Endemism and evolution in the littoral woodlouse Halophiloscia Verhoeff, 1908 (Crustacea, Isopoda, Oniscidea) from the Canary Islands: implications for conservation policies

The woodlouse genus Halophiloscia Verhoeff, 1908 includes littoral halophilous species distributed along the coasts of the Mediterranean Sea, the Atlantic coasts of Europe and northern Africa. The species Halophiloscia couchii has been introduced to the Americas, Hawaii and Australia. The Canary Islands harbour four species, two of which are included in catalogues of endangered species. One mitochondrial and one nuclear gene sequenced from over 100 specimens, including outgroups, were analysed to infer the colonisation and diversification processes of Halophiloscia in the Canary Islands and shed light on their conservation status. The Canary Islands were independently colonised by three distinct Halophiloscia lineages: (i) the endemic species H. rodriguezi, collected in several western Canary Islands, and the troglobiomorphic H. microphthalma from La Palma, (ii) the endemic H. canariensis, found throughout the eastern Canaries, and (iii) the cosmopolitan H. couchii, present on Gran Canaria and Tenerife.Halophiloscia microphthalma is not sister to the extant epigean Halophiloscia species present on the same island, which together with the low levels of genetic variability detected in the species may warrant a higher conservation status than presently given. The mitochondrial marker revealed a fine-scale phylogeographic structure in H. canariensis, and rejected recent sharp declines in its population size, which in addition to its widespread distribution challenge its consideration as an endangered species. The presence of H. couchii in the archipelago is interpreted as a recent introduction. Although no evidence of introgression was detected, more thorough sampling and monitoring of introduced populations are recommended to discard either hybridisation or competitive displacement of native species.