Inverse of Rensch’s Rule of Allometry for Sexual Size Dimorphism in Bufo andrewsi

Difference in body size between males and females(sexual size dimorphism:SSD)and its variation are a common phenomenon in animal kingdom.Rensch’s rule predicts that the degree of SSD variation increases with the enlarged mean body size when males are larger than females and decreases when females are larger than males.Here,whether the patterns of variations in SSD in the Andrew’s toad(Bufo andrewsi)follow Rensch’s rule was tested using unpublished data from 14 populations and published data from 17 populations.Results show the reduced major axis regression of log10(male size)on log10(female size)across all populations displayed a significant hyperallometric relationship,which was consistent with inverse Rensch’s rule(the degree of SSD increased with enlarged mean body size).SSD could also be explained by sexual age difference(SAD)due to a positive SSD–SAD relationship among all populations.The findings suggest that the occurrence of inverse Rensch’s rule in B.andrewsi is likely to be a result of fecundity selection on increased reproductive investments in larger females.

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 be- tween 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 ofP. przewalskii.

Significant Male Biased Sexual Size Dimorphism in Leptobrachium leishanensis

Sexual size dimorphism（SSD） is a widespread phenomenon among animals, and whose evolution and maintenance has been a central topic in evolutionary biology since Darwin＇s time. SSD varies in direction among the major taxonomic groups of animals and even within the same groups. In anurans, female biased SSD is the rule in many lineages, whereas male biased SSD is a rare phenomenon. In this paper, we analyze whether SSD exists inLeptobrachium leishanensis by comparing morphological characteristics between the sexes. Our results show that all six morphological characteristics measured are significantly different between the sexes. Males are significantly larger than females, indicating that the male biased SSD of this species is apparent. The size of the nuptial spines, a special secondary sex trait of males, is significantly and positively correlated with body size. We suggest that the resource defense polygyny mating system and parental care behavior may be explanations for the evolution of male biased SSD and nuptial spine development in this species.

Variation and Sexual Dimorphism of Body Size in the Plateau Brown Frog along an Altitudinal Gradient

Variation in body size and sexual size dimorphism（SSD） can have important consequences for animal ecology, behavior, population dynamics and the evolution of life-history traits. Organisms are expected to be larger in colder climate（i.e., Bergmann＇s rule） and SSD varies with body size（i.e., Rensch＇s rule）. However, the underlying mechanisms are still elusive. The plateau brown frog（Rana kukunoris）, a medium-sized anuran species with femalebiased SSD, is endemic to the Qinghai-Tibetan Plateau（QTP）. From 1797 m（Maoxiang＇ping） to 3453 m（Heihe＇qiao） in the eastern margin of the QTP, we surveyed 10 populations of R. kukunoris and collected phalanges and snout vent length（SVL） data for 258 adult individuals（199 males versus 59 females）. Based on these data, we explored how body size and SSD varying along the altitudinal gradient and examined the corresponding effects of temperature. We found body size to be larger at higher altitude for males but not for females, with likely effects from the temperature on the variation in male body size. Sex differences in growth rates may be the main cause of the variation in SSD. Our results suggested that only males follow the Bergmann＇s rule and variation in SSD of R. kukunoris do not support the Rensch＇s rule and its inverse. Therefore, the variations of body size can be different between sexes and the applicability of both Bergmann＇s rule and Rensch＇s rule should depend on species and environment where they live.

Sex Ratio and Sexual Size Dimorphism in a Toad-headed Lizard, Phrynocephalus guinanensis

Phrynocephalus guinanensis has sexual dimorphism in abdominal coloration, but its ontogenetic development of sexual size dimorphism （SSD） is unknown. Using mark-recapture data during four days each year from August from 2014 to 2016, we investigated the development of sex ratios, SSD, sex-specific survivorship and growth rates in a population of P guinanensis. Our results indicated that the sex ratio of males to females was 1：2.8. Males had a lower survival rate （6%） than females （14%） across the age range from hatchling to adult, which supported the discovered female-biased sex ratio potentially associated with the low survival rate of males between hatchlings and juveniles. Male-biased SSD in tail length and head width existed in adults rather than in hatchling or juvenile lizards. The growth rates in body dimensions were undistinguishable between the sexes during the age from hatchling to juvenile, but the growth rate in head length from juvenile to adult was significantly larger in males than females. Average growth rate of all morphological measurements from hatchling to juvenile were larger compared with corresponding measurements from juvenile to adult, but only being significant in tail length, head width, abdomen length in females and snout-vent length in males. We provided a case study to strengthen our understanding of the important life history traits on how a viviparous lizard population can survive and develop their morphology in cold climates.

