Geographic variation in offspring size of a widespread lizard (Takydromus septentrionalis): importance of maternal investment

Geographic variation in offspring size is widespread, but the proximate causes of this variation have not yet been explicitly determined. We compared egg size and egg contents among five populations of a lizard (Takydromus septentrionalis, Günther, 1864) along a latitudinal gradient, and incubated eggs at two temperatures to determine the influence of maternal investment and incubation temperature on offspring size. The mean values for female size and egg size were both greater in the two northern populations (Chuzhou and Anji) than in the three southern populations (Lishui, Dongtou, and Ningde). The larger eggs were entirely attributable to the body size of females in the Anji population, but their increased size also stemmed from further enlargement of egg size relative to female body size in Chuzhou, the northernmost population sampled in this study. Eggs of the Chuzhou population contained more yolk and less water than those of southern populations. Despite the lower lipid content in the yolk, eggs from the Chuzhou population had higher energy contents than those from the two southern populations, owing to the larger egg size and increased volume of yolk. Hatchling size was not affected by incubation temperature, but differed significantly among populations, with hatchlings being larger in the Chuzhou population than in the other populations. Our data provide an inference that oviparous reptiles from cold climates may produce larger offspring, not only by increasing egg size but also by investing more energy into their eggs. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 59–67.     

The importance of energetic versus pelvic constraints on reproductive allocation by the eastern fence lizard (Sceloporus undulatus)

In ectothermic species, females often produce larger eggs in colder environments. Models based on energetic constraints suggest that this pattern is an adaptation to compensate for the slower growth of offspring in the cold. Yet, females in cold environments also tend to be larger than females in warm environments. Consequently, thermal clines in egg size could be caused by pelvic constraints, which stem from the inability of large eggs to pass through a small pelvic aperture. Models based on energetic constraints and models based on pelvic constraints predict similar relationships between maternal size and egg size. However, pelvic constraints should produce these relationships both within and among populations, whereas energetic constraints would not necessarily do so. If pelvic constraints are important, we might also expect small females to compensate by producing eggs that are relatively rich in lipids (i.e. high energy density). The present study aimed to assess whether energetic or pelvic constraints generate geographical variation in egg size of the lizard Sceloporus undulatus . Pelvic width is very highly correlated with body length in S. undulatus , making maternal size a suitable measure of pelvic constraint. Although maternal size and egg mass (dry and wet) covaried among populations, these variables were generally not related within populations. Energetic density of eggs tended to increase with decreasing egg mass (dry and wet), but this relationship was strongest in populations where no relationship between maternal size and egg mass was observed. Our results do not support the pelvic constraint model and thus indicate energetic constraints play a greater role in generating geographical variation in egg size.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 513–521.     

Geographical variation in reproductive traits and trade‐offs between size and number of eggs in the king ratsnake,Elaphe carinata

We collected gravid king ratsnakes (Elaphe carinata) from three geographically separated populations in Chenzhou (CZ), Lishui (LS) and Dinghai (DH) of China to study the geographical variation in female reproductive traits and trade‐offs between the size and number of eggs. Not all reproductive traits varied among the three populations. Of the traits examined, five (egg‐laying date, post‐oviposition body mass, clutch size, egg mass and egg width) differed among the three populations. The egg‐laying date, ranging from late June to early August, varied among populations in a geographically continuous trend, with females at the most northern latitude (DH) laying eggs latest, and females at the most southern latitude (CZ) laying eggs earliest. Such a trend was less evident or even absent in the other traits that differed among the three populations. CZ and DH females, although separated by a distance of approximately 1100 km as the crow flies, were similar to each other in most traits examined. LS females were distinguished from CZ and DH females by the fact that they laid a greater number of eggs, but these were smaller. The egg size–number trade‐off was evident in each of the three populations and, at a given level of relative fecundity, egg mass was significantly greater in the DH population than in the LS population. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 701–709.     

