Matrotrophy and polyandry partially regulate postcopulatory mechanisms and sexual selection in a bimodal viviparous salamander

The evolution of matrotrophic viviparity creates new scenarios within which evolutionary processes can operate, including postcopulatory events, family conflicts, and selective processes, which are expected to intensify with polyandry. We evaluated the effect of matrotrophic viviparity and polyandry on the reproductive output and offspring fitness of a bimodal reproductive vertebrate, the fire salamander (Salamandra salamandra), which presents two forms of viviparity: larviparity (i.e. females deliver many aquatic larvae) and pueriparity (i.e. females deliver a few terrestrial juveniles). Polyandry is present in both strategies, but matrotrophy only occurs in pueriparity. Analyses of paternity and offspring life-history traits in 18 pueriparous and 13 larviparous mother–offspring arrays suggest the presence of sibling conflicts in pueriparous salamanders, especially with polyandry. However, these postcopulatory processes did not increase reproductive skew in the pueriparous strategy compared to the larviparous one or lead to fitness differences across sires within a clutch, suggesting other selective processes operating earlier in the reproductive sequence. Observed male–female pairs were found to be genetically more similar than other potential pairings, although no relationship between males’ genetic traits and reproductive success was detected. This work advances our understanding of how sibling conflicts and sexual selection affect the evolution of viviparous matrotrophy and mating strategies.