Female Body Size Research Articles

Flexibility in foraging strategies of Brown Skuas in response to local and seasonal dietary constraints

The Brown Skua Stercorarius antarcticus lonnbergi is an opportunistic species that displays a high degree of flexibility in foraging tactics. We deployed glo- bal positioning system (GPS) and immersion (activity) loggers on breeding Brown Skuas of known sex, body size and condition at Admiralty Bay, King George Island with the aim to examine the impacts of spatial and seasonal fluctuations in prey availability on movement and foraging behavior. We also investigated whether reversed sexual size dimorphism (females larger than males) in this species leads to differences between sexes in foraging behavior and whether this or other factors contribute to variation in breeding success. Analysis of the GPS data highlighted the high degree of plasticity in foraging behavior among individuals. Although most Brown Skuas were flexible in their feeding tactics, this was not enough to ensure a suc- cessful breeding season, as few pairs fledged chicks. Dur- ing early chick rearing, Brown Skuas spent most of their time on land, feeding almost exclusively on penguin chicks. By late chick rearing, when the availability of penguins had diminished, Brown Skuas supplemented the food obtained on land by traveling to the ocean. All for- aging trips to sea occurred during daylight, mostly during the early morning. Despite marked sexual size dimorphism, we failed to find any difference in foraging tactics between males and females. Furthermore, although laying date affected the number of chicks hatched (earlier pairs were more successful), no relationship was found between breeding success and male or female body size, condition or degree of dimorphism within pairs.

Body Size, Fecundity, and Sexual Size Dimorphism in the Neotropical Cricket Macroanaxipha macilenta (Saussure) (Orthoptera: Gryllidae)

Body size is directly or indirectly correlated with fitness. Body size, which conveys maximal fitness, often differs between sexes. Sexual size dimorphism (SSD) evolves because body size tends to be related to reproductive success through different pathways in males and females. In general, female insects are larger than males, suggesting that natural selection for high female fecundity could be stronger than sexual selection in males. I assessed the role of body size and fecundity in SSD in the Neotropical cricket Macroanaxipha macilenta (Saussure). This species shows a SSD bias toward males. Females did not present a correlation between number of eggs and body size. Nonetheless, there were fluctuations in the number of eggs carried by females during the sampling period, and the size of females that were collected carrying eggs was larger than that of females collected with no eggs. Since mating induces vitellogenesis in some cricket species, differences in female body size might suggest male mate choice. Sexual selection in the body size of males of M. macilenta may possibly be stronger than the selection of female fecundity. Even so, no mating behavior was observed during the field observations, including audible male calling or courtship songs, yet males may produce ultrasonic calls due to their size. If female body size in M. macilenta is not directly related to fecundity, the lack of a correlated response to selection on female body size could represent an alternate evolutionary pathway in the evolution of body size and SSD in insects.

How Women’s Perceptions of Peer Weight Preferences Are Related to Drive for Thinness

The purpose of this study was to examine how women’s perceptions of their peers’ weight preferences were related to drive for thinness. First, we examined the degree to which women were accurate in their perceptions of the female body sizes that their male and female peers preferred. Second, we examined the perceived weight preferences of women’s female peers, male peers, close peers, and distant peers to determine whether women perceived these peer groups as having different weight preferences for women’s body size. Finally, we investigated whether drive for thinness was related to the degree that women felt discrepant from their peers’ weight preferences. One hundred and thirty-three women from a small, liberal arts college in the Northeastern United States completed an online survey that included measures of actual and perceived weight preferences, drive for thinness, and demographic information. Information on actual weight preferences were also collected from 44 men to provide information about male peers’ weight preferences. Results indicated that women underestimated the body size that both women and men most preferred. Second, women perceived their female peers as preferring a thinner female size than their male peers, and their distant peers as preferring a thinner body size than their close peers. Finally, women who perceived their body size as being discrepant from the preferences of their close peers’ weight preferences, particularly close female peers, exhibited greater drive for thinness.

