Nuptial pad (“breeding gland”) morphology is related to non‐random mating in wild male common frogs (Rana temporaria)

Abstract

Androgen levels are closely linked with breeding in male amphibians. Development of the nuptial pad is driven by androgens and is believed to have importance for determining mating success in anurans, but this has not been tested in wild populations. We investigated the association between nuptial pad morphology (length, colour) and mating (amplexus) success in wild male common frogs (Rana temporaria) in the UK (Devon in Southern England and central Scotland). Once active breeding had been confirmed, pond water (25 L) was placed in 1–6 replicate mesocosms (66 cm diameter circular, black plastic tubs) in situ. Eight male and two female frogs were placed into each mesocosm, and success observed by identifying the male frog(s) in amplexus. The length of nuptial pads for male frogs observed in amplexus was greater than those that did not achieve amplexus. There was no difference in the absolute dark colour of nuptial pads (determined by red/green/blue analysis, Adobe photoshop©) for male frogs observed in amplexus versus those that did not achieve amplexus. However, within each mesocosm, the nuptial pad was relatively darker for winning male frogs compared to losing male frogs. Overall, 91% of winning male frogs from Devon, and 89% winning male frogs from Scotland, possessed either a longer and/or a darker nuptial pad, compared with frogs that did not achieve amplexus. These data suggest that features of nuptial pad morphology are associated with amplexus (and thus mating) success in male common frogs. Given that nuptial pads have been identified in all anuran amphibian species analysed to date, nuptial pad morphology may contribute to non‐random mating strategies across a broad range of species.