Loss of genetic diversity in harpacticoid copepods as a result of contaminant exposure.

摘要

Measuring genetic diversity in a population can detect a response to environmental change. Environmental change can cause lethal or sublethal effects. If reproductive success decreases in certain females, they are likely to contribute less to the gene pool than other females. Thus, differential reproduction can lead to a loss in genetic diversity. Populations of Harpacticoida (Crustacea: Copepoda) were studied in the field and in the laboratory to determine if chronic exposure to contaminants can decrease genetic diversity. In the field, genetic diversity was estimated in populations of five species of harpacticoids around offshore oil platforms with a known contaminant gradient on the Gulf of Mexico outer continental shelf. In addition to genetic diversity, a spectrum of community and population variables was measured, such as species abundance and reproductive effort, in order to provide phenotypic evidence of natural selection that could account for lower genetic diversity. The laboratory component of this research involved exposing successive generations of harpacticoids to contaminants and measuring genetic diversity, adult mortality and larval production. Genetic diversity was estimated by comparing restriction fragment length polymorphisms of mitochondrial DNA generated from the polymerase chain reaction of individual copepods. Around the oil platforms, populations nearer the platforms had lower genetic diversity than populations of the same species further away. Reduced abundance and possible lower reproduction were also found in populations near the platform, which could account for lower genetic diversity. In the laboratory, hydrocarbons led to a decrease in adult survivorship, number of surviving larvae, and genetic diversity of the entire population. Therefore, not only was lower genetic diversity observed near platforms, but a reproductive mechanism was observed in the field that could account for the lower diversity. Furthermore, the loss of genetic diversity and reproductive success could be reproduced in a controlled experiment. The conclusion of this dissertation is that contaminants may lead to a decrease in population genetic diversity through differential reproduction. It is possible that in addition to anthropogenic contamination, a variety of disturbance events could also lead to lower genetic diversity. This research may help scientists to understand how disturbance manifests changes on communities. Measuring genetic diversity may provide a powerful tool to detect subtle community change.