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.     

Relationship between gape size and feeding selectivity of fish larvae from a Neotropical reservoir

Larvae feeding selectivity of Iheringichthys labrosus , Hypophthalmus edentatus and Plagioscion squamosissimus was assessed, examining the role of mouth gape in prey selection. Fish larvae were sampled in the Itaipu Reservoir (Brazil–Paraguay). Iheringichthys labrosus and H. edentatus larvae, with small and similar gape sizes, exhibited slightly different diets; I. labrosus preferred cladocerans ( Bosmina hagmanni , Bosmina huauriensis and Bosminopsis deitersi ) and the rotifer Brachionus calyciflorus . Hypophthalmus edentatus , however, primarily ingested the cladocerans B. hagmanni , Ceriodaphnia cornuta , Daphnia gessneri and Diaphanosoma spinulosum . Plagioscion squamosissimus , with a greater gape size, preferred Calanoida. The mechanistic processes that determine food selectivity of fish larvae in temperate aquatic systems were similar in the Neotropical system. The trophic spectrum of these species is characterized by small- to intermediate-sized prey. Plagioscion squamosissimus larvae, which have larger mouths, exploit primarily larger prey differing from the most abundant species or size classes; consequently, their diet is quite different from I. labrosus larvae and modestly similar to H. edentatus larvae, opportunistic feeders that they eat more abundant prey.     

Egg-cases and size at hatching of Sympterygia acuta in the south-western Atlantic

Ten egg-cases of Sympterygia acuta were collected from the surf line at Cassino Beach, Rio Grande do Sul, Brazil, and incubated in the laboratory. The egg-cases and neonates (77–84 mm total length) are described.     

Egg size and offspring quality: a meta‐analysis in birds

Parents affect offspring fitness by propagule size and quality, selection of oviposition site, quality of incubation, feeding of dependent young, and their defence against predators and parasites. Despite many case studies on each of these topics, this knowledge has not been rigorously integrated into individual parental care traits for any taxon. Consequently, we lack a comprehensive, quantitative assessment of how parental care modifies offspring phenotypes. This meta‐analysis of 283 studies with 1805 correlations between egg size and offspring quality in birds is intended to fill this gap. The large sample size enabled testing of how the magnitude of the relationship between egg size and offspring quality depends on a number of variables. Egg size was positively related to nearly all studied offspring traits across all stages of the offspring life cycle. Not surprisingly, the relationship was strongest at hatching but persisted until the post‐fledging stage. Morphological traits were the most closely related to egg size but significant relationships were also found with hatching success, chick survival, and growth rate. Non‐significant effect sizes were found for egg fertility, chick immunity, behaviour, and life‐history or sexual traits. Effect size did not depend on whether chicks were raised by their natural parents or were cross‐fostered to other territories. Effect size did not depend on species‐specific traits such as developmental mode, clutch size, and relative size of the egg, but was larger if tested in captive compared to wild populations and between rather than within broods. In sum, published studies support the view that egg size affects juvenile survival. There are very few studies that tested the relationship between egg size and the fecundity component of offspring fitness, and no studies on offspring survival as adults or on global fitness. More data are also needed for the relationships between egg size and offspring behavioural and physiological traits. It remains to be established whether the relationship between egg size and offspring performance depends on the quality of the offspring environment. Positive effect sizes found in this study are likely to be driven by a causal effect of egg size on offspring quality. However, more studies that control for potential confounding effects of parental post‐hatching care, genes, and egg composition are needed to establish firmly this causal link.     

Direct yolk sac volume manipulation of zebrafish embryos and the relationship between offspring size and yolk sac volume

Through direct manipulation of yolk sac volume ( V _y), in the zebrafish Danio rerio , V _y and offspring size was positively correlated and the relationship was independent of geographical location, parental size or age and, most importantly, parental genetic factors. Larval survivorship, under a non-feeding regime and up until hatch, was not significantly affected by the manipulation. Decreased V _y significantly decreased maximum standard length ( L _S), maximum body surface area ( A _B), time to yolk sac absorption, L _S and A _B at yolk sac absorption, and the L _S and A _B at starvation. The methodology of V _y adjustment will be useful for the studies of the interaction between early life-history traits and offspring size, egg quality variables and early vertebrate development.     

The influence of different parental combinations and incubation temperature on the RNA and DNA content of herring larvae at hatching: a pilot study

In four half-sib pairings, herring mothers affected the standard length, dry weight, and RNA and DNA content of their progeny, while fathers affected larval RNA and DNA content. The amounts of RNA and DNA in offspring from one male were also influenced by temperature in that the highest RNA contents were found at the lowest temperature and highest DNA contents at the highest temperature. The results indicate that both environmental and genetic factors influence nucleic acid contents of young herring larvae, and this may limit the suitability of RNA : DNA ratio as a condition measure of newly hatched herring larvae.     

