Systematics of two Fundulus species complexes

Fundulus heteroclitus and Fundulus majalis are brackish water killifish which occur abundantly from southern Canada to northeastern Florida. Fundulus grandis which is morphologically similar to F. heteroclitus, and Fundulus similis, which is morphologically similar to F. majalis, occur along the Gulf of Mexico and along the east coast of Florida. This study attempted to determined the evolutionary relationships among these killifish by examination of variation in morphology, isoenzyme and in mitochondrial DNA sequence variation. Stepwise discriminant analyses using morphological variables were successful in distinguishing heteroclitus and F. grandis from F. majalis. and F. similis, electrophoretic variables were able to distinguish F. heteroclitus from F. grandis and F. majalis from F. similis, while mtDNA fragment variables were successful in distinguishing all four taxons. Electrophoresis demonstrated that heterOGlit-US and F. majalis differ by 48.35 + 24.94 percent of their codons, F. grandis and F. heteroclitus differed by 7.30 + 8.70 percent of their codons, while F. similis and F. majalis differed by 6.93 + 8.47 percent. The net mtDNA nucleotide diversity estimate between F. heteroclitus and Ej. grandis was 4.68 percent, while F. similis and F. maialis differed by 4.32 percent of their nucleotides. It appears that grandis and H1. similis may be subspecies of H1. heteroclitus and F. majalis, respectively, with F. heteroclitus and F. majalis having diverged approximately 14.51 Myr ago and F. grandis and F. similis having evolved from F. heteroclitus and F. majalis, respectively, approximately 2 Myr ago. Among these killifish, morphological variables are better suited for studying at the specific level, electrophoretic variables at the specific and subspecific level, while mtDNA fragment variables are better suited for studying at the subspecific and populational level.