Subtle sexual plumage color dimorphism and size dimorphism in a South American colonial breeder, the Monk Parakeet(Myiopsitta monachus)

Background:Parrots(Psittacidae Family)are one of the most colorful groups of birds in the world,their colors pro-duced both structurally and via unusual pigments(psittacofulvins).Most species are considered to be monogamous,and many have been viewed historically as sexually monomorphic and monochromatic.However,studies using morphometric analysis and spectrophotometric techniques have revealed sexual size dimorphism and also sexual plumage color dimorphism among some species.The Monk Parakeet(Myiopsitta monachus),a native parrot of South America,is an interesting species for the study of plumage coloration and size since it is considered sexually mono-chromatic and monomorphic.Furthermore,recent studies show that the Monk Parakeet has extra-bond paternity behavior and even breeding trios,which suggests that sexual selection may play an important role in this species,and that it might have sexually dimorphic plumage(albeit imperceptible by humans)and be dimorphic in size.Methods:For the determination of plumage color we used spectrophotometry in the range of avian vision(300-700 nm)and performed a morphological analysis.Results:Our spectrophotometric results indicate that the Monk Parakeet shows subtle sexual plumage color dimor-phism in three(crown,nape and wing)out of twelve body regions.Similarly,our morphometric analysis showed that there are subtle sex differences in body size(bill and weight).Conclusions:Although the Monk Parakeet shows extra-bond paternity and breeding trio behaviors which could increase sexual dimorphism,these behaviors occur among highly related individuals;perhaps the high rate of inbreeding is responsible for the attenuation of sexual plumage color dimorphism and sex differences in body size observed.

Reexamination of Sexual Dimorphism and Female Reproduction in the Many-Lined Sun Skink Eutropis multifasciata from China

We reexamined sexual dimorphism and female reproduction in the Many-Lined Sun Skink Eutropis multifasciata from Hainan,China. Our data confirm that adults are sexually dimorphic in body size and shape,with males being the larger sex and larger in head size but shorter in abdomen length than females of the same snoutvent length(SVL). The rate at which head width increased with SVL was greater in males as opposed to the previous conclusion that the rate does not differ between the sexes. Maternal size was the main determinant of reproductive investment,with larger females generally producing more,as well as larger,offspring. Females produced up to nine offspring per litter as opposed to the previously reported 2–7. Most females gave birth between March and August,a time period approximately four months longer than that(May–June) reported previously. Females with a higher fecundity tended to produce smaller offspring as opposed to the previous conclusion that females do not tradeoff offspring size against number. Litter size,neonate mass and litter mass remained remarkably constant among years,and litter mass was more tightly related to female body size than litter size or neonate mass. Smaller females could produce relatively heavier litters without a concomitant reduction in postpartum body condition.

Thermoregulatory function and sexual dimorphism of the throat sack in Helmeted Guineafowl(Numida meleagris)across Africa

The responses of ground-dwelling birds to heat and cold stress encompass a variety of behavioural,physiological and even morphological mechanisms.However,the role of glabrous skin in this respect has been marginally addressed so far.The Helmeted Guineafowl(Numida meleagris)is a landfowl distributed across Sub-Saharan Africa with eight traditionally recognised extant subspecies.Among the most prominent morphological traits underlying intraspecific variability are size and pigmentation of the bare throat skin(or sack),which might be related to the different habitats and environmental conditions across its wide range.In order to explore the Helmeted Guineafowl range-wide sack variation and pigmentation in relation to thermoregulation and sexual signalling,we collected morphometric and environmental information for N.m.coronata integrating field data with the inspection of photographic material encompassing seven subspecies and environmental information from their habitats.Field data evidenced that sack size was significantly correlated with ambient temperature,thus pointing to a likely involvement of the throat sack in thermoregulation.When the pictorial data from all subspecies were pooled,sack size correlated negatively with biomass,rainfall and humidity,while a positive correlation was found with annual solar irradiation.Sack size correlated positively with monthly temperature variation among the bluethroated subspecies from southern Africa as opposed to the black-throated subspecies ranging north to Zambia and Mozambique.Still,in this latter group the sack was often larger during winter months,possibly to maximise solar radiation absorbance.Noteworthy,sack size was related to sex dimorphism in two subspecies.Sack morphology and colour in the Helmeted Guineafowl likely modulate body temperature by evaporative cooling or heating upon needs,but in some subspecies it is also seemingly related to sexual signalling.Additional studies are needed to fully understand the multifunctionality of this important morphological feature in this species.

