MtDNA sequencing was used to assess the phylogeographic structure of four species of Hawaiian freshwater fishes: Lentipes concolor, Stenogobius hawaiiensis, Sicyopterus stimpsoni, and Awaous guamensis. Samples of each species were collected from streams on the northeast side of Kauai, Maul, Molokai, Oahu, and Hawaii. We sequenced segments from both coding and noncoding regions (638-1391 bp) in each species. Sequence analysis uncovered genetic variability In these fishes but no evidence of strong geographic structure among island populations. This result is most readily explained by the fishes' larval marine life stage (amphidromy), which likely facilitates germ flow among island populations. By constraining genetic differentiation among populations, amphidromy may impede speciation in these fishes, possibly explaining why the Hawaiian freshwater fish fauna is depauperate compared to other species-rich Hawaiian faunas. It may also provide them with a kind of evolutionary flexibility atypical of other, more isolated island faunas and allow natural restocking to occur in streams that have been restored to suitable conditions. Comparisons of restriction site and sequence data suggested similar population genetic conclusions for all species except S. stimpsoni, for which the restriction site data is questioned.
Bibliographical noteFunding Information:
From the J. F. Bell Museum, 100 Ecology Bldg., 1987 Upper Buford Rd., University of Minnesota, St. Paul, MN 55108 (Chubb and Zink), and the Museum of Natural Science and Department of Zoology and Physiology, Louisiana State University, Baton Rouge, Louisiana (Fitzsimons). A. Chubb is currently at the Museum of Vertebrate Zoology, University of California, Berkeley, California. We thank R. Nishimoto for significant contributions throughout this project. We thank S. Hau, W. Puleloa, W. Ishikawa, D. Kuamo’o, and M. Yamamoto for assistance in collecting specimens, D. Dittmann and R. Blackwell for their technical support in the lab, and L. Park for sharing primers. Work was funded by LEQSF #86-LBR-(048)-08 from the Louisiana Board of Regents and NSF BSR-8906621 to R.M.Z., and a grant from the Division of Aquatic Resources, Department of Land and Natural Resources, State of Hawaii (Dingell–Johnson/ Wallop–Breaux Sport Fish Restoration Project F-14-R-18). We appreciate the helpful comments made by B. Vondracek, R. Holzenthal, E. Bermingham, R. Wayne, and an anonymous reviewer on the manuscript. Address correspondence to R. M. Zink at the address above or e-mail email@example.com.