Amphibian reproductive modes are diverse and are characterised by complex adaptations, including vast variability in life history traits and different parental investment strategies. For instance, viviparity is rare in urodeles despite the potential ecological advantages gained in such populations by having semi-independency from water. The fire salamander, Salamandra salamandra, shows remarkable intraspecific variation in reproductive modes, with two strategies co-occurring: a common reproductive mode, larviparity (parturition of aquatic larvae), and a phylogenetically derived reproductive mode, pueriparity (parturition of terrestrial juveniles). Pueriparous populations of S. salamandra have at least two independent origins, the first originating from its northern distribution in the Iberian Peninsula, and the second at two insular populations on the northwestern Iberian coast. Here, we analyse the patterns of variability of some life-history traits in larviparous and pueriparous populations of S. salamandra, including pueriparous populations from the two independent origins, to understand how these traits relate to the evolutionary transitions in reproductive modes in S. salamandra. Our study shows differences in female body size and clutch and brood size between larviparous and pueriparous fire salamanders. We did not find differences in female investment between reproductive modes, and thus, the evolution to pueriparity in S. salamandra is likely characterised by the re-allocation of eggs to matrotrophy. Our study also confirms pueriparity and larviparity as the characteristic reproductive modes for insular and coastal/mainland S. s. gallaica populations, respectively, revealing the potential presence of pueriparity in one coastal population. This comparative analysis sheds light on the maternal factors that might have driven, or are related to, the evolution of pueriparity in this unique biological system and sets up the basis for testing different hypotheses that include climatic, ecological, physiological, and genetic factors as drivers of this evolutionary transition.
Journal: Evolutionary Ecology