Agonistic behavior, a critical component of territoriality, is widespread throughout terrestrial plethodontid salamanders, though geographic variation in this behavior is poorly understood. Using color polymorphic Eastern Red-backed Salamanders (Plethodon cinereus), we conducted same-sex laboratory trials to compare aggressive and submissive behaviors between two genetically distinct groups in northern Ohio. For each group, we tested 120 individuals from 3 populations. We predicted that the genetic group with a single color morph would exhibit a higher degree of agonistic and territorial behavior compared to the genetic group with two morphs as an adaptive consequence of altered social dynamics in monomorphic populations. Contrary to our prediction, laboratory trials demonstrated that residents from the polymorphic group were significantly more aggressive than residents from the monomorphic group. This finding was corroborated by a strong residency effect in the polymorphic group, an effect that was weaker in the monomorphic group. Our results suggest that individuals in the polymorphic group are more aggressive and territorial than individuals in the monomorphic group, signifying a greater propensity to secure a territory and defend it against intruders. Our results add important insight into how geographic variation and differences in morph frequency can be attributed to behavioral differences.

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