Population distribution, sexual dimorphism, and reproductive parameters in the crab Pinnixa valdiviensis Rathbun, 1907 (Decapoda: Pinnotheridae), a symbiont of the ghost shrimp Callichirus garthi (Retamal, 1975) in the southeastern Pacific

Pinnixa valdiviensis Rathbun, 1907 inhabits burrows of the ghost shrimp Callichirus garthi (Retamal, 1975) in the south-eastern Pacific. We described the host-use pattern and sexual dimorphism of P. valdiviensis to test for monogamy considering that the few other studied species of Pinnixa White inhabit their respective hosts as male-female pairs. Against expectations, P. valdiviensis lived either solitarily, or in small groups of up to four individuals; only a few burrows were inhabited by two crabs (either male-female or female-female pairs). The observations above argue against the notion that P. valdiviensis is monogamous. Furthermore, that a high frequency of solitary females were found brooding embryos and that the population sex ratio was skewed toward females suggests that males might roam among hosts in search of receptive females. We argue in favour of additional long-term (seasonal, >1 year) descriptive and experimental studies to reveal the mating tactics used by both males and females of P. valdiviensis. We also examined individual-level reproductive parameters in the studied species as little is known about reproduction in symbiotic crabs. Fecundity varied between 383 and 1052 eggs crab−1 with a mean ± SD of 774 ± 160 eggs crab−1 and increased significantly with female body size. Embryo volume varied between 0.0169 and 0.0443 with a mean ± SD of 0.0222 ± 0.0063 mm3 and did not vary with female body size. Reproductive output (RO) represented a mean ± SD of 5.74% ± 0.86% of crab body dry weight and increased proportionally with crab body weight. The RO in P. valdiviensis is lower than that reported for other free-living and symbiotic crabs.

Importance of reproductive biology of a harvest lizard, Tupinambis merianae, for the management of commercial harvesting

Context Management of the exploitation of resources requires biological information on exploited species. The skins of large reptiles have a commercial value as luxury leather items and Tupinambis lizards from southern South America have historically been exploited for this purpose. Argentina implemented management plans for Tupinambis lizards since 1988 that established a minimum capture size based on the width of dried skins, but this prescription has not been linked to local reproductive attributes of species. Aim In this study, we aim to determine the reproductive parameters of Tupinambis merianae and evaluate which class sizes of individuals are susceptible to commercial trade in central Argentina to generate local and species-specific information to improve available management tools. Methods We determined the relationship between the width of dried skins and live body sizes. We identified size at sexual maturity in males and females. Moreover, we determined status of reproductive individuals by body size and characterised gonadal development and seasonal reproductive events in central Argentina. We evaluated the relationship between female body size and clutch size. Key results Reproduction of T. merianae in central Argentina is markedly seasonal, with both sexes concentrating their reproductive activities between October and December. Size at sexual maturity was smaller for males than females, and the percentage of reproductive females was lower than males. In both sexes, the frequency of reproductive individuals was low in smaller lizards, and bigger females had bigger clutch size. The width of dried skins was positively related to body size. Conclusions Size at sexual maturity, and reproductive period, should be taken into account when management plans are designed to minimise any negative impacts of harvesting. Implications In central Argentina, the breeding season coincides with hunting periods set by national legislation. The results of our study have prompted local authorities to impose hunting closures for part of December and to raise the minimum catch size. Further, we offer an equation that can be used as a monitoring tool for estimating snout to vent length of live animals from skins. Studies like ours should be replicated in different areas and extrapolated to other models.

Physiological improvement in the copepodEurytemora affinisthrough thermal and multi-generational selection

As a major part of fish larval diet in nature, copepods constitute an appropriate live prey for aquaculture purposes. Considering the difficulty of mastering copepod mass production, studies on their growth performance at different environmental conditions are needed to improve their productivity. In this study a new selective approach based on temperature control is proposed to improve the physiological (body size, fecundity and lipid storage) performance of copepods. The estuarine copepod Eurytemora affinis known to have a high genetic variance in temperature tolerance was used as a biological model. First two different copepod lines were obtained after long-term culture at constant cold (7°C) and warm (20°C) temperatures. Then both populations were transferred to a higher temperature of 24°C appropriate for aquaculture use and followed during five generations. During the first two generations (F1–F2) of a cold-acclimated population, female body size and fecundity decreased significantly whereas the survival rate remained high. The high lipid content of this population was used by females to compensate the heat shock of more than 10°C. However, the survival rate decreased dramatically in F3 but allowed the selection of robust individuals which progressively improved their fitness during the following generations. So, compared to the warm acclimated population, the cold acclimated one showed larger body size, higher fecundity and better lipid storage. After only five generations at 24°C the cold-acclimated population showed a significant genetic gain in prosome length compared to the warm acclimated one.

