Early Life Conditions and Physiological Stress following the Transition to Farming in Central/Southeast Europe: Skeletal Growth Impairment and 6000 Years of Gradual Recovery

Early life conditions play an important role in determining adult body size. In particular, childhood malnutrition and disease can elicit growth delays and affect adult body size if severe or prolonged enough. In the earliest stages of farming, skeletal growth impairment and small adult body size are often documented relative to hunter-gatherer groups, though this pattern is regionally variable. In Central/Southeast Europe, it is unclear how early life stress, growth history, and adult body size were impacted by the introduction of agriculture and ensuing long-term demographic, social, and behavioral change. The current study assesses this impact through the reconstruction and analysis of mean stature, body mass, limb proportion indices, and sexual dimorphism among 407 skeletally mature men and women from foraging and farming populations spanning the Late Mesolithic through Early Medieval periods in Central/Southeast Europe (~7100 calBC to 850 AD). Results document significantly reduced mean stature, body mass, and crural index in Neolithic agriculturalists relative both to Late Mesolithic hunter-gatherer-fishers and to later farming populations. This indication of relative growth impairment in the Neolithic, particularly among women, is supported by existing evidence of high developmental stress, intensive physical activity, and variable access to animal protein in these early agricultural populations. Among subsequent agriculturalists, temporal increases in mean stature, body mass, and crural index were more pronounced among Central European women, driving declines in the magnitude of sexual dimorphism through time. Overall, results suggest that the transition to agriculture in Central/Southeast Europe was challenging for early farming populations, but was followed by gradual amelioration across thousands of years, particularly among Central European women. This sex difference may be indicative, in part, of greater temporal variation in the social status afforded to young girls, in their access to resources during growth, and/or in their health status than was experienced by men.     

Growth,body condition and contest performance after early‐life food restriction in a long‐lived tropical fish

Adverse conditions during early life can cause lasting body size deficits with effects on social and sexual competition, while an accelerated growth response can allow animals to catch up in body size but can be physiologically costly as well. How animals balance growth deficits and growth compensation is predicted to depend on the effects of each on lifetime fitness. We investigated the effects of experimental early‐life food restriction on growth, body condition, and adult contest competition in a cichlid fish (Tropheus sp.). Their longevity and aseasonal breeding suggest that, with view on lifetime reproductive success, temporarily growth‐restricted Tropheus should rather invest extra time in reaching competitive body size than risk the potential costs of accelerated growth. However, size‐selective predation pressure by gape size‐limited piscivores may have favored the evolution of an accelerated growth response to early‐life delays. Experimentally food‐restricted fish temporarily reduced their growth rate compared to a control group, but maintained their body condition factor at the control level throughout the 80‐week study period. There was no evidence for an accelerated growth response following the treatment, as the food‐restricted fish never exceeded the size‐specific growth rates that were measured in the control group. Food‐restricted fish caught up with the body size of the control group several months after the end of the treatment period and were as likely as control fish to win size‐matched contests over territories. Regardless of feeding regime, there were sex‐specific differences in growth rates and in the trajectories of condition factors over time. Females grew more slowly than males but maintained their condition factors at a high level throughout the study period, whereas the males'' condition factors declined over time. These differences may reflect sex‐specific contributions of condition and body size to adult fitness that are associated with female mouthbrooding and male competition for breeding territories.     

Catch-up growth in Japanese quail (Coturnix Japonica): relationships with food intake, metabolic rate and sex

The effects of early environmental conditions can profoundly affect individual development and adult phenotype. In birds, limiting resources can affect growth as nestlings, but also fitness and survival as adults. Following periods of food restriction, individuals may accelerate development, undergoing a period of rapid “catch-up” growth, in an attempt to reach the appropriate size at adulthood. Previous studies of altricial birds have shown that catch-up growth can have negative consequences in adulthood, although this has not been explored in species with different developmental strategies. Here, we investigated the effects of resource limitation and the subsequent period of catch-up growth, on the morphological and metabolic phenotype of adult Japanese quail (Coturnix japonica), a species with a precocial developmental strategy. Because males and females differ in adult body size, we also test whether food restriction had sex-specific effects. Birds that underwent food restriction early in development had muscles of similar size and functional maturity, but lower adult body mass than controls. There was no evidence of sex-specific sensitivity of food restriction on adult body mass; however, there was evidence for body size. Females fed ad lib were larger than males fed ad lib, while females subjected to food restriction were of similar size to males. Adults that had previously experienced food restriction did not have an elevated metabolic rate, suggesting that in contrast to altricial nestlings, there was no metabolic carry-over effect of catch-up growth into adulthood. While Japanese quail can undergo accelerated growth after re-feeding, timing of food restriction may be important to adult size, particularly in females. However, greater developmental flexibility compared to altricial birds may contribute to the lack of metabolic carryover effects at adulthood.     

