MEPS 277:197-207 (2004)  -  doi:10.3354/meps277197

ABSTRACT: The genetic variability of southern European populations of the marine amphipod Gammarus locusta (L.) was analyzed using randomly amplified polymorphic DNA (PCR-RAPD). We analyzed 4 populations along the Portuguese coast with 10 arbitrary primers, which produced a total of 114 interpretable bands. The average percentage of polymorphism was 77% and the within-population average similarity index was high (0.841). Between-population differentiation was low, as determined by Wright¹s fixation index, F_ST (0.074), analysis of molecular variance (AMOVA) Φ_ST (0.048), and Nei¹s unbiased distances (mean 0.032). These results are consistent with those of previous allozyme analysis, which indicated that G. locusta has low intra- and inter-population genetic variability. Low between-population differentiation indicates that G. locusta has efficient dispersal mechanisms for an organism lacking larval stages and that disperses passively. Despite the low level of genetic differentiation it was still possible to detect some genetic subdivision. The Sado and Alvor populations clustered together consistently in dendograms based on several genetic distances, and AMOVA analysis indicated some level of differentiation between populations located to the north (Aveiro and Foz do Arelho) versus southern populations (Sado and Alvor), albeit this was very low (<1.5%). Analysis of migration patterns suggested that dispersal is unbalanced, occurring primarily from west coast populations to the south coast population of Alvor, with much less reciprocal dispersal. It would be worthwhile inspecting the significance of this unbalanced north-south flow, by determining whether populations located east of Alvor also exibit such unbalanced dispersal relative to west coast populations.

KEY WORDS: Gammarus locusta · Amphipod · Genetic variability · Random amplified polymorphic DNA · Allozymes · Gene flow · Dispersal · Migration