Evolution Of Sexual Size Dimorphism Research Articles

Evolution of sexual dimorphism and Rensch's rule in the beetle genus Limnebius (Hydraenidae): is sexual selection opportunistic?

Sexual size dimorphism (SSD) is widespread among animals, with larger females usually attributed to an optimization of resources in reproduction and larger males to sexual selection. A general pattern in the evolution of SSD is Rensch’s rule, which states that SSD increases with body size in species with larger males but decreases when females are larger. We studied the evolution of SSD in the genus Limnebius (Coleoptera, Hydraenidae), measuring SSD and male genital size and complexity of ca. 80% of its 150 species and reconstructing its evolution in a molecular phylogeny with 71 species. We found strong support for a higher evolutionary lability of male body size, which had an overall positive allometry with respect to females and higher evolutionary rates measured over the individual branches of the phylogeny. Increases in SSD were associated to increases in body size, but there were some exceptions with an increase associated to changes in only one sex. Secondary sexual characters (SSC) in the external morphology of males appeared several times independently, generally on species that had already increased their size. There was an overall significant correlation between SSD, male body size and male genital size and complexity, although some lineages with complex genitalia had low SSD, and some small species with complex genitalia had no SSD. Our results suggest that the origin of the higher evolutionary variance of male body size may be due to lack of constraints rather than to sexual selection, that may start to act in species with already larger males due to random variation.

Hormonally Mediated Increases in Sex-Biased Gene Expression Accompany the Breakdown of Between-Sex Genetic Correlations in a Sexually Dimorphic Lizard.

The evolution of sexual dimorphism is predicted to occur through reductions in between-sex genetic correlations (rmf) for shared traits, but the physiological and genetic mechanisms that facilitate these reductions remain largely speculative. Here, we use a paternal half-sibling breeding design in captive brown anole lizards (Anolis sagrei) to show that the development of sexual size dimorphism is mirrored by the ontogenetic breakdown of rmf for body size and growth rate. Using transcriptome data from the liver (which integrates growth and metabolism), we show that sex-biased gene expression also increases dramatically between ontogenetic stages bracketing this breakdown of rmf. Ontogenetic increases in sex-biased expression are particularly evident for genes involved in growth, metabolism, and cell proliferation, suggesting that they contribute to both the development of sexual dimorphism and the breakdown of rmf. Mechanistically, we show that treatment of females with testosterone stimulates the expression of male-biased genes while inhibiting the expression of female-biased genes, thereby inducing male-like phenotypes at both organismal and transcriptomic levels. Collectively, our results suggest that sex-specific modifiers such as testosterone can orchestrate sex-biased gene expression to facilitate the phenotypic development of sexual dimorphism while simultaneously reducing genetic correlations that would otherwise constrain the independent evolution of the sexes.

The interplay between natural and sexual selection in the evolution of sexual size dimorphism in Sceloporus lizards (Squamata: Phrynosomatidae).

Sexual size dimorphism (SSD) evolves because body size is usually related to reproductive success through different pathways in females and males. Female body size is strongly correlated with fecundity, while in males, body size is correlated with mating success. In many lizard species, males are larger than females, whereas in others, females are the larger sex, suggesting that selection on fecundity has been stronger than sexual selection on males. As placental development or egg retention requires more space within the abdominal cavity, it has been suggested that females of viviparous lizards have larger abdomens or body size than their oviparous relatives. Thus, it would be expected that females of viviparous species attain larger sizes than their oviparous relatives, generating more biased patterns of SSD. We test these predictions using lizards of the genus Sceloporus. After controlling for phylogenetic effects, our results confirm a strong relationship between female body size and fecundity, suggesting that selection for higher fecundity has had a main role in the evolution of female body size. However, oviparous and viviparous females exhibit similar sizes and allometric relationships. Even though there is a strong effect of body size on female fecundity, once phylogenetic effects are considered, we find that the slope of male on female body size is significantly larger than one, providing evidence of greater evolutionary divergence of male body size. These results suggest that the relative impact of sexual selection acting on males has been stronger than fecundity selection acting on females within Sceloporus lizards.

