Genetic differentiation in the genus Uroconger in the Indo-Pacific region

Only a few species of congrid eels of the genus Uroconger (Congridae) have been described worldwide, but between these species each of the adult and larval morphologies are very similar. U. lepturus is the only species currently recognized in the Indo-Pacific, however, previous morphological counts of the total myomeres of Uroconger leptocephali suggest that more than 1 spe- cies may occur in this region. In this study, 1222 sites of the mitochondrial 16S rRNA gene were deter- mined from 54 Uroconger leptocephali and one adult U. lepturus collected from 2 different regions of the Indo-Pacific to examine their genetic differentiations. The neighbor-joining tree based on Kimura's 2-parameter distances showed 4 major groups among the specimens examined, including one with the U. lepturus adult. The average inter-group genetic distances were 0.0348 to 0.0648, almost 20 times greater than the intra-group distances (0.0028 to 0.0036), and the former were larger than the distances between species in some other eels, such as those of the genera Conger and Anguilla. No clear geographic differentiation was found, but a highly significant difference was found between the 2 closest sister Groups A and B (FST = 0.90062, p < 0.05). However, the key char- acters of both the total number of myomeres and the position of the last vertical blood vessel over- lapped among the genetic groups. These findings suggest the possibility of the presence of cryptic lineages within the genus Uroconger in the Indo-Pacific region.