Conservation of North American freshwater fishes: The micro and macro of speciation and extinction (Cyprinodon pecosensis, Cyprinodon variegatus)

Freshwater fish species are imperiled by a diverse array of environmental disturbances including water development and pollution, terrestrial habitat destruction, air pollution, overfishing and exotic species introductions. Here, I employ two different levels of analysis to investigate the mechanisms driving fish species. First, I use the extremely rapid genetic introgression between Cyprinodon pecosensis and C. variegatus as a case study to investigate the role of mating behavior in promoting interspecific genetic fusion. I found that (1) C. pecosensis females prefer heterospecific males over conspecific males and (2) F1 hybrid males are superior to males of both parental species in competition for access to females. These results challenge common assumptions about hybridization and the formation of hybrid zones. Second, in a separate study of biogeographic patterns in North American freshwater fish, I ask whether endangered species display common and predictable patterns in body size and range size. The results reveal that (1) freshwater fish species have small geographic ranges compared to terrestrial species, (2) fish with small geographic ranges relative to their body size experience a high risk of endangerment, and (3) speciation rates of small-bodied fishes are probably greater than those of large-bodied species. The data suggest minimum preserve sizes for freshwater fishes and may identify at-risk species before they are officially recognized as endangered. Mechanisms that promote extinction are intimately related to those that produce speciation; thus, these investigations of extinction provide insight into the processes of freshwater fish speciation.