Mating system, male territoriality and agility as predictors of the evolution of sexual size dimorphism in hummingbirds (Aves: Trochilidae)

AbstractMale and female animals often exhibit differences in body size; this difference is known as sexual size dimorphism (SSD). Hummingbirds are an excellent model system to test functional hypotheses of SSD because they exhibit a wide range of body sizes and reproductive behaviour between the sexes. Here, using phylogenetic comparative methods, we tested whether mating system, male territoriality and agility predicted the evolution of SSD in this avian family. Our results first suggest that evolutionary increases in male-biased SSD are related to increases in lekking behaviour. Second, we found that male agility is positively related to increases in male biased-SSD albeit this is only likely to occur in males of territorial species. Finally, we found an allometric pattern for SSD consistent with Rensch’s rule that was not explained by our estimates of male competition and agility.

Sex hormones and the development of sexual size dimorphism: 5α-dihydrotestosterone inhibits growth in a female-larger lizard (Sceloporus undulatus).

Sexual differences in adult body size [sexual size dimorphism (SSD)] and color (sexual dichromatism) are widespread, and both male- and female-biased dimorphisms are observed even among closely related species. A growing body of evidence indicates testosterone can regulate growth, thus the development of SSD, and sexual dichromatism. However, the mechanism(s) underlying these effects are conjectural, including possible conversions of testosterone to estradiol (E2) or 5α-dihydrotestosterone (DHT). In the present study, we hypothesized that the effects of testosterone are physiological responses mediated by androgen receptors, and we tested two specific predictions: (1) that DHT would mimic the effects of testosterone by inhibiting growth and enhancing coloration, and (2) that removal of endogenous testosterone via surgical castration would stimulate growth. We also hypothesized that females share downstream regulatory networks with males and predicted that females and males would respond similarly to DHT. We conducted experiments on eastern fence lizards (Sceloporus undulatus), a female-larger species with striking sexual dichromatism. We implanted Silastic® tubules containing 150 µg DHT into intact females and intact and castrated males. We measured linear growth rates and quantified color for ventral and dorsal surfaces. We found that DHT decreased growth rate and enhanced male-typical coloration in both males and females. We also found that, given adequate time, castration alone is sufficient to stimulate growth rate in males. The results presented here suggest that: (1) the effects of testosterone on growth and coloration are mediated by androgen receptors without requiring aromatization of testosterone into E2, and (2) females possess the androgen-receptor-mediated regulatory networks required for initiating male-typical inhibition of growth and enhanced coloration in response to androgens.

Lack of Evolution of Sexual Size Dimorphism in Heteromyidae (Rodentia): The Influence of Resource Defense and the Trade-Off between Pre- and Post-Copulatory Trait Investment

One paradoxical finding in some mammals is the presence of male–male intrasexual competition in the absence of sexual size dimorphism. It has been a major goal of evolutionary biologists for over a century to understand why some species in which large males can monopolize multiple mates while excluding smaller competitors, exhibit little or no sexual dimorphism. In this paper I examine three of the main hypotheses that have been proposed to explain this conundrum using as study case the Heteromyidae, a rodent family with subtle sexual size dimorphism. Using a phylogenetic comparative approach, I address the potential influence of (1) fecundity selection, (2) covariation between pre- and post-copulatory traits, and (3) environmental constraints (resource shortage) in explaining patterns of body size and sexual size dimorphism (SSD) across 62 heteromyid species. Baculum size, a proxy of the strength of post-copulatory sexual selection, and SSD were negatively correlated suggesting that heteromyid rodents balance their reproductive investment between pre- and post-copulatory traits, which may prevent the evolution of extensive SSD. Results also support a role for resource competition in moderating SSD. The amount of SSD correlated negatively with latitude. This can be explained if high productivity relaxes the level of intrasexual competition among females, leading to more male-biased dimorphism since forces acting on both sexes are not cancelled. In line with this argument, territorial species exhibited a higher dimorphism in comparison with social species. No support was found for the fecundity selection hypothesis. Overall, this study provides insight into the factors driving observed patterns of sexual dimorphism in this iconic group and highlights the need to consider a broader framework beyond sexual selection for better understanding the evolution of dimorphism in this family.

