Seasonal shifts in clutch size and egg size in the side-blotched lizard,Uta stansburiana Baird and Girard

Summary There is evidence that the side-blotched lizard, Uta stansburiana, and some other organisms of temperate latitudes produce fewer and larger eggs as the reproductive season progresses. There are at least two models that could explain this phenomenon.Proponents of the parental investment model claim that females are selected to increase egg size, at the cost of clutch size, late in the season in order to produce larger and competitively superior hatchlings at a time when food for hatchlings is in low supply and when juvenile density is high. In this model the selective agent is relative scarcity of food available to hatchlings late in the reproductive season, and the adaptive response is production of larger offspring.The alternative explanation (bet-hedging model) proposed in this paper is based on the view that the amount of food available to females for the production of late-season clutches is unpredictable, and that selection has favored conservatively small clutches in the late season to insure that each egg is at least minimally provisioned. Smaller clutches, which occur most frequently late in the season, are more likely to consist of larger eggs, compared to larger clutches, for two reasons. Firstly, unlike birds, oviparous lizards cannot alter parental investment after their eggs are deposited, and therefore, in cases of fractional optimal clutch size, the next lower integral clutch size is selected with the remaining reproductive energy allocated to increased egg size. With other factors constant, eggs of smaller clutches will increase more in size than eggs of larger clutches when excess energy is divided among the eggs of a clutch. Secondly, unanticipated energy that may become available for reproduction during energy-rich years will similarly increase egg size a greater amount if divided among fewer eggs.     

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.     

Squamate hatchling size and the evolutionary causes of negative offspring size allometry

Although fecundity selection is ubiquitous, in an overwhelming majority of animal lineages, small species produce smaller number of offspring per clutch. In this context, egg, hatchling and neonate sizes are absolutely larger, but smaller relative to adult body size in larger species. The evolutionary causes of this widespread phenomenon are not fully explored. The negative offspring size allometry can result from processes limiting maximal egg/offspring size forcing larger species to produce relatively smaller offspring (‘upper limit’), or from a limit on minimal egg/offspring size forcing smaller species to produce relatively larger offspring (‘lower limit’). Several reptile lineages have invariant clutch sizes, where females always lay either one or two eggs per clutch. These lineages offer an interesting perspective on the general evolutionary forces driving negative offspring size allometry, because an important selective factor, fecundity selection in a single clutch, is eliminated here. Under the upper limit hypotheses, large offspring should be selected against in lineages with invariant clutch sizes as well, and these lineages should therefore exhibit the same, or shallower, offspring size allometry as lineages with variable clutch size. On the other hand, the lower limit hypotheses would allow lineages with invariant clutch sizes to have steeper offspring size allometries. Using an extensive data set on the hatchling and female sizes of > 1800 species of squamates, we document that negative offspring size allometry is widespread in lizards and snakes with variable clutch sizes and that some lineages with invariant clutch sizes have unusually steep offspring size allometries. These findings suggest that the negative offspring size allometry is driven by a constraint on minimal offspring size, which scales with a negative allometry.     

Elevational variation in adult body size and growth rate but not in metabolic rate in the tree weta Hemideina crassidens

Populations of the same species inhabiting distinct localities experience different ecological and climatic pressures that might result in differentiation in traits, particularly those related to temperature. We compared metabolic rate (and its thermal sensitivity), growth rate, and body size among nine high- and low-elevation populations of the Wellington tree weta, Hemideina crassidens, distributed from 9 to 1171 m a.s.l across New Zealand. Our results did not indicate elevational compensation in metabolic rates (metabolic cold adaptation). Cold acclimation decreased metabolic rate compared to warm-acclimated individuals from both high- and low-elevation populations. However, we did find countergradient variation in growth rates, with individuals from high-elevation populations growing faster and to a larger final size than individuals from low-elevation populations. Females grew faster to a larger size than males, although as adults their metabolic rates did not differ significantly. The combined physiological and morphological data suggest that high-elevation individuals grow quickly and achieve larger size while maintaining metabolic rates at levels not significantly different from low-elevation individuals. Thus, morphological differentiation among tree weta populations, in concert with genetic variation, might provide the material required for adaptation to changing conditions.     