Allocation of offspring size and sex by female black ratsnakes

How females allocate resources to each offspring and how they allocate the sex of their offspring are two powerful potential avenues by which mothers can affect offspring fitness. Previous research has focussed extensively on mean offspring size, with much less attention given to variance in offspring size. Here we focussed on variation in offspring size in black ratsnakes, Elaphe obsoleta . We collected and hatched 105 clutches (1283 eggs) over 9 years. We predicted that females should lay larger eggs, or more variable eggs, when the environment is less predictable. We also predicted that females laying early or laying larger eggs should produce mostly sons because adult males are larger than adult female ratsnakes. The largest hatchling was more than twice the length and almost four times the mass of the smallest hatchling. Variation in offspring size was itself highly variable, with CVs in offspring mass among clutches ranging from 1% to 25%. With one exception, the variables we expected should influence variation in offspring size had little effect. We found that clutch size increased with maternal size and that egg size decreased with clutch size, but we found no evidence that variance in egg size among clutches increased as the season progressed or that females increased the mean size of their offspring the later in the season they laid their eggs. Females in better condition after they finish laying their eggs did produce larger eggs. There was no relationship between within-clutch variation in egg size and laying date or mean egg size. Finally, sex ratio did not vary with mean egg size or hatching date. Given evidence that offspring size in snakes affects survival, selection should reduce variation in offspring size unless that variance enhances maternal fitness and yet we found little support for hypothesized advantages of varying offspring size.     

Interpopulation variation in egg size in the winter cherry bug relative to oviposition site selection

To investigate whether or not oviposition on substrates other than host plants (e.g., non‐host plants, abiotic materials) would affect the evolution of egg size in phytophagous insects, we studied the winter cherry bug, Acanthocoris sordidus (Thunberg) (Heteroptera: Coreidae), as a model organism for its interpopulation variation in oviposition preference. The rate of oviposition off host plants is much higher in the Amami Island population than in either the Kyoto or Kochi populations. We compared egg size and number among the three local populations from Kyoto, Kochi, and Amami Island. In addition, to evaluate the adaptive significance of larger eggs for offspring in terms of searching for host plants, we examined the relationship between egg size and first‐instar body size. We also searched for a relationship between egg size and starvation tolerance in the second instars because first instars can develop to second instars without food intake, and thus the substantial host‐searching stage is the second instar, when females lay their eggs off host plants. Females from the Amami population produced fewer larger eggs than females from either the Kyoto or Kochi population. Regardless of the local population, the body size of first instars that emerged from larger eggs was larger, and the second instars originating from larger eggs had a higher starvation tolerance. The larger body size and higher starvation tolerance should enable nymphs to disperse further, which may enhance the probability of successfully reaching host plants. These results suggest that egg size in A. sordidus may be determined in relation to its oviposition habits to maximize reproductive success, resulting in interpopulation variation in egg size.     

Temperature‐mediated plasticity and genetic differentiation in egg size and hatching size among populations of Crepidula (Gastropoda: Calyptraeidae)

Offspring size is a key characteristic in life histories, reflecting maternal investment per offspring and, in marine invertebrates, being linked to mode of development. Few studies have focused explicitly on intraspecific variation and plasticity in developmental characteristics such as egg size and hatching size in marine invertebrates. We measured over 1000 eggs and hatchlings of the marine gastropods Crepidula atrasolea and Crepidula ustulatulina from two sites in Florida. A common‐garden experiment showed that egg size and hatching size were larger at 23 °C than at 28 °C in both species. In C. ustulatulina, the species with significant genetic population structure in cytochrome oxidase I (COI), there was a significant effect of population: Eggs and hatchlings from the Atlantic population were smaller than those from the Gulf. The two populations also differed significantly in hatchling shape. Population effects were not significant in C. atrasolea, the species with little genetic population structure in COI, and were apparent through their marginal interaction with temperature. In both species, 60–65% of the variation in egg size and hatching size was a result of variation among females and, in both species, the population from the Atlantic coast showed greater temperature‐mediated plasticity than the population from the Gulf. These results demonstrate that genetic differentiation among populations, plastic responses to variation in environmental temperature, and differences between females all contribute significantly to intraspecific variation in egg size and hatching size. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 489–499.     

