Variation of clutch size and trophic egg proportion in a ladybird with and without male-killing bacterial infection

Maternally inherited bacterial endosymbionts can kill male embryos of their arthropod hosts to enhance the transmission efficiency of the endosymbionts. The resources from killed male eggs can be reallocated to infected female hatchlings as additional maternal investment. As a result, the number of offspring per patch and the maternal investment per offspring are expected to differ from the original optimal values for the host mother. Thus, in response to infection, these trait values should be adjusted to maximize the lifetime reproductive success of host females and the fitness of inherited endosymbionts as well. Here, we examined clutch size, egg size, and the proportion of trophic eggs (i.e., production of unhatched eggs, a maternal phenotype) per clutch of host mothers infected with male-killing bacteria. First, we developed a mathematical model to predict the optimal clutch size and trophic egg proportion in uninfected and infected females. Next, we experimentally compared these life-history traits in a ladybird, Harmonia yedoensis, between females infected or uninfected with male-killing Spiroplasma bacteria. Consistent with our predictions, clutch size was larger, egg size was smaller, and trophic egg proportion was lower in infected H. yedoensis females, compared with uninfected females. To our knowledge, this is the first empirical demonstration of variation in these life-history traits depending on infection with bacterial endosymbionts.     

Don'T put all your eggs in one nest: spread them and cut time at risk

Abstract In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are obscure. Using mathematical modeling and field observations, we analyze an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, by spreading her eggs a parasitic female can reduce offspring time in the vulnerable nest at risk of predation or other destruction. The model suggests that she can achieve much of this benefit by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a clutch that is much larger than average without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproductive success. These results help explain the puzzle of nesting parasites in some precocial birds, which lay eggs in the nests of other females before laying eggs in their own nest. Risk reduction by egg spreading may also play a role in the evolution of other breeding systems and taxa-for instance, polyandry with male parental care in some birds and fishes.     

Sex allocation in haplodiploids is mediated by egg size: evidence in the spider mite Tetranychus urticae Koch

Haplodiploid species display extraordinary sex ratios. However, a differential investment in male and female offspring might also be achieved by a differential provisioning of eggs, as observed in birds and lizards. We investigated this hypothesis in the haplodiploid spider mite Tetranychus urticae, which displays highly female-biased sex ratios. We show that egg size significantly determines not only larval size, juvenile survival and adult size, but also fertilization probability, as in marine invertebrates with external fertilization, so that female (fertilized) eggs are significantly larger than male (unfertilized) eggs. Moreover, females with on average larger eggs before fertilization produce a more female-biased sex ratio afterwards. Egg size thus mediates sex-specific egg provisioning, sex and offspring sex ratio. Finally, sex-specific egg provisioning has another major consequence: male eggs produced by mated mothers are smaller than male eggs produced by virgins, and this size difference persists in adults. Virgin females might thus have a (male) fitness advantage over mated females.     

Lifetime egg production and egg mortality in the damselflyPyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae)

Artificial oviposition sites were used to estimate egg deposition rates in the field. Females laid an average of 10.76 eggs/minute with a mean duration of 22.81 minutes, giving an average clutch size of 245 eggs. Since one mating corresponded to one clutch of eggs, lifetime mating success was used as a measure of the number of clutches produced. Mean lifetime clutch production was 5.91 clutches per female, equating to 1447 eggs per female per lifetime. Eggs were hatched in the laboratory at temperatures comparable with those in the field. Hatching was highly synchronised and the overall hatching success was 75.1%. Causes of egg mortality in the laboratory were limited to infertility and unhatchability. Since no other sources of egg mortality could be found at the study site, this value was a good reflection of hatching success in the field. Lifetime egg production and hatching success were used to estimate the number of viable offspring produced per female, giving a higher order estimate of reproductive success than has previously been published for a zygopteran.     

The costs of egg production and incubation in great tits (Parus major).