Allometry of reproduction in two species of gekkonid lizards (Gehyra): effects of body size miniaturization on clutch and egg sizes

In squamate reptiles there is an allometric pattern for small-bodied females to have smaller clutches and proportionally larger eggs than large-bodied females, and this pattern occurs both among and within species. The allometric patterns in two species of the gecko Gehyra were studied to see how evolutionary reductions in adult body size affect fecundity and offspring size among species, and how these changes affect allometric relationships within species. Gehyra dubia has two eggs per clutch (the typical clutch size for gekkonid lizards), whereas the smallerbodied G. variegata has a single egg per clutch. Within both species, egg size increased with female body size. The data are consistent with at least two mechanistic hypotheses: (1) that the width of the pelvis constrains egg size; and (2) in species with invariant clutch sizes, larger females can only allocate additional energy towards egg size and not number. More direct tests of these hypotheses are warranted. Miniaturization of body sizes in Gehyra is correlated with a clutch size reduction of 50% (from two to one), and a large (1.7-fold) compensatory increase in relative egg mass. However, the small-bodied G. variegata (one egg per clutch) had a lower relative clutch mass than did G. dubia. These findings have implications for understanding the influence of evolutionary reductions in body size on reproductive traits, and for allometric trends in squamate reptiles in general.     

Phenotypic plasticity in reproductive traits induced by food availability in a lacertid lizard, Takydromus septentrionalis

Understanding the proximate determinants of phenotypic variations in life-history traits can provide powerful insights into a species' life-history strategies. I experimentally manipulated availability of food (high vs low) to examine plasticity in the reproductive traits of northern grass lizards, Takydromus septentrionalis (Lacertidae), from eastern China. Food availability significantly affected reproductive frequency and thereby seasonal reproductive output, but had little effect on reproductive output per clutch. Low-food females postponed reproduction and produced less clutches in the reproductive season than did high-food females. After producing their second clutches, low-food females were in lower body condition than the high-food counterparts. By the end of the experiment, however, all females exhibited similar body condition. Clutch size and clutch mass differed between the first and second clutches but not between the treatments. Egg size and phenotypic traits of hatchlings (body size, morphology and locomotor performance) in T. septentrionalis did not vary significantly from first to second clutches nor between the two treatments. These results support optimal egg size (offspring) theory. Female T. septentrionali s "decide" whether or not to reproduce largely based on current energy intake; lowered feeding rates thus delay oviposition and reduce reproductive frequency. In contrast, clutch size, egg size and relative clutch mass remain unchanged.     

Maternal effects and their consequences for offspring fitness in the Yellow Dung Fly

1. Maternal adult diet and body size influence the fecundity of a female and possibly the quality and the performance of her offspring via egg size or egg quality. In laboratory experiments, negative effects in the offspring generation have often been obscured by optimal rearing conditions.
2. To estimate these effects in the Yellow Dung Fly, Scathophaga stercoraria , how maternal body size and adult nutritional status affected her fecundity, longevity and egg size were first investigated.
3. Second, it was investigated how female age and adult nutritional experience, mediated through the effects of egg size or egg quality, influenced the performance of offspring at different larval densities.
4. Maternal size was less important than maternal adult feeding in increasing reproductive output. Without food restriction, large females had larger clutch sizes and higher oviposition rates, whereas under food restriction this advantage was reversed in favour of small females.
5. Offspring from mothers reared under nutritional stress experienced reduced fitness in terms of egg mortality and survival to adult emergence. If the offspring from low-quality eggs survived, the transmitted maternal food deficiency only affected adult male body size under stressful larval environments.
6. Smaller egg sizes due to maternal age only slightly affected the performance of the offspring under all larval conditions.     

