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Robert F. Rockwell - One of the best experts on this subject based on the ideXlab platform.
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Estimating Repeatability of Egg Size
The Auk, 2001Co-Authors: Paul L. Flint, Robert F. Rockwell, James S. SedingerAbstract:Abstract Measures of repeatability have long been used to assess patterns of variation in Egg Size within and among females. We compared different analytical approaches for estimating repeatability of Egg Size of Black Brant. Separate estimates of repeatability for Eggs of each clutch Size and laying sequence number varied from 0.49 to 0.64. We suggest that using the averaging Egg Size within clutches results in underestimation of variation within females and thereby overestimates repeatability. We recommend a nested design that partitions Egg-Size variation within clutches, among clutches within females, and among females. We demonstrate little variation in estimates of repeatability resulting from a nested model controlling for Egg laying sequence and a nested model in which we assumed laying sequence was unknown.
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Female age and Egg Size in the Lesser Snow Goose
Journal of Avian Biology, 1994Co-Authors: Gregory J. Robertson, Robert F. Rockwell, David B. Lank, Evan G. Cooch, F. CookeAbstract:We studied the relationship between female age and Egg Size of the Lesser Snow Goose Anser caerulescens caerulescens at La Perouse Bay, Manitoba, Canada, over a period of 15 years (1976-90). Two and three years old birds laid significantly lighter Eggs than the rest of the population in a given year, laying sequence and clutch Size. Analysis of repeated measures of individual birds showed equivalent results. Younger birds also laid Eggs which were significantly longer and thinner than Eggs laid by older birds. The pattern of intraclutch Egg Size variation was the same in both young and old birds, with younger birds laying slightly smaller Eggs in each position within the laying sequence. Some physiological maturation process was probably responsible for the smaller Eggs younger birds laid because the pattern held within individuals. However, changes in Egg Size and shape may be due to breeding experience rather than age itself. We detected no evidence for age-specific differences in Egg Size of older birds. Thus, neither senescent declines in Egg Size nor an increased allocation of reserves to reproduction appear to be occurring in this species.
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Fitness consequences of Egg-Size variation in the lesser snow goose
Oecologia, 1993Co-Authors: T. D. Williams, F. Cooke, David B. Lank, Robert F. RockwellAbstract:We investigated the relationship between EggSize variation and (a) Egg hatching success, (b) chick survival to fledging and recruitment, and (c) adult female survival, over 12 years in the lesser snow goose (Anser caerulescens caerulescens). By comparing the means and variances of Egg Size for successful and unsuccessful Eggs, our aim was to assess the relative fitness of Eggs of different Sizes and to determine the type of selection operating on Egg Size in this species. As both Egg Size and reproductive success vary with age in the lesser snow goose we controlled for the effects of female age. Egg-Size variation is very marked in this population, varying by up to 52% for Eggs hatching successfully. However, there was no relationship between Egg Size and post-hatching survival of goslings to fledging or recruitment, either within or between broods, pooling across years. Egg Size varied significantly between successful and unsuccessful clutches in only 2 of 33 individual year comparisons. First-laid Eggs surviving to onset of incubation, and Eggs hatching successfully, were on average larger than unsuccessful Eggs, but this was probably due to the confounding effects of female age-specific and sequence-specific Egg survival. Variance of Egg Size differed significantly between successful and unsuccessful Eggs in only 3 of 24, and 0 of 21, individual year comparisons for pre- and post-hatching survival respectively. We therefore found little evidence for a relationship between Egg-Size variation and offspring fitness, or for strong directional, normalising or diversifying selection operating on Egg Size, in the lesser snow goose. In addition, there was only weak support for the hypothesis that Egg-Size variation is maintained by temporal variation in selection pressure (sensu Ankney and Bisset 1973). It is likely that Egg-Size variation represents the pleiotropic expression of alleles affecting more general physiological or metabolic processes. While this does not rule out the existence of alleles with more direct effects on Egg Size we suggest that their contribution to heritable Egg Size is small.