Sexual selection on male size drives the evolution of male-biased sexual size dimorphism via the prolongation of male development.

Sexual size dimorphism (SSD) arises when the net effects of natural and sexual selection on body size differ between the sexes. Quantitative SSD variation between taxa is common, but directional intraspecific SSD reversals are rare. We combined micro- and macroevolutionary approaches to study geographic SSD variation in closely related black scavenger flies. Common garden experiments revealed stark intra- and interspecific variation: Sepsis biflexuosa is monomorphic across the Holarctic, while S. cynipsea (only in Europe) consistently exhibits female-biased SSD. Interestingly, S. neocynipsea displays contrasting SSD in Europe (females larger) and North America (males larger), a pattern opposite to the geographic reversal in SSD of S. punctum documented in a previous study. In accordance with the differential equilibrium model for the evolution of SSD, the intensity of sexual selection on male size varied between continents (weaker in Europe), whereas fecundity selection on female body size did not. Subsequent comparative analyses of 49 taxa documented at least six independent origins of male-biased SSD in Sepsidae, which is likely caused by sexual selection on male size and mediated by bimaturism. Therefore, reversals in SSD and the associated changes in larval development might be much more common and rapid and less constrained than currently assumed.

Incorporating an ontogenetic perspective into evolutionary theory of sexual size dimorphism.

Sexual size dimorphism (SSD) describes divergent body sizes of adult males and females. While SSD has traditionally been explained by sexual and fecundity selection, recent advances in physiology and developmental biology emphasize that SSD would occur proximately because of sexual differences in ontogenetic growth trajectories (i.e., growth rate and duration). Notably, these ontogenetic traits are subject to energetic or time constraints and thus traded off with fitness components (e.g., survival and reproduction). To elucidate the importance of such ontogenetic trade-offs in the evolution of SSD, we developed a new theoretical framework by extending quantitative genetic models for the evolution of sexual dimorphism in which we reinterpret the trait as body size and reformulate sex-specific fitness in size-dependent manners. More specifically, we assume that higher growth rate or longer growth duration leads to larger body size and higher reproductive success but incurs the cost of lower survivorship or shorter reproduction period. We illustrate how two sexes would optimize ontogenetic growth trajectories in sex-specific ways and exhibit divergent body sizes. The present framework provides new insights into the evolutionary theory of SSD and predictions for empirical testing.

Sexual size dimorphism in the viviparous caecilian amphibian Geotrypetes seraphini seraphini (Gymnophiona: Dermophiidae) including an updated overview of sexual dimorphism in caecilian amphibians

Sexual size dimorphism (SSD) describing intersexual size differences of a given taxon is a widespread phenomenon in the animal kingdom. SSD plays a significant role in understanding life history and mating system evolution. The snakelike morphology of limbless caecilian amphibians lacking obvious secondary sexual characters (in contrast to frogs and salamanders) impedes an accurate comparison between sexes.Here, the phylogenetically derived teresomatan and viviparous caecilianGeotrypetes seraphini seraphiniwas analysed for patterns of sexual dimorphism. In terms of body size females were the larger sex, but when body length was adjusted male-biased intersexual differences in cloacal shape appeared. The larger female size is likely explained by fecundity selection as clutch size was positively correlated to female body length. Unexpectedly a cryptic, ontogeny related variation of the nuchal collars was found. An overview of SSD in caecilians including data for 27 species of nine out of ten existing families revealed a quite high number of taxa showing sexually dimorphic head size dimensions exclusively present among phylogenetically derived teresomatan caecilians. Still further research including insights into the behavioural ecology and molecular ecology of mating systems is warranted to better understand the evolution of sexual size dimorphism of caecilian amphibians.