THE EVOLUTION OF MATERNAL INVESTMENT IN LIZARDS: AN EXPERIMENTAL AND COMPARATIVE ANALYSIS OF EGG SIZE AND ITS EFFECTS ON OFFSPRING PERFORMANCE

I used comparative and experimental analysis of egg size in a Sceloporus lizard to examine a fundamental tenet of life-history theory: the presumed trade-offs among offspring number, offspring size, and performance traits related to offspring size that are likely to influence fitness. I analyzed latitudinal and elevational patterns of egg life-history characteristics among populations and experimentally manipulated egg size and hatchling size by removing yolk from the eggs to examine the causal bases of population differences in offspring traits. Mean clutch size among populations increased to the north (seven vs. 12 eggs/clutch, California vs. Washington), whereas egg size decreased (0.65 g vs. 0.40 g). The elevational patterns in southern California paralleled the latitudinal trends. Several offspring life-history traits that are correlated with egg size also varied geographically; these traits included incubation time, hatchling size, growth rate, and hatchling sprint performance. Hatchling viability of experimentally reduced eggs was remarkably high (~70%), even when up to 50% of the yolk was removed. The experimentally reduced eggs and hatchlings demonstrated the degree to which size influences each of the offspring life-history traits considered. Northern eggs hatched sooner, in part because of their small size. Though growth rate is allometrically related to size within each population (i.e., smaller hatchlings grow faster on a mass-specific basis), population differences in growth rate, as measured in the laboratory, are likely to reflect genetic differentiation in the underlying physiology of growth. Moreover, smaller juveniles, because of experimental reduction, had slower sprint speeds than larger juveniles. The slower sprint speed of hatchlings from Washington compared to hatchlings from California is thus largely due to the fact that eggs are smaller in the Washington population. These results provide a basis for interpreting the evolutionary divergence of the suite of traits involved in the evolution of maternal investment per offspring in lizards. For example, evolutionary divergence in some offspring traits functionally related to size (e.g., sprint speed) may be constrained, relative to traits that are determined by other aspects of development or physiology (e.g., growth). I also discuss issues relating to the evolution of maternal investment that could be tested in laboratory and natural populations using experimentally reduced offspring.     

Reproductive performance of a lacertid lizard at the core and the periphery of the species' range

The range boundaries of organisms are frequently interpreted in terms of a decline in the extent to which the life histories of outer populations are able to adapt to local environmental conditions. To test this hypothesis, we compared the reproductive characteristics of two Iberian populations of the lizard Psammodromus algirus (Linnaeus, 1758). One of them (Lerma) is close to the northern edge of the species' range, whereas the other one (El Pardo) occupies a typical core habitat 200 km further south. Gravid females were captured in the field and transported to the lab for egg laying. Second clutches were less frequent at Lerma (where clutch size and clutch mass were larger for first than for second clutches) than at El Pardo. The total mass of both clutches combined was similar at both sites. Thus, the higher frequency of second clutches at El Pardo appeared to balance the between-sites difference in energy allocation to the first clutch. Females from Lerma laid more but smaller eggs than those from El Pardo. When incubated at the same temperature, eggs from Lerma hatched sooner even when controlling for between-sites differences in mean egg size. These differences are interpreted in the light of the advantages of early hatching and high fecundity in the northern population, as opposed to large offspring size in the core population. We conclude that the life-history traits studied show enough variation, presumably of an adaptive nature, to cope with environmental challenges at the edge of the species' range.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 87–96.     