Don R Levitan - One of the best experts on this subject based on the ideXlab platform.
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The relationship between Egg Size and fertilization success in broadcast-spawning marine invertebrates
Integrative and comparative biology, 2006Co-Authors: Don R LevitanAbstract:Synopsis Egg Size is a critical life-history trait because it can profoundly influence offspring fitness and the number of offspring that can be produced. Recently, interest has grown in how Egg Size influences fertilization rate and in turn how sperm availability might influence the evolution of Egg Size among broadcast-spawning marine invertebrates. In this article I review the empirical evidence on the ways in which Egg Size and Egg accessory structures influence fertilization and theoretical models of the ways sperm availability might influence the evolution of Egg Size. Evidence suggests that Egg Size does influence the collision frequency with sperm, and models suggest that sperm availability can influence selection on Egg Size. Sperm availability appears to be one of the several factors that influence optimal Egg Size in broadcast-spawning marine invertebrates.
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optimal Egg Size in marine invertebrates theory and phylogenetic analysis of the critical relationship between Egg Size and development time in echinoids
The American Naturalist, 2000Co-Authors: Don R LevitanAbstract:abstract: Life‐history models for marine invertebrate larvae generally predict a dichotomy in Egg Size in different species: Eggs should be either minimal in Size or large enough to support development fully without larval feeding. This prediction is contradicted, however, by the empirical observation of wide, continuous variation in Egg Size between these extremes. The prediction of dichotomy rests on the assumption of a negative linear relationship between Egg Size and development time. Here, I present a simple model in which development time is inversely proportional to Egg Size. Incorporating this relationship into an optimality model produces predictions of intermediate rather than extreme Egg Size. Modeled variations in mortality, food availability, fertilization rates, and temperature all produce continuous shifts in the value of the intermediate optimal Size, in direct contrast to those produced by previous models, which predict shifts between two extreme optima. Empirical data on echinoid Egg siz...
Klaus Fischer - One of the best experts on this subject based on the ideXlab platform.
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Maternal body Size as an evolutionary constraint on Egg Size in a butterfly.
Evolution; international journal of organic evolution, 2007Co-Authors: Stephanie Sandra Bauerfeind, Klaus FischerAbstract:Genetic and developmental constraints have often been invoked to explain patterns of existing morphologies. Yet, empirical tests addressing this issue directly are still scarce. We here set out to investigate the importance of maternal body Size as an evolutionary constraint on Egg Size in the tropical butterfly Bicyclus anynana, employing an artificial two-trait selection experiment on simultaneous changes in body and Egg Size (synergistic and antagonistic selection). Selection on maternal body Size and Egg Size was successful in both the synergistic and the antagonistic selection direction. Yet, responses to selection and realized heritabilities varied across selection regimes: the most extreme values for pupal mass were found in the synergistic selection directions, whereas in the antagonistic selection direction realized heritabilities were low and nonsignificant in three of four cases. In contrast, for Egg Size the highest values were obtained in the lines selected for low pupal mass. Thus, selection on body Size yielded a stronger correlated response in Egg Size than vice versa, which is likely to bias (i.e., constrain), if weakly, evolutionary change in body Size. However, it seems questionable whether this will prevent evolution toward novel phenotypes, given enough time and that natural selection is strong. Correlated responses to selection were overall weak. Egg and larval development times tended to be associated with changes in maternal Size, whereas variation in pupal development times weakly tended to follow variation in Egg Size. Lifetime fecundity was similar across selection regimes, except for females simultaneously selected for large body mass and small Egg Size, exhibiting increased fecundity. Multiple regressions showed that lifetime fecundity and concomitantly reproductive investment were primarily determined by longevity, as expected for an income breeder, whereas Egg Size was primarily determined by pupal mass. Evidence for a phenotypic trade-off between Egg Size and number was weak.
