Breeding behaviour of the foam nest frog, chiromantis xerampelina: sperm competition and polyandry.

[摘要] Breeding was observed in the foam nest frog, Chiromantis xerampelina,over three breeding seasons The mating pattern was characterized by anextended breeding season with a male-biased operational sex ratio andasynchronous and unpredictable female arrival. At more than 90% of nests,from one to seven unpaired males ('peripheral males') gathered around theamplexing pair during nest construction. Those peripheral males closest tothe pair competed 'With each other, and with the amplexing male, to positiontheir cloacae against the female's cloaca during oviposition bouts. In adetailed study of a single population, over 80% of males were observed asperipheral males, and 57% of males were observed both in amplexus and asperipheral males. Male mating success and participation at nests wasunrelated to size or weight. Chorus participation was the best predictor ofmale, mating success and participation at nests.The most plausible explanation for the presence of peripheral males was asperm competition hypothesis; namely that peripheral males compete withthe amplexing male for fertilizations by shedding sperm into the nest. Icollected data on body mass and testis mass for 13 African anurans. Usingadditional published data on 19 Japanese anurans, an allometric relationshipbetween body mass and testis mass was calculated. using 16 genera asindependent data points. This revealed that C. xerampelina have testesfourteen times heavier than predicted on the basis of body mass. This isconsistent with a trend seen in several taxa where testis size is related to theintensity of sperm competition. An additional experiment, in which thearnplexing male was prevented from shedding sperm into the nest, showedthat peripheral males are capable of fertilizing eggs. I conclude thatperipheral males are engaged in an opportunistic alternative mating tacticinvolving sperm cosnpetition. More than half the observed females bredpolyandrously, some mating with up to three males, This was the result ofamplexing males dismounting between nesting sessions, and males displacingone another from amplexus.

[发布机构] University of the Witwatersrand