Maternal investment in reproduction and its consequences in leatherback turtles

Maternal investment in reproduction by oviparous non-avian reptiles is usually limited to pre-ovipositional allocations to the number and size of eggs and clutches, thus making these species good subjects for testing hypotheses of reproductive optimality models. Because leatherback turtles (Dermochelys coriacea) stand out among oviparous amniotes by having the highest clutch frequency and producing the largest mass of eggs per reproductive season, we quantified maternal investment of 146 female leatherbacks over four nesting seasons (2001–2004) and found high inter- and intra-female variation in several reproductive characteristics. Estimated clutch frequency [coefficient of variation (CV) = 31%] and clutch size (CV = 26%) varied more among females than did egg mass (CV = 9%) and hatchling mass (CV = 7%). Moreover, clutch size had an approximately threefold higher effect on clutch mass than did egg mass. These results generally support predictions of reproductive optimality models in which species that lay several, large clutches per reproductive season should exhibit low variation in egg size and instead maximize egg number (clutch frequency and/or size). The number of hatchlings emerging per nest was positively correlated with clutch size, but fraction of eggs in a clutch yielding hatchlings (emergence success) was not correlated with clutch size and varied highly among females. In addition, seasonal fecundity and seasonal hatchling production increased with the frequency and the size of clutches (in order of effect size). Our results demonstrate that female leatherbacks exhibit high phenotypic variation in reproductive traits, possibly in response to environmental variability and/or resulting from genotypic variability within the population. Furthermore, high seasonal and lifetime fecundity of leatherbacks probably reflect compensation for high and unpredictable mortality during early life history stages in this species.     

Measuring temporal variation in reproductive output reveals optimal resource allocation to reproduction in the northern grass lizard, Takydromus septentrionalis

We measured the reproductive output of Takydromus septentrionalis collected over 5 years between 1997 and 2005 to test the hypothesis that reproductive females should allocate an optimal fraction of accessible resources in a particular clutch and to individual eggs. Females laid 1–7 clutches per breeding season, with large females producing more, as well as larger clutches, than did small females. Clutch size, clutch mass, annual fecundity, and annual reproductive output were all positively related to female size (snout–vent length). Females switched from producing more, but smaller eggs in the first clutch to fewer, but larger eggs in the subsequent clutches. The mass-specific clutch mass was greater in the first clutch than in the subsequent clutches, but it did not differ among the subsequent clutches. Post-oviposition body mass, clutch size, and egg size showed differing degrees of annual variation, but clutch mass of either the first or the second clutch remained unchanged across the sampling years. The regression line describing the size–number trade-off was higher in the subsequent clutch than in the first clutch, but neither the line for first clutch, nor the line for the second clutch varied among years. Reproduction retarded growth more markedly in small females than in large ones. Our data show that: (1) trade-offs between size and number of eggs and between reproduction and growth (and thus, future reproduction) are evident in T. septentrionalis ; (2) females allocate an optimal fraction of accessible resources in current reproduction and to individual eggs; and (3) seasonal shifts in reproductive output and egg size are determined ultimately by natural selection.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 315–324.     

Nonlinear continuum of egg size-number trade-offs in a snake: is egg-size variation fitness related?

The relationship between offspring size and offspring number is crucial to life history evolution. To examine how these two life history variables are coupled and whether an altered balance between them will result in changes in maternal fitness, we manipulated clutch size of the Chinese cobra (Naja atra) by using the techniques of hormonal manipulation and follicle ablation. Females receiving exogenous follicle-stimulating hormone produced more but smaller eggs, and females undergoing follicle ablation produced fewer but larger eggs. Neither body size (body mass and snout-vent length) at hatching nor egg mass at oviposition had a role in determining hatchling survival and growth. Female hatchlings were more likely to die in early post-hatching days and grew more slowly than male hatchlings. Our data show that: (1) there is a nonlinear continuum of egg size-number trade-offs in N. atra within which there is a single inflexion where the rate at which egg size decreases with increasing clutch size, or clutch size increases with decreasing egg size, is maximized; (2) there is a fixed upper limit to egg size for a given-sized female, and the limit is not determined by her body volume; (3) egg size has no role in determining hatchling survival and growth; and (4) the extent to which females may enjoy reproductive benefits in a given reproductive episode depends on how well egg size and egg number are balanced.     