The costs of egg production and incubation may have a crucial effect on avian reproductive decisions, such as clutch size and the timing of reproduction. We carried out a brood-size enlargement experiment on the great tit (Parus major), in which the birds had to lay and incubate extra eggs (full costs), only incubate extra eggs (free eggs) or did not pay any extra cost (free chicks) in obtaining a larger brood. We used female fitness (half the recruits produced plus female survival) as a fitness measure because it is the female which pays the costs of egg production and incubation, and because clutch size is under female control. Female fitness decreased with increasing costs (fitness of free chicks females is higher than that of free eggs females which is higher than that of full costs females). These fitness differences were due to differences in female survival rather than in the number of recruits produced. This is the first time that the costs of egg production and incubation have been estimated using such a complete fitness measure, including, as our measure does, the local survival to the following year of both the female and her offspring. Our results emphasize that reproductive decisions cannot be understood without taking egg production and incubation costs into account.     

Male-biased sex ratio increases female egg laying and fitness in the housefly, Musca domestica

A biased operational sex ratio (OSR) can have multiple, confounding effects on reproductive fitness. A biased OSR can increase harassment and mating activity directed towards potential mates but may also increase the ability of potential mates to choose a good partner if lower quality mates are screened out through competitive interactions. Additionally, a biased OSR may affect reproductive fitness through changes in male ejaculate content or in female reproductive response. We quantified how a male-biased OSR (1:1, 2:1, or 5:1 male to female) affected the size of a female??s first egg clutch and her offspring??s survivorship in the housefly, Musca domestica. A male-biased OSR increased female fitness: females laid more eggs in their first clutch, had increased offspring survivorship at a 2:1 versus 1:1 OSR, and had equivalent fitness with a 5:1 male to female OSR. Courtship activity increased when the OSR was male-biased but was not a significant predictor of female fitness. Trials where females chose their mates versus trials where a random male was chosen for them had equivalent first clutch sizes and offspring survivorship. These results suggest that there are cryptic effects from a male-biased OSR on female fitness that are most likely driven by pre-copulatory social environment.     

Age-dependent clutch size in a koinobiont parasitoid

Abstract.  1. The Lack clutch size theory predicts how many eggs a female should lay to maximise her fitness gain per clutch. However, for parasitoids that lay multiple clutches it can overestimate optimal clutch size because it does not take into account the future reproductive success of the parasitoid.
2. From egg-limitation and time-limitation models, it is theoretically expected that (i) clutch size decreases with age if host encounter rate is constant, and (ii) clutch size should increase with host deprivation and hence with age in host-deprived individuals.
3. Clutch sizes produced by ageing females of the koinobiont gregarious parasitoid Microplitis tristis Nees (Hymenoptera: Braconidae) that were provided daily with hosts, and of females ageing with different periods of host deprivation were measured.
4. Contrary to expectations, during the first 2 weeks, clutch size did not change with the age of the female parasitoid, neither with nor without increasing host-deprivation time.
5. After the age of 2 weeks, clutch size decreased for parasitoids that parasitised hosts daily. The decrease was accompanied by a strong decrease in available eggs. However, a similar decrease occurred in host-deprived parasitoids that did not experience egg depletion, suggesting that egg limitation was not the only factor causing the decrease in clutch size.
6. For koinobiont parasitoids like M. tristis that have low natural host encounter rates and short oviposition times, the costs of reproduction due to egg limitation, time limitation, or other factors are relatively small, if the natural lifespan is relatively short.
7. Koinobiont parasitoid species that in natural situations experience little variation in host density and host quality might not have strongly evolved the ability to adjust clutch size.     

Effects of maternal care on the lifetime reproductive success of females in a neotropical harvestman

