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.

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.

Natural variation in social conditions affects male mate choosiness in the amphipod Gammarus roeselii

The extent of male mate choosiness is driven by a trade-off between various environmental factors associated with the costs of mate acquisition,quality assessment and opportunity costs.Our knowledge about natural variation in male mate choosiness across different populations of the same species,however,remains limited.In this study,we compared male mate choosiness across 10 natural populations of the freshwater amphipod Gammarus roeselii(Gervais 1835),a species with overall high male mating investments,and evaluated the relative influence of population density and sex ratio(both affecting mate availability)on male mate choosiness.We investigated amplexus establishment after separating mating pairs and presenting focal males with a novel,size-matched female from the same population.Our analysis revealed considerable effects of sex ratio and(to a lesser extent)population density on time until amplexus establishment(choosiness).Male amphipods are able to perceive variable social conditions(e.g.,sex ratio)and modify their mating strategy accordingly:We found choosiness to be reduced in increasingly male-biased populations,whereas selectivity increases when sex ratio becomes female biased.With this,our study expands our limited knowledge on natural variations in male mate choosiness and illustrates the importance of sex ratio(i.e.,level of competition)for male mating decisions in natural environments.Accounting for variation in sex ratios,therefore,allows envisioning a distinctive variation of choosiness in natural populations and highlights the importance of considering social background information in future behavioral studies.