Short- and long-term effects of litter size manipulation in a small wild-derived rodent

Iteroparous organisms maximize their overall fitness by optimizing their reproductive effort over multiple reproductive events. Hence, changes in reproductive effort are expected to have both short- and long-term consequences on parents and their offspring. In laboratory rodents, manipulation of reproductive efforts during lactation has however revealed few short-term reproductive adjustments, suggesting that female laboratory rodents express maximal rather than optimal levels of reproductive investment as observed in semelparous organisms. Using a litter size manipulation (LSM) experiment in a small wild-derived rodent (the common vole; Microtus arvalis), we show that females altered their reproductive efforts in response to LSM, with females having higher metabolic rates and showing alternative body mass dynamics when rearing an enlarged rather than reduced litter. Those differences in female reproductive effort were nonetheless insufficient to fully match their pups’ energy demand, pups being lighter at weaning in enlarged litters. Interestingly, female reproductive effort changes had long-term consequences, with females that had previously reared an enlarged litter being lighter at the birth of their subsequent litter and producing lower quality pups. We discuss the significance of using wild-derived animals in studies of reproductive effort optimization.     

Egg environments have large effects on embryonic development,but have minimal consequences for hatchling phenotypes in an invasive lizard

Plastic responses of embryos to developmental environments can shape phenotypes in ways that impact fitness. The mechanisms by which developmental conditions affect offspring phenotypes vary substantially among taxa and are poorly understood in most systems. In this study, we evaluate the effects of thermal and hydric conditions on patterns of egg water uptake, embryonic development and yolk metabolism in embryos of the lizard Anolis sagrei to gain insights into how these factors shape morphological variation in hatchlings. Our 3 × 2 experimental design (3 thermal and 2 hydric conditions) revealed that developmental temperature has strong effects on rates of development and yolk metabolism, but the impacts of moisture were minimal. Increased water uptake by eggs under relatively wet conditions resulted in larger hatchlings with less internalized residual yolk than hatchlings from dry‐incubated eggs. However, the relatively small phenotypic differences among treatments may have small fitness consequences. These results demonstrate that embryos of A. sagrei can tolerate a broad range of environmental conditions without substantial impacts on critical morphological traits. Such embryonic tolerances may facilitate colonization and establishment in novel environments. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 25–41.     

Effects of two Avtemia diets with different contents of polyunsaturated fatty acids on the lipid composition of larvae of Atlantic herring (Clupea harengus

Atlantic herring larvae ( Clupea harengus ) were fed two enriched Artemia diets with different contents of (n-3) highly unsaturated fatty acids (HUFA), one containing low levels of 20: 5(n-3) and no 22: 6(n-3), the other containing substantial levels of both 20: 5(n-3) and 22: 6(n-3). After 30 days of culture, fatty acid compositions of lipid classes in the heads, bodies and eyes of the larvae were analysed. Fish fed Artemia with the low (n-3) HUFA diet lacking 22: 6(n-3) had lower amounts of total (n-3)HUFA and, in particular, of 22:6(n-3) in individual phospholipids and total neutral lipids of heads, bodies and eyes as compared to fish fed Artemia with high levels of (n-3)HUFA. The amount of 22: 6(n-3) in the fatty acids of phosphatidyl-ethanolamine of eyes was particularly susceptible to dietary depletion. The implications of these findings are discussed, particularly in relation to dietary requirements for 22: 6(n-3) during development of neural tissue in predatory fish iarvae.     

Evolution of sex-biased maternal effects in birds: I. Sex-specific resource allocation among simultaneously growing oocytes

Females in species that produce broods of multiple offspring need to partition resources among simultaneously growing ova, embryos or neonates. In birds, the duration of growth of a single egg exceeds the ovulation interval, and when maternal resources are limited, a temporal overlap among several developing follicles in the ovary might result in a trade-off of resources among them. We studied growth of oocytes in relation to their future ovulation order, sex, and overlap with other oocytes in a population of house finches (Carpodacus mexicanus) where strongly sex-biased maternal effects are favoured by natural selection. We found pronounced differences in growth patterns between oocytes that produced males and females. Male oocytes grew up to five times faster and reached their ovulation size earlier than female oocytes. Early onset and early termination of male oocytes' growth in relation to their ovulation resulted in their lesser temporal overlap with other growing ova compared with female oocytes. Consequently, ovulation mass of female but not male oocytes was strongly negatively affected by temporal overlap with other oocytes. In turn, mass of male oocytes was mostly affected by the order of ovulation and by maternal incubation strategy. These results provide a mechanism for sex-biased allocation of maternal resources during egg formation and provide insights into the timing of the sex-determining meiotic division in relation to ovulation in this species.     