Growth and fecundity of Daphnia after diapause and their impact on the development of a population

Laboratory and field investigations revealed that the life history traits of exephippial and parthenogenetic generations of Daphnia differ substantially. Daphniids hatching from resting eggs grow faster and their definitive body sizes are bigger than of hatchlings from subitaneous eggs. Size at maturity for exephippial animals is significantly larger. In spite of this, they mature a few days earlier than parthenogenetic females. In this study, the difference was 3–4 days for the laboratory experiments and 1–3 days for the field. Fecundity of the exephippial generation is markedly higher. Here, the clutch size for this generation was up to 3.5–4.0 times as large as for the parthenogenetic generation. Moreover, obtained results suggest that the relationship between clutch size and body length for both generations differ significantly.Estimates of the intrinsic rate of increase for field Daphnia populations demonstrated that life history traits of exephippial animals lead to a two or threefold higher rate of increase in the conditions of invertebrate predation pressure. Under moderate fish pressure, obtained r values for the daphniids hatching from resting eggs were larger than those from subitaneous. High growth rate of exephippial females is disadvantageous only under the conditions of severe pressure by fish. Obtained results suggest that hatchlings from diapausing eggs an acceleration of population increase by several times during the beginning of the development of a population with periodical re-establishment from resting eggs.     

Fitness of juvenile lizards depends on seasonal timing of hatching,not offspring body size

To understand how selection shapes life-history traits, we need information on the manner in which offspring phenotypes influence fitness. Life-history allocation models typically assume that “bigger offspring are better”, but field data paint a more complex picture: larger offspring size sometimes enhances fitness, and sometimes not. Additionally, higher survival and faster growth of larger offspring might be due to indirect maternal effects (e.g., mothers allocate hormones or nutrients differently to different-sized eggs), and not to offspring size per se. Alternative factors, such as seasonal timing of hatching, may be more important. We examined these issues using 419 eggs from captive jacky dragon lizards (Amphibolurus muricatus). The mothers were maintained under standardized conditions to minimize variance in thermal and nutritional history, and the eggs were incubated under controlled conditions to minimize variance in offspring phenotypes due to incubation temperature and moisture. We reduced the size of half the eggs (and, thus, the size of the resultant hatchlings) from each clutch by yolk extraction. The hatchlings were marked and released at a field site over a 3-month period, with regular recapture surveys to measure growth and survival under natural conditions. Growth rates and survival were strongly enhanced by early-season hatching, but were not affected by hatchling body size.     

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.     

中国石龙子雌体繁殖特征和卵孵化的地理变异

浙江丽水和广东韶关中国石龙子均年产单窝卵,窝卵数,窝卵重和卵重均与雌体SVL呈正相关,雌体头部形态,繁殖特征,产卵起始时间和孵孵化的热依赖性等有显著的地理变异;韶关石龙子产卵起始时间为5月中旬,比丽水经子约早两周,韶关石龙子窝卵数较大,卵较小,窝卵重与丽水石龙子无显著差异。韶关石龙子特定SVL的窝卵数比丽水石龙子多2．8枚卵,中国经子卵数量和大小之间有种群间权衡,无种数内权衡,同一种群内卵数量与卵大小无关,孵化温度影响石龙子孵出幼体的一些特征,24℃孵出细幼体比32℃孵出幼体大,躯干发育好,剩余卵黄少,韶关24℃孵出幼体的体重,躯干干重小于丽水幼体,韶关32℃孵出幼体的SVL小于丽水幼体,剩余卵黄大于丽水幼体,表明适宜卵孵化温度范围有地理变异。丽水石龙子卵对极端高温和低温的耐受性较强,适宜卵孵化温度范围较宽。     

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.     

