Multiple male spawnings in a frog

This month's issue of Evolution features my latest paper on sperm competition in the Australian quacking frog Crinia georgiana, which I co-authored with Evan Thyer, Dale Roberts and Leigh Simmons. For this paper we video-recorded over thirty multiple male amplexus in this species, and then collected the offspring for molecular paternity analyses. We found that amplexus time and position were very important for fertilization success of males under competition (amplexing dorsally resulted in higher success!), and that testis size also had a positive effect on fertilization success, but only for males amplexing the female in the ventral position. It seems that in this species larger testes are an advantage in high population densities, where more multiple male spawnings occur and where males more commonly end up in a non-ideal amplexus position, such as holding on to the female in a ventral or lateral position.