Seasonal change in sexual differences in nestling size and survival： a framework to evaluate sex-dependent environmental sensitivity in the wild

Background: Sexual size dimorphism(SSD) occurs in a wide range of species in birds and other animals, but the magnitude of SSD often varies with environmental conditions. In general, in the developmental stages, the larger sex is more vulnerable to adverse environmental conditions because the larger sex requires more energy than the smaller sex. However, this may not hold true for birds with large brood sizes; the larger sex can acquire more food by suppressing the smaller sex. In addition, most previous studies have been experimental, such as by manipulating clutch size and ectoparasites, which may not reflect natural conditions.Methods: In the present study, we propose a general framework to assess sexual differences in environmental sensitivity in natural populations. Because environmental conditions change throughout the breeding season, seasonal changes of nestling SSD and sex ratio should reflect sexual differences in environmental sensitivity. We applied this approach to a large dataset(1555 nestlings over 5 years) of Japanese Tits(Parus minor). In this population, the male nestling is generally larger than the female(5% SSD in body weight).Results: We found that the magnitude of SSD(weight, tarsus, wing) and fledgling sex ratio increased both in the beginning and the end of the breeding season.Conclusion: Our study suggested that female nestlings are more valuable to poor environmental conditions in the relatively fecund species. This study underscores the importance of brood size on sexual differences in environmental stochasticity and our framework encourages comparative analysis among different bird species.

Factors determining the average body size of geographically separated Arctodiaptomus salinus （Daday, 1885） populations

Arctodiaptomus salinus inhabits water bodies across Eurasia and North Africa. Based on our own data and that from the literature, we analyzed the influences of several factors on the intra- and inter-population variability of this species. A strong negative linear correlation between temperature and average body size in the Crimean and African populations was found, in which the parameters might be influenced by salinity. Meanwhile, a significant negative correlation between female body size and the altitude of habitats was found by comparing body size in populations from different regions. Individuals from environments with highly varying abiotic parameters, e.g. temporary reservoirs, had a larger body size than individuals from permanent water bodies. The changes in average body mass in populations were at 11.4 times, whereas, those in individual metabolic activities were at 6.2 times. Moreover, two size groups of A. salinus in the Crimean and the Siberian lakes were observed. The ratio of female length to male length fluctuated between 1.02 and 1.30. The average size of A. salinus in populations and its variations were determined by both genetic and environmental factors. However, the parities of these factors were unequal in either spatial or temporal scales.

Different paths to sexual size dimorphism in two praying mantids, Pseudomantis albofimbriata and Hierodula majuscula

Sexual size dimorphism （SSD） is widespread among diverse animal taxa and has attracted the attention of evolutionary biologists for over a century. SSD is likely to be adaptive and the result of divergent selection on different size optima for males and females, given their different roles in reproduction. The developmental trajectory leading to SSD may help us to understand how selection acts on male and female size. Here, we describe the growth and development of two Australian praying mantids, Pseudomantis albofimbriata and Hierodula majuscula including the number of moults, time to adulthood, size at each moult, and the degree of SSD. While both species exhibit the common pattern of female-biased SSD, the number of moults required for individuals to reach adulthood differed between males and females and between species. Despite their larger adult size, P. albofimbriata females require fewer moults and less time than males to reach adulthood, but are significantly larger than males from the second instar onwards. In contrast, H. majuscula males reached adulthood in fewer moults, and less time than females, however males and females did not differ in size until females went through their final moult into adulthood. H. majuscula also required more time and more moults to reach adulthood than 17. albofimbriata. We discuss these different developmental pathways in light of the existing knowledge of reproductive biology for each species. We also suggest that these differences may relate to the different phenologies that occur in strongly seasonal temperate environments compared with those in the tropics. This study provides evidence that SSD can result from two different patterns of growth and development in closely related species.