Sex-biased parental care and sexual size dimorphism in a provisioning arthropod

The diverse selection pressures driving the evolution of sexual size dimorphism (SSD) have long been debated. Whilst the balance between fecundity selection and sexual selection has received much attention, explanations based on sex-specific ecology have proven harder to test. In ectotherms, females are typically larger than males, and this is frequently thought to be because size constrains female fecundity more than it constrains male mating success. However, SSD could additionally reflect maternal care strategies. Under this hypothesis, females are relatively larger where reproduction requires greater maximum maternal effort—for example where mothers transport heavy provisions to the nests. To test this hypothesis, we focussed on digger wasps (Hymenoptera: Ammophilini), a relatively homogeneous group in which only females provision offspring. In some species, a single large prey item, up to ten times the mother’s weight, must be carried to each burrow on foot; other species provide many small prey, each flown individually to the nest. We found more pronounced female-biased SSD in species where females carry single, heavy prey. More generally, SSD was negatively correlated with the numbers of prey provided per offspring. Females provisioning multiple small items had longer wings and thoraxes, probably because smaller prey are carried in flight. Despite much theorising, few empirical studies have tested how sex-biased parental care can affect SSD. Our study reveals that such costs can be associated with the evolution of dimorphism, and this should be investigated in other clades where parental care costs differ between sexes and species.

Independent evolution of the sexes promotes amphibian diversification.

Classic ecological theory predicts that the evolution of sexual dimorphism constrains diversification by limiting morphospace available for speciation. Alternatively, sexual selection may lead to the evolution of reproductive isolation and increased diversification. We test contrasting predictions of these hypotheses by examining the relationship between sexual dimorphism and diversification in amphibians. Our analysis shows that the evolution of sexual size dimorphism (SSD) is associated with increased diversification and speciation, contrary to the ecological theory. Further, this result is unlikely to be explained by traditional sexual selection models because variation in amphibian SSD is unlikely to be driven entirely by sexual selection. We suggest that relaxing a central assumption of classic ecological models-that the sexes share a common adaptive landscape-leads to the alternative hypothesis that independent evolution of the sexes may promote diversification. Once the constraints of sexual conflict are relaxed, the sexes can explore morphospace that would otherwise be inaccessible. Consistent with this novel hypothesis, the evolution of SSD in amphibians is associated with reduced current extinction threat status, and an historical reduction in extinction rate. Our work reconciles conflicting predictions from ecological and evolutionary theory and illustrates that the ability of the sexes to evolve independently is associated with a spectacular vertebrate radiation.

Sex-specific phenotypic plasticity in response to the trade-off between developmental time and body size supports the dimorphic niche hypothesis

Female-biased sexual size dimorphism (SSD) is widespread in many invertebrate taxa. One hypothesis for the evolution of SSD is the dimorphic niche hypothesis, which states that SSD evolved in response to the different sexual reproductive roles. While females benefit from a larger body size by producing more or larger eggs, males benefit from a faster development, which allows them to fertilize virgin females (protandry). To test this hypothesis, we studied the influence of temperature and intraspecific density on the development of Chorthippus montanus. We reared them in monosexual groups under different conditions and measured adult body size, wing length, nymphal mortality, and development time. The present study revealed an inverse temperature–size relationship: body size increased with increasing temperature in both sexes. Furthermore, we found intersexual differences in the phenotypic response to population density, supporting the dimorphic niches hypothesis. At a lower temperature, female development time increased and male body size decreased with increasing density. Because there was no food limitation, we conclude that interference competition hampered development. By contrast to expectations, mortality decreased with increasing density, suggesting that interference did not negatively affect survival. The present study shows that sex-specific niche optima may be a major trigger of sexual dimorphisms. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 48–57.

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.

Male size predicts extrapair paternity in a socially monogamous bird with extreme sexual size dimorphism

Lay Summary The New Zealand tui is an iconic bird exhibiting extreme sexual size dimorphism. This is an unusual trait for a monogamous species and so we tested whether a male’s body size was related to his paternity success. First, we found that tūī had very high rates of extrapair paternity compared to other monogamous species. Second, larger males had higher paternity success. Thus, in contrast with previous studies, our results show that extrapair paternity can lead to the evolution of sexual size dimorphism.

Phylogeny suggests nondirectional and isometric evolution of sexual size dimorphism in argiopine spiders.

