The Effect of Attendance Patterns on the Lek Mating System in the Omei Treefrog(Rhacophorus omeimontis)

Attendance patterns are a key factor affecting sexual selection and mating systems in lekbreeding species.However,there are few systematic studies on attendance patterns in lek-breeding anurans.In this study,we monitored a population of Omei treefrogs(Rhacophorus omeimontis) for four consecutive years to reveal in detail the effects of attendance patterns on mating systems.We found that(1) female nightly attendance was affected by male nightly attendance,and operational sex ratios(determined by male and female nightly attendance) ultimately determined the extent of female polyandry;(2) males surviving more than one breeding season maintained high chorus attendance and mating success,suggesting that male chorus attendance is a good predictor of male genetic quality;(3) the distributions of male mating success were not significantly different from a Poisson distribution,indicating a random mating pattern;and male mating success was not related to body size(size-assortative mating was not evident) but was significantly correlated with chorus attendance.Since the chorus attendance is a predictor of male genetic quality,females performing random mating were more likely to mate with more frequently present males and could therefore gain indirect benefits from mating with higher-than-average quality males,thereby producing good offspring without incurring the significant costs involved in prolonged searching for,and assessing males.Our systematic survey on the relationship between attendance patterns and the lek mating system in R.omeimontis could help us better understand in-depth anuran lek mating systems.

Allelic Polymorphism,Gene Duplication and Balancing Selection of MHC Class ⅡB Genes in the Omei Treefrog(Rhacophorus omeimontis)

The worldwide declines in amphibian populations have largely been caused by infectious fungi and bacteria. Given that vertebrate immunity against these extracellular pathogens is primarily functioned by the major histocompatibility complex（MHC） class Ⅱ molecules, the characterization and the evolution of amphibian MHC class Ⅱ genes have attracted increasing attention. The polymorphism of MHC class Ⅱ genes was found to be correlated with susceptibility to fungal pathogens in many amphibian species, suggesting the importance of studies on MHC class Ⅱ genes for amphibians. However, such studies on MHC class Ⅱ gene evolution have rarely been conducted on amphibians in China. In this study, we chose Omei treefrog（Rhacophorus omeimontis）, which lived moist environments easy for breeding bacteria, to study the polymorphism of its MHC class Ⅱ genes and the underlying evolutionary mechanisms. We amplified the entire MHC class ⅡB exon 2 sequence in the R. omeimontis using newly designed primers. We detected 102 putative alleles in 146 individuals. The number of alleles per individual ranged from one to seven, indicating that there are at least four loci containing MHC class ⅡB genes in R. omeimontis. The allelic polymorphism estimated from the 102 alleles in R. omeimontis was not high compared to that estimated in other anuran species. No significant gene recombination was detected in the 102 MHC class ⅡB exon 2 sequences. In contrast, both gene duplication and balancing selection greatly contributed to the variability in MHC class ⅡB exon 2 sequences of R. omeimontis. This study lays the groundwork for the future researches to comprehensively analyze the evolution of amphibian MHC genes and to assess the role of MHC gene polymorphisms in resistance against extracellular pathogens for amphibians in China.

Social Polyandry and Multiple Paternity in the Omei Treefrog in the Southwest China

Group spawning, polyandry reproductive behaviors, and multiple paternity are increasingly reported in anuran species. The Omei treefrog （Rhacophorus omeimontis）, endemic to subtropical and mountainous forests of central and southwestern China, is a polyandrous lek-patterned breeder commonly showing multiple males-one female matings during the breeding season. To detect the traits of social and genetic polyandry in this species and explore the relationships between these traits, we investigated the breeding behaviors of a population of R. omeimontis in the Fengtongzhai National Nature Reserve, Baoxing County, Sichuan, China. We conducted paternity analyses using six microsatellite genetic markers. A total of 30 matings were recorded in the field （four monogamous pairs and 26 spawning groups）. Our results revealed high proportions of social polyandry （86.7%） and multiple paternity （70.0%） and the numbers of joining males and genetic fathers among matings ranged from 1 to 8 and from 1 to 4, respectively. There was a significantly positive correlation between the intensities of social and genetic polyandry, indicating that multiple males-one female breeding behaviors could be an important promoter of multiple paternity. We considered the intense social polyandry and multiple paternity as consequences of intense male-male competition under a male-biased sex ratio and genetic benefits pursuing of the females. However, the proportion of genetic fathers in a spawning decreased with the increase of joining male number and most of their offspring belonged to a few males. This might be caused by a ＂making the best of a bad lot＂ reproductive strategy of the inferior male individuals.