This is a proposal to study the processes by which new species are formed. the project focuses on two key processes: (1) the origin of incompatibility in mating behavior, and (2) the origin of hybrid inviability and hybrid sexual incompetence. Woodland salamanders (genus Plethodon) are being used for the proposed work because, of all land-based animals with backbones, their hybrid zones are the best known. Furthermore, initial work (over 4000 pair mating trials) has shown that the proposed behavioral studies are feasible. The overall plan is to conduct studies of mating compatibility and hybrid viability in (1) a series of mountain- top isolates of one species (P. jordani) and (2) a series of contact zones between two species (P. jordani and P. teyahalee). In some of these zones, the two speices do not hybridize (overlap zones), while in others they form relatively narrow hybrid zones or extensive hybrid swarms. The evolutionary predictions that will be tested are: (1) Sexual incompatibility evolves as a by-product of differences in sexual behavior that evolve in spatially separated populations. (2) Sexual incompatibility is strengthened if two spatially separated populations come back into contact with each other. (3) Sexual incompatibility is more pronounced in overlap zones than in hybrid zones, and is greater in relatively narrow zones than in extensive hybrid swarms. (4) Hybrid inviability evolves as a by-product of evolutionary change in spatially separated populations.
