Cryptic Genetic Diversity in the Coastal Isopod Alloniscus oahuensis from the Pacific Ocean

The isopod sub-order Oniscidea includes over 3,700 species and is known to occur in all terrestrial environments, except those at extreme elevations and polar latitudes. Current estimates of the biodiversity of the Oniscidea may be underestimates, as recent molecular studies have uncovered high levels of cryptic diversity in several taxa in the sub-order. High levels of cryptic diversity have been found in coastal species, species from remote and isolated regions, and species with complex taxonomic histories. Alloniscus oahuensis is a good candidate to harbor cryptic diversity, as it is a coastal isopod species with a geographic range that spans several remote and isolated archipelagos in the Pacific Ocean and has a complex taxonomic history. In this study, we used sequences for three mitochondrial genes and one nuclear gene to determine whether A. oahuensis harbors highly divergent lineages that may represent cryptic species. By characterizing 60+ A. oahuensis individuals from 17 localities from various Pacific Ocean archipelagos, we uncovered two deeply divergent lineages with disjunct distributions. The levels of genetic divergence observed amongst the two lineages match or exceed those reported across other cryptic species in the Oniscidea, suggesting that A. oahuensis may represent a cryptic species complex in need of a taxonomic revision. The extremely low lineage diversities within A. oahuensis indicate that the lineages may have spread across the Pacific Ocean recently, potentially due to anthropogenic activity.