Detection of latent heritable genetic damage in populations of aquatic snails, Lymnaea stagnalis, exