Mitochondrial DNA and allozyme patterns of Hediste diversicolor (Polychaeta: Nereididae): the importance of small scale genetic structuring

Abstract

A hierarchical sampling design was used to describe scales of genetic structuring of Hediste diversicolor (Polychaeta: Nereididae) along the North Adriatic coast of Italy and investigate possible relationships with patterns of heavy metal contamination. Analyses of a fragment of the mitochondrial cytochrome oxidase 1 (COI) gene yielded 10 different haplotypes showing that the genetic structuring at this locus is more complex than previously hypothesised. Both COI and allozyme data suggest that most of the total genetic variance is due to genetic differentiation among (1) sites within estuaries and (2) individuals within sites. These results suggest that within estuaries H. diversicolor does not form contiguous panmictic populations, but rather is structured in frag- mented populations isolated at small spatial scales. Sediment concentrations of Zn, Cu and Ni in sed- iments were above effects range-low (ERL) guideline values at several of the investigated sites. Yet, we did not observe any relationship between heavy metal concentrations of metals and either the estimators of genetic diversity in H. diversicolor or the distribution of Aldolase genotypes expected from previous toxicity tests. These results suggest that, within North Adriatic estuaries, populations of H. diversicolor are structured by chaotic genetic patchiness and that stochastic processes (e.g. genetic drift or sweepstake recruitment) have a major role in promoting small scale genetic struc- turing.