Sex-specific niche partitioning and sexual size dimorphism in Australian pythons (Morelia spilota imbricata)

Sexual dimorphism is usually interpreted in terms of reproductive adaptations, but the degree of sex divergence also may be affected by sex-based niche partitioning. In gape-limited animals like snakes, the degree of sexual dimorphism in body size (SSD) or relative head size can determine the size spectrum of ingestible prey for each sex. Our studies of one mainland and four insular Western Australian populations of carpet pythons ( Morelia spilota ) reveal remarkable geographical variation in SSD, associated with differences in prey resources available to the snakes. In all five populations, females grew larger than males and had larger heads relative to body length. However, the populations differed in mean body sizes and relative head sizes, as well as in the degree of sexual dimorphism in these traits. Adult males and females also diverged strongly in dietary composition: males consumed small prey (lizards, mice and small birds), while females took larger mammals such as possums and wallabies. Geographic differences in the availability of large mammalian prey were linked to differences in mean adult body sizes of females (the larger sex) and thus contributed to sex-based resource partitioning. For example, in one population adult male snakes ate mice and adult females ate wallabies; in another, birds and lizards were important prey types for both sexes. Thus, the high degree of geographical variation among python populations in sexually dimorphic aspects of body size and shape plausibly results from geographical variation in prey availability.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 113–125.     

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.     

The seasonal timing of oviposition in sand lizards (Lacerta agilis): why early clutches are better

We studied a population of sand lizards (Lacerta agilis) near the northern edge of the species' range in coastal Sweden. We captured, marked, released and recaptured 98 adult female lizards over 5 years. Hatchlings from 146 laboratory-incubated clutches (1279 eggs) from field-caught gravid females were measured, weighed, marked and released at the study site. Female sand lizards usually laid only a single clutch of 4 to 15 eggs each year, but varied considerably in the time of year at which they laid their eggs. Oviposition dates shifted between years depending on weather (basking opportunities), but the relative timing of oviposition was consistent within a given female from year-to-year. The first females to oviposit each year were large animals in good physical condition, that had grown rapidly in previous years. “Early” clutches were larger than “later” clutches, had higher hatching success, and tended to have higher post-hatching survival rates. Offspring from early clutches were larger than “later” hatchlings, and differed in body proportions (probably because seasonal changes in maternal temperatures directly modified offspring phenotypes). Overall, our study documents several strong correlates of the timing of oviposition, and suggests that variation in this trait among females has strong fitness consequences, perhaps related to maternal “quality”. The correlations we observed between oviposition date and other traits that have been invoked as determinants of hatchling survival in reptiles (e.g., hatchling size, body shape, opportunities for multiple mating by the mother) suggest that hypotheses advocating simple causal connections between these traits and hatchling success should be viewed with caution.     

Age structure and body size of the Chuanxi Tree Frog Hyla annectans chuanxiensis from two different elevations in Sichuan (China)

Age, body size, and growth patterns in the subtropical anuran Hyla annectans chuanxiensis from high (Dengchigou Protection Station) and low (Lingguan Town) elevations in Baoxing County of Sichuan province (China) were described using skeletochronology. Females were significantly older than males at the low-elevation site, but there was no significant difference between the sexes at the high-elevation site. Age at sexual maturity of both males and females was 2 years at the high-elevation site, whereas males matured at 1 year and females at 2 years at the low-elevation site. Males and females from the low-elevation population reached a maximum age of 3 and 4 years, respectively, whereas males and females from the high-elevation population reached a maximum age of 4 and 5 years, respectively. At both sites, females were significantly larger than males. Females and males from the high-elevation population were larger than individuals from the low-elevation population. When the effect of age was controlled, the differences in body size of the two populations were significant only for females. Von Bertalanffy growth curves indicated that the growth rates in males was greater than in females in both populations. They also showed that the growth of both sexes slowed at an earlier age in the low-elevation population than in the high-elevation population. The findings suggest that age is a major factor underlying body size patterns for both sexes, but that the elevation of the locality affects the body size of females.     

