Incongruence between molecular and morphological characters in the southern king crabs Lithodes santolla and Lithodes confundens (Decapoda: Anomura)

The use of genetic tools has a relevant role in fishery resource management and conservation, for example, when used in species delimitation. Morphological variation can occur as an adaptative or plastic response to environmental variation, and therefore, be mistakenly used as a criterion to delimit species. Particularly, Lithodes santolla and Lihodes confundens, two commercially important lithodid species from sub-Antarctic South America, are mainly differentiated by the number and size of spines on the carapace and pereiopods. However, variability in the size of spines of L. santolla has been reported. We evaluated whether these two morphospecies constitute reciprocally monophyletic clades at the molecular level using mitochondrial markers, and performed a detailed morphological analysis of the carapace to search for correspondence between genetic and morphological differences. The Bayesian phylogenetic reconstruction showed that L. santolla and L. confundens belong to two sister clades. However, individuals identified as L. santolla and L. confundens did not resolve as reciprocally monophyletic groups. Instead, one clade was formed by individuals belonging to both morphospecies and was widely distributed, while the other one was exclusively formed by L. santolla, and its members were only found near Puerto Montt and in the Beagle Channel. No morphological characters were found on the carapace that could differentiate individuals belonging to each genetic clade. Either if the two genetic clades constitute species or remnants of two species that are merging through introgression, they represent two evolutionary significant lineages, and measures should be taken to preserve both. Our study suggests the need to revise the use of the number of spines as a relevant taxonomic character in the taxonomy of Lithodes, and to implement molecular genetic methods to control fisheries.