Geographic variation among three isolated populations of the hadal amphipod Hirondellea gigas (Crustacea: Amphipoda: Lysianassoidea)

The relative homogeneity and cont~nuity of the deep sea may provide a habitat in which species can maintain widespread, genetically homogeneous populations.This study examines the lysianassoid amphipod Hirondellea gigas (Birstein & Vinogradov 1955) to determine whether populations from spatially-disjunct habitats in the deep sea maintain genetic homogeneity.H. gigas is a scavenger which rapidly responds to and consumes experimental baitfalls at depths of > 10000 m.It appears to be endemic to western Pacific trenches, having been collected only within the Kurile-Kanichatka, Japan, Izu-Bonin, Volcano, Yap, Mariana, Palau, and Philippine Trenches.To estimate the degree of isolation of populations from the last 3 trenches, morphological variation was quantified through a discriminant analysis of surficial morphometric characters.Discriminant classification results were compared to 'null-populations', generated using a bootstrap randomization procedure, to determine the significance of the discrimination.Variation was sufficient to allow 68.4 to 84.5 % of individuals to be correctly reclassified into their population using discriminant functions.Bootstrapped randomizations of the data indicate that the classification success was significantly greater than random.Results indicate that these geographically-isolated trench populations may have reduced levels of gene flow between them, causing them to diverge lnorphologically