Pen size and parity effects on maternal behaviour of Small-Tail Han sheep

The aim of this experiment was to study the effects of pen size and parity on maternal behaviour of twin-bearing Small-Tail Han ewes. A total of 24 ewes were allocated to a 2×2 design (six per pen), with parity (primiparous or multiparous) and pen size (large: 6.0×3.0 m; small: 6.0×1.5 m) as main effects at Linyi University, Shandong Province, China. Behaviour was observed from after parturition until weaning. All ewes were observed for 6 h every 5 days from 0700 to1000 h and from 1400 to 1700 h. Continuous focal animal sampling was used to quantify the duration of maternal behaviours: sucking, grooming and following as well as the frequency of udder accepting, udder refusing and low-pitched bleating. Oestradiol and cortisol concentrations in the faeces (collected in the morning every 5 days) were detected using EIA kits. All lambs were weighed 24 h after parturition and again at weaning at 35 days of age. The small pen size significantly reduced following (P<0.005), grooming (P<0.001) and suckling durations (P<0.05), as well as the frequency of udder refusals (P<0.001). However, there was a significant interaction with ewe parity, with decreased grooming and suckling in the small pen largely seen in the multiparous ewes (P<0.001). Independent of pen size, multiparous ewes accepted more sucking attempts by their lambs (P<0.05) and made more low-pitched bleats than primiparous ewes (P<0.001). Multiparous ewes had higher faecal oestradiol concentrations than primiparous ewes (P<0.001), and ewes in small pens had higher faecal cortisol levels compared with ewes in larger pens (P<0.001). As lambs increased in age, the duration of maternal grooming, following and suckling as well as frequency of udder acceptance and low-pitched bleating all declined, and the frequency of udder refusing increased (P<0.001 for all). Ewe parity, but not pen size, affected lamb weight gain during the period of observation (P<0.001). This is the first study to show that pen size, interacting with parity, can affect the expression of maternal behaviour in sheep during lactation. The study is also the first to report on the maternal behaviour of Chinese native sheep breeds (Small-Tail Han sheep), with implications for the production of sheep in China.     

Developmental plasticity and maternal effects of reproductive characteristics in the frog,Bombina orientalis

Summary Life history theory suggests that reproductive characteristics such as ovum size and clutch size should be well buffered against vararies of the environment. However, studies which demonstrate environmental sensitivity of reproductive characteristics are increasing in number, as are studies which find that maternal effects are responsible for much of the variation in developmental and growth rates in embryonic and larval fish and amphibians. The data reported here demonstrate that the environment, in terms of temperature and food availability that a specific individual encounters during vitellogenesis, exerts a strong influence on both egg size and number. Warmer temperatures and less food decrease ovum size, while colder temperatures and less food decrease clutch size. The variation in ovum size that is induced by the environment can exert a strong influence on variation in offspring development and growth and serve as an excellent model for studies on the evolution of developmental plasticity.     

The separate effects of egg size and parental quality on the development of ornamental plumage coloration

The fitness‐related consequences of egg size, independent of the influences of parental quality, are poorly understood in altricial birds. Not only can egg size and parental quality influence growth and survival, but each could influence the development of condition‐dependent plumage coloration in offspring. The Eastern Bluebird Sialia sialis is an altricial, multi‐brooded, cavity‐nesting passerine in which juveniles display dichromatic UV‐blue plumage. Previous research suggests that plumage coloration acts as a signal of individual quality among juvenile and adult Eastern Bluebirds. Here, we separate the effects of egg size and parental quality (defined by egg size laid) on nestling growth and plumage ornamentation by exchanging clutches of large eggs with clutches of small eggs. Nestlings were significantly larger immediately post‐hatching when hatched from a large egg, but to maintain a larger size, nestlings needed to have hatched from a large egg and to have been reared by high‐quality parents. Nestlings were brighter when reared by high‐quality parents and this relationship was strongest later in the breeding season. Nestlings exhibited greater UV chroma if hatched early in the season, but UV chroma was not significantly affected by egg size or parental quality. These findings demonstrate varying influences of both egg size and parental quality on offspring growth and plumage ornamentation but suggest that quality of post‐hatching investment is more influential than pre‐hatching investment.     

