Melita plumulosa as a bioindicator of anthropogenic contamination in estuarine environments

Abstract

Since Charles Darwin proposed the theory of evolution by natural selection, efforts have been made to understand the interactions between genotypes and environmental selective forces. Currently, the potential effect of anthropogenic activities as a selective force has come under scrutiny, particularly the effect of contaminants. The overall aim of this thesis is to determine whether anthropogenic contaminants are a selective force. Specifically, the goal is to determine the relationship between genotypes and contaminant exposure response in the model bioindicator species Melita plumulosa. Bioindicators are organisms that demonstrate sensitivity to the presence of environmental stressors, and are employed as detectors of the presence of contaminants. A classic example is the coal miners canary, alerting miners to the build-up of toxic fumes in mineshafts. The key advantage of bioindicators is that they provide a biologically relevant indication of the effects of contaminants. Traditional endpoints of biomonitoring involve organismal and life-history trait measurements, such as mortality and developmental differences. In this era of molecular biology, interest is also being invested in understanding the effects of contaminant exposure at the genetic level. In this thesis, the amphipod M. plumulosa is employed as the model due to its sensitivity to a range of anthropogenic contaminants. This amphipod is broadly distributed across a range of environmental conditions, is easily sampled and cultured, and shows inter-population genetic variability. To determine whether M. plumulosa is an informative bioindicator, patterns of genetic variability in natural populations were investigated temporally and spatially, under both clean and contaminated conditions. Additionally, the contaminant exposure response of naturally occurring genetic variants was also examined. The findings show that the genetic structure of amphipod populations is impacted by contaminant exposure, and differences in tolerance and recovery between different genotypes following exposure were also identified. Populations of M. plumulosa are not, however, homogeneous across its distribution, and show temporal genetic isolation resulting in geographically distinct populations. The major implication for employing M. plumulosa as a genetic bioindicator is that sampling strategies need to consider the genetic subdivision that exists within this species when selecting appropriate test and reference populations.