Phenotypic and genetic integration of personality and growth under competition in the sheepshead swordtail,Xiphophorus birchmanni

Competition for resources including food, physical space, and potential mates is a fundamental ecological process shaping variation in individual phenotype and fitness. The evolution of competitive ability, in particular social dominance, depends on genetic (co)variation among traits causal (e.g., behavior) or consequent (e.g., growth) to competitive outcomes. If dominance is heritable, it will generate both direct and indirect genetic effects (IGE) on resource‐dependent traits. The latter are expected to impose evolutionary constraint because winners necessarily gain resources at the expense of losers. We varied competition in a population of sheepshead swordtails, Xiphophorus birchmanni, to investigate effects on behavior, size, growth, and survival. We then applied quantitative genetic analyses to determine (i) whether competition leads to phenotypic and/or genetic integration of behavior with life history and (ii) the potential for IGE to constrain life history evolution. Size, growth, and survival were reduced at high competition. Male dominance was repeatable and dominant individuals show higher growth and survival. Additive genetic contributions to phenotypic covariance were significant, with the G matrix largely recapitulating phenotypic relationships. Social dominance has a low but significant heritability and is strongly genetically correlated with size and growth. Assuming causal dependence of growth on dominance, hidden IGE will therefore reduce evolutionary potential.     

Costs of compensation: effect of early life conditions and reproduction on flight performance in zebra finches

Conditions experienced in early life have been shown to affect the development or programming of physiological processes. While animals may recover from earlier periods of adversity, this process can carry long-term costs. Such long-term effects are likely to be most evident when individuals are placed in demanding situations that require high performance. Escape flight speed in passerine birds is crucial to predator evasion and requires very rapid take-off. Here, we examine whether the ability to maintain escape flight performance during the immediate post-breeding period is influenced by conditions in early life. We manipulated the early life conditions experienced by zebra finches (Taeniopygia guttata) by rearing them on either low or high quality food through the growth period, or by changing conditions halfway through the nestling period, moving from high to low or vice versa. While there was no difference amongst the treatment groups in body size attained by adulthood, amongst the birds that experienced low quality food, the body size of those that were switched to a high quality diet halfway through the nestling growth period recovered faster than those that had low quality food until fledging. We found no differences amongst the dietary groups in flight performance at adulthood prior to breeding, and all groups showed a decline in average escape flight performance over the breeding period. However, the magnitude of the post-breeding decline in flight performance for a given level of reproductive output was significantly greater for those females that had experienced a switch from a low to a high quality diet during the nestling phase. These results suggest that this diet-induced rapid recovery of body size, which may have immediate competitive advantages, nonetheless carries locomotory costs in later life manifest in the capacity to sustain the high performance escape response during the post-reproductive recovery phase.     

Growth hormone transgenesis does not influence territorial dominance or growth and survival of first-feeding Atlantic salmon Salmo salar in food-limited stream microcosms

This study explored the relative competitive ability and performance of first-feeding growth hormone (GH) transgenic and non-transgenic Atlantic salmon Salmo salar fry under low food conditions. Pair-wise dominance trials indicated a strong competitive advantage for residents of a contested foraging territory. Transgenic and non-transgenic individuals, however, were equally likely to be dominant. Similarly, in stream environments with limited food, the transgene did not influence the growth in mass or survival at high or low fry densities. Fry in low-density treatments, however, performed better than fry in high-density treatments. These results indicate that, under the environment examined, the growth performance of GH-transgenic and non-transgenic S. salar may be similar during first feeding, an intense period of selection in their life history. Similarities in competitive ability and growth performance with wild-type fish suggest that the capacity of transgenic S. salar to establish in natural streams may not be inhibited during early life history.     

