Alternate Title

Character Displacement and Coexistence in Two Poeciliid Fishes of the Genus Poecilia (Mollienesia) from Hispaniola


Character displacement in animals, particularly in fishes, is reviewed and the new approach of Grant (1975) is used in this study to demonstrate character displacement in P. hispaniolana and P. dominicensis, two closely related and partly sympatric species of mollies endemic to Hispaniola. Background information is given on the probable origin, evolution, attainment of present partial sympatry and length of coexistence of the two species, as indicated by their present distribution and the paleogeography of Hispaniola. It is hypothesized that a common ancestor to both species existed on the island prior to the Miocene about 20 million years ago. It is also hypothesized that the ancestral population was split during the Miocene-Pliocene for a period of about 18 million years, that the two species evolved during that time, and that the barrier to their dispersal was eliminated in late Pliocene about two million years ago. It is assumed that during that last period the present distribution and partial sympatry were attained, and that the two species have coexisted twice as long in the localities where character displacement shows greater magnitude. Analyses of meristics, morphometries, and reproduction are given to demonstrate character displacement in fin ray, scale, and gill-raker number, and in body size and fecundity. Divergent, convergent, and parallel displacement were found to occur as well as a change of reproductive strategy for P. dominicensis in sympatry. Causes and effects of displacement in the two species are discussed and later summarized in combination with tentative conclusions.