Morphology is Decoupled from Interspecific Competition in Plethodon Salamanders in the Shenandoah Mountains, USA

Interspecific competition plays an important role in structuring ecological communities and generating patterns of phenotypic diversification. In the Shenandoah Mountains of Virginia, strong interspecific competition between P. cinereus and P. shenandoah shapes the geographic distributions of these species and relegates P. shenandoah to sub-optimal habitat. However, while many Plethodon salamander communities exhibit phenotypic shifts resulting from interspecific competition, the morphological consequences of competition in this system have not been investigated. We examined head shape variability of Plethodon cinereus and P. shenandoah to determine whether phenotypic patterns of variation were consistent with the hypothesis of interspecific competition. Across all three mountains where P. shenandoah is found, we identified significant species-specific differences in head shape. We also found significant phenotypic shifts between allopatric P. cinereus located at lower elevations and sympatric P. cinereus located at higher elevations. However, there was no evidence of accentuated phenotypic divergence in the sympatric contact zone between the two species. Thus, while there was evidence of a character shift in P. cinereus, patterns of character divergence between species associated with interspecific competition were not found. These observations suggest that morphological variation is decoupled from ecological interactions in this system, and aggressive interactions between the two species do not elicit a phenotypic response as seen in other Plethodon communities.