Abstract An isolated population of the gill louse Salmincola californiensis (Dana, 1852) infecting native Rio Grande cutthroat trout, Oncorhynchus virginalis virginalis (Girard, 1856), in Whale Creek, Colorado, USA, was recently identified as a putative cryptic species based on its phylogenetic position relative to other populations, comprising a distinct clade that is reciprocally monophyletic to a second clade that included all other S. californiensis individuals examined. We assessed morphological features coupled with DNA barcode sequences to test this hypothesis. Our results reveal only slight morphological and genetic differences between the Whale Creek population and other populations of S. californiensis distributed across the range of the species. In particular, S. californiensis from Whale Creek has slightly fewer mandibular teeth (five) than other North American populations (usually six) and exhibits ∼4.5% genetic distance from other haplotypes of the species. All other morphological characters were indicative of S. californiensis, and the genetic distance is less than the ∼10–19% distances observed between other Salmincola species. These morphological and genetic differences do not justify recognition of the Whale Creek population as a new species, merely as an isolated population that appears to be in the process of diverging.
Houston et al. (Wed,) studied this question.