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The evolutionary genetics of Egg Size plasticity in a butterfly
Journal of evolutionary biology, 2005Co-Authors: Marc J. Steigenga, Bas J Zwaan, Paul M. Brakefield, Klaus FischerAbstract:The evolution of phenotypic plasticity requires that it is adaptive, genetically determined, and exhibits sufficient genetic variation. For the tropical butterfly Bicyclus anynana there is evidence that temperature-mediated plasticity in Egg Size is an adaptation to predictable seasonal change. Here we set out to investigate heritability in Egg Size and genetic variation in the plastic response to temperature in this species, using a half-sib breeding design. Egg Size of individual females was first measured at a high temperature 4 days after eclosion. Females were then transferred to a low temperature and Egg Size was measured after acclimation periods of 6 and 12 days respectively. Overall, additive genetic variance explained only 3–11% of the total phenotypic variance, whereas maternal effects were more pronounced. Genotype–environment interactions and cross-environmental correlations of less than unity suggest that there is potential for short-term evolutionary change. Our findings strengthen the support for the adaptive nature of temperature-mediated plasticity in Egg Size.
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genetic and environmental sources of Egg Size variation in the butterfly bicyclus anynana
Heredity, 2004Co-Authors: Bas J Zwaan, Klaus Fischer, Paul M. BrakefieldAbstract:By dividing families of the tropical butterfly, Bicyclus anynana, among different larval (including early pupal) and adult (including late pupal) temperatures, we investigate the genetic and environmental effects on Egg Size. Both sources of variation affected Egg Size to similar extents. As previously found in other arthropods, Egg Size tended to increase at lower temperatures. Our data suggest that the plastic response in Egg Size can be induced during the pupal stage. Females reared as larvae at the same high temperature tended to lay larger Eggs when transferred to a lower temperature, either as prepupae or pupae, compared to those remaining at the high temperature. Additionally, females reared as larvae at different temperatures, but maintained at the same temperature from the early pupal stage onwards, laid larger Eggs after larval growth at a low temperature. Heritability estimates for Egg Size were about 0.4 (parent–offspring regression) and 0.2 (variance component estimates using the full-sib families). Although there seemed to be some variation in the plastic response to temperature among families, genotype–environment interactions were nonsignificant.
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How does Egg Size relate to body Size in butterflies
Oecologia, 2002Co-Authors: Klaus Fischer, Bas J Zwaan, Paul M. BrakefieldAbstract:Although arthropod Egg Size is an evolutionarily and ecologically significant trait, there is still a poor understanding of the specific factors determining it. For butterflies there is evidence from an interspecific comparison that Egg Size is related to adult Size, suggesting a morphological constraint. Using laboratory populations of the tropical butterfly Bicyclus anynana, we show that larger Eggs produce larger hatchlings, and that there is considerable intra-populational variation in Egg Size. However, the correlation between Egg Size and female Size is weak and explains only 1% of the variation found within a population; even development time is a slightly better predictor for Egg Size than female Size. We conclude that there is no evidence that body Size imposes a constraint on the evolution of Egg Size within butterfly populations. However, populations that have diverged in body Size under artificial selection show correlated responses in Egg Size. Thus, correlations between body Size and Egg Size may represent an emergent property, visible only when a large range of differences in body Size is considered.
Tony D. Williams - One of the best experts on this subject based on the ideXlab platform.
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Experimental (antiestrogen-mediated) reduction in Egg Size negatively affects offspring growth and survival.
Physiological and biochemical zoology : PBZ, 2007Co-Authors: Emily C. Wagner, Tony D. WilliamsAbstract:Abstract The relationship between Egg Size and offspring phenotype is critical to our understanding of the selective pressures acting on the key reproductive life‐history traits of Egg Size and number. Yet there is surprisingly little empirical evidence to support a strong, positive relationship between Egg Size and offspring quality (i.e., offspring growth, condition, and survival) in birds, in part because of confounding effects of parental quality and the lack of experimental techniques for directly manipulating avian Egg Size independently of maternal condition. Previously, we showed that treatment of laying female zebra finches (Taeniopygia guttata) with the antiestrogen tamoxifen can decrease Egg Size by ca. 8% but that this reduction in Egg Size had few effects on offspring mass and Size at fledging. Here, we extend the use of this technique to induce larger decreases in Egg Size (up to 50% in individual females) and show that a reduction in Egg Size of ca. 18% is associated with decreased embryo v...