Regeneration from Injury and Resource Allocation in Sponges and Corals – a Review

The ability of bottom‐dwelling marine epifauna to regenerate injured or lost body parts is critical to the survival of individuals from disturbances that inflict wounds. Numerous studies on marine sponges (Phlyum Porifera) and corals (of the orders Scleractinia and Alcyonacea) suggest that regeneration is limited by many intrinsic (individual‐dependent) and extrinsic (environment‐dependent) factors, and that other life history processes may compete with regeneration for energetic and cellular resources. We review how intrinsic (size, age, morphology, genotype) and extrinsic (wound characteristics, water temperature, food availability, sedimentation, disturbance history, selection) factors limit regeneration in sponges and corals. We then review the evidence for impaired somatic growth and sexual reproduction, and altered outcomes of interactions (anti‐predator defenses, competitive abilities, self‐ and non‐self recognition abilities) with other organisms in regenerating sponges and corals. We demonstrate that smaller, older sponges and corals of decreasing morphological complexities tend to regenerate less well than others, and that regeneration can be modulated by genotype. Large wounds with small perimeters inflicted away from areas where resources are located tend to be regenerated less well than others, as are injuries inflicted when food is limited and when the animal has been previously or recently injured. We also demonstrate that regeneration strongly impairs somatic growth, reduces aspects of sexual reproduction, and decreases the ability for sponges and corals to defend themselves against predators, to compete, and to recognize conspecifics. Effects of limited regeneration and impaired life histories may manifest themselves in higher levels of biological assembly e.g., reduced accretion of epifaunal biomass, reduced recruitment and altered biotic associations, and thus affect marine community and ecosystem recovery from disturbances. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Potential causes and life-history consequences of sexual size dimorphism in mammals

1. Male-biased sexual size dimorphism (SSD) in mammals has been explained by sexual selection favouring large, competitive males. However, new research has identified other potential factors leading to SSD. The aim of this review is to evaluate current research on the causes of SSD in mammals and to investigate some consequences of SSD, including costs to the larger sex and sexual segregation. 2. While larger males appear to gain reproductive benefits from their size, studies have also identified alternative mating strategies, unexpected variance in mating success and found no clear relationship between degree of polygyny and dimorphism. This implies that sexual selection is unlikely to be the single selective force directing SSD. 3. Latitude seems to influence SSD primarily through variation in overall body size and seasonal food availability, which affect potential for polygyny. Likewise, population density influences resource availability and evidence suggests that food scarcity differentially constrains the growth of the sexes. Diverging growth patterns between the sexes appear to be the primary physiological mechanism leading to SSD. 4. Female-biased dimorphism is most adequately explained by reduced male–male competition resulting in a decrease in male size. Female–female competition for dominance and resources, including mates, may also select for increased female size. 5. Most studies found that sexual segregation arises through asynchrony of activity budgets between the sexes. The larger sex can suffer sex-biased mortality through increased parasite load, selective predation and the difficulty associated with sustaining a larger body size under conditions of resource scarcity. 6. None of the variables considered here appears to contribute a disproportionate amount to SSD in mammals. Several promising avenues of research are currently overlooked and long-term studies, which have previously been biased toward ungulates, should be carried out on a variety of taxa.     

山地麻蜥个体发育过程中头部两性异形和食性的变化

研究了山地麻蜥(Eremias brenchleyi)个体发育过程中头部两性异形和食性的变化．成体个体大小(SVL)无显著的两性差异,但雄体具有较大的头部(头长和头宽)．头部两性异形在孵出幼体就已存在,成体头部两性异形比幼体(包括孵出幼体)更为显著,雄性较大的头部与其头部随SVL的增长速率大于雌性有关．两性头部总体上随SVL呈异速增长,表现为个体发育过程中头长和头宽与SVL的线性回归方程斜率有显著的变化．孵出幼体有相对较大的头部,这种形态特征是胚胎优先保证生态学意义更为显著的头部生长的结果,有利于孵出幼体的早期生存和生长．相对头部大小在个体发育过程中有显著的变化．不同性别和大小的山地麻蜥摄入食物的种类及各种食物在摄入食物中所占的比例有一定程度的差别,食物生态位宽度和重叠度因此有一定的差别．然而,没有直接的证据表明头部两性异形能导致两性食物生态位的明显分离,并有利于减缓两性个体对食物资源的竞争。     

Optimum body size: effects of food quality and temperature,when reproductive growth rate is restricted,with examples from aphids

