Who is moving where? Molecular evidence reveals patterns of range shift in the acorn barnacle Hexechamaesipho pilsbryi in Asia

Abstract

Global warming is predicted to cause a shift in the geographic ranges of marine organisms. Such shifts have already been observed with the polar retreat of temperate species and northern expansion of more tropical species. Hexechamaesipho pilsbryi is an intertidal acorn barnacle first identified by Hiro in 1936. Hiro reported the southern limit of H. pilsbryi as southern Kyushu Island, Japan. However, H. pilsbryi has recently been recorded in Taiwan as well as Maritime Southeast Asia -suggesting a recent southward range extension into tropical waters that would be contrary to general predictions. To test this hypothesis, we compared the mitochondrial COI gene sequences of 200 individuals sampled from two sites in the previously reported range, and nine sites in the newly reported localities. Two highly diverged lineages were found: a northern lineage, predominantly in Japan and Okinawa, and a southern lineage, primarily in Taiwan and Southeast Asia. The unimodal mismatch distribution and the star-like shaped haplotype network suggest recent demographic expansion in the southern lineage. The molecular data, therefore, rejected the southward extension hypothesis, and instead supported an alternative scenario of a northward range shift of the southern lineage from Southeast Asia to Taiwan. Our results reveal that range shifts in cryptic or poorly studied marine taxa may confound the identification of species' distributions and consequent interpretation of possible changes in ranges and sources of invasion. The application of molecular data to identify and monitor such changes can address these problems and permits a rapid and sensitive confirmation of such events.