GENETIC DIVERSITY OF THE CADDO MADTOM, NOTURUS TAYLORI, WITH COMMENTS ON FACTORS THAT PROMOTE GENETIC DIVERGENCE IN FISHES ENDEMIC TO THE OUACHITA HIGHLANDS

摘要

We studied allozyme diversity of the endemic Caddo madtom, Noturus taylori, over its small geographic range (<2,000 km~2) in the Ouachita Highlands of southwestern Arkansas. This small catfish species exhibited marked genetic divergence among rivers and low levels of genetic variation within sampling localities. The more widely distributed brindled madtom, Noturus miurus, exhibited nearly identical patterns of genetic divergence among river localities separated by similar geographic distance, and similarly low levels of variation within localities were observed. We compared genetic results from madtoms to those obtained in a previous study of 2 co-distributed, endemic darter species and found that habitat specialists, especially those restricted toheadwaters, are likely to show high levels of genetic divergence at relatively small spatial scales. Comparative genetic and ecological study of these endemic species suggests that an interaction of extrinsic (larger rivers with higher silt loads) and intrinsic (habitat preferences) barriers to fish movement contributes to population structure in the Ouachita Highlands. Species that specialize on headwater habitats might be particularly vulnerable to local extirpation because natural recol-onization from adjacent rivers is unlikely.