Identification and description of hybrids of Fundulus heteroclitus and F. diaphanus (Pisces: Cyprinodontidae) from Porters Lake, Nova Scotia, with evidence for absence of backcrossing

Phenotypic analysis of 2143 killifish (Cyprinodontidae) collected in Porters Lake. Halifax County, Nova Scotia, from May 1971 to September 1972, indicated that 1973 killifish were of two readily distinguishable species, either Fundulus heteroclitus or F. diaphanus, and 170 individuals were an apparent hybrid of the two which was intermediate for the eight morphometric, meristic, and molecular characters analyzed. Character index analysis and consistent electrophoretic patterns of muscle malate dehydrogenase and lactate dehydrogenase suggested that the hybrids, which comprised four age-classes, were invariably F 1 hybrids. There was no indication of backcrossing. Reciprocal interspecific fertility and postlarval viability were confirmed in F 1 laboratory crosses. These forms possessed structural measures, character indices, and electrophoretic patterns that were virtually identical with those of the natural hybrids.