American Society of Naturalists

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“Morphological polymorphism associated with alternative reproductive tactics in a plethodontid salamander”

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Todd W. Pierson, Jennifer Deitloff, Stanley K. Sessions, Kenneth H. Kozak, and Benjamin M. Fitzpatrick (April 2019)

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Pierson et al. describe alternative reproductive tactics and morphologies in a plethodontid salamander

“Searching” and “guarding” male salamanders reveal different strategies for reproduction

Adult male Blue Ridge two-lined salamanders (<i>Eurycea</i> cf. <i>wilderae</i>) with alternative reproductive tactics—“searching” male (top left) and “guarding” male (bottom right).<br />(Photograph by T.&nbsp;W. Pierson)
Adult male Blue Ridge two-lined salamanders (Eurycea cf. wilderae) with alternative reproductive tactics—“searching” male (top left) and “guarding” male (bottom right).
(Photograph by T. W. Pierson)

In populations of many organisms, several discrete reproductive tactics (called “alternative reproductive tactics” or “ARTs”) coexist. Often, these divergent tactics can be identified by different morphologies. The lungless salamanders (Family Plethodontidae) are a diverse group of amphibians with a center of diversity in the Appalachian Mountains of North America. Prior to the external transfer of a spermatophore, most male plethodontid salamanders court females through the performance of a ritualized “dance” and the delivery of complex reproductive pheromones. While these behaviors are variable among species, they are typically conserved within species.

In this paper, Todd W. Pierson (University of Tennessee Knoxville), Jennifer Deitloff (Lock Haven University), Stanley K. Sessions (Hartwick College), Kenneth H. Kozak (University of Minnesota), and Benjamin M. Fitzpatrick (University of Tennessee Knoxville) use a combination of genetic, behavioral, and field observational data to describe an example of alternative reproductive tactics in a group of plethodontid salamanders—the two-lined salamander (Eurycea bislineata) species complex. “Searching” males have morphological traits and behaviors suited for locating and courting females in terrestrial habitats, while “guarding” males have morphological traits and behaviors suited for guarding females at aquatic nesting sites. Pierson et al. demonstrate that these two forms coexist in three putative species in the E. bislineata species complex, while other species in the group have only form or the other. The authors also demonstrate that these alternative reproductive tactics have divergent reproductive phenologies, describe the potential implications for parental care, and highlight directions for future research on this system.

Typical habitat of Blue Ridge two-lined salamander (<i>Eurycea</i> cf. <i>wilderae</i>) from the Blue Ridge of the Southern Appalachian Mountains.<br />(Photograph by T.&nbsp;W. Pierson)
Typical habitat of Blue Ridge two-lined salamander (Eurycea cf. wilderae) from the Blue Ridge of the Southern Appalachian Mountains.
(Photograph by T. W. Pierson)

Abstract

Understanding polymorphism is a central problem in evolution and ecology, and alternative reproductive tactics (ARTs) provide compelling examples for studying the origin and maintenance of behavioral and morphological variation. Much attention has been given to examples where “parasitic” individuals exploit the reproductive investment of “bourgeois” individuals, but some ARTs are instead maintained by environmental heterogeneity, with alternative tactics exhibiting differential fitness in discontinuous reproductive niches. We use genomic, behavioral, karyological, and field observational data to demonstrate one such example in plethodontid salamanders. These ARTs (“searching” and “guarding” males) are associated with different reproductive niches and, unlike most other examples in amphibians, demonstrate substantial morphological differences and inflexibility within a reproductive season. Evidence suggests the existence of these ARTs within three putative species in the two-lined salamander (Eurycea bislineata) species complex, with other members of this clade fixed for one of the two tactics. We highlight directions for future research in this system, including the relationship between these ARTs and parental care.