1. Few studies have experimentally quantified the costs and benefits of female egg-guarding behaviour in arthropods under field conditions. Moreover, there is also a lack of studies assessing separately the survival and fecundity costs associated with this behavioural trait. 2. Here we employ field experimental manipulations and capture-mark-recapture methods to identify and quantify the costs and benefits of egg-guarding behaviour for females of the harvestman Acutisoma proximum Mello-Leit?o, a maternal species from south-eastern Brazil. 3. In a female removal experiment that lasted 14 days, eggs left unattended under natural conditions survived 75.6% less than guarded eggs, revealing the importance of female presence preventing egg predation. 4. By monitoring females' reproductive success for 2 years, we show that females experimentally prevented from guarding their eggs produced new clutches more frequently and had mean lifetime fecundity 18% higher than that of control guarding females. 5. Regarding survival, our capture-mark-recapture study does not show any difference between the survival rates of females prevented from caring and that of control guarding females. 6. We found that experimentally females prevented from guarding their eggs have a greater probability to produce another clutch (0.41) than females that cared for the offspring (0.34), regardless of their probability of surviving long enough to do that. 7. Our approach isolates the ecological costs of egg-guarding that would affect survival, such as increased risk of predation, and suggests that maternal egg-guarding also constrains fecundity through physiological costs of egg production. 8. Weighting costs and benefits of egg-guarding we demonstrate that the female's decision to desert would imply an average reduction of 73.3% in their lifetime fitness. Despite the verified fecundity costs of egg-guarding, this behaviour increases female fitness due to the crucial importance of female presence aimed to prevent egg predation.     

Clutch frequency affects the offspring size-number trade-off in lizards

Background

Studies of lizards have shown that offspring size cannot be altered by manipulating clutch size in species with a high clutch frequency. This raises a question of whether clutch frequency has a key role in influencing the offspring size-number trade-off in lizards.

Methodology/Principal Findings

To test the hypothesis that females reproducing more frequently are less likely to tradeoff offspring size against offspring number, we applied the follicle ablation technique to female Eremias argus (Lacertidae) from Handan (HD) and Gonghe (GH), the two populations that differ in clutch frequency. Follicle ablation resulted in enlargement of egg size in GH females, but not in HD females. GH females switched from producing a larger number of smaller eggs in the first clutch to a smaller number of larger eggs in the second clutch; HD females showed a similar pattern of seasonal shifts in egg size, but kept clutch size constant between the first two clutches. Thus, the egg size-number trade-off was evident in GH females, but not in HD females.

Conclusions/Significance

As HD females (mean  = 3.1 clutches per year) reproduce more frequently than do GH females (mean  = 1.6 clutches per year), our data therefore validate the hypothesis tested. Our data also provide an inference that maximization of maternal fitness could be achieved in females by diverting a large enough, rather than a higher-than-usual, fraction of the available energy to individual offspring in a given reproductive episode.     

Maternal investment increases with altitude in a frog on the Tibetan Plateau

Reproducing females can allocate energy between the production of eggs or offspring of different size or number, both of which can strongly influence fitness. The physical capacity to store developing offspring imposes constraints on maximum clutch volume, but individual females and populations can trade off whether more or fewer eggs or offspring are produced, and their relative sizes. Harsh environments are likely to select for larger egg or offspring size, and many vertebrate populations compensate for this reproductive investment through an increase in female body size. We report a different trade‐off in a frog endemic to the Tibetan Plateau, Rana kukunoris. Females living at higher altitudes (n = 11 populations, 2000–3500 m) produce larger eggs, but without a concomitant increase in female body size or clutch size. The reduced diel and seasonal activity at high altitudes may impose constraints on the maximum body size of adult frogs, by limiting the opportunity for energy accumulation. Simultaneously, producing larger eggs likely helps to increase the rate of embryonic development, causing tadpoles to hatch earlier. The gelatinous matrix surrounding eggs, more of which is produced by large females, may help buffer developing embryos from temperature fluctuations or offer protection from ultraviolet radiation. High‐altitude frogs on the Tibetan Plateau employ a reproductive strategy that favours large egg size independent of body size, which is unusual in amphibians. The harsh and unpredictable environmental conditions at high altitudes can thus impose strong and opposing selection pressures on adult and embryonic life stages, both of which can simultaneously influence fitness.     