주거 공간에서의 행위별 주요 시점 및 작업면 측정점 기준

In this study, the subjects were divided into those in their 20s to 30s and 40s to 50s. While they were engaging in particular behaviors in each living space, the visual points were analyzed and the distance of working surface was measured. This study is significant in that it can help improve the evaluation tool as to photometric quantities, and the findings are as follows. First, the point of gaze of each age group depending on the behavior in each space was not much different. The following were the main factors: the working space, the main object of their behavior, and the visual point of their behavior. Second, assessing the major visual points were different from the standards on eye level they varied depending on the living environment and roles of the subjects. Third, assessing the major visual points varied depending on the color, furniture type, and furniture size; it also varied depending on the behavior in each living space. Based on the findings, the following are suggested. First, more studies on visual points depending on gender and roles should be conducted. Second, more evaluation variables should be developed, given the average body size of Korean males and females, for more systematic studies.

Maternal investment in egg production: Substrate- and population-specific effects on offspring performance of the symbiotic crab Pachycheles monilifer (Anomura: Porcellanidae)

The porcelain crab Pachycheles monilifer is a non-obligate symbiotic species, living in association with marine invertebrates. In view of the importance of this relationship for the life cycle, this study investigated the reproductive performance of this crab in relation to its hosts. The crabs were collected in symbiosis with bryozoan and polychaete colonies on the southeastern coast of Brazil. Only the initial egg stages were used to estimate the fecundity and reproductive output (RO). To obtain the RO, the female and the egg-mass dry weight were used. Additionally, the genetic distance between the crab populations from the two substrates was evaluated, using partial sequences of the mitochondrial genes 16S and COI, in order to determine the intra- and interspecific genetic variation. The crabs found in bryozoans (CL, carapace length=4.6±1.3mm) were larger than those living among polychaetes (CL=4.1±1.1mm). The fecundity and RO of crabs inhabiting the bryozoans increased with carapace length, but in the females inhabiting the polychaetes only the fecundity was correlated with the female body size. In the polychaete colonies, the space available for the symbiotic porcelain crab is more restricted since it is a closed habitat, which could limit the size of its inquilines and consequently the reproductive fitness, whereas the females associated with polychaete colonies have a lower fecundity and RO. Our molecular results confirmed the existence of low genetic divergence and of potential gene flow between the two populations. Taken together, this information suggests that the differences in reproductive traits of these crab populations were due to the difference in hosts.

Interdependent effects of male and female body size plasticity on mating behaviour of predatory mites

The adaptive canalization hypothesis predicts that traits with low phenotypic plasticity are more fitness relevant, because they have been canalized via strong past selection, than traits with high phenotypic plasticity. Based on differing male body size plasticities of the predatory mites Phytoseiulus persimilis (low plasticity) and Neoseiulus californicus (high plasticity), we accordingly hypothesized that small male body size entails higher costs in female choice and male–male competition in P. persimilis than N. californicus. Males of both species are highly polygynous but females differ in the level of polyandry (low level in P. persimilis; medium level in N. californicus). We videotaped the mating interactions in triplets of either P. persimilis or N. californicus, consisting of a virgin female (small or standard-sized) and a small and a standard-sized male. Mating by both small and standard-sized P. persimilis females was biased towards standard-sized males, resulting from the interplay between female preference for standard-sized males and the inferiority of small males in male–male competition. In contrast, mating by N. californicus females was equally balanced between small and standard-sized males. Small N. californicus males were more aggressive (‘Napoleon complex’) in male–male competition, reducing the likelihood of encounter between the standard-sized male and the female, and thus counterbalancing female preference for standard-sized males. Our results support the hypothesis that male body size is more important to fitness in the low-level polyandrous P. persimilis than in the medium-level polyandrous N. californicus and provide a key example of the implications of sexually selected body size plasticity on mating behaviour.

Altitudinally divergent adult phenotypes in Iberian wall lizards are not driven by egg differences or hatchling growth rates.

