Ovotestis (intersex) and raised plasma vitellogenin in male fish are widely employed biomarkers of estrogen contamination in the aquatic environment. In the present study, these biomarkers were used to determine whether Irish rivers contain estrogenic chemicals at levels capable of affecting the reproductive health and success of exposed fish populations. A number of aquatic ecosystems were investigated (the rivers Liffey, Lee, and Bandon and the Killarney lakes). A survey of male wild brown trout (Salmo trutta) was carried out to assess the incidence of endocrine disruption in the feral fish population; no evidence of intersex was found in any of the wild fish sampled. Raised plasma vitellogenin was detected, however, in the wild brown trout downstream of a major municipal wastewater treatment plant on the river Liffey.
Microsatellite DNA loci, when used in population genetic studies, are usually assumed to be neutral (unaffected by natural selection, either directly or as a result of tight linkage), but this assumption is rarely tested. Here, the assumption of neutrality is examined using established methods, principally that based on the expected relationship between F ST and heterozygosity, at 12 putative neutral microsatellite loci utilised in a study of Atlantic herring Clupea harengus in the north east Atlantic (west of Great Britain and around Ireland) and in the Baltic Sea. All but two of these loci demonstrate relationships that suggest that they may be regarded as neutral genetic markers. Of the other two loci, however, one shows a relationship suggestive of the action of directional selection and the other of balancing natural selection, though other locusspecific effects may operate. Thus, the latter two loci may provide inaccurate inference if used in phylogeographic studies and also demonstrate the danger of assuming neutrality at all microsatellite loci without explicit testing. However, such loci, particularly those affected by directional as opposed to balancing selection, may be of great use in stock discrimination studies, and selected loci in general, have considerably potential in studies of adaptation.
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