Evolutionary ecology of egg size and number in a seed beetle: genetic trade-off differs between environments

Abstract In many organisms, large offspring have improved fitness over small offspring, and thus their size is under strong selection. However, due to a trade-off between offspring size and number, females producing larger offspring necessarily must produce fewer unless the total amount of reproductive effort is unlimited. Because differential gene expression among environments may affect genetic covariances among traits, it is important to consider environmental effects on the genetic relationships among traits. We compared the genetic relationships among egg size, lifetime fecundity, and female adult body mass (a trait linked to reproductive effort) in the seed beetle, Stator limbatus , between two environments (host-plant species Acacia greggii and Cercidium floridum ). Genetic correlations among these traits were estimated through half-sib analysis, followed with artificial selection on egg size to observe the correlated responses of lifetime fecundity and female body mass. We found that the magnitude of the genetic trade-off between egg size and lifetime fecundity differed between environments–a strong trade-off was estimated when females laid eggs on C. floridum seeds, yet this trade-off was weak when females laid eggs on A. greggii seeds. Also differing between environments was the genetic correlation between egg size and female body mass–these traits were positively genetically correlated for egg size on A. greggii seeds, yet uncorrelated on C. floridum seeds. On A. greggii seeds, the evolution of egg size and traits linked to reproductive effort (such as female body mass) are not independent from each other as commonly assumed in life-history theory.     

How within-group behavioural variation and task efficiency enhance fitness in a social group

How task specialization, individual task performance and within-group behavioural variation affects fitness is a longstanding and unresolved problem in our understanding of animal societies. In the temperate social spider, Anelosimus studiosus, colony members exhibit a behavioural polymorphism; females either exhibit an aggressive 'asocial' or docile 'social' phenotype. We assessed individual prey-capture success for both phenotypes, and the role of phenotypic composition on group-level prey-capture success for three prey size classes. We then estimated the effect of group phenotypic composition on fitness in a common garden, as inferred from individual egg-case masses. On average, asocial females were more successful than social females at capturing large prey, and colony-level prey-capture success was positively associated with the frequency of the asocial phenotype. Asocial colony members were also more likely to engage in prey-capture behaviour in group-foraging situations. Interestingly, our fitness estimates indicate females of both phenotypes experience increased fitness when occupying colonies containing unlike individuals. These results imply a reciprocal fitness benefit of within-colony behavioural variation, and perhaps division of labour in a spider society.     

Effects of a food supplementation experiment on reproductive investment and a post-mating sexually selected trait in magpies Pica pica

Food availability is an important factor affecting breeding success in birds. Food supplementation experiments in birds have in general focused on the effects on reproductive success in terms of female investment (laying date, clutch size, egg size), however, it is also known that the estimation of mate quality based on sexually selected signals influences female reproductive investment. In the particular case of magpies, females use nest size, a post-mating sexually selected signal, to assess male's likelihood to invest in reproduction, and accordingly adjust reproductive investment (clutch size). Then, the possible effects of food supplementation on female reproductive investment could be mediated by other variables related to parental quality, such as nest size in magpies. In the present study, we explore if higher food availability in a magpie territory affected both male sexually selected traits (i.e. nest size) and female reproductive investment (laying date, egg size, clutch size). We performed a food supplementation experiment in which we experimentally increased food availability in several magpie territories, keeping others as controls. In food-supplemented territories, males built significantly larger nests and females significantly increased egg size by 4.1% compared to control females. Results suggest that the continuous provisioning of protein rich food allowed magpie females to increase egg size. However, laying date and clutch size did not differ between control and food-supplemented magpie pairs. Food availability also affected the relationship between female reproductive investment and nest size. In control territories, females decreased their egg size in response to a larger nest, whereas a tendency for the opposite relationship was revealed in food-supplemented territories. We discuss the possibility that magpie females adopt different strategies for reproductive investment according to food availability.     