Sexual dimorphism, reproductive biology, and food habits of two species of African filesnakes (Mehelya, Colubridae)

The ecology and general biology of African snakes remains virtually unstudied, even in highly distinctive species such as the filesnakes (genera Mehelya and Gonionotophis ). Our measurements and dissections of preserved specimens provided information on body sizes, sexual dimorphism in size and bodily proportions, clutch sizes, and food habits of two Mehelya species. In both M. capensis and M. nyassae , females attain sexual maturity at the same size as conspecific males, but grow to much larger sizes. Mehelya capensis displays extreme differences in body shape between males and females at the same body length: females have longer and wider heads, thicker bodies, and larger eyes (relative to both head length and head width) than do conspecific males. Dimorphism in body proportions is less marked in M. nyassae. Female reproductive cycles are seasonal in M. capensis , and clutch sizes are larger in this species than in its smaller congener (5-11 eggs in M. capensis , 2-6 eggs in M. nyassae ).
Contrary to popular wisdom, Mehelya are not specialized ophiophages. Mehelya nyassae feeds primarily upon lygosomatine skinks, including many fossorial taxa. Mehelya capensis has a broader diet, feeding on a wide variety of terrestrial lizards (especially agamids and gerrhosaurids) and snakes. Toads are also common prey items. The diversity of prey types taken by M. capensis suggests that these snakes may use ambush predation as well as active foraging. Mehelya is strongly convergent with Asian elapids of the genus Bungarus in its morphology (triangular body shape; powerful jaws; visible interstitial skin), behaviour (nocturnality; reluctance to bite when harassed), and diet (feeding on elongate reptiles, including snakes). Observations of preyhandling and ingestion by captive snakes are needed to clarify possible selective forces for the evolution of the unusual traits shared by these taxa.     

Absence of the trade-off between the size and number of offspring in the natterjack toad (Bufo calamita)

Summary A trade-off between size and number of offspring was not found for females of similar sizes of the natterjack toad (Bufo calamita). Moreover, for large females, clutches with higher number of eggs had larger eggs as well. This suggests that larger females produce more numerous and larger eggs because they potentially have more energy available for reproduction. Egg size diminished allometrically with clutch size. Egg size, however, did not increase offspring fitness. Therefore, this allometric decrease may be considered a consequence of phylogenetic constraints rather than a result of optimizing selection.     

Reproductive output,costs of reproduction,and ecology of the smooth snake,Coronella austriaca,in the eastern Italian Alps

A 5-year mark-recapture study of smooth snakes (Coronella austriaca) in the Carnic Alps (1100 m above sea level) of north-eastern Italy provided extensive information on the biology and life-history of these small viviparous snakes. Offspring were relatively large (mean=15 cm total length, 2.9 g) when they were born in late summer, and females grew to maturity (44 cm, 50 g) in approximately 4 years. Larger neonates retained their size advantage for at least 12 months, but did not have a higher probability of survival. Although sexual size dimorphism (at birth and at mean adult body sizes) was minor, the sexes differed significantly in several respects. Females grew faster than males during juvenile life, and adult females diverged in dietary habits from the rest of the population. Whereas juveniles (of both sexes) and adult males fed primarily on lizards, larger females shifted to feeding less frequently, but taking larger prey (mammals and snakes). Reproductive output increased strongly with maternal body size: larger females reproduced more frequently, produced larger litters of larger neonates, had higher relative clutch masses (RCMs), and had a lower proportion of stillborn off-spring. Most females produced a litter every 2nd or 3rd year. We did not detect significant year-to-year variation in reproductive traits over the 5 years of our study. Females were consistent from one litter to the next in several traits (e.g., litter sizes, offspring sizes and shapes, proportions of stillborn neonates, RCMs), but this consistency was due to differences in body size among females rather than to size-independent maternal effects. Overall litter sex ratios averaged 50/50, but sex ratios tended to be more male-biased in litters that were unusually large relative to maternal body size, and in litters containing a high proportion of stillborn offspring. Costs of reproduction appear to be high in this population, in terms of both energy allocation and risk. Reproduction reduced growth rates, and females that recovered condition more quickly in the year after reproduction were able to reproduce again after a briefer delay. Mortality was highest in reproducing females with high RCMs, and in females that were very emaciated after parturition. The marked increase in reproductive output with increasing maternal body size in C. austriaca may reflect a reduction in costs as females grow larger, and the dietary shift to larger prey may enhance the rate that females can accumulate energy for reproduction.