejos, E.E. ; Martinez-Ramos, M. ; Meave, J.A. ; Poorter, L. ; Bongers, F. - \ 2015
PLoS ONE 10 (2015)4. - ISSN 1932-6203
plant economics spectrum - leaf life-spans - seed size - secondary succession - neotropical forests - shade-tolerance - woody-plants - trade-off - drought - dispersal
Global plant trait studies have revealed fundamental trade-offs in plant resource economics. We evaluated such trait trade-offs during secondary succession in two species-rich tropical ecosystems that contrast in precipitation: dry deciduous and wet evergreen forests of Mexico. Species turnover with succession in dry forest largely relates to increasing water availability and in wet forest to decreasing light availability. We hypothesized that while functional trait trade-offs are similar in the two forest systems, the successful plant strategies in these communities will be different, as contrasting filters affect species turnover. Research was carried out in 15 dry secondary forest sites (5-63 years after abandonment) and in 17 wet secondary forest sites (
Hydraulics and life history of tropical dry forest tree species: coordination of species' drought and shade tolerance
Markesteijn, L. ; Poorter, L. ; Bongers, F. ; Paz, H. ; Sack, L. - \ 2011
New Phytologist 191 (2011)2. - ISSN 0028-646X - p. 480 - 495.
woody-plants - cavitation resistance - xylem cavitation - desiccation-tolerance - leaf traits - trade-off - photosynthetic traits - regeneration niche - biomass allocation - water potentials
Plant hydraulic architecture has been studied extensively, yet we know little about how hydraulic properties relate to species’ life history strategies, such as drought and shade tolerance. The prevailing theories seem contradictory. We measured the sapwood (Ks) and leaf (Kl) hydraulic conductivities of 40 coexisting tree species in a Bolivian dry forest, and examined associations with functional stem and leaf traits and indices of species’ drought (dry-season leaf water potential) and shade (juvenile crown exposure) tolerance. Hydraulic properties varied across species and between life-history groups (pioneers vs shade-tolerant, and deciduous vs evergreen species). In addition to the expected negative correlation of Kl with drought tolerance, we found a strong, negative correlation between Kl and species’ shade tolerance. Across species, Ks and Kl were negatively correlated with wood density and positively with maximum vessel length. Consequently, drought and shade tolerance scaled similarly with hydraulic properties, wood density and leaf dry matter content. We found that deciduous species also had traits conferring efficient water transport relative to evergreen species. Hydraulic properties varied across species, corresponding to the classical trade-off between hydraulic efficiency and safety, which for these dry forest trees resulted in coordinated drought and shade tolerance across species rather than the frequently hypothesized trade-off.
Predation danger can explain changes in timing of migration: the case of the Barnacle goose
Jonker, R.M. ; Eichhorn, G. ; Langevelde, F. van; Bauer, S. - \ 2010
PLoS ONE 5 (2010)6. - ISSN 1932-6203 - 8 p.
optimal avian migration - branta-leucopsis - heart-rate - oxygen-consumption - spring migration - range expansion - bird migration - climate-change - stopover site - trade-off
Understanding stopover decisions of long-distance migratory birds is crucial for conservation and management of these species along their migratory flyway. Recently, an increasing number of Barnacle geese breeding in the Russian Arctic have delayed their departure from their wintering site in the Netherlands by approximately one month and have reduced their staging duration at stopover sites in the Baltic accordingly. Consequently, this extended stay increases agricultural damage in the Netherlands. Using a dynamic state variable approach we explored three hypotheses about the underlying causes of these changes in migratory behavior, possibly related to changes in (i) onset of spring, (ii) potential intake rates and (iii) predation danger at wintering and stopover sites. Our simulations showed that the observed advance in onset of spring contradicts the observed delay of departure, whereas both increased predation danger and decreased intake rates in the Baltic can explain the delay. Decreased intake rates are expected as a result of increased competition for food in the growing Barnacle goose population. However, the effect of predation danger in the model was particularly strong, and we hypothesize that Barnacle geese avoid Baltic stopover sites as a response to the rapidly increasing number of avian predators in the area. Therefore, danger should be considered as an important factor influencing Barnacle goose migratory behavior, and receive more attention in empirical studies
Life-history traits in closely related secondary parasitoids sharing the same primary parasitoid host: evolutionary opportunities and constraints
Harvey, J.A. ; Wagenaar, R. ; Bezemer, T.M. - \ 2009
Entomologia Experimentalis et Applicata 132 (2009)2. - ISSN 0013-8703 - p. 155 - 164.