Most models of optimum energy partitioning predict variability in adult size, although not always explicitly. Increase in size is usually attributed to an increase in the growth rate or decline in mortality. The model presented shows that this may not always be the case. Even when mortality is kept constant in organisms with overlapping generations, a constraint on the maximum reproductive growth rate may lead, when the rate of overall growth increases, to either an increase or a decline in the optimum adult body size. It is shown that adult size could be a consequence of the differential responses of life history traits to changes in temperature and food quality. This is clearly advantageous for short lived organisms, like aphids, each generation of which only experience a very small part of the great seasonal range in conditions. This hypothesis complements Iwasa's (1991) explanation of the phenotypic plasticity observed in long lived organisms. The predictions are illustrated with empirical data from aphids. The model presented, which has been verified against a very large data set, indicates that for aphids the adult weight observed at a particular combination of temperature and food quality is that at which the population growth rate, r_m, is maximized. We conclude that predictions about adult size from models based on the partitioning of energy are more likely to apply to organisms that scramble for resources, i.e., “r” selected species. The size of organisms that contest for resources is more likely to be determined by competitive status and avoidance of natural enemies.     

Benefits of extra food to reproduction depend on maternal condition

The amount of food resources available to upper‐level consumers can show marked variations in time and space, potentially resulting in food limitation. The availability of food resources during reproduction is a key factor modulating variation in reproductive success and life‐history tradeoffs, including patterns of resource allocation to reproduction versus self‐maintenance, ultimately impacting on population dynamics. Food provisioning experiments constitute a popular approach to assess the importance of food limitation for vertebrate reproduction. In this study of a mesopredatory avian species, the lesser kestrel Falco naumanni, we provided extra food to breeding individuals from egg laying to early nestling rearing. Extra food did not significantly affect adult body condition or oxidative status. However, it increased the allocation of resources to flight feathers moult and induced females to lay heavier eggs. Concomitantly, it alleviated the costs of laying heavier eggs for females in poor body condition, and reduced their chances of nest desertion (implying complete reproductive failure). Extra food provisioning improved early nestling growth (body mass and feather development). Moreover, extra food significantly reduced the negative effects of ectoparasites on nestling body mass, while fostering forearm (a flight apparatus trait) growth among highly parasitized nestlings. Our results indicate that lesser kestrels invested the extra food mainly to improve current reproduction, suggesting that population growth in this species can be limited by food availability during the breeding season. In addition, extra food provisioning reduced the costs of the moult–breeding overlap and affected early growth tradeoffs by mitigating detrimental ectoparasite effects on growth and enhancing development of the flight apparatus with high levels of parasitism. Importantly, our findings suggest that maternal condition is a major trait modulating the benefits of extra food to reproduction, whereby such benefits mostly accrue to low‐quality females with poor body condition.     

Early learning affects social dominance: interspecifically cross-fostered tits become subdominant

Social dominance influences the outcome of competitive interactionsover limited resources, and may hence be important for individualfitness. Theory thus predicts that its heritability will below and that non-genetic determinants of dominance should prevail.In this field experiment we reciprocally cross-fostered greattits (Parus major) to blue tits (Parus caeruleus) to investigatethe impact of early social experience on dominance status incompetition over food during winter. Controlling for potentialeffects of age, size, sex and site-related dominance, we showthat cross-fostered birds of both species were subdominant toconspecific immigrants, while controls originating from unmanipulatedbroods were dominant to conspecific immigrants. Furthermore,blue tits reared by blue tit parents but with at least one greattit broodmate had lower dominance status relative to conspecificimmigrants than did controls. Although great tits generallydominated blue tits, cross-fostered birds of both species initiatedmarginally more fights against the other species than did theirrespective controls, suggesting faulty species recognition.Since both social parents and broodmates strongly influencethe dominance behavior of offspring later in life, we concludethat social conditions experienced at an early age are crucialfor the determination of subsequent social dominance.     

Where do all the maternal effects go? Variation in offspring body size through ontogeny in the live-bearing fish Poecilia parae

Maternal effects are an important source of adaptive variation, but little is known about how they vary throughout ontogeny. We estimate the contribution of maternal effects, sire genetic and environmental variation to offspring body size from birth until 1 year of age in the live-bearing fish Poecilia parae. In both the sexes, maternal effects on body size were initially high in juveniles, and then declined to zero at sexual maturity. In sons, this was accompanied by a sharp rise in sire genetic variance, consistent with the expression of Y-linked loci affecting male size. In daughters, all variance components decreased with time, consistent with compensatory growth. There were significant negative among-dam correlations between early body size and the timing of sexual maturity in both sons and daughters. However, there was no relationship between early life maternal effects and adult longevity, suggesting that maternal effects, although important early in life, may not always influence late life-history traits.     

