Nectophrynoides asperginis (Bufonidae) is a small toad endemic to the spray zone of the Kihansi River waterfall in Tanzania, Africa. This species was declared extinct-in-the-wild by the International Union for Conservation of Nature (IUCN) following construction of a hydroelectric dam that reduced the flow of the waterfall. The species is now limited to ex situ populations at the Wildlife Conservation Society's (WCS) Bronx Zoo, New York, the Toledo Zoo, Ohio, and two newer facilities in Tanzania. Much of the natural history of N. asperginis remains unknown, though it is known they are a sexually dimorphic species. Typically, males are smaller than females and possess distinctive dorsolateral inguinal patches (IP). Males appear to display these patches to conspecifics, but their function remains unknown. We created a five-grade schema to categorize the IPs by visual prominence accounting for both patch size and color, with Grade 1 being the least and Grade 5 being the most prominent. We hypothesized that a positive association exists between male IP grade and the snout–urostyle length (SUL) of females they amplexed. Therefore, we measured SUL and body mass in 91 pairs of amplexing N. asperginis and assessed the relationship of IP grade to female SUL in the amplexed pairs. Statistical analysis revealed a significant positive correlation (Spearman's rho = 0.250, P = 0.017) between male IP grade and the SUL of females being amplexed. This study suggests that IP grade is associated with mate assortment in N. asperginis, and it represents one of the first glimpses into the complex social interactions of this extinct-in-the-wild amphibian.

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