Population genetic structures of two New Zealand corophiid amphipods and the presence of morphologically cryptic species: Implications for the conservation of diversity

Abstract

We evaluated the population genetic structures (allozyme variation) of Chaetocorophium lucas i (Hurley 1954) Karaman 1979 and Paracoro‐phium excavatum (Thomson 1884) Stebbing 1899 (Amphipoda: Crustacea) from the North Island and South Island of New Zealand. Individuals of C. lucasi were found in both freshwater and estuarine habitats, whereas P. excavatum was restricted to estuarine sites. Allele frequencies showed significant inter‐ and intra‐specific differences among populations of both C. lucasi and P. excavatum. C. lucasi appears to be a single species, albeit with considerable genetic differentiation among populations (FSX = 0.51). However, P. excavatum revealed even greater levels of genetic differentiation among populations (FST = 0.81), and may consist of at least three genetically distinct species. Geographic distance, perhaps dictated by prevailing ocean currents and overland dispersal routes, best explained observed patterns of differentiation among populations of both species. From a conservation perspective, the presence of morphologically cryptic species suggests that current taxonomic inventories of aquatic amphipods may be grossly underestimated.