Effects of variation in nutrition on male morph development in the bulb mite Rhizoglyphus robini

In male dimorphic species, growth influences morph expression and thereby the reproductive success of males. However, how variation in nutritional conditions affects male morph development and whether males can compensate for lost growth is poorly known. Here, we performed an experiment where males of the bulb mite (Rhizoglyphus robini)—which are fighters, able to kill other mites, or benign scramblers—were offered high quality food during the larval stage, but food of high or low quality during the protonymph and tritonymph (=final) stage. When food quality was low during the latter two stages, males matured smaller, later and were more likely to be a scrambler than when food quality was high. We found no evidence for compensatory growth: when males had low quality food only during the protonymph stage, they matured at the same age, but grew at a slower rate and matured at a smaller size than males that had high quality food throughout ontogeny. Furthermore, males that experienced this transient period of low food quality were less likely to mature as a fighter. Interestingly, scrambler increase in body size during the protonymph and tritonymph stages was always lower than that of fighters. Given the strong link between adult size and fitness, combined with the different development times and life histories of the male morphs, the lack of ability to compensate for a transient period of food deprivation during ontogeny is likely to have consequences for the dynamics of bulb mite populations.     

中国石龙子个体发育过程中头部两性异型和食性的变化

许多动物呈现个体大小、局部形态特征 (头部大小 )和体色的两性异形[5,14 ,15,2 1,2 2 ] 。 Darwin[12 ] 认为两性谋求各自最大的繁殖利益导致了两性异形 ,因此两性异形是性选择压力作用的结果。自 Darwin以来 ,许多同行认为性选择压力和非性选择压力均能导致动物的两性异形 ,两种选择压力在不同的动物中所起的作用是不同的 [2～ 5,7,10 ,16,2 1～ 2 6] 。性选择压力导致的两性异形与繁殖成功率直接有关。非性选择压力导致的两性异形与繁殖成功率无关或无直接的关系 ,如两性寿命的差异 [13 ]、两性食性的分离 [6,2 1]和两性分配用于生长的…     

Non‐sex‐biased Dominance in a Sexually Monomorphic Electric Fish: Fight Structure and Submissive Electric Signalling

Males and females commonly compete for limited resources. When interaction costs are similar for both sexes and there are no sexual differences in resource value estimation, a non‐sex‐biased dominance is expected. Moreover, only non‐sex‐biased assessment of contenders fighting ability (Resource Holding Potential, RHP) should influence contest decisions. To test these predictions, we evaluated non‐breeding agonistic intra‐ and intersexual dyadic interactions in the weakly electric fish, Gymnotus omarorum. During the non‐breeding season, resource value is not expected to depend on individuals’ reproductive status and should thus be equal for males and females. In addition, as G. omarorum presents no sexual differences in body size, interaction costs can be considered symmetric between sexes. We confirmed that body size differences, but not individuals’ gender, is the best predictor of dominance. We correlated RHP asymmetries with contest duration and evidenced that body size but not sex influences assessment in intrasexual and intersexual encounters. All dyads tested engaged in agonistic interactions (N = 33) in which a clear dominant emerged. The analysis of conflict phases evidenced the submissive role of electric displays. Electric organ discharge (EOD) interruptions appear early in the contest as an electric hiding attempt, whereas chirps are post‐resolution signals of subordinate status. Interestingly, the decision of interrupting the EOD was also influenced by RHP asymmetries, whereas chirping activity was influenced by the intensity of the attacks received. Our results confirm that body size is the best RHP proxy in non‐breeding intra‐ and intersexual contests of this monomorphic species and demonstrated a sequential pattern of submissive signalling by means of two different electric displays.     

The Ontogeny of Sexual Size Dimorphism of a Moth: When Do Males and Females Grow Apart?