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intraspecific variation in Egg Size and Egg composition in birds effects on offspring fitness
Biological Reviews, 1994Co-Authors: Tony D. WilliamsAbstract:: 1. There is little unequivocal evidence to date in support of a positive relationship between Egg Size and offspring fitness in birds. Although 40 studies (of 34 species) have considered the effect of variation in Egg Size on chick growth and/or survival up to fledgling only 12 studies have controlled for other characters potentially correlated both with Egg Size and offspring fitness. Of these only two have reported a significant residual effect of Egg Size on chick growth (in the roseate tern and European blackbird) and three a residual effect on chick survival (all in seabirds: common tern, lesser black-backed gull and kittiwake). 2. More consistent evidence exists, though from fewer studies, for a positive relationship between Egg Size and offspring fitness early in the chick-rearing period; chick growth and chick survival being dependent on Egg Size in 8 of 10 studies and 4 of 5 studies respectively. It is suggested that the most important effect of variation in Egg Size might be in determining the probability of offspring survival in the first few days after hatching. 3. Egg Size explains on average 66% of the variation in chick mass at hatching (n = 35 studies) but only 30% of the variation in chick body Size (n = 18). When effects of hatching body Size are controlled for chick mass remains significantly correlated with Egg Size, though the reverse is not true. This supports the hypothesis that large Eggs give rise to heavier chicks at hatching, i.e., chicks with more nutrient (yolk) reserves, rather than structurally larger chicks. 4. Egg composition increased isometrically with increasing Egg Size in about half the studies so far reported (n equals approximately 20). However, in seabirds, and some passerines, larger Eggs contain disproportionately more albumen, whilst in some waterfowl percentage yolk content increases with increasing Egg Size. Changes in albumen content largely reflect variation in the water content of Eggs, but changes in yolk content involve variation in lipid content, and therefore in Egg 'quality.' The adaptive significance of variation in Egg composition is considered; females may adjust Egg composition facultatively to maximise the benefits to their offspring of increased reproductive investment. 5. Considerations for future research are discussed with particular emphasis on experimental studies and the application of new techniques.
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INTRASPECIFIC VARIATION IN Egg Size AND Egg COMPOSITION IN BIRDS: EFFECTS ON OFFSPRING FITNESS
Biological reviews of the Cambridge Philosophical Society, 1994Co-Authors: Tony D. WilliamsAbstract:1. There is little unequivocal evidence to date in support of a positive relationship between Egg Size and offspring fitness in birds. Although 40 studies (of 34 species) have considered the effect of variation in Egg Size on chick growth and/or survival up to fledgling only 12 studies have controlled for other characters potentially correlated both with Egg Size and offspring fitness. Of these only two have reported a significant residual effect of Egg Size on chick growth (in the roseate tern and European blackbird) and three a residual effect on chick survival (all in seabirds: common tern, lesser black-backed gull and kittiwake). 2. More consistent evidence exists, though from fewer studies, for a positive relationship between Egg Size and offspring fitness early in the chick-rearing period; chick growth and chick survival being dependent on Egg Size in 8 of 10 studies and 4 of 5 studies respectively. It is suggested that the most important effect of variation in Egg Size might be in determining the probability of offspring survival in the first few days after hatching. 3. Egg Size explains on average 66% of the variation in chick mass at hatching (n = 35 studies) but only 30% of the variation in chick body Size (n = 18). When effects of hatching body Size are controlled for chick mass remains significantly correlated with Egg Size, though the reverse is not true. This supports the hypothesis that large Eggs give rise to heavier chicks at hatching, i.e., chicks with more nutrient (yolk) reserves, rather than structurally larger chicks. 4. Egg composition increased isometrically with increasing Egg Size in about half the studies so far reported (n equals approximately 20). However, in seabirds, and some passerines, larger Eggs contain disproportionately more albumen, whilst in some waterfowl percentage yolk content increases with increasing Egg Size. Changes in albumen content largely reflect variation in the water content of Eggs, but changes in yolk content involve variation in lipid content, and therefore in Egg 'quality.' The adaptive significance of variation in Egg composition is considered; females may adjust Egg composition facultatively to maximise the benefits to their offspring of increased reproductive investment. 5. Considerations for future research are discussed with particular emphasis on experimental studies and the application of new techniques.
