Two different mental disc forms in the Tashan cave Garra: different species or ecotypes?

Abstract

In the Tashan Cave barb Garra tashanensis, inhabiting a small cave in south west Iran, two mental disc forms were observed. To assess their phylogenetic relationships, disc-less and disc-bearing individuals were analyzed using mitochondrial cytochrome oxidase subunit I (COI) partial DNA sequences. Both mental disc forms nested within one clade with absolute bootstrap support (BS = 100), and the genetic distances between the disc-bearing and disc-less individuals (0.3-0.7%) was considerably lower than inter-species mtDNA sequence distances reported among members of the genus Garra. Hence, the observed mental disc variation was not inferred to be a taxonomic feature or a consequence of character displacement. Instead, it was inferred as a case of character release to diversify among ecological niches in the limited subterranean habitat, which should be clarified in follow-up ecological and population genetic studies in more detail.