Heritability of dispersal rate and other life history traits in the Glanville fritillary butterfly

Knowing the variances and heritabilities (h(2)) of life history traits in populations living under natural conditions is necessary for a mechanistic understanding of respective evolutionary processes. I estimated heritabilities of several life history traits, including dispersal rate, body mass, age at first reproduction, egg mass, clutch size and lifetime reproductive success, in the Glanville fritillary butterfly (Melitaea cinxia) using parent-offspring regression. Experiments were conducted under field conditions in a large population cage (32 x 26 m). Heritability estimates ranged from zero to almost one and several were significantly different from zero. Body size for both sexes, female age at first reproduction and egg weight were all moderately to highly heritable, whereas heritabilities were low or non-existent in clutch size and lifetime egg production. Heritability estimates for dispersal rate varied between the sexes, so that dispersal was heritable from mother to her female offspring only. This finding is consistent with previous results showing that the F1 female but not male offspring of females that naturally established new populations in the field are significantly more dispersive than butterflies in old populations.     

Field evidence challenges the often‐presumed relationship between early male maturation and female‐biased sexual size dimorphism

Female‐biased sexual size dimorphism (SSD) is often considered an epiphenomenon of selection for the increased mating opportunities provided by early male maturation (i.e., protandry). Empirical evidence of the adaptive significance of protandry remains nonetheless fairly scarce. We use field data collected throughout the reproductive season of an SSD crab spider, Mecaphesa celer, to test two hypotheses: Protandry provides fitness benefits to males, leading to female‐biased SSD, or protandry is an indirect consequence of selection for small male size/large female size. Using field‐collected data, we modeled the probability of mating success for females and males according to their timing of maturation. We found that males matured earlier than females and the proportion of virgin females decreased abruptly early in the season, but unexpectedly increased afterward. Timing of female maturation was not related to clutch size, but large females tended to have more offspring than small females. Timing of female and male maturation was inversely related to size at adulthood, as early‐maturing individuals were larger than late‐maturing ones, suggesting that both sexes exhibit some plasticity in their developmental trajectories. Such plasticity indicates that protandry could co‐occur with any degree and direction of SSD. Our calculation of the probability of mating success along the season shows multiple male maturation time points with similar predicted mating success. This suggests that males follow multiple strategies with equal success, trading‐off access to virgin females with intensity of male–male competition. Our results challenge classic hypotheses linking protandry and female‐biased SSD, and emphasize the importance of directly testing the often‐assumed relationships between co‐occurring animal traits.     

A lengthy solution to the optimal propagule size problem in the large-bodied South American freshwater turtle, <Emphasis Type="Italic">Podocnemis unifilis</Emphasis>

In oviparous vertebrates lacking parental care, resource allocation during reproduction is a major maternal effect that may enhance female fitness. In general, resource allocation strategies are expected to follow optimality models to solve the energy trade-offs between egg size and number. Such models predict that natural selection should optimize egg size while egg number is expected to vary with female size, thus maximizing offspring fitness and consequently, maternal fitness. Deviations from optimality predictions are commonly attributed to morphological constraints imposed by female size, such as reported for small-bodied turtle species. However, whether such anatomical constraints exist in smaller-bodied females within large-bodied clades remains unstudied. Here we tested whether resource allocation of the river turtle Podocnemis unifilis (a relatively smaller member of the large-bodied Podocnemididae) follows optimality theory, and found a pattern of egg elongation in smaller females that provides evidence of morphological constraints and of a reproductive trade-off with clutch size, whereas egg width supports the existence of an optimal egg size and no trade-off. Moreover, larger females laid larger clutches composed of rounder eggs, while smaller females laid fewer and relatively more elongated eggs. Elongated eggs from smaller females have larger volume relative to female size and to round eggs of equal width. We propose that elongated eggs represent a solution to a potential morphological constraint suffered by small females. Our results suggest that larger females may optimize fitness by increasing the number of eggs, while smaller females do so by producing larger eggs. Our data supports the notion that morphological constraints are likely more widespread than previously anticipated, such that they may not be exclusive of small-bodied lineages but may also exist in large-bodied lineages.     

