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.     

Age and Body Size of the Shangcheng Stout Salamander Pachyhynobius shangchengensis(Caudata: Hynobiidae) from Southeastern China

Age and body size a re critical for understanding life history evolution and ecology. In this study, the age and body size of the Shangcheng stout salamander, Pachyhynobius shangchengensis, from a population in Anhui Province, China, were studied by skeletochronology. The mean age was 8.8 ± 0.2(mean ± SD) years in females and 9.6 ± 0.2 in males and ranged 5–13 years for both sexes. The mean age was significantly different between sexes. The mean body size and mass were(100.21 ± 0.91) mm and(31.76 ± 0.73) g in females, and(105.31 ± 1.23) mm and(37.14 ± 1.12) g in males, respectively. Males were significantly larger and heavier than females, indicating sexual size dimorphism.There was a significant positive correlation among body size, body mass, and age, suggesting that the oldest individuals are larger and heavier. The growth rate in males was significantly higher than in females. The present study provides preliminary data on life-history traits which can be helpful for future studies of this species and other hynobiid salamanders.     

Fighting and aggressive sound determines larger male to win male-male competition in a bark beetle

Intrasexual selection occurs in male-male competition over access to females and usually results in the larger male winning.While much research has documented that size matters,little is known about how the larger male wins.Dendroctonus vale ns is an aggregating monogamous bark beetle in which males have large variation in body size and display intense competition over females.Behavioral observation showed two males fight each other within the gallery by pushing/shoving and stridulated more when two males encountered each other.Experiments using two different-sized males synchronously competing showed that larger males won 95%of contests.Reciprocal displacement experiments using muted and intact males of different or equal size were used to simulate male-male competition.Larger males displaced the smaller resident male in 90%of contests,while smaller males prevailed over larger residents in 6.7%of contests.With both males silenced,larger males displaced smaller males in 80%of con tests,while smaller males prevailed in 8%of con tests.Further experiments using equal-sized males showed aggressive soundemitting males displaced muted males in 67%of contests,yet intact males displaced other intact males in only 37.5%of con tests.Sound analysis showed sound pressure level is an honest signal of body size and males chose soft sounds over loud aggressive sounds in assays.Therefore,D.valens males have evolved dual behaviors,fighting and aggressive sounds associated with body size,to assess rivals to compete for a partner,gaining insights in male-male competition for this species and for other animals.     

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.     

Sexual Dimorphism in Mass of the Hindlimb Muscles of the Piebald Odorous Frog （Odorrana schmackeri）

Male-biased sexual dimorphism in hind limb muscles is widespread in anuran species where scramble competition is common among males. Such sexual difference is thought to result from sexual selection. In this view, we tested the differences in muscle mass between the sexes and between amplectant and non-amplectant males by quantifying the mass of four hindlimb muscles （triceps femoris, sartorius, gracilis and plantaris longus） of females and males of Odorrana schmackeri. The results showed that females significantly exceeded males for muscle triceps femoris, gracilis, plantaris longus and total mass when controlled for body size. There are no significant differences between amplectant and non-amplectant males. It is probable that the maintenance of the amplectant position in O. schmackeri may depend on the strength of hindlimb muscles in females to support the pair.     

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.     

Large males have a mating advantage in a species of darter with smaller,allopaternal males Etheostoma olmstedi

<正> Theory suggests that males that are larger than their competitors may have increased mating success, due to bothgreater competitive ability and increased attractiveness to females. We examined how male mating success varies with male sizein the tessellated darter Etheostoma olmstedi. Previous work has shown that large males tend to move around and breed in vacantbreeding sites, and consequently provide less care for their eggs, while smaller individuals can be allopaternal, caring for the eggsof other males as well as for their own. We studied female egg deposition in a natural breeding population using artificial breedingsites and in the laboratory, where female choice of spawning site was restricted to two breeding sites tended by two males ofdifferent sizes. In both the field and the laboratory, nests tended by larger males were more likely to receive new eggs. Additionally,the mean size of males associated with a nest was positively correlated with both the maximum coverage of eggs at the nestand the number of times new eggs were deposited. We discuss how the increased mating success of larger males, despite their decreasedparental care, may help explain allopaternal care in this species     