Evolution of sex-biased maternal effects in birds: II. Contrasting sex-specific oocyte clustering in native and recently established populations

In species that produce broods of multiple offspring, parents need to partition resources among simultaneously growing neonates that often differ in growth requirements. In birds, multiple ovarian follicles develop inside the female at the same time, resulting in a trade-off of resources among them and potentially limiting maternal ability for sex-specific allocation. We compared resource acquisition among oocytes in relation to their future sex and ovulation order in two populations of house finches with contrasting sex-biased maternal strategies. In a native Arizona population, where mothers do not bias offspring sex in relation to ovulation order, the male and female oocytes did not show sex-specific trade-offs of resources during growth and there was no evidence for spatial or temporal segregation of male and female oocytes in the ovary. In contrast, in a recently established Montana population where mothers strongly bias offspring sex in relation to ovulation order, we found evidence for both intra-sexual trade-offs among male and female oocytes and sex-specific clustering of oocytes in the ovary. We discuss the importance of sex-specific resource competition among offspring for the evolution of sex-ratio adjustment and sex-specific maternal resource allocation.     

The positive correlation between maternal size and offspring size: fitting pieces of a life‐history puzzle

The evolution of investment per offspring (I) is often viewed through the lens of the classic theory, in which variation among individuals in a population is not expected. A substantial departure from this prediction arises in the form of correlations between maternal body size and I, which are observed within populations in virtually all taxonomic groups. Based on the generality of this observation, we suggest it is caused by a common underlying mechanism. We pursue a unifying explanation for this pattern by reviewing all theoretical models that attempt to explain it. We assess the generality of the mechanism upon which each model is based, and the extent to which data support its predictions. Two classes of adaptive models are identified: models that assume that the correlation arises from maternal influences on the relationship between I and offspring fitness [w(I)], and those that assume that maternal size influences the relationship between I and maternal fitness [W(I)]. The weight of evidence suggests that maternal influences on w(I) are probably not very general, and even for taxa where maternal influences on w(I) are likely, experiments fail to support model predictions. Models that assume that W(I) varies with maternal size appear to offer more generality, but the current challenge is to identify a specific and general mechanism upon which W(I) varies predictably with maternal size. Recent theory suggests the exciting possibility that a yet unknown mechanism modifies the offspring size–number trade‐off function in a manner that is predictable with respect to maternal size, such that W(I) varies with size. We identify two promising avenues of inquiry. First, the trade‐off might be modified by energetic costs that are associated with the initiation of reproduction (‘overhead costs’) and that scale with I, and future work could investigate what specific overhead costs are generally associated with reproduction and whether these costs scale with I. Second, the trade‐off might be modified by virtue of condition‐dependent offspring provisioning coupled with metabolic factors, and future work could investigate the proximate cause of, and generality of, condition‐dependent offspring provisioning. Finally, drawing on the existing literature, we suggest that maternal size per se is not causatively related to variation in I, and the mechanism involved in the correlation is instead linked to maternal nutritional status or maternal condition, which is usually correlated with maternal size. Using manipulative experiments to elucidate why females with high nutritional status typically produce large offspring might help explain what specific mechanism underlies the maternal‐size correlation.     

The community ecology of Aedes egg hatching: implications for a mosquito invasion

Abstract. 1. A recently introduced treehole mosquito from Asia, Aedes albopictus , is spreading throughout eastern North America, especially in tyre-refuse piles. Previous studies have identified inhibitory effects of larvae on egg hatch as a potential population regulatory mechanism within Aedes. Larva-egg interactions may also occur between species. This experiment assesses the ability of larvae of A. albopictus and two possible competitors in North America, A.triseriatus and A.aegypti , to suppress hatching of conspecific and congeneric eggs.
2. We exposed eggs of each species to varying combinations of larval species and density for 24h and assessed subsequent hatch rates. Aedes albopictus eggs exhibited the lowest level of inhibition when exposed to high larval densities; moreover, at the lowest larval density they imposed the most intense interspecific hatch inhibition.
3. Discretionary hatching in response to larval density may influence community composition by promoting the spread of A.albopictus , perhaps even leading to its dominance within North American Aedes communities.     

Variation in body size in the giant rhinoceros beetle Trypoxylus dichotomus is mediated by maternal effects on egg size

1. The egg size of insects can vary depending on maternal body size or resource status, and it may influence offspring body size by determining initial resource level. 2. The giant rhinoceros beetle Trypoxylus dichotomus exhibits considerable variation in body size, some of which is attributed to the variation in larval food (humus) quality, although a substantial amount of variation in body size remains unexplained. In the present study, changes in the egg size and offspring body size in response to several maternal variables were examined (i.e. body size, age, and, nutritional status). 3. Nutritional intake of the females during the adult stage did not affect the egg size. Larvae hatched from small eggs partially recovered from the initial disadvantage during their ontogenetic processes by increasing growth rate (i.e. compensatory growth); however, there was still a positive relationship between egg size and pupal body size. 4. Older females produced small eggs, but because of compensatory growth, the pupae were no longer small. By contrast, due to a lack of compensatory growth, small females produced small eggs as well as small pupae. 5. These results suggest that maternal body size affects offspring body size through effects on egg size. This transgenerational effect may account for some of the variation in adult body size of T. dichotomus.