The interplay between ecological conditions and life histories has been widely acknowledged in vertebrates, particularly in lizards. Environmental conditions may exert different selective pressures and produce divergent phenotypes even in geographically and genetically close populations. The Iberian wall lizard constitutes a perfect model organism as it is considered a species complex with a complicated evolutionary history. Here, we focus on two proximate populations in which we examined adult morphology and reproductive investment of wild-caught lizards along a 500-m altitudinal gradient with contrasting environmental conditions, where adults show marked morphological differences in spite of being closely related. Also, we performed a common garden experiment to examine embryonic and hatchling growth. We focused on reproductive investment per clutch, incubation time, egg size, morphology and growth rate of hatchlings. Results showed clutch size differences between populations that were independent of the larger body size of highland females. However, there were no egg morphological differences between populations, except for egg width, and this difference disappeared after controlling for female body size. Hatchling lizards from both populations did not differ in morphology. Moreover, we did not observe differences between populations or sexes in hatchling growth. Overall, we provide evidence that the differences in adult body size and clutch size are not driven by size at hatching which is not contributed to by egg size, nor are intrinsic hatchling growth rates associated with the environmental conditions experienced in our common garden experiment, suggesting that adult phenotypes are not the result of intrinsic differences between populations.

Bergmann meets Scholander: geographical variation in body size and insulation in the koala is related to climate

AbstractAimBody size often varies clinally, with dominant explanations centred on how body size influences heat exchange (e.g. Bergmann's rule). However, for endotherms, pelage properties can also dramatically alter heat exchange – a point emphasized by Scholander in the 1950s but which has received little attention in biogeographical analyses. Here, we investigate how geographical variation in both body size and fur properties of the koala (Phascolarctos cinereus) is related to climate.LocationEastern Australia.MethodsWe measured head length and fur depths of koala museum specimens from across its geographical range, and quantified the relationship between fur depth and insulation. We used linear regression and regression tree analyses to test for associations between morphological traits and climate variables relating to four hypotheses: heat conservation (Bergmann's rule), heat dissipation, fasting endurance/survival of extremes, and productivity.ResultsBoth body size and fur depth of koalas decrease substantially towards the tropics. Consistent with Scholander's view, fur properties showed stronger associations with climate than body size. Males, the larger sex, had shorter fur than females in hot environments but not in more temperate regions, suggesting that shorter fur compensates for sexual size dimorphism. While fur depth and male body size were more strongly associated with variables relating to heat dissipation, female body size was most strongly associated with minimum temperatures.Main conclusionsBody size interacts strongly with other traits, such as fur properties, to influence how animals experience climate. Our results emphasize how the consideration of geographical variation in suites of functionally related traits can provide important insight into how species persist across broad environmental gradients.

Courtship and Mating inPhausis reticulata(Coleoptera: Lampyridae): Male Flight Behaviors, Female Glow Displays, and Male Attraction to Light Traps

Abstract In contrast to most other North American fireflies that use flash dialogs for courtship, males of Phausis reticulata Say (Coleoptera: Lampyridae) (Fender 1966), often called blue ghost fireflies, glow as they fly slowly over the forest floor searching for flightless, neotenic females that are likewise bioluminescent. Recently, these Blue Ghost firefly displays have become increasingly popular as ecotourist attractions. Nevertheless, surprisingly little work has been done on P. reticulata courtship and mating behavior, and little is known of female oviposition patterns. Extensive field observations were conducted at 2 locations in Tennessee USA, leading to the description of new categories of male mate-searching search behaviors and nightly display activities. Spectrophotometric measures of bioluminescence were similar in both sexes (λ max = 552 nm). There was a 3-fold variation in female body size, and size was correlated to the number of dorsal photic organs (3 to 9). Field experiments suggested...

Andrew meets Rensch: sexual size dimorphism and the inverse of Rensch's rule in Andrew's toad (Bufo andrewsi).

Variation in sexual size dimorphism (SSD) is a widespread phenomenon and is commonly attributed to variation in sex-specific patterns of selection. According to Rensch's rule, SSD increases with increasing body size when males are the larger sex, and decreases when females are the larger sex. Using data from 17 populations of Andrew's toad (Bufo andrewsi), we tested whether the patterns of SSD conform to Rensch's rule. Using field experiments, we also evaluated the hypothesis that sexual selection favours large male body size and that fecundity selection favours large female body size. The results revealed that the degree of SSD increased with increasing mean size in females, consistent with the inverse of Rensch's rule. Although experiments revealed evidence for a large-male mating advantage, selection for large male size was weak at best, and hence unlikely to be an important source of variation in SSD. However, fecundity selection favouring large females was evident, and likely to explain the observed inverse of Rensch's rule. After correcting male and female body size for age differences, the patterns of SSD remained the same, suggesting that the intra- and interpopulational variation in SSD is not driven by sex differences in age structure. Hence, these findings suggest that the strong fecundity selection favouring large females drives the evolution of female-biased SSD in B. andrewsi, providing an explanation for the inverse of Rensch's rule. As such, the study provides an important addition to the small body of literature that uses an intraspecific approach to demonstrate the inverse of Rensch's rule.