Body-size effect on egg size in eublepharid geckos (Squamata: Eublepharidae), lizards with invariant clutch size: negative allometry for egg size in ectotherms is not universal

Within a single clutch, smaller species of ectotherms generally lay a smaller number of relatively larger eggs than do larger species. Many hypotheses explaining both the interspecific negative allometry in egg size and egg size–number trade-off postulate the existence of an upper limit to the egg size of larger species. Specifically, in lizards, large eggs of large species could have too long a duration of incubation, or they could be too large to pass through the pelvic opening, which is presumably constrained mechanically in larger species. Alternatively, negative allometry could be a result of limits affecting eggs of smaller species. Under the latter concept, hatchling size in smaller species may be close to the lower limit imposed by ecological interactions or physiological processes, and therefore smaller species have to invest in relatively larger offspring. Contrary to these lower limit hypotheses, explanations based on the existence of an upper limit always predict negative egg-size allometry even in animals with invariant clutch size, in which naturally there is no egg size–number trade-off. We studied egg-size allometry in lizards of the family Eublepharidae, a monophyletic group of primitive geckos with large variance in body size and an invariant number of two eggs per clutch. We found an isometric relationship between egg and female size that does not support the upper limit hypotheses.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 527–532.     

Geographic variation in reproductive traits and trade-offs between size and number of eggs of the Chinese cobra (Naja atra)

We collected gravid Chinese cobras (Naja atra) from one island (Dinghai) and three mainland (Yiwu, Lishui and Quanzhou) populations in south‐eastern China to study geographical variation in female reproductive traits and the trade‐off between the size and number of eggs. We then conducted an common experiment on cobras from two of the four populations to further identify factors contributing to the observed trade‐offs. The mean size (snout–vent length) of the smallest five reproductive females increased with increasing latitude. Oviposition occurred between late June and early August, with females from the warmer localities laying eggs earlier than those from the colder localities. Maternal size was a major determinant of the reproductive investment in all populations, with larger females producing not only more but also larger eggs. Clutch size was more variable than egg size within and among populations. The observed geographical variation in clutch size, egg size, clutch mass and post‐oviposition body condition was not a simple consequence of variation in maternal size among populations, because interpopulation differences in these traits were still evident when the influence of maternal size was removed. The upper limit to reproductive investment was more likely to be set by the space availability in the island population, but by the resource availability in the three mainland populations. Trade‐offs between size and number of eggs were detected in all populations, with females that had larger clutches for their size having smaller eggs. Egg size at any given level of relative fecundity differed among populations, primarily because of interpopulation differences in the resource availability rather than the space availability. Except for the timing date of oviposition and the mean size of the smallest five reproductive females, all other examined traits did not vary in a geographically continuous trend. The common garden experiment, which standardized environmental factors, synchronized the timing date of oviposition, but it did not modify the conclusion drawn from the gravid females collected from the field. The observed geographical variation in the female reproductive traits could be attributed to the consequence of the effects of either proximate or ultimate factors. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 27–40.     

Phenotypic consequences of incubation environment in the African elapid genus Aspidelaps

Eggs and embryos of the African elapid genus Aspidelaps were tested for phenotypic plasticity in response to incubation temperature and hygration. Fifty-two fertile eggs, representing both A. lubricus and A. scutatus, were utilized over two successive breeding seasons. Interspecific difference in hatchling snout-vent length (SVL) was significant, but the two species were equivalent in initial egg mass and hatchling mass. Hatchling mass was unaffected by temperature and incubation substrate moisture, but was positively correlated to initial egg mass. In A. lubricus, SVL was influenced by an incubation temperature-substrate moisture interaction. In A. scutatus, SVL was unaffected by the experimental variables. The secondary sex ratio among hatchlings was significantly female skewed under mesic incubation conditions, and male skewed under xeric conditions. One explanation for the biased sex ratios is differential mortality at wet and dry conditions. The results indicate the two species of Aspidelaps are uniform with regard to female investment in egg and hatchling biomass, yet they partition resources differently during embryogenesis to yield morphologically distinct neonates. © 1996 Wiley-Liss, Inc.     