Sexual dimorphism describes substantial differences between male and female phenotypes. In spiders, sexual dimorphism research almost exclusively focuses on size, and recent studies have recovered steady evolutionary size increases in females, and independent evolutionary size changes in males. Their discordance is due to negative allometric size patterns caused by different selection pressures on male and female sizes (converse Rensch's rule). Here, we investigated macroevolutionary patterns of sexual size dimorphism (SSD) in Argiopinae, a global lineage of orb-weaving spiders with varying degrees of SSD. We devised a Bayesian and maximum-likelihood molecular species-level phylogeny, and then used it to reconstruct sex-specific size evolution, to examine general hypotheses and different models of size evolution, to test for sexual size coevolution, and to examine allometric patterns of SSD. Our results, revealing ancestral moderate sizes and SSD, failed to reject the Brownian motion model, which suggests a nondirectional size evolution. Contrary to predictions, male and female sizes were phylogenetically correlated, and SSD evolution was isometric. We interpret these results to question the classical explanations of female-biased SSD via fecundity, gravity, and differential mortality. In argiopines, SSD evolution may be driven by these or additional selection mechanisms, but perhaps at different phylogenetic scales.

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.

Ecological divergence and sexual selection drive sexual size dimorphism in new world pitvipers (Serpentes: Viperidae)

Hypotheses for the origin and maintenance of sexual size dimorphism (SSD) fall into three primary categories: (i) sexual selection on male size, (ii) fecundity selection on female size and (iii) ecological selection for gender-specific niche divergence. We investigate the impact of these forces on SSD evolution in New World pitvipers (Crotalinae). We constructed a phylogeny from up to eight genes (seven mitochondrial, one nuclear) for 104 species of NW crotalines. We gathered morphological and ecological data for 82 species for comparative analyses. There is a strong signal of sexual selection on male size driving SSD, but less evidence for fecundity selection on female size across lineages. No support was found for allometric scaling of SSD (Rensch's rule), nor for directional selection for increasing male size (the Fairbairn-Preziosi hypothesis) in NW crotalines. Interestingly, arboreal lineages experience higher rates of SSD evolution and a pronounced shift to female-biased dimorphism. This suggests that fecundity selection on arboreal females exaggerates ecologically mediated dimorphism, whereas sexual selection drives male size in terrestrial lineages. We find that increasing SSD in both directions (male- and female-biased) decreases speciation rates. In NW crotalines, it appears that increasing magnitudes of ecologically mediated SSD reduce rates of speciation, as divergence accumulates within species among sexes, reducing adaptive divergence between populations leading to speciation.

Sexual Dimorphism of Head Size in Phrynocephalus przewalskii: Testing the Food Niche Divergence Hypothesis

Sexual size dimorphism (SSD) is a general phenomenon in lizards, and can evolve through sexual selection or natural selection. But natural selection, which was thought to operate mainly through reducing the competition between the two sexes (niche divergence hypothesis), gave rise to a lot of controversy. We tested the niche divergence hypothesis in the toad-headed lizard Phrynocephalus przewalskii by comparing diet composition and prey sizes between males and females. The species was found to be sexual dimorphic, with males having relatively larger snout-vent length, head width, head length, and tail length, while females have relatively larger abdomen length. Based on analysis of 93 studied stomachs, a total of 1359 prey items were identified. The most common prey items were formicid, lygaeid and tenebrionid. The two sexes did not differ in the relative proportions of prey size categories they consumed and the dietary overlap based on prey species was high (O = 0.989). In addition, the meal size, the volume or any maximal dimension of the largest prey item in the stomach was not explained by the sexes. According to our results, food niche divergence might not play an important role in the SSD evolution of P przewalskii.

