Agonum decorum (Say) and A. elongatulum (Dejean) are sibling sister species. Discriminant function analysis based on 13 mensural characters was used to ordinate 10 population samples of A. decorum and 7 samples of A. elongatulum . The discriminant function scores on function 1 were analyzed using the simultaneous test procedure UNIVAR algorithm. Results support circumscription of A. elongatulum as a peninsular Floridian species and A. decorum as a wide-ranging species found throughout North America, Mexico, and the Greater Antilles. Morphometric, electrophoretic, and ecological preference data support the hypothesis that A. elongatulum arose as a peripheral isolate of A. decorum , which colonized Florida from an Antillean source during the Pleistocene. Present distributions indicate that this complex represents a case of circular overlap with speciation. Comparison with other carabid taxa shows that 1) the Straits of Florida serve as a potent force delimiting species distributions, 2) speciation in Florida from a southern source is not currently recognized as a general pattern.
Annals of The Entomological Society of America