Sexual dimorphism in body size (sexual size dimorphism) is common in many species. The sources of selection that generate the independent evolution of adult male and female size have been investigated extensively by evolutionary biologists, but how and when females and males grow apart during ontogeny is poorly understood. Here we use the hawkmoth, Manduca sexta, to examine when sexual size dimorphism arises by measuring body mass every day during development. We further investigated whether environmental variables influence the ontogeny of sexual size dimorphism by raising moths on three different diet qualities (poor, medium and high). We found that size dimorphism arose during early larval development on the highest quality food treatment but it arose late in larval development when raised on the medium quality food. This female-biased dimorphism (females larger) increased substantially from the pupal-to-adult stage in both treatments, a pattern that appears to be common in Lepidopterans. Although dimorphism appeared in a few stages when individuals were raised on the poorest quality diet, it did not persist such that male and female adults were the same size. This demonstrates that the environmental conditions that insects are raised in can affect the growth trajectories of males and females differently and thus when dimorphism arises or disappears during development. We conclude that the development of sexual size dimorphism in M. sexta occurs during larval development and continues to accumulate during the pupal/adult stages, and that environmental variables such as diet quality can influence patterns of dimorphism in adults.     

Sex‐specific life history responses to nymphal diet quality and immune status in a field cricket

Individual fitness is expected to benefit from earlier maturation at a larger body size and higher body condition. However, poor nutritional quality or high prevalence of disease make this difficult because individuals either cannot acquire sufficient resources or must divert resources to other fitness‐related traits such as immunity. Under such conditions, individuals are expected to mature later at a smaller body size and in poorer body condition. Moreover, the juvenile environment can also produce longer‐term effects on adult fitness by causing shifts in resource allocation strategies that could alter investment in immune function and affect adult lifespan. We manipulated diet quality and immune status of juvenile Texas field crickets, Gryllus texensis, to investigate how poor developmental conditions affect sex‐specific investment in fitness‐related traits. As predicted, a poor juvenile diet was related to smaller mass and body size at eclosion in both sexes. However, our results also reveal sexually dimorphic responses to different facets of the rearing environment: female life history decisions are affected more by diet quality, whereas males are affected more by immune status. We suggest that females respond to decreased nutritional income because this threatens their ability to achieve a large adult body size, whereas male fitness is more dependent on reaching adulthood and so they invest in immunity and survival to eclosion.     

Organizing effects of adverse early‐life condition on body mass,compensatory growth and reproduction: experimental studies in rock pigeons

Early‐life food conditions can have profound impact on adult behavioural performance. In song birds, early‐life food conditions affect adult physiology and cognitive performance such as song learning and spatial learning. However, effects on reproductive behaviour other than song, such as visual courtship display, pair formation, and egg laying, which are all important determinants of fitness, received hardly any attention. In this study, rock pigeons Columba livia were raised either in a food ad‐libitum or at impoverished (quality) and restricted (quantity) food conditions, in which the latter was applied for either 26 or 8 d after hatching and in slightly different severity. Their growth and reproductive behaviour in adulthood was analysed under semi‐natural conditions. Impoverished and restricted food (IRF) negatively affected adult body mass, pair‐bonding behaviour, courtship (males) and being courted (females), and induced incomplete compensatory growth. Further analyses suggest that the effects of IRF on behaviour could result from the strong effects on body mass, and perhaps also from detrimental effects of compensatory growth. These results provide evidence that adverse early‐life condition can negatively impact on reproductive success, as suggested by the significant effect on egg production, which will very likely lead to a lower life‐time fitness. The detrimental effects on male courtship indicate that IRF can affect sexual displays via other pathways than by impaired cognition as has been suggested for bird song, since courtship in the pigeons is not learned.     

Growth in early life and relative body size among adult polar bears (Ursus maritimus)

Data on the body length (cm) of polar bear ( Ursus maritimus ), collected as part of a long-term ecological study in the Hudson Bay region of Canada, were examined to test the hypothesis that growth early in life influences adult body size. Data for 42 females and 30 males that were captured as two-year-olds (2.6-2.9 years), after the period of maternal care, and later recaptured as adults were analysed. On average, females increased in length by 11.2% and males by 23.1 % between captures. Relative adult body length was significantly correlated with relative length as a two-year-old in females but not in males. Thus, body length attained by two-year-olds is a weaker determinant of adult body length in males than in females. We suggest that, in comparison with females, prolonged growth beyond the period of maternal care may predispose the growth and eventual adult body size of male offspring to a greater degree of environmentally mediated variation. Furthermore, while data on maternal investment strategies in polar bears are lacking, variation in the allocation of maternal resources to cubs, within and among litters, may have a limited impact on the eventual adult body size of any surviving male offspring.