鲶鱼和胡子鲶的两性异形与雌性个体生育力

PDF HTML阅读 XML下载 导出引用 引用提醒 鲶鱼和胡子鲶的两性异形与雌性个体生育力 DOI: 10.5846/stxb201306021274 作者: 作者单位: 丽水学院,丽水学院生态学院,丽水学院生态学院,丽水学院生态学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金癣项目（31270443，30970435）；丽水市科技计划资助项目（20110426）；浙江省大学生科技创新活动计划资助项目（2011R429008） Sexual size dimorphism and female individual fecundity of Silurus asotus and Clarias fuscus Author: Affiliation: College of Ecology,Lishui University,College of Ecology,Lishui University,College of Ecology,Lishui University,College of Ecology,Lishui University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:检测了鲶鱼（Silurus asotus）和胡子鲶（Clarias fuscus）繁殖期18个形态特征的两性异形以及雌性个体生育力。结果表明，鲶鱼和胡子鲶雌雄性别比例均符合1：1。One-way ANOVA显示，鲶鱼雌雄个体体长差异不显著，胡子鲶雌性个体体长显著小于雄性个体（P < 0.05）。以体长为协变量的One-way ANCOVA显示，特定体长的鲶鱼雌性个体的眼间距和体高显著大于雄性个体（P < 0.05），两性间其它局部特征不存在显著的两性差异；特定体长的胡子鲶雌性个体的体高、腹鳍基前距和腹鳍臀鳍间距显著大于雄性个体，雌性个体的臀鳍基长、尾柄高和尾鳍长显著小于雄性个体（P < 0.05），两性间其它局部特征不存在显著的两性差异。Two-way ANOVA显示，胡子鲶体长显著大于鲶鱼（P < 0.05），性别及物种与性别两因素的相互作用对体长影响不显著。以体长为协变量的Two-way ANCOVA显示，胡子鲶的头长、头宽、吻长、眼间距、尾柄高、尾鳍长、背鳍基前距、背鳍基长、腹鳍基前距、腹鳍臀鳍间距、体重和去内脏体重显著大于鲶鱼，头高、体高、臀鳍基长显著小于鲶鱼（P < 0.05），物种间的其他形态特征变量差异不显著；雌性个体的体高、背鳍基前距、腹鳍基前距、腹鳍臀鳍间距显著大于雄性个体，臀鳍基长、尾柄高、尾鳍长、背鳍基长显著小于雄性个体（P < 0.05），两性间的其他形态特征变量差异不显著；物种与性别两因素的相互作用对体高、臀鳍基长、尾柄高、尾鳍长、背鳍基长和腹鳍臀鳍间距影响显著，对其余的形态特征变量影响不显著。15个形态特征变量的主成分分析（Eigenvalue ≥ 1）发现，前2个主成分共解释68.4%的变异。头宽、眼间距、尾柄高、尾鳍长、背鳍基前距、背鳍基长、腹鳍基前距和腹鳍臀鳍间距在第一主成分有较高的正负载系数，臀鳍基长在第一主成分有较高的负负载系数（解释51.2%变异）；眼后头长在第二主成分有较高的负负载系数（解释17.2%变异）。胡子鲶在第一主成分和第二主成分的分值均显著大于鲶鱼，雌雄两性的差异以及两因素的相互作用对分值的影响均不显著。实验检测的鲶鱼、胡子鲶的怀卵数量与体长和体重回归关系显著。One-way ANCOVA及矫正平均值Tukey's检验显示，特定体长的胡子鲶的产卵数量显著大于鲶鱼。性选择是胡子鲶大个体雄性形成的主要原因，同时影响与运动相关的尾部特征。生育力选择更多的影响与雌性胡子鲶较大腹腔容积相关的形态特征变异。环境因子、食物可得性和营养状况同时影响了个体大小两性异形的形成。 Abstract:We measured the sexual size dimorphism in eighteen morphological traits and female individual fecundity of Silurus asotus and Clarias fuscus collected from Lishui (Zhejiang, eastern China) in reproductive seasons. It had been found that their sex ratios were both 1:1. One-way ANOVA showed the adults of S. asotus were not sexually dimorphic in body length, while body length was significantly larger in adult males than in adult females of C. fuscus (P < 0.05). One-way ANCOVA with body length as a covariate showed that the females of S. asotus with special body length were significantly larger than the males in interorbital width and body depth (P < 0.05), while other examined morphological traits did not differ between the sexes. Furthermore, the females of C. fuscus with special body length were significantly larger than the males in body depth, pelvic fin precoxal length, and length between pelvic fin and anal fin (P < 0.05), whereas their anal fin coxal length, caudal peduncle depth and caudal fin length were significantly shorter in females than in males, and there were no significant differences between the sexes in any other of the examined morphological traits. Two-way ANOVA showed that body length of C. fuscus was significantly larger than one of S. asotus (P < 0.05), both sex and the interaction of sex and species had no effects on the body length. Two-way ANCOVA with body length as a covariate showed that head length, head width, snout length, interorbital width, caudal peduncle depth, caudal fin length, dorsal fin precoxal length, dorsal fin coxal length, length between pelvic fin and anal fin, body mass and carcass mass of C. fuscus were significantly larger than them of S. asotus, while head depth, body depth and anal fin length of C. fuscus were significantly shorter than ones of S. asotus (P < 0.05). Meanwhile, there were no significant differences in other morphological traits between them. Body depth, dorsal fin precoxal length, pelvic fin precoxal length, length between pelvic fin and anal fin were significantly larger among females than among males, while anal fin coxal length, caudal peduncle depth, caudal fin length and dorsal fin coxal length were significantly shorter among females than among males (P < 0.05). There were no significant differences in other morphological traits between the sexes. The interaction of species and sex had significant effects on body depth, anal fin coxal length, caudal peduncle depth, caudal fin length, dorsal fin coxal, length between pelvic fin and anal fin, but it had no effect on the other morphological traits. A principal component analysis resolved two components (with eigenvalues≥1) from fifteen size-free morphological variables, accounting for 68.4% of variation in the original data. The first component (51.2% variance explained) had high positive loading for size-free values of head width, interorbital width, caudal peduncle depth, caudal fin length, dorsal fin precoxal length, dorsal fin coxal length, dorsal fin coxal length, pelvic fin precoxal length, pelvic fin precoxal length, length between pelvic fin and anal fin, wherea the first component had high negative loading for size-free values of anal fin coxal length. The second component (17.2% variance explained) had high negative loading for size-free values of postorbital head length. C. fuscus had higher scores on the first and the second axes of a principal component analysis than did S. asotu, but both sex and the interaction of sex and species had no critical effect on the scores. The individual fecundity was significantly correlated with the body length and body mass in C. fuscus and S. asotus positively. One-way ANCOVA and Tukey's test showed that C. fuscus with special body length laid significantly more eggs than S. asotus. Sexual selection was the major evolutionary reasons for large males of C. fuscus, simultaneously had effects on tail traits correlated with locomotion. Fecundity selection affected the variations of morphological traits associated with abdominal cavity volume to a large extent. Environmental factors, food availability and nutritional status affected the evolution of sexual size dimorphism at the same time. 参考文献 相似文献 引证文献