egg-production - body-size - hymenopteran parasitoids - reproductive strategies - endoparasitoid wasp - cotesia-glomerata - asobara-tabida - lysibia-nana - trade-off - allocation
Thus far, few studies have compared life-history traits amongst secondary parasitoids attacking and developing in cocoons of their primary parasitoid hosts. This study examines development and reproduction in Lysibia nana Gravenhorst and Acrolyta nens Hartig (both Hymenoptera: Ichneumonidae), two related and morphologically similar secondary parasitoids that attack pupae of the gregarious endoparasitoid, Cotesia glomerata L. (Hymenoptera: Braconidae). On black mustard, Brassica nigra L. (Brassicaceae) plants in a field plot, adults of L. nana and A. nens frequently emerged from the same cocoon broods of C. glomerata. Based on similarities in their phylogeny and morphology, it was hypothesized that both species would exhibit considerable overlap in other life-history traits. In both L. nana and A. nens, adult wasp size increased with host cocoon mass at parasitism, although L. nana wasps were slightly larger than A. nens wasps, and completed their development earlier. Adult females of both species emerged with no eggs but matured eggs at similar rates over the following days. When provided with 20 host cocoons daily, fecundity in female L. nana was slightly more skewed towards early life than in A. nens, although lifetime fecundity did not differ between the two species. Longevity was significantly reduced in females of both species that were provided with hosts. Both parasitoids were found to exhibit strong similarities in life-history and development traits and in their ecological niche, thereby supporting our general hypothesis. Competition between L. nana and A. nens is presumably diffused because their preferred host (C. glomerata) is relatively abundant in open habitats.
Improving the scale and precision of hypotheses to explain root foraging ability
Kembel, S.W. ; Kroon, H. de; Cahill, J.F. ; Mommer, L. - \ 2008
Annals of Botany 101 (2008)9. - ISSN 0305-7364 - p. 1295 - 1301.
morphological plasticity - trade-off - nutrient heterogeneity - phenotypic plasticity - resource capture - plants bother - growth-rate - proliferation - grassland - responses
Background: Numerous hypotheses have been proposed to explain the wide variation in the ability of plants to forage for resources by proliferating roots in soil nutrient patches. Comparative analyses have found little evidence to support many of these hypotheses, raising the question of what role resource-foraging ability plays in determining plant fitness and community structure. Scope: In the present viewpoint, we respond to Grime's (2007; Annals of Botany 99: 1017–1021) suggestion that we misinterpreted the scope of the scale–precision trade-off hypothesis, which states that there is a trade-off between the spatial scale over which plant species forage and the precision with which they are able to proliferate roots in resource patches. We use a meta-analysis of published foraging scale–precision correlations to demonstrate that there is no empirical support for the scale–precision trade-off hypothesis. Based on correlations between foraging precision and various plant morphological and ecophysiological traits, we found that foraging precision forms part of the ‘fast’ suite of plant traits related to rapid growth rates and resource uptake rates. Conclusions: We suggest there is a need not only to examine correlations between foraging precision and other plant traits, but to expand our notion of what traits might be important in determining the resource-foraging ability of plants. By placing foraging ability in the broader context of plant traits and resource economy strategies, it will be possible to develop a new and empirically supported framework to understand how plasticity in resource uptake and allocation affect plant fitness and community structure
The LEDA Traitbase: a database of life-history traits of the Northwest European flora
Kleyer, M. ; Bekker, R.M. ; Knevel, I.C. ; Bakker, J.P. ; Thompson, K. ; Sonnenschein, M. ; Poschlod, P. ; Groenendael, J.M. van; Klimes, L. ; Klimesova, J. ; Klotz, S. ; Rusch, G.M. ; Hermy, M. ; Adriaens, D. ; Boedeltje, G. ; Bossuyt, B. ; Dannemann, A. ; Endels, P. ; Götzenberger, L. ; Hodgson, J.G. ; Jackel, A.K. ; Kühn, L. ; Kunzmann, D. ; Ozinga, W.A. ; Römermann, C. ; Stadler, M. ; Schlegelmilch, J. ; Steendam, H.J. ; Tackenberg, O. ; Wilmann, B. ; Cornelissen, J.H.C. ; Eriksson, O. ; Garnier, E. ; Peco, B. - \ 2008
Journal of Ecology 96 (2008). - ISSN 0022-0477 - p. 1266 - 1274.
