Novel reproductive behavior in an Asian frog: sex-reversed inguinal amplexus

Abstract

Amphibians exhibit diverse reproductive behaviors, including nine documented types of amplexus, the behavior in which male and female frogs position themselves for courtship, oviposition, and fertilization. All known forms of amplexus involve the male on top of or in line horizontally (cloacal apposition) with the female. Here, we report a novel form of amplexus observed in Lau’s leaf litter toad (Leptobrachella laui; Megophryidae) in Hong Kong, China. Termed “sex-reversed inguinal amplexus,” the female climbs on top of a male and the male transports the female to a concealed breeding site. We were unable to determine whether this was the amplectant position in which frogs engaged during oviposition or solely during courtship and prior to oviposition, but there are a number of possible evolutionary drivers that may have given rise to this behavior, including limiting suitable oviposition sites or strong competition for males among females. Further research will be necessary to understand the evolutionary origins of this novel reproductive behavior.