Does coastal Philonthus nudus Sharp (Coleoptera: Staphylinidae: Staphylininae) comprise cryptic species?

Abstract

The taxonomy of the marine littoral Philonthus nudus Sharp is reviewed to investigate whether it comprises cryptic species. Philonthus nudus is widely distributed along the Pacific coasts of the Northern Hemisphere, from China, Korea, and Japan through Russia (Kuril Islands and Kamchatka) and Canada (British Columbia) to the United States (Washington). A comparative micro-morphological study and molecular analyses based on COI and 28S are presented. The P. nudus specimens from different localities from Korea to Canada and the United States were extremely similar, including the form of the aedeagus. The molecular analyses also support the one-species concept of P. nudus based on morphological characters. The genetic divergence of COI using the uncorrected p-distance among individuals of the species ranged from 0 % to 1.69 % and all tree-building methods suggested that all P. nudus populations comprise a single valid species, with no cryptic species. Philonthus nudus is redescribed with illustrations of diagnostic characters.