Sexual selection in cane toads Rhinella marina： A male＇s body size affects his success and his tactics

Abstract Male body size can play an important role in the mating systems of anuran amphibians. We conducted labora- tory-based trials with cane toads Rhinella （Bufo） marina from an invasive population in the wet-dry tropics of northern Australia, to clarify the effects of a male＇s body size on his reproductive success and behavior （mate choice）. Males were stimulated with a synthetic hormone to induce reproductive readiness. Larger body size enhanced a male toad＇s ability to displace a smaller rival from amplexus, apparently because of physical strength： more force was required to dislodge a larger than a smaller amplectant male. A male＇s body size also affected his mate-choice criteria. Males of all body sizes were as likely to attempt amplexus with another male as with a female of the same size, and preferred larger rather than smaller sexual targets. However, this size prefe- rence was stronger in larger males and hence, amplexus was size-assortative. This pattern broke down when males were given access to already-amplectant male-female pairs： males of all body sizes readily attempted amplexus with the pair, with no size discrimination. An amplectant pair provides a larger visual stimulus, and prolonged amplexus provides a strong cue for sex iden- tification （one of the individuals involved is almost certainly a female）. Thus, a male cane toad＇s body size affects both his ability to defeat rivals in physical struggles over females, and the criteria he uses when selecting potential mates, but the impacts of that selectivity depend upon the context in which mating occurs     

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 fro...     

Refuge size variation and potential for sperm competition in Wellington tree weta

Ecological variation in resources can in flue nee the distributi on and en counter rates of potential mates and competitors and, con sequently, the opport unity for sexual selection. Factors that influence the likelihood that females mate multiply could also affect the potential for sperm competition. In Wellington tree weta (Hemideina crassidens, plural "weta"), the size of tree cavities (called galleries) used as refuges affects weta distribution and thus the opport unity for sexual selection and selection on male weaponry size. We examined the predicted effects of gallery size and male weap onry size on the potential for sperm competition. We asked if gallery size in flue need the potential for multiple mating by females and potential for sperm competition, if male weaponry size was associated with relative expected sperm competition intensity (SCI), and if estimated male mating success was correlated with pote ntial SCI. To qua ntify relative competitive envir on merits of males, we created and analyzed networks of potential competitors based on which males could have mated with the same females. We found that small galleries had higher potential for female multiple mating and higher potential for sperm competition. Size of male weaponry was not associated with expected relative SCI. Regardless of gallery size, males with more potential mates were expected to face lower expected relative sperm competition. Thus, in this system, variation in the size of available refuges is likely to in flue nee the pote ntial for sperm competiti on, in a way that we might expect to in crease variation in overall reproductive success.     

Sexual Dimorphism,Female Reproductive Characteristics and Egg Incubation in an Oviparous Forest Skink(Sphenomorphus incognitus) from South China

