Temporal and geographical genetic variation in the amphipod Melita plumulosa (Crustacea: Melitidae): Link of a localized change in haplotype frequencies to a chemical spill

Genetic Diversity and Population Structure Analysis of Three Deep-Sea Amphipod Species from Geographically Isolated Hadal Trenches in the Pacific Ocean

Amphipods of the superfamily Lysianassoidea that inhabit the hadal zone ( > 6000 m) have large bathymetric ranges and play a key role in deep ocean ecosystems. The endemism of these amphipod species makes them a good model for investigating potent natural selection and restricted dispersal in deep ocean trenches. Here, we describe genetic diversity and intraspecific population differentiation among three amphipod species from four Pacific trenches based on a mtDNA concatenated dataset (CO Ι and 16S rRNA genes) from 150 amphipod individuals. All amphipod populations had low genetic diversity, as indicated by haplotype and nucleotide diversity values. Population geographic relationship analysis of two Alicella gigantea populations revealed no genetic differentiation between these two localities (pairwise genetic differentiation coefficient = 0.00032, gene flow = 784.58), and the major variation (99.97%) was derived from variation within the populations. Historical demographic events were investigated using Tajima's D and Fu's F neutrality tests and analysis of mismatch distribution. Consistent results provided strong evidence to support the premise that demographic expansion occurred only for the Mariana population of Hirondellea gigas, possibly within the last 2.1-3.4 million years. These findings suggest that the formation of amphipod population structure might be the result of multiple factors including high hydrostatic pressure, food distribution, trench topographic forcing and potential ecological interactions.

Differential survival and reproductive performance across three mitochondrial lineages in Melita plumulosa following naphthalene exposure

Populations subject to anthropogenic contaminants often display altered patterns of genetic variation, including decreased genetic variability. Selective pressures of contaminant exposure are also reflected in differential tolerance between genotypes. An industrial chemical spill in a major eastern Australian waterway in July 2006 resulted in altered patterns of genetic variability in a nearby population of the amphipod, Melita plumulosa for up to one year post-spill, despite the site being declared clean after 48 h. Here, we investigate the toxicant response of three mitochondrial lines naturally occurring at the impacted site by comparing survivorship and life-history trait variables following naphthalene exposure. Overall, M. plumulosa demonstrated differential survivorship between mitochondrial lines under exposure to high concentrations of naphthalene. In addition, we identified differential fecundity and frequencies of gravidity in female amphipods between the mitochondrial haplotypes examined. These findings suggest that the patterns of genetic variability previously identified may be linked with differential tolerance and/or reproductive performance between mitochondrial lineages.

Sharp decrease of genetic variation in two Spanish localities of razor clam Ensis siliqua: natural fluctuation or Prestige oil spill effects?

Pollution is one of the main concerns in marine ecosystems nowadays. Environmental anthropogenic-mediated toxicants may affect genetic diversity both at the individual and ecosystem levels and may also alter the genetic structure of populations. This study examined the temporal pattern of genetic diversity among populations of the benthic bivalve Ensis siliqua in two locations of Galicia, following the Prestige oil spillage. On November 13, 2002 the oil tanker Prestige sank at 240 km from Galician coast and 63,000 tonnes of heavy fuel were released to the marine environment. E. siliqua samples were sampled between 2001 and 2006. Genetic variation was assessed by means of Random Amplification of Polymorphic DNA (RAPD). A significant decrease in genetic diversity was observed for the 2006 samples. Nei's genetic distance, fixation index (PhiPT), and PCA values also supported differences in the 2006 samples. We hypothesize that the temporal genetic variation observed in E. siliqua populations is due to a strong effect of genetic drift caused by a reduction in population size and that the indirect effects of the Prestige spill possibly caused this reduction.