Mobility and mating frequency in the scramble competition polygyny of a chrysomelid beetle

In scramble competition polygyny, male and female mobility may be under strong selection as a result of fitness effects of searching for reproductive resources such as mates, oviposition sites, or resources for egg production. We analyzed the relationship between mating frequency, mobility, and body size in males and females of the chrysomelid beetle Leptinotarsa undecimlineata. We obtained a detailed data set of movement and mating frequency of an entire population (1037 adults) over a full reproductive season using individual tagging and direct behavioral observations. Unlike previous studies, we found a negative relationship between mobility and mating success for both sexes. Size was positively correlated to mating frequency in females, but negatively in males. High male mobility may be the result, and not a cause, of low mating success in scramble mating polygynies where rejected or displaced males switch plants more often searching for mating opportunities. More mobile females may be looking for competition-free oviposition substrate and thus experiencing fewer sexual encounters.

Invasive black spiny‐tailed iguanas (Ctenosaura similis) on Gasparilla Island, Florida, USA

The native range of Ctenosaura similis extends from southern Mexico through Panama. From an initial introduction of 3 animals in 1979, the species now numbers in the thousands on Gasparilla Island in southwest Florida. In response to complaints of property damage from residents and threats to native species, local officials and the US Department of Agriculture Wildlife Services began a removal program in 2008. Through 2011, trappers removed 9467 ctenosaurs. The number removed declined from 32 iguanas/day in 2008 to 1.9 iguanas/day in 2011 despite no easing of the control effort. We necropsied 2757 ctenosaurs to document aspects of their natural history. Females outnumbered males overall, although the largest size class (>300 mm snout-vent length) included 32 males and just 2 females. Reproduction was seasonal. We found oviducal eggs in females from early Apr to early Jun, approximately 2 months later than C. similis in its native range. We trapped hatchlings from late Jul to early Oct coincident with the summer rainy season. Clutch size increased with female body size, with 62 being the largest clutch size recorded. In general, the biology of the invasive population on Gasparilla Island resembles native C. similis populations in Central America, except for the lack of large individuals. We suggest that shorter day length and colder temperatures create environmental conditions that are suboptimal for individual growth compared to those in the native range.

Size-dependent selective mechanisms on males and females and the evolution of sexual size dimorphism in frogs.

Sexual size dimorphism (SSD) varies in animals from male biased to female biased. The evolution of SSD is potentially influenced by a number of factors, such as territoriality, fecundity, and temporal breeding patterns (explosive vs. prolonged). In general, frogs show female-biased SSD with broad variance among species. Using comparative methods, we examine how different selective forces affect male and female sizes, and we test hypotheses about size-dependent mechanisms shaping SSD in frogs. Male size was weakly associated with SSD in all size classes, and we found no significant association among SSD, male size, temporal breeding pattern, and male territoriality. In contrast, female size best explained SSD variation across all size classes but especially for small-bodied species. We found a stronger evolutionary association between female body size and fecundity, and this fecundity advantage was highest in explosively breeding species. Our data indicate that the fecundity advantage associated with female body size may not be linear, such that intermediate and large females benefit less with body size increases. Therefore, size-dependent selection in females associated with fecundity and breeding patterns is an important mechanism driving SSD evolution in frogs. Our study underscores the fact that lineage-specific ecology and behavior should be incorporated in comparative analyses of animal SSD.

Mating success is predicted by the interplay between multiple male and female traits in the small hairy maggot blowfly

