No Male Preference for Large Females in the Asian Common Toad(Duttaphrynus melanostictus):Effect of the Sex Ratio and Breeding System

Mating preferences are common in natural populations of animals.Numerous studies have shown that male mate choice can occur in a wide range of taxa.However,male mating preferences are still poorly understood in anurans.Sexual selection theory predicts that male mate choice is not expected to arise if 1) adult population exhibited a highly male-biased sex ratio which will diminish male mating success;2) males provide less parental care;3) mating success of males is associated with chorus tenure in which males would maximize their fitness by mating with multiple mates.We tested these predictions in the Asian common toad Duttaphrynus melanostictus from southeastern Tibet,China.Our field experimental results indicated that,the breeding population exhibited a highly male-biased sex ratio,called males did not defend sites which contain significant resources required by females and offspring,both sexes provided no parental care after egg-laying,and the toad species was characterized with prolonged breeding season chorus attendance.In male mate choice experiment,males did not show preferences for a larger gravid female over a smaller gravid female.We suggest that male mating success in the Asian common toad is likely determined by the number but not the quality of mates.Future research should focus on how sexual selection on male acoustic signaling and how female preference exert different types of selection pressure on male call traits in this Tibet toad.

Strong Limb Tactics of the Boulenger's Lazy Toad,Scutiger boulengeri:Inferred from Limb Muscles

Theory predicts that well-developed limb musculature can result from sexual selection favoring strong males.We tested for this prediction in the Boulenger's lazy toad(Scutiger boulengeri),a species that exhibits inguinal amplexus.As expected,we found that males had more massive forelimbs and hindlimbs than those of females.In addition,amplectant males had relatively more massive hindlimbs than non-amplectant males.This pattern can be explained by sexual selection,as the greater forelimb muscles allow males to hold females more tightly and massive hindlimbs likely confer a locomotor advantage in defending mates.This study contributes to an increasing body of literature clarifying the role of sexual selection in producing sexual dimorphism in anuran limbs.