plant functional traits - trade-off - communities - dispersal - mechanisms - consequences - regeneration - biodiversity - divergence - attributes
An international group of scientists has built an open internet data base of life-history traits of the Northwest European flora (the LEDA-Traitbase) that can be used as a data source for fundamental research on plant biodiversity and coexistence, macro-ecological patterns and plant functional responses. The species-trait matrix comprises referenced information under the control of an editorial board, for ca. 3000 species of the Northwest European flora, combining existing information and additional measurements. The data base currently contains data on 26 plant traits that describe three key features of plant dynamics: persistence, regeneration and dispersal. The LEDA-Traitbase is freely available at http://www.leda-traitbase.org. We present the structure of the data base and an overview of the trait information available. Synthesis. The LEDA Traitbase is useful for large-scale analyses of functional responses of communities to environmental change, effects of community trait composition on ecosystem properties and patterns of rarity and invasiveness, as well as linkages between traits as expressions of fundamental trade-offs in plants.
Coexistence in North Sea fish communities: implications for growth and natural mortality
Gislason, H. ; Pope, J.G. ; Rice, J.C. ; Daan, N. - \ 2008
ICES Journal of Marine Science 65 (2008)4. - ISSN 1054-3139 - p. 514 - 530.
cod gadus-morhua - life-history - marine fishes - trade-off - environmental-temperature - teleost fishes - west-coast - population - predation - biology
For a fish community to persist over time, all species must be able on average to replace themselves on a one-for-one basis over their lifetime. We use this principle and a size-based equilibrium model where asymptotic length is used as a functional trait to investigate how natural mortality should scale with size within and across pelagic and demersal species of North Sea teleosts. The model predicts natural mortality to scale with body length raised to a power of ¿1.66 at current levels of exploitation. Additionally, natural mortality of demersal species should be proportional to asymptotic length raised to a power of 0.80, so generating a higher natural mortality at a given length for large species than for small ones. The model also suggests that the exponent in the scaling of the von Bertalanffy growth parameter K with asymptotic length should be more negative for pelagic than for demersal species. We test our results by analysing independent estimates of predation mortality, the scaling of maximum recruitment per unit of spawning-stock biomass with asymptotic length, and the general relationship between K and asymptotic length for demersal and pelagic families of fish. All tests are consistent with our modelling results.
Food intake, growth, and reproduction as affected by day length and food availability in the pond snail Lymnaea stagnalis
Maat, A. ter; Zonneveld, C. ; Visser, J.A.G.M. de; Jansen, R.F. ; Montagne-Wajer, K. ; Koene, J.M. - \ 2007
American Malacological Bulletin 23 (2007)1-2. - ISSN 0740-2783 - p. 113 - 120.
