Dimorphism And Speciation In The Hawaiian Freshwater Goby Genus Lentipes

Abstract

The Hawaiian freshwater goby genus Lentipes is presently represented by two endemic species, L. concolor (Gill) and L. seminudus Gunther. The two species were investigated to define and compare their respective external and internal morphology. Ninety-eight specimens of Lentipes were gathered over a period of 11 years from 7 stream sites. Electrofishing was employed to capture these specimens. Examination of these two closely related species showed dissimilarities in scalation, dentition, coloration, head shape and dorsal fin spacing. The results from determination of sex showed all L. concolor to be male and all L. seminudus to be female. This evidence led to the hypothesis that the genus Lentipes is actually represented by only one species, L. concolor. This was substantiated by the findings of the investigation on the internal morphology. Employing an alizarin staining technique using trypsin and 2% KOH, the fin ray arrangement, the vertebrae, the caudal skeleton, the suspensorium, the pectoral and pelvic girdles, the hyoid bar and the gill arches and gill rakers were found invariable within the species but comparatively different when contrasted against Sicydium stimpsoni, another endemic freshwater goby that coinhabits the streams with Lentipes. In addition, certain anatomical features were found manifest in the Lentipes food habits. Its omnivorous food habits are also influenced by size (age) and environment.