Intersexual selection drives the evolution of reproductive traits, including ornamentation and courtship behaviour. However, most studies attempting to explain the relationships between reproductive traits are oversimplified because traits are evaluated independently, and assessment of mate choice is restricted to one sex. Further research is required to understand the extent to which interactions between traits influence mating decisions in both sexes. The small hairy maggot blowfly, Chrysomya varipes, offers an ideal opportunity to examine how interactions between foreleg ornamentation (males have conspicuous white and black hairs, whereas females have only black hairs) and complex courtship behaviour influence mating success in males and females. This study involved mate choice trials between single females and males that varied in foreleg ornamentation. Courtship investment was quantified for males, and ornamentation and body size were quantified for both sexes. Mating success was predicted by time invested in courtship, but not by either male and female ornamentation or body size alone. However, there was a significant interaction between courtship investment, ornamentation and body size. At any given courtship investment, males with more ornamentation had an increased probability of mating success. Females with more ornamentation also had an increased probability of mating success, because males invested more courtship in more ornamented females. Furthermore, the lightest males had an increased probability of mating success compared to the heaviest males, as lighter males invested more in courtship. Female weight, however, did not significantly affect the probability of mating. The results suggest that male foreleg ornamentation in C. varipes acts as an amplifier of the visual courtship display, adding to a small but growing body of evidence that multiple male and female traits can interact to influence mating decisions.

Sexual selection on female ornaments in the sex-role-reversed Gulf pipefish (Syngnathus scovelli).

Understanding how selection acts on traits individually and in combination is an important step in deciphering the mechanisms driving evolutionary change, but for most species, and especially those in which sexual selection acts more strongly on females than on males, we have no estimates of selection coefficients pertaining to the multivariate sexually selected phenotype. Here, we use a laboratory-based mesocosm experiment to quantify pre- and post-mating selection on female secondary sexual traits in the Gulf pipefish (Syngnathus scovelli), a sexually dimorphic, sex-role-reversed species in which ornamented females compete for access to choosy males. We calculate selection differentials and gradients on female traits, including ornament area, ornament number and body size for three episodes of selection related to female reproductive success (number of mates, number of eggs transferred and number of surviving embryos). Selection is strong on both ornament area and ornament size, and the majority of selection occurs during the premating episode of selection. Interestingly, selection on female body size, which has been detected in previous studies of Gulf pipefish, appears to be indirect, as evidenced by a multivariate analysis of selection gradients. Our results show that sexual selection favours either many bands or larger bands in female Gulf pipefish.

Suitability of five mealybug species (Hemiptera, Pseudococcidae) as hosts for the solitary parasitoid Anagyrus sp. nr. pseudococci (Girault) (Hymenoptera: Encyrtidae)

Anagyrus sp. nr. pseudococci is an endoparasitoid which has been used as a biological control agent of mealybug pests. In this study, we compared the suitability of five mealybugs species with different phylogenetic relationships and geographical origins as hosts of this parasitoid. The selected mealybugs were: (1) a Mediterranean-native species, Planococcus ficus, sharing a long co-evolutionary history with the parasitoid; (2) three exotic species, the Afrotropical Planococcus citri, the Australasian Pseudococcus calceolariae and the Neotropical Pseudococcus viburni, with a recent history; and (3) the Neotropical Phenacoccus peruvianus, with no previous common history with the parasitoid. Host suitability was assessed based on different fitness parameters, such as body size, developmental time, emergence rate and sex ratio. The parasitoid was able to complete development in all mealybug species. Nevertheless, its emergence rate significantly varied among mealybug species, with the highest values observed in Pl. ficus and Pl. citri, intermediate values in Ps. calceolariae and the lowest ones in Ps. viburni and Ph. peruvianus. The body size of adult wasp females varied with host suitability and was positively correlated with other measures of parasitoid fitness, including the emergence rate and the sex ratio. The parasitoid developmental time differed among mealybug species but did not correlate with any other measure of fitness. A female biased sex ratio was found in the parasitoid progeny emerged from all mealybug species, except in Ps. viburni and Ph. peruvianus. There was a direct relationship between the proportion of females in the parasitoid progeny and the emergence rate.

The influence of female body size and shape on the trade‐off between offspring number and offspring size in two viviparous snakes

AbstractAlthough the trade‐off between offspring size and the number of offspring is a critical component of life‐history theory, many empirical tests fail to show that such trade‐off exists. Although this may be due to statistical issues (i.e. failure to control for maternal body size), other complications such as female body shape may play a role as well. Here, we examined reproductive traits in two species of viviparous garter snakes with very different body morphologies (Thamnophis marcianus and T. proximus) to see how female body shape affects this trade‐off. In the more slender species (T. proximus), we found a strong, negative relationship between brood size and offspring size, with the effect most notable in smaller females. However, in the more robust snake (T. marcianus), there was no significant trade‐off seen in either the sample as a whole or for either larger or smaller females. Our data support earlier work on ectotherms, which indicates that body shape can act to constrain how offspring size and clutch or litter size are related.