The loss of sexual size dimorphism in urban populations of a widespread reptile,the European grass snake Natrix natrix

Ciries represent a unique ecosystem dominated by humans and highdensity man-made infrastructure,associated with modifications or entire loss of local habitats.Thus,urbanization constitutes a consid-erable challenge for wildlife,and only a minority of species is able to persist in cities(Niemela et al.2011).Species that maintain popula-tions in cities are usually characterized by significant changes in life history characteristics,population structure,and ecological relations(Niemela et al.2011).

Sexual size dimorphism in lizards:Rensch’s rule,reproductive mode,clutch size,and line fitting method effects

Rensch’s rule relates to a pattern whereby sexual size dimorphism is more female-biased in small-sized species and more male-biased in large-sized ones.We collected literature and museum data on the body size of males and females belonging to 4032 lizard species,as well as data on their reproductive modes and clutch sizes.We used phylogenetic comparative analyses,and general linear mixed models,to test Rensch’s rule and examined how re-productive mode and clutch size affect sexual size dimorphism.Sexual size dimorphism was independent of clutch size in lizard species with variable clutch sizes and in oviparous lizards.Large litters were associated with female-biased sexual dimorphism in viviparous and in scincomorph lizards.Inference regarding Rensch’s rule depended on the analytical method used to identify it.The widely used,but less conservative,reduced major axis regression usually support Rensch’s rule while ordinary least squares regressions mostly show isometric relationships.The rule tended to apply more to oviparous than to viviparous lizards.We infer that Rensch’s rule is,at best,a weak pattern in lizards.This is especially true in viviparous lineages where females reproduce infrequently and therefore evolve large sizes to maximise fecundity,resulting in female-biased dimorphism.

Genes for sexual body size dimorphism in hybrid tilapia(Oreochromis sp.x Oreochromis mossambicus)

Tilapias are important aquaculture species.Male-biased sexual size dimorphism is very common and males are preferred for aquaculture in tilapia.However,the mechanisms underlying sexual dimorphism remain to be elucidated.One hundred and thirty-six sex-biased genes,of which 23 were male-biased and 113 were femalebiased,were identified via reanalysis of a muscle transcriptome data using the latest reference genome assembly.These genes were mapped to KEGG pathways that are related to somatic cell metabolism,growth and differentiations,such as MAPK,FoxO4 and metabolism pathways as well as developmental processes responsible for skeletal muscle development.Pathways related to cell growth and proliferations such as MAPK signaling pathways are upregulated in males while pathways regulating cell division such as FoxO4 are upregulated in females.Sex-biased genes in tilapia skeletal muscle have higher evolution rates(dN/dS)compared to unbiased genes.Female-biased and male-biased genes showed 17.4%and 13.5%higher dN/dS,respectively,compared to unbiased genes.Our results suggest that some of the male and female sex-biased genes were under selection pressures.Three SNPs located in the promoter region of one sex-biased gene RASGRF1 on LG1 were associated with bodyweight differences in the hybrid tilapia.These sex-biased genes identified in this study may serve as candidate genes for future functional analysis on sexual size dimorphism and for developing DNA markers for selecting fast-growing saline tilapia in aquaculture.

Bare-throated spurfowl(Pternistis spp.)males across Africa impress females with bright throat colours during courtship

The role of bare body parts in sexual signalling in birds has received relatively little attention.I describe how the bare-throated spurfowl males saturate the colours of their throats to attract females.Of the 23 Afrotropical spurfowl species,the bare-throated subgroup includes Yellow-necked Spurfowl(Pternistis leucosceptus),Rednecked Spurfowl(P.afer),Grey-breasted Spurfowl(P.rufopictus) and Swainson’s Spurfowl(P.swainsonii).The rest of the species include fully feathered throated spurfowls.Throat colour intensity of bare throats was scored using an extensive online digital photographic archive encompassing the four species across the year’s seasons.Each throat(n=836) was assigned to one of four colour-intensity categories to explore the relationship between colour intensities,breeding cycles,and environmental variation.Except for Swainson’s Spurfowl male saturation of throat colours correlated with monthly rainfall,which peaks one or two months before egg laying.Swainson’s Spurfowl peaks during egg laying.Yellow-necked Spurfowl has the largest bare throat.Bare-throated spurfowl males perform an elevated courtship display posture above the female to feature their throat colour.No such displays occur in feather-throated spurfowl.Males with low throat colour saturation harbour more ectoparasites on their bare throats than birds with saturated throats.Male Red-necked Spurfowls have significantly larger bare throats than females.The primary function of bare throats probably assists in thermoregulation,particularly in arid regions.The bare throat may have evolved a secondary role in mating.Yellow-necked,Red-necked,and Greybreasted Spurfowls use their saturated throat colours as ornaments to court females during the breeding season.Unobtrusive female throat colours(unsaturated) may discourage male interlopers and predation during egg laying.Saturation appears to be carotenoid-food based.The different colours among the bare-throated species may serve as prezygotic mechanisms that inhibit cross-breeding and explain why females also have coloured throats.

