Intrasexual selection and group spawning in quacking frogs (Crinia georgiana)

In the Australian frog Crinia georgiana, matings frequentlyinvolve a single female and multiple males (group spawning).The aim of the present study was to demonstrate a connectionbetween variation in the intensity of intrasexual competition,measured by using male density and operational sex ratio (OSR),and the incidence of group spawning. Over a 3-month breedingperiod, male density and OSR varied substantially and were significantlyinfluenced by climatic conditions. The frequency of agonisticinteractions between males was higher in denser choruses. Fightswere typically over the possession of sites used to broadcastadvertisement calls and were almost always won by larger males.At higher densities, males allocated significantly less timeto calling to attract females and spent more time as nonmovingsatellites or roaming through an aggregation (searching). However,large males always called more than did small males. The numberof males involved in a spawning correlated positively with variationin both male density and OSR. Observation of group spawningsrevealed that they generally arose when a satellite male joineda mating pair after a female chose to mate with a calling maleor when a female was seized by a searching male and the pairwas joined by other searching males. These findings, coupledwith past research documenting costs but no benefits of multiplepaternity to females, suggest that competitively inferior malesforce group spawns.