Differential survival of three mitochondrial lineages of a marine benthic copepod exposed to a pesticide mixture.

In South Carolina estuaries, the harpacticoid copepod Microarthridion littorale (Poppe 1881) consists of three distinct mitochondrial lineages (liI, liII, and liIII), whose distributions may be partially explained by the presence of toxic contaminants in the sampled habitats. The frequencies of liII and liIII are greatly diminished and sometimes absent in South Carolina contaminated tidal creeks where liI is omnipresent. In this study, representatives of these lineages or haplotype groups were collected from sediments of an estuarine creek containing low to undetectable levels of toxicants and then exposed to a toxic (approximately LC90) aqueous mixture containing an organophosphate (chlorpyrifos) and organochlorine pesticide (DDT, mixed isomers). A comparison was conducted for the frequency of each of the three haplotypes among the survivors of the exposed animals relative to that among the survivors of the control group. The haplotype group with the highest frequency in contaminated SC estuaries (liI) was statistically higher in frequency in survivors of the pesticide-exposed group than in the control group. The two rarer groups (liII and liIII) were less abundant among the survivors of the pesticide-exposed group than the control group. The frequencies of liI, liII, and liIII did not change significantly among the survivors of the control group. The differential survival of the three haplotype groups in the pesticide mixture may be one of the reasons that some haplotype groups are more likely to be found in clean or contaminated tidal creeks on the South Carolina coast.