Ethological Isolation and Variation in Allozymes and Dorsolateral Pattern between Parapatric Forms in the Desmognathus ochrophaeus Complex

Questions regarding the nature of species (here defined as genetically cohesive, reproductively isolated groups) are central to understanding the evolutionary history of a group of organisms. Insight into the processes responsible for creating and maintaining genetically cohesive units can be attained by examining areas where such units contact one another. Clearly, it seems most pertinent to examine the maintenance of a species upon secondary contact with related taxa, assessing the genetic structure and possible outcomes of these interactions. Research on secondary contact has focused on hybrid zones, usually those marked by sharp clines in particular characters. A hybrid zone is characterized as an area where genetically distinct groups meet, mate, and produce some offspring of mixed ancestry (Barton and Hewitt, 1985; Harrison, 1990,Harrison, 1993). Upon secondary contact, a number of outcomes are possible. Narrow zones may be maintained by a balance between dispersal and selection against hybrids (Barton and Hewitt, 1985). Alternatively, there can be fusion of the two taxa (Hewitt, 1988) or replacement of one taxon by another (Shapiro, 1998). Various degrees of introgression may occur (Arnold and Bennett, 1993) or a hybrid swarm may develop (Heiser, 1947).