GEOGRAPHIC-VARIATION AMONG 3 ISOLATED POPULATIONS OF THE HADAL AMPHIPOD HIRONDELLEA GIGAS (CRUSTACEA, AMPHIPODA, LYSIANASSOIDEA)

The relative homogeneity and continuity 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 > 10 000 m. It appears to be endemic to western Pacific trenches, having been collected only within the Kurile-Kamchatka, 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 morphologically.