Fluctuations in the incubation moisture environment affect growth but not survival of hatchling lizards

Few studies have collected longitudinal data that follow the complete microevolutionary path of an organism linking sources of variation (e.g. environmental versus genetic) to a trait and its subsequent relationship with fitness. Identifying the links within this pathway is imperative for understanding the ecological relevance of effects found at the phenotypic level. Furthermore, experimental studies that examine parts of the pathway in ectothermic organisms often fail to mimic the complexities of the natural developmental environment. Temperature and moisture conditions in reptile nests, for example, can fluctuate greatly on a seasonal and daily basis. Despite the potential effects of fluctuating environments, the vast majority of studies have held environmental treatments constant during the developmental period. We investigated the effects of fluctuating moisture regimes during incubation on eggs, hatchling phenotypes, and subsequent survival in the eastern fence lizard Sceloporus undulatus. Moisture fluctuations during embryonic development caused water absorption by eggs to follow the environmental availability of moisture. Initial hatchling tail length was affected by the pattern of moisture fluctuations, and hatchling growth rates in fluctuating treatments were significantly faster than those in a constant treatment, resulting in larger hatchlings after 4 weeks. A release–recapture experiment conducted in the field did not detect a treatment effect on survival despite the larger body sizes. In summary, although fluctuations affected water absorption by eggs and some hatchling traits, these effects did not have subsequent fitness consequences. The results obtained suggest that egg and hatchling survival are buffered against natural soil moisture fluctuations during incubation, even when egg and hatchling traits are significantly affected. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 89–102.     

两种麻蜥卵和孵出幼体的特征

研究了山地麻蜥和丽斑麻蜥实验条件下的卵及孵出幼体的特征.山地麻蜥产卵雌体的体长大于丽斑麻蜥,窝卵重小于丽斑麻蜥,但平均卵重和相对窝卵重与丽斑麻蜥相似.两种蜥蜴均通过增加卵长径和卵短径来增加卵重,但卵的外形不同,山地麻蜥卵较长.两种蜥蜴卵孵化过程中均吸水增重.相似孵化条件(波动温度、-12 kPa)下,山地麻蜥的孵化期明显比丽斑麻蜥长.山地麻蜥幼体的尾、头部大于丽斑麻蜥,但体重和SVL相似.     

Temperature,size, reproductive allocation,and life‐history evolution in a gregarious caterpillar

The present study aimed to investigate the relationship between growth rate, final mass, and larval development, as well as how this relationship influences reproductive trade‐offs, in the context of a gregarious life‐style and the need to keep an optimal group size. We use as a model two sympatric populations of the pine processionary moth Thaumetopoea pityocampa, which occur in different seasons and thus experience different climatic conditions. Thaumetopoea pityocampa is a strictly gregarious caterpillar throughout the larval period, which occurs during winter in countries all over the Mediterranean Basin. However, in 1997, a population in which larval development occurs during the summer was discovered in Portugal, namely the summer population (SP), as opposed to the normal winter population (WP), which coexists in the same forest feeding on the same host during the winter. Both populations were monitored over 3 years, with an assessment of the length of the larval period and its relationship with different climatic variables, final mass and adult size, egg size and number, colony size, and mortality at different life stages. The SP larval period was reduced as a result of development in the warmer part of the year, although it reached the same final mass and adult size as the WP. Despite an equal size at maturity, a trade‐off between egg size and number was found between the two populations: SP produced less but bigger eggs than WP. This contrasts with the findings obtained in other Lepidoptera species, where development in colder environments leads to larger eggs at the expense of fecundity, but corroborates the trend found at a macro‐geographical scale for T. pityocampa, with females from northern latitudes and a colder environment producing more (and smaller) eggs. The results demonstrate the importance of the number of eggs in cold environments as a result of an advantage of large colonies when gregarious caterpillars develop in such environments, and these findings are discussed in accordance with the major theories regarding size in animals. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 340–349.     