Paul M. Brakefield - One of the best experts on this subject based on the ideXlab platform.
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The evolutionary genetics of Egg Size plasticity in a butterfly
Journal of evolutionary biology, 2005Co-Authors: Marc J. Steigenga, Bas J Zwaan, Paul M. Brakefield, Klaus FischerAbstract:The evolution of phenotypic plasticity requires that it is adaptive, genetically determined, and exhibits sufficient genetic variation. For the tropical butterfly Bicyclus anynana there is evidence that temperature-mediated plasticity in Egg Size is an adaptation to predictable seasonal change. Here we set out to investigate heritability in Egg Size and genetic variation in the plastic response to temperature in this species, using a half-sib breeding design. Egg Size of individual females was first measured at a high temperature 4 days after eclosion. Females were then transferred to a low temperature and Egg Size was measured after acclimation periods of 6 and 12 days respectively. Overall, additive genetic variance explained only 3–11% of the total phenotypic variance, whereas maternal effects were more pronounced. Genotype–environment interactions and cross-environmental correlations of less than unity suggest that there is potential for short-term evolutionary change. Our findings strengthen the support for the adaptive nature of temperature-mediated plasticity in Egg Size.
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genetic and environmental sources of Egg Size variation in the butterfly bicyclus anynana
Heredity, 2004Co-Authors: Bas J Zwaan, Klaus Fischer, Paul M. BrakefieldAbstract:By dividing families of the tropical butterfly, Bicyclus anynana, among different larval (including early pupal) and adult (including late pupal) temperatures, we investigate the genetic and environmental effects on Egg Size. Both sources of variation affected Egg Size to similar extents. As previously found in other arthropods, Egg Size tended to increase at lower temperatures. Our data suggest that the plastic response in Egg Size can be induced during the pupal stage. Females reared as larvae at the same high temperature tended to lay larger Eggs when transferred to a lower temperature, either as prepupae or pupae, compared to those remaining at the high temperature. Additionally, females reared as larvae at different temperatures, but maintained at the same temperature from the early pupal stage onwards, laid larger Eggs after larval growth at a low temperature. Heritability estimates for Egg Size were about 0.4 (parent–offspring regression) and 0.2 (variance component estimates using the full-sib families). Although there seemed to be some variation in the plastic response to temperature among families, genotype–environment interactions were nonsignificant.
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How does Egg Size relate to body Size in butterflies
Oecologia, 2002Co-Authors: Klaus Fischer, Bas J Zwaan, Paul M. BrakefieldAbstract:Although arthropod Egg Size is an evolutionarily and ecologically significant trait, there is still a poor understanding of the specific factors determining it. For butterflies there is evidence from an interspecific comparison that Egg Size is related to adult Size, suggesting a morphological constraint. Using laboratory populations of the tropical butterfly Bicyclus anynana, we show that larger Eggs produce larger hatchlings, and that there is considerable intra-populational variation in Egg Size. However, the correlation between Egg Size and female Size is weak and explains only 1% of the variation found within a population; even development time is a slightly better predictor for Egg Size than female Size. We conclude that there is no evidence that body Size imposes a constraint on the evolution of Egg Size within butterfly populations. However, populations that have diverged in body Size under artificial selection show correlated responses in Egg Size. Thus, correlations between body Size and Egg Size may represent an emergent property, visible only when a large range of differences in body Size is considered.