LACK OF DEVELOPMENT OF POLLUTANT-RESISTANCE OR GENETIC DIFFERENTIATION IN DARTER GOBIES (GOBIONELLUS-BOLEOSOMA) INHABITING A PRODUCED-WATERDISCHARGE SITE

Physiological acclimation, genetic adaptation and genetic differentiat ion were examined in darter gobies (Gobionellus boleosoma) inhabiting a coastal marsh with a long history of PAH contamination. No acclimati on was detected; a 2-week pre-exposure at the polluted site resulted i n a decreased rather than an increased resistance in a subsequent labo ratory exposure to polluted sediment. Similarly, fish collected from s ires with elevated sediment PAH levels did not exhibit an increased re sistance in bioassays with polluted sediment, confirming the lack of a cclimation and indicating a lack of adaptation to the pollutants. No d ifferences were detected in frequencies of allozyme genotypes when com paring gobies from the polluted area to those from a nearby control si te, and overall levels of heterozygosity were similar in the two popul ations. While lack of UV-induced toxicity in the laboratory exposures could have played a role, at least four other factors may explain the apparent lack of adaptive responses and genetic differences. First, bi oavailability, of the contaminants to the darter goby could have been low, though other evidence contradicts this. Second, the contaminated marsh contains a large number of different chemicals and acclimation, adaptation and genetic differentiation are expected to be less likely when more contaminants are involved. Third, the hydrocarbon distributi on at the contaminated marsh is very patchy, such that fish may avoid exposure to the highly-contaminated sediment. Fourth, gene flow may be sufficiently high in this mobile species to prevent local adaptation. (C) 1997 Elsevier Science Ltd.