Keratinized Nuptial Spines Are Used for Male Combat in the Emei Moustache Toad (Leptobrachium boringii)

We describe the natural history and reproductive behaviour of the Emei Moustache Toad (Leptobrachium boringii) with an emphasis on the development of keratinized nuptial spines in males and document combat behaviour for the first time in this species. Between February and March of 2011, 19 female and 43 male L. boringii from Mount Emei UNESCO World Heritage Site, Sichuan, China were observed throughout the breeding season. This species exhibits male-biased sexual size dimorphism (SSD) with limited evidence of paternal care (nest guarding by males). Prior to the breeding season males grow 10 - 16 keratinized spines on their upper lip, which fall off once the season has ended. Throughout the breeding season males construct and defend aquatic nests where they produce advertisement calls to attract females. During this time we documented 14 cases involving a total of 22 males where males used their moustaches for aggressive interaction. Combat typically occurred at the beginning of the season when males would compete for a limited number of available nest sites. Neither male body size, nor body condition significantly affects the outcome of an aggressive interaction, suggesting that size may not be the only factor influencing an individual's chance of victory. Our evidence for male competition and aggression, along with observed paternal care are potential mechanisms to explain the evolution of male-biased SSD observed in this species.