caudo-dorsal cells - egg-laying behavior - freshwater snail - ovulation hormone - energy budgets - trade-off - neurohormone - photoperiod - precursor - peptides
With the aim of integrating the physiology and evolutionary ecology of Lymnaea stagnalis (Linnaeus, 1758), we studied the effects of day length and food availability on the energy budget. Snails were assigned to two different photoperiods and three levels of food availability. The snails were kept individually, and food consumption, growth, and egg production were measured for about 2 months. Snails could nearly compensate for a one-day starvation period by increasing the rate of food-intake. However, food-intake rates did not increase further after a starvation period of 2 days. Growth was well described by the Von Bertalanffy growth equation. The ultimate size of snails kept under medium-day conditions (MD; light:dark = 12:12 h) was not affected by food availability. By contrast, the ultimate size of snails kept under long-day conditions (LD; light:dark = 16:8 h) depended on food availability; those fed the lowest quantities grow the least. Dry-weight densities (dry weight/wet weight) of MD snails were considerably above those of LD snails. In MD snails, food availability did not appreciably affect dry-weight density. By contrast, in LD snails, dry-weight density decreased with decreasing food availability. The reproductive output of LD snails declined with declining food availability, but was 2 to 4 times that of MD snails. The difference in reproductive output was largely accounted for by the difference in stored energy, i.e. dry-weight density. To gauge the extent to which the conclusions from our laboratory work applied to free-living snails, a field study was conducted. The wild-caught snails' dry-weight density was also lowest in long-day conditions when most eggs were laid. However, the dry-weight densities during medium and short days were lower than the dry-weight densities of laboratory animals under LD conditions. Thus, in the field, snails stored less energy than in the laboratory.
Effects of host deprivation and egg expenditure on the reproductive capacity of Mastrus ridibundus, an introduced parasitoid for the biological control of codling moth in California
Hougardy, E. ; Bezemer, T.M. ; Mills, N.J. - \ 2005
Biological Control 33 (2005)1. - ISSN 1049-9644 - p. 96 - 106.
asobara-tabida - oviposition behavior - trade-off - hymenoptera - allocation - field - load - survival - parasitization - availability
The effect of host deprivation and egg expenditure on egg load, realized fecundity, and parasitism of the ichneumonid Mastrus ridibundus, a gregarious parasitoid introduced for the control of codling moth in California, were investigated under laboratory conditions. Females deprived of hosts had a greater egg load than females provided with excess hosts and no egg resorption was observed, the results even suggesting that females continue to add reserves to eggs over time. Host-deprived females were able to immediately use the eggs stored in their ovarioles, even after 6 days of host deprivation, and egg laying peaked on the first day of host availability. However, beyond the first day of reproduction, both daily oviposition and host attack rates were reduced, and overall, host-deprived females had a lower lifetime fecundity and attacked a lower number of hosts compared to females that were provided with excess host since their emergence. The occurrence of a potential trade-off between early and late reproduction and between reproduction and survival was also investigated. Early oviposition did not affect future reproduction nor survival. These results are discussed in the context classical biological control, with the view to understand how to manipulate host availability during the pre-release period to increase the reproductive potential, and therefore the fitness and establishment potential of M. ridibundus
Genetic basis and fitness consequences of winglessness in the two-spot ladybird beetle, Adalia bipunctata
Ueno, H. ; Jong, P.W. de; Brakefield, P.M. - \ 2004
Heredity 93 (2004)3. - ISSN 0018-067X - p. 283 - 289.
wing dimorphism - gryllus-rubens - sand cricket - trade-off - evolution - insects - polymorphism - coleoptera - flightlessness - populations
The genetic basis and fitness consequences of winglessness were investigated in the two-spot ladybird beetle, Adalia bipunctata. By breeding lines from a wingless individual found at The Uithof, Utrecht in The Netherlands, the wingless condition was confirmed to be under the control of a major allele, recessive to the wild type. Wingless individuals, on average, had a longer developmental period, a lower egg production and a shorter lifespan than the wild type with wings, suggesting that the expression of the wingless allele has functionally interrelated gene actions involving a wide range of fitness components. While the wingless allele influences various traits, significant among-family variation in the degree of winglessness suggests that its phenotypic expression is also dependent on the genetic background and modifier loci. Furthermore, there was a consistent pattern of correlation between the degree of winglessness and life history traits; the most extreme wingless individuals showed the lowest fitness while those with more fully developed wings tended to have the highest fitness. This correlation suggests that the modifier genes influence both wing formation and fitness components. The significance of such epistatic effects to the evolution of flightlessness in insects is discussed.