Resource-Dependent Clutch Size Decisions and Size-Fitness Relationships in a Gregarious Ectoparasitoid Wasp, <Emphasis Type="Italic">Bracon brevicornis</Emphasis>

Gregarious parasitic wasps, which lay more than one egg into or onto a host arthropod’s body, are usually assumed to lay an optimal number of eggs per host. If females would lay too few eggs, some resources may be wasted, but if females lay too many eggs, offspring may develop into substantially smaller-sized adults or may not develop successfully and die. The availability of hosts can further influence a female’s clutch size decision, as more eggs should be laid when hosts are scarce. Here, we analyzed clutch size decisions and the fitness consequences thereof in the ectoparasitic wasp Bracon brevicornis (Hymenoptera: Braconidae), a potential biocontrol agent against pest moth species. For experiments, larvae of the Mediterranean flower moth, Ephestia kuehniella (Lepidoptera: Pyralidae) were used. Using artificially created as well as naturally laid clutches of eggs, the effects of clutch size on fitness of first (F1) and second (F2) generation offspring were investigated. Our results revealed that the fitness consequences of large clutches included both increased mortality and smaller adult sizes of the emerging offspring (F1). Smaller F1 females matured fewer eggs during their lifetime and their offspring (F2) had reduced egg-to-adult survival probability. Naturally laid clutches varied with host size up to a maximum, which probably reflects egg limitation. Clutches remained smaller than the calculated optimal (Lack) clutch size and females responded to high host availability with a decreased number of eggs laid. We thus conclude that large clutches may result in significantly smaller offspring with reduced fitness, and that host size as well as host availability influence the clutch size decision made by B. brevicornis females.     

Does follicle excision always result in enlargement of offspring size in lizards?

An experimental reduction of offspring number has been reported to result in enlargement of offspring size in lizards. We applied the “follicle excision” technique to a lacertid lizard (Takydromus septentrionalis) to examine whether this effect is generalisable to lizards. Of the 82 females that produced 3 successive clutches in the laboratory, 23 females underwent follicle excision after they oviposited the first clutch. Follicle excision reduced clutch size, but did not alter egg size. This result indicates that egg size is not altered during vitellogenesis in T. septentrionalis. Females undergoing follicle excision produced a third clutch (a second post-surgical clutch) as normally as did control females. Females switched from producing more but smaller eggs early in the breeding season to fewer but larger eggs later in the season. Our results indicate that female T. septentrionalis maximize reproductive success by diverting an optimal, rather than a higher, fraction of the available energy to individual offspring. This optimized allocation of the available energy to offspring production explains why follicle excision does not result in enlargement of egg size in this species. Our study provides evidence that an experimental reduction of offspring number does not always result in enlargement of offspring size in lizards.     

Incubation capacity contributes to constraints on maximal clutch size in Brent Geese Branta bernicla nigricans

Lack ( 1967 ) proposed that clutch size in species with precocial young was determined by nutrients available to females at the time of egg formation; since then others have suggested that regulation of clutch size in these species may be more complex. We tested whether incubation limitation contributes to ultimate constraints on maximal clutch size in Black Brent Geese (Black Brant) Branta bernicla nigricans. Specifically, we investigated the relationship between clutch size and duration of the nesting period (i.e. days between nest initiation and the first pipped egg) and the number of goslings leaving the nest. We used experimental clutch manipulations to assess these questions because they allowed us to create clutches that were larger than the typical maximum of five eggs in this species. We found that the per‐capita probability of egg success (i.e. the probability an egg hatched and the gosling left the nest) declined from 0.81 for two‐egg clutches to 0.50 for seven‐egg clutches. As a result of declining egg success, clutches containing more than five eggs produced, at best, only marginally more offspring. Manipulating clutch size at the beginning of incubation had no effect on the duration of the nesting period, but the nesting period increased with the number of eggs a female laid naturally prior to manipulation, from 25.4 days (95% CI 25.1–25.7) for three‐egg clutches to 27.7 days (95% CI 27.3–28.1) for six‐egg clutches. This delay in hatching may result in reduced gosling growth rates due to declining forage quality during the brood rearing period. Our results suggest that the strong right truncation of Brent clutches, which results in few clutches greater than five, is partially explained by the declining incubation capacity of females as clutch size increases and a delay in hatching with each additional egg laid. As a result, females laying clutches with more than five eggs would typically gain little fitness benefit above that associated with a five‐egg clutch.     

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.