In some animals, individuals of the same sex adopt one of several distinct mating strategies—a phenomenon known as alternative reproductive tactics. For amphibians, alternative reproductive tactics are typically environmentally determined, plastic (and reversible), and without accompanying morphological differentiation. A striking exception can be found in the Two-lined Salamander (Eurycea bislineata) species complex, in which some populations exhibit two distinct male phenotypes. "Searching" males use elongate cirri and mental glands for mate location and courtship on land, while “guarding” males develop hypertrophied jaw musculature used in mate-guarding at nesting sites. Kalki and Pierson (2025) analyzed genome-wide SNP data from Eurycea cf. wilderae of known sex and reproductive and provide evidence for XY sex determination and for a Y-linked polymorphism underlying alternative reproductive tactics. They also developed and validated a PCR-based genotyping assay for characterizing the sex ratio and relative frequency of male tactics from a sample of larvae, providing intriguing avenues for future research.

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