Morphological and molecular variation in Rhinogobius rubromaculatus (Pisces: Gobiidae) in Taiwan

A new color type was discovered in the Linbian River of southern Taiwan while investigating morphological and genetic variations of Rhinogobius rubromaculatus. The technical approaches we used included allozyme starch gel electrophoresis and partial mitochondrial DNA sequence analysis. Specimens from the Linbian River were characterized by smaller body and egg sizes, and indicated a significant negative correlation with temperature. None of the alleles was fixed among the new color type and R. rubromaculatus populations, with an allozyme genetic distance of from 0.001 to 0.078, which greatly differed from those of R. candidianus (0.523-0.687) and 2 other undetermined Rhinogobius species from the Ryukyus, Japan (0.326-0.464). The complete sequences of the cytochrome b gene, tRNA genes, and the control region of mtDNA revealed substitution differences within R. rubromaculatus at 207 base pairs (bp) and among the 3 species at 363 bp. The sequence diversity within the population was from 0.000 to 0.004. Among local populations of R. rubromaculatus, the sequence mean distance diversities were from 0.005 to 0.074, which is smaller than that between R. rubromaculatus and another Rhinogobius species (0.094-0.113). Both markers were congruent in revealing significant differences between samples of R. rubromaculatus (global F_ST = 0.404 for the allozyme and Φ_ST = 0.986 for the mitochondrial DNA data). The molecular trees of R. rubromaculatus constructed based on both allozyme and mtDNA data revealed a closer relationship between central and southern populations than with a northern population. Discrete phenotypes could have been produced by phenotypic plasticity.