亚洲玉米螟体重和体型的地理变异

为探明亚洲玉米螟Ostrinia furnacalis体重和体型地理变异,我们详细比较了来自4个不同地理种群(海南乐东18.8°N,109.2°E,广西阳朔24.8°N,110.5°E,江西南昌28.8°N,115.9°E和河北廊坊39.5°N,116.7°E)亚洲玉米螟的体重、体型大小及其与采集地纬度的关系。结果表明:不同地理种群的亚洲玉米螟卵重随纬度的升高而逐渐增大,符合贝格曼法则(Bergmann's law),而雌雄蛹重及成虫体长、后足腿节长和前翅长均随纬度的升高而逐渐减小,符合反贝格曼法则(Converse Bergmann's law)。雌虫的前翅显著长于雄虫,其性体型二型性符合任希法则(Rensch'srule),即在雌虫体型较大的种群中,雄虫前翅比雌虫前翅增长幅度相对较大。本文结果进一步揭示了即使在同一种类昆虫中,其各个虫态体重和体型的地理变异也可能不同。

蜡皮蜥的两性异形和繁殖输出

为研究蜡皮蜥 (Leiolepisreevesii)两性异形和繁殖输出 ,于 2 0 0 2、 2 0 0 3年 4月下旬从海南乐东一种群捕获 4 2 3头蜡皮蜥。经检测得到繁殖雌体的最小体长为 89 0mm ,据此判定≥ 89 0mm的个体为性成熟。研究结果表明 :①蜡皮蜥具有两性异形 ,雄性大于雌性且具有较大的头部。成体雄性头长和头宽随体长的增长速率大于雌性 ,幼体头长和头宽随体长的增长速率无显著的两性差异。以性别和年龄 (成、幼体 )为因子的双因子ANOVA比较两性头长和头宽与体长的回归剩余值发现 ,雄性头部大于雌性 ,幼体头部相对大于成体。②饲养于实验室的母体中有 4 2头于 2 0 0 2、 2 0 0 3年 5月 2 2日～ 7月 16日产出正常卵 ,这些繁殖雌体具有年产多窝卵的潜力。窝卵数和卵重的变异系数分别为 0 18和 0 13,前者变异度大于后者。窝卵数、窝卵重和卵重均与母体体长无关。卵重与相对生育力之间无显著的负相关性 ,表明蜡皮蜥缺乏卵数量与卵大小之间的权衡。相对窝卵重与母体体长呈显著的负相关 ,表明较小的母体具有相对较大的繁殖输出。因雌体繁殖会滞缓其生长 ,小母体具有相对较大的繁殖输出 ,至少部分地解释了雌性蜡皮蜥的成体为什么个体较小。

大猿叶虫生活史特性的地理变异

【目的】比较不同地理种群生活史特性的差异,是揭示生物体对环境适应机制的最有效方法之一。本研究旨在探明大猿叶虫Colaphellus bowringi不同地理种群生活史特性随纬度变异的特点。【方法】在室内恒温19℃、光周期16L∶8D条件下,观察测定了来自6个不同纬度的大猿叶虫种群从卵孵化到化蛹和化蛹到成虫羽化的时间,以及蛹和成虫体重。【结果】幼虫历期随纬度的升高逐渐延长,生长速率与纬度呈负相关,这两个生活史特性显示了顺梯度的变异。蛹历期在种群间没有显著差异。体重随纬度的升高逐渐减小,显示了反贝格曼法则。在所有的种群中,雌性蛹和成虫个体均显著大于雄虫,显示了雌性偏向的性体型二型性(SSD)。不同纬度的种群SSD指数存在差异,中纬度种群显示了最大的SSD指数。雄蛹在变态中比雌蛹丢失了更多的体重,导致成虫期的SSD指数大于蛹期。【结论】结果表明,大猿叶虫幼虫发育历期、生长速率和体重在不同纬度间呈现了显著变异。