Evolutionary divergence in life history traits among populations of the Lake Malawi cichlid fish Astatotilapia calliptera

During the early stages of adaptive radiation, populations diverge in life history traits such as egg size and growth rates, in addition to eco‐morphological and behavioral characteristics. However, there are few studies of life history divergence within ongoing adaptive radiations. Here, we studied Astatotilapia calliptera, a maternal mouthbrooding cichlid fish within the Lake Malawi haplochromine radiation. This species occupies a rich diversity of habitats, including the main body of Lake Malawi, as well as peripheral rivers and shallow lakes. We used common garden experiments to test for life history divergence among populations, focussing on clutch size, duration of incubation, egg mass, offspring size, and growth rates. In a first experiment, we found significant differences among populations in average clutch size and egg mass, and larger clutches were associated with smaller eggs. In a second experiment, we found significant differences among populations in brood size, duration of incubation, juvenile length when released, and growth rates. Larger broods were associated with smaller juveniles when released and shorter incubation times. Although juvenile growth rates differed between populations, these were not strongly related to initial size on release. Overall, differences in life history characters among populations were not predicted by major habitat classifications (Lake Malawi or peripheral habitats) or population genetic divergence (microsatellite‐based F_ST). We suggest that the observed patterns are consistent with local selective forces driving the observed patterns of trait divergence. The results provide strong evidence of evolutionary divergence and covariance of life history traits among populations within a radiating cichlid species, highlighting opportunities for further work to identify the processes driving the observed divergence.     

Differential effects of egg albumen content on barn swallow nestlings in relation to hatch order

In diverse animal taxa, egg mass variation mediates maternal effects with long-term consequences for offspring ontogeny and fitness. Patterns of egg mass variation with laying order differ considerably among birds, but no study has experimentally investigated the function of variation in albumen or yolk egg content in the wild. In barn swallows (Hirundo rustica), absolute and relative albumen mass increased with egg laying order. Experimental albumen removal delayed hatching, had larger negative effects on growth of late-hatched nestlings, and reduced nestling survival. Laying order positively predicted hatch order. Because nestling competitive ability depends on size, and albumen egg content influences hatchling size, present results suggest that by increasing albumen content of late eggs mothers reduce hatching asynchrony and enhance growth particularly of late-hatched nestlings. Thus, variation in albumen mass with laying order may function to mitigate the negative phenotypic consequences of hatching late in species that adopt a 'brood-survival' strategy.     

Effect of population bottlenecks on the egg morphology of introduced birds in New Zealand

Hatching failure is inversely correlated with population bottleneck size among exotic birds introduced to New Zealand, but the mechanism for this is unclear. We assess whether the bottlenecks these species experienced during their introduction have affected hatching failure through deleterious changes in egg morphology. We measured egg size and shape of 13 species that passed through bottlenecks of 11–800 individuals during their establishment in the 19th century. Eggs were also measured in the source populations ('pre-bottleneck') of each species to compare pre- and post-bottleneck egg morphology directly. Significant changes in egg volume were found in six of 13 species, with most laying smaller eggs in New Zealand. Egg shape changed in four of 13 species but there was no directional bias; two species developed more elongated eggs and two species broader eggs. There was no relationship between bottleneck size and change in egg volume, but species passing through severe bottlenecks had greater variability in egg volume and were more likely to have eggs that deviated in shape from their source populations. There was no relationship between changes in either egg volume or shape and rates of hatching failure. Further work is needed to assess whether changes in egg morphology have negative consequences on offspring fitness and whether the observed changes are the result of differing environmental conditions in the introduced range.