Rapid change in life-cycle polyphenism across a subspecies boundary of the Eastern Newt, Notophthalmus viridescens

Abstract

Life-cycle polyphenism has been hypothesized to facilitate ecological speciation in salamanders. A recent study demonstrated that the Eastern Newt (Notophthalmus viridescens) subspecies genetically differ in expression of life-cycle polyphenism. However, we currently lack direct evidence that the life-history divergence among the newt subspecies is associated with the suggested ecological parameters, namely availability of wetlands and suitable terrestrial habitats. To test such associations, we examined life-history traits of two subspecies, Notophthalmus viridescens viridescens and Notophthalmus viridescens dorsalis, across the subspecies boundary, which corresponds with changes in those ecological parameters between the Piedmont Plateau and the Coastal Plain. We reared larval newts derived from the two focal subspecies across the contact zone in outdoor mesocosms under two different hydroperiod treatments (three-month drying and permanent water). We found striking genetically based differences in life-history traits. The vast majority of larval N. v. viridescens metamorphosed to terrestrial juveniles (efts) regardless of pond hydroperiod treatments. In contrast, only a small portion of larval N. v. dorsalis (<30%) metamorphosed to efts under either hydroperiod treatment, whereas more than 70% of its larvae became aquatic metamorphic or paedomorphic adults under permanent water conditions. Notophthalmus viridescens viridescens also metamorphosed to efts at a smaller body size and over a shorter larval period than N. v. dorsalis. The pattern of the life-history change was closely related to the environmental change across the subspecies boundary. The present study provides direct evidence of divergent selection associated with the ecological parameters driving the life-history divergence among the newt subspecies. © 2011 Society for the Study of Amphibians and Reptiles.

Publication Title

Journal of Herpetology

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