We studied sexual dimorphism and female reproduction in an oviparous forest skink(Sphenomorphus incognitus)from South China.We incubated eggs under five thermal regimes(22,25,28,25±3 and 27±5°C)to examine the effects of constant versus fluctuating temperatures on incubation length and hatchling morphology.In our sample the largest male and female were 110 mm and 108 mm snout-vent length(SVL),respectively.Adult males and females did not differ in mean SVL;adult males were larger in head size(both length and width),longer in foreand hind-limb lengths and shorter in abdomen length than females of the same SVL.Accordingly,we conclude that S.incognitus is a sexually monomorphic species in terms of SVL but shows sexual dimorphism in head size,abdomen length and appendage length.Females laid a single clutch of 3-10 eggs per breeding season from early May to midAugust,with larger females generally laying more(but not always larger)eggs per clutch than did smaller ones.Embryonic stages at laying ranged from Dufaure and Hubert's(1961)stage 31 to 32,with a mean stage of 31.3.The positive relationship between clutch mass and female SVL was not significant.The offspring size-number trade-off does not exist in S.incognitus,as revealed by the fact that egg mass was independent of relative fecundity.Incubation length decreased as temperature increased,and stable temperatures resulted in delayed hatching.Hatchlings incubated under the five thermal regimes did not differ from each other in any examined trait,suggesting that S.incognitus is among oviparous reptilian species where incubation temperature has no role in modifying hatchling morphology as long as eggs are not exposed to extreme temperatures for prolonged periods of time.     

Nonlinear Phenomena Conveying Body Size Information and Improving Attractiveness of the Courtship Calls in the Males of Odorrana tormota

Nonlinear phenomena are commonly shown in the vocalization of animals and exerts different adaptive functions.Although some studies have pointed out that nonlinear phenomena can enhance the individual identification of male Odorrana tormota,whether the nonlinear phenomena play a specific role in the sexual selection of O.tormota remain unclear.Here we presented evidence that there was a significant negative correlation(Pearson:n=30,r=0.65,P<0.001)between the nonlinear phenomena content and snout-vent length in the male O.tormota,and two-choice amplexus experiments showed that female O.tormota preferred male with smaller body size containing higher nonlinear phenomena content in its calls.Phonotaxis experiments also revealed that females preferred calls with higher nonlinear phenomena content.Additionally,compared to the calls with lower nonlinear phenomena content and higher fundamental frequency,there was shorter response time in phonotactic behaviour of female induced by the calls with higher nonlinear phenomena content and lower fundamental frequency.We argue that the nonlinear phenomena content in the calls of male O.tormota can convey its body size information and may provide important clues for female frogs in darkened surroundings to identify males’body size during mate choice,meanwhile,higher nonlinear phenomena content in males’calls may increase the attractiveness of males to females.The results of this study provide confirmation that,for O.tormota,nonlinear phenomena have specific function in mate choice.     

Kinship alters the effects of forced cohabitation on body weight,mate choice and fitness in the rat-like hamster Tscheskia triton

It has been documented that social isolation imparts deleterious effects on gregarious rodents species, but caging in group imparts such effects on solitary rodents. This study was attempted at examining how kinship to affect body weight, behavioral interaction, mate choice and fitness when we caged male and female rat-like hamsters Tscheskia triton in pair, a solitary species. We found that females paired with nonsibling males became heavier than the females paired with sibling males, but both agonistic and amicable behavior between paired males and females did not differ between sibling and nonsibling groups. This indicated that kinship might reduce females＇ obesity in response to forced cohabitation, and dissociation might exist between physiological and behavioral responses. Furthermore, binary choice tests revealed that social familiarity between either siblings or nonsiblings decreased their investigating time spent in opposite sex conspeeifie of cage mates and/or their scents as compared with those of nonmates, suggesting effects of social association on mate and kin selection of the hamsters. On the other side, both females and males caged in pair with siblings show a preference between unfamiliar siblings or their scents and the counterparts of nonsiblings after two month separation, indicating that the kin recognition of the hamsters might also rely on phenotype matching. In addition, cohabitation （or permanent presence of fathers） elicited a lower survival of pups in nonsibling pairs than sibling pairs, but did not affect litter size, suggesting that kinship affects fitness when housing male and female ratlike hamsters together. Therefore, inbreeding might be adapted for rare and endangered animals.     

