Thermal Plasticity Changes Competitive Ability Across a Woodland Salamander Hybrid System

Abstract

Temperature mediates performance in ectotherms, affecting their ability to grow, survive, and reproduce. Aggression and evasion are key examples of thermally dependent behaviors that can impact fitness. However, we know relatively little about how the thermal plasticity of such behaviors varies among close relatives and impacts competitive outcomes. Woodland salamanders (Genus: Plethodon) from the Appalachian Mountains are distributed across wide thermal gradients in accordance with latitude or elevation. These plethodontid (lungless) salamanders compete for space and develop hybrid zones where territories overlap among species. Plethodontids tend to exhibit increased aggression at warmer temperatures, suggesting that as temperatures rise, behavioral interactions may be altered in ways that impact hybrid zone dynamics. It is thus far unclear, however, how salamander hybrids, which may encroach on their parent populations and drive competitive exclusion, respond behaviorally to warming. Here, we used staged bouts to examine the effects of temperature on aggression and evasion in the Plethodon shermani and Plethodon teyahalee hybrid system from the southern Appalachians. The behavior of salamanders from parent populations, particularly P. shermani, appears to be more sensitive to thermal changes than that of hybrid individuals. Additionally, evasive behavior was significantly more plastic than aggressive behavior in response to warming. Our results suggest that rising temperatures may increase competition for preferable microhabitats, but the effects on behavior among parental and hybrid salamanders will be asymmetric. Temperature may therefore alter the outcomes of competition, determining which populations can persist under rapid warming.