Evolution of sexual size dimorphism and its relationship with sex ratio in carabid beetles of Genus Ceroglossus Solier

Abstract Although the degree of mate competition, given extreme differences in sex ratio, explains much of the pattern of male-biased size dimorphism among diverse taxa, it fails for some species which have potential for intense male competition for mates and yet exhibit little or no sexual size dimorphism (SSD). This fact suggest that species with low SSD should be express the effect of evolutionary pressure in non-obvious geometrical shape promoted by sex ratio in an evolutionary time scale. To evaluate this hypothesis we used phylogenetic comparative method in a Bayesian framework to investigate the evolution of SSD and the role of sex ratio at inter-specific level in the species of Ceroglossus (Coleoptera: Carabidae). In our results the proportion farthest from 1:1 is associated with more disparate body shape, even though the entire group has minimum variation in sex ratio, which is an intrinsic life history character of this group considering its phylogenetic conservatism or phylogenetic signal. We suggest that the sex ratio has determined the dimorphism degree during evolution of this group, since both traits have increased or decreased together during the species divergence (i.e. positive phylogenetic correlation: r2≈0.85). We suggest that morphological studies of SSD will benefit from using comparative method with Bayesian approaches to assess the effect of phylogenetic history and its uncertainty. Finally, this will be allow to researchers to quantify the uncertainty of specific evolutionary hypotheses accounting for observed sexual dimorphism patterns.