Body Size and Reproductive Tactics in Varanid lizards

Body size and female reproduction in the water adult females larger than 500 mm SVL and 32 adult males Ledong, Hainan under permit to our laboratory in Hainan monitor lizard （Varanus salvator） were studied. Forty-two larger than 400 mm SVL were donated by local people in in 2013 and 2014. The largest male and female measured 745 and 755 mm SVL, respectively. The mean SVL was greater in adult females than in adult males. Males had larger heads （head width） than females of the same SVL. The smallest reproductive female in our sample was 565 mm SVL. Females produced a single clutch of 17.1 （10-23） pliable-shelled eggs per breeding season stretching from mid-June and mid-September. Clutch size and clutch mass were all positively related to female SVL. However, there was no significant linear relationship between egg mass and female SVL. Larger females generally produced more eggs, and thus heavier clutches than did smaller ones. There was no significant linear relationship between relative clutch mass and female SVL. Phylogenetic generalized least squares （PGLS） analysis, accounting for phylogenetic relationships, showed that clutch size was positively correlated with mean maternal SVL in varanid lizards. PGLS analysis showed that phylogenetic relationships did not affect clutch （or/and egg） mass and the SVL although there were significant linear relationship between clutch （or/and egg） mass and mean maternal SVL. Therefore, we could draw some general conclusions about the body size and reproductive tactics in varanid lizards that larger females generally produced more eggs, larger eggs and thus heavier clutches than did smaller ones.     

Dispersing male Parnassius smintheus butterflies are more strongly affected by forest matrix than are females

Dispersal is a central aspect of the ecology, evolution, and conservation of species. Predicting how species will respond to changing environmental conditions requires understanding factors that produce variation in dispersal. We explore one source of variation, differences between sexes within a spatial population network. Here, we compare the dispersal patterns of male and female Parnassius smintheus among 18 subpopulations over 8 years using the Virtual Migration Model. Estimated dispersal parameters differed between males and females, particularly with respect to movement through meadow and forest matrix habitat. The estimated dispersal distances of males through forest were much less than for females. Observations of female movement showed that, unlike males, females do not avoid forest nor does forest exert an edge effect. We explored whether further forest encroachment in this system would have different effects for males and females by fitting mean parameter estimates to the landscape configuration seen in 1993 and 2012. Despite differences in their dispersal due presumably to both habitat and physiological differences, males and females are predicted to respond in similar ways to reduced meadow area and increased forest isolation.     

Dewlap size in male water anoles associates with consistent inter-individual variation in boldness

Male sexually selected signals can indicate competitive ability by honestly signaling fitnessrelevant traits such as condition or performance. However, behavior can also influence contest outcomes;in particular, boldness often predicts dominance rank and mating success. Here, we sought to determi ne whether male ornament size is associated with consiste nt in dividual differences in boldness in water anoles Anol is aquaticus. We measured the relative size of the dewlap, a flap of skin under the chin that is a sexually selected ornament in Anolis lizards, and tested for associations with responses to a novel and potentially risky environment: time to emerge from a refuge into an arena and number of head sea ns post-emergence. We found that in dividuals con siste ntly differed in both time to emerge and head sea nning (i.e., in dividual resp on ses were repeatable), and that dewlap size was negatively related to nu mber of head sea ns. This suggests that orname nt size could indicate male boldness if seanning represents antipredator vigilance. We found that males that had larger relative dewlaps were also in better body condition, but boldness (i.e., head scann ing) was not related to condition. Lastly, we found con siste nt d iff ere nces in behavior betwee n trials, showing that anoles were becoming habituated or sensitized to the testing arena. Overall, our study shows that in additi on to indicating con dition and perform a nee, dewlap size could also honestly indicate male boldness in Anolis lizards.     

