IS DECREASED FREQUENCY OF MATING AMONG CONSPECIFICS A COST OF SYMPATRY IN SALAMANDERS?

Abstract

Reproductive interactions among species in areas of and contact zones have long fascinated evolutionary biologists. Much interest and fierce debate has centered on the potential for natural selection to prevent interspecific mating between species in cases in which the progeny from such unions exhibit reduced fitness (see papers in Otte and Endler 1989). The potential risk of interspecific mating may be regarded as an important cost of sympatry for many species. Other reproductive costs of may exist even for species that are sexually incompatible and thus never engage in interspecific mating. For example, individuals of different species may use similar resources necessary for successful mating. In odonates, this may result in lost mating opportunities with conspecifics because of courtship misdirected toward heterospecific females (Singer 1990). Negative interspecific interactions also may arise during the process of mate attraction in the form of signal interference, an unintended by-product of two or more species broadcasting signals in the same sensory modality while in close physical proximity. Anuran choruses are prime examples of situations in which interspecific acoustic interference may result in a decreased probability of encounters between conspecifics (e.g., Schwartz and Wells 1983). Levels of sexual incompatibility typically are high among sympatric species of plethodontid salamanders ofthe genus Desmognathus, and thus the risk of interspecific mating probably is not a reproductive cost of for contemporary populations (Maksymovitch and Verrell 1993). Nevertheless, the presence of a heterospecific individual could still exert a negative influence on