Mating Patterns of Minshan's Toad (Bufo minshanicus) from Three Populations along an Altitudinal Gradient

Atypical assortative mating based on body size in an explosive-breeding toad from a tropical island of southern China

Mating patterns exhibit considerable intra- and interspecific variation. Sexual selection can lead to the occurrence of random and assortative mating in different populations of the same species. Thus, understanding variation in mating decisions is crucial to understanding variation in the direction of sexual selection. We investigated natural mating patterns in Black-spectacled toads (Duttaphrynus melanostictus), an explosive-breeding species that breeds throughout the year. We captured amplectant pairs (137) and non-amplectant males (212) during breeding seasons from November 2016 to April 2017 in tropical-island population of southern China. Our study found no significant difference in snout-vent length (SVL) between amplectant and non-amplectant males. Female and male SVL were positively correlated with each other. Small females were paired more frequently with small males, less frequently with large males, but had no preference for or against medium males. Medium females exhibited no preference. Large females showed no preference for large males, but were paired less frequently with small males. These data suggested that successful amplectant males had body sizes representative of the entire population. Both random and size-assortative mating were present simultaneously in the same population and within the same breeding season. Female choice was important in shaping the mating behavior of Black-spectacled toads, promoting genotype-frequency stabilization and body-size diversity in the population.

Does relatedness influence the intensity of competition in Bufo gargarizans minshanicus tadpoles?

Kin selection theory predicts that mechanisms should evolve to reduce kin competition when this maximizes inclusive fitness. In this study, we tested these predictions by investigating the effects of relatedness on fitness-related metamorphic traits (e.g., length of larval period, size at metamorphosis, body condition and survival rate). We did this in a laboratory experiment by exposing individuals of Bufo gargarizans minshanicus to competition with full-sibling or non-sibling larvae. Although tadpoles seemed to grow slightly better in environments when their competition consisted of full-siblings than when their competitors consisted of non-siblings, these effects of relatedness on the growth and development were not significant. Therefore, we suggest that interference competition may be equally intense in in full-sibling and non-sibling groups.

The effect of size-assortative mating on fertilization success of the common toad (Bufo bufo)

Although size-assortative mating (SAM) is a frequently studied phenomenon in anurans, its effect on fitness rarely has been evaluated. Using a controlled experiment, we assessed the presence of SAM in the common toad,Bufo bufo, and evaluated the effect on fertilization success of male-female size (snout-vent length, SVL) difference and ratio in mated pairs. Even though the toads paired non-randomly with respect to size, the difference and ratio of female and male SVL in pairs had no significant effect on fertilization success. Our findings and the majority of other studies suggest that the commonly accepted idea that SAM serves to maximize fitness may not be completely accurate. The statistical power and effect size in these studies are often poor, however, and the methods used are inconsistent. We conclude that more manipulative experiments with appropriate sample sizes are needed to fully understand this phenomenon.

The effect of sex ratio on size-assortative mating in two explosively breeding anurans

Size-assortative mating (SAM) is a widespread phenomenon related to individual fitness. In our study, we examined: (i) the appearance of SAM, and (ii) the effect of sex ratio on intensity of SAM in wild populations of two explosively breeding anurans, common frogs,Rana temporaria, and common toads,Bufo bufo. Despite a higher male-biased operational sex ratio (OSR) in toads, the body lengths of the paired males and females were significantly correlated only in frogs. Increasing male-male competition, assessed via the OSR, resulted in a stronger correlation also in frogs only. Thus, great variability in the presence and intensity of SAM has been observed within both studied species.

Sex recognition and mate choice by male Bufo gargarizans in central China

Mate choice is important for successful reproduction, and consequently species have evolved various ways to choose potential high-quality mates. Anuran mate choice and underlying processes have been the subject of several recent investigations, however we are far from a complete understanding of mate choice in this system. In the present study, when given a simultaneous choice between a male and a female of identical size, males did not discriminate between the sexes, and attempted to clasp a male or a female with equal frequency. Test males only released the stimulus toad when a release call was emitted by the stimulus male. When two males with distinct size differences were provided with a male, the male chose the larger one. Moreover, males discriminated between gravid females that differed in body size, choosing larger gravid females over smaller ones. These results suggest that male Bufo gargarizans can discriminate between the sexes, probably based on male release calls, and prefer to mate with larger individual using visual cues.