Habitat productivity is a poor predictor of body size in rodents

The"resource availability hypothesis"predicts occurrence of larger rodents in more productive habitats.This prediction was tested in a dataset of 1,301 rodent species.We used adult body mass as a measure of body size and normalized difference vegetation index(NDVI)as a measure of habitat productivity.We utilized a cross-species approach to investigate the association between these variables.This was done at both the order level(Rodentia)and at narrower taxonomic scales.We applied phylogenetic generalized least squares(PGLS)to correct for phylogenetic relationships.The relationship between body mas and NDVI was also investigated across rodent assemblages.We controlled for spatial autocorrelation using generalized least squares(GLS)analysis.The cross-species approach found extremely low support for the resource availability hypothesis.This was reflected by a weak positive association between body mass and NDVI at the order level.We find a positive association in only a minority of rodent subtaxa.The best fit GLS model detected no significant association between body mass and NDVI across assemblages.Thus,our results do not support the view that resource availability plays a major role in explaining geographic variation in rodent body size.     

Sexual conflict and deception in poison frogs

I review evidence that females deceive males in the context of sexual selection and sexual conflict in the green poison frog, Dendrobates auratus. In this species, males mate polygynously when they have the opportunity, but polygyny imposes a cost on female reproductive success. Some females attempt to guard their mates when those males are approached by other fe- males. This behavior involves both aggression toward other females and active ＂pseudo-courtship＂ of the male. This courtship is hypothesized to be a deceptive signal that ffmctions to prevent the male from mating with other females. Observational and com- parative evidence is presented in support of the predictions of this hypothesis. This form of deception is compared to similar be- haviors that occur in other species, and the possibility that other forms of deception occur in poison frogs is discussed     

Age, growth and reproduction of Sarcocheilichthys nigripinnis from the Qingyi Stream in the Huangshan Mountains

Identifying the life-history strategies of fish and their associations with the surrounding environment is the basic foundation in the conservation and sustainable utilization of fish species.We examined the age,growth,and reproduction of Sarcocheilichthys nigripinnis using 352 specimens collected monthly from May 2009 to April 2010 in the Qingyi Stream.We found the sex ratio of this study population was 0.58:1(female:male),significantly different from expected 1:1.Females and males both comprised four age groups.The annuli on the scales were formed during February and March.No obvious between-sex difference was observed in length-weight and length-scale-radius relationships.The total length in back-calculation significantly increased with age for both sexes,but did not differ significantly at each age between the two sexes.An inflection point was observed in the growth curves given by the von Bertalanffy growth function for total weight.At this inflection point,fish were 3.95 years.Both sexes reach their 50% sex maturity at age 2,when females and males were 94.7 mm and 103.0 mm total length.The temporal pattern of the gonado-somatic index corresponded to a spawning period that occurred from April through July.The non-synchronicity of egg diameter in each mature ovary during the breeding period suggested these fish may be batch spawners.The absolute fecundity increased significantly with total length and weight,whereas no significant correlation was observed between the relative fecundity and body size.     

Neither Biased Sex Ratio nor Spatial Segregation of the Sexes in the Subtropical Dioecious Tree Eurycorymbus cavaleriei （Sapindaceae）

Knowledge of sex ratio and spatial distribution of males and females of dioecious species is both of evolutionary interest and of crucial importance for biological conservation. Eurycorymbus cavaleriei, the only species in the genus Eurycorymbus （Sapindaceae）, is a dioecious tree endemic to subtropical montane forest in South China. Sex ratios were investigated in 15 natural populations for the two defined ages （young and old）. Spatial distribution of males and females was further studied in six large populations occurring in different habitats （fragmented and continuous）. The study revealed a slight trend of male- biased sex ratio in both ages of E. cavaleriei, but sex ratio of most populations （13 out of 15） did not display statistically significant deviation from equality. All of the four significantly male-biased populations in the young class shifted to equality or even female-biased, The Ripley＇s K analysis of the distribution of males with respect to females suggested that individuals of the opposite sexes were more randomly distributed rather than spatially structured. These results suggest that the male-biased sex ratio in E. cavaleriei may result from the precocity of males and habitat heterogeneity. The sex ratio and the sex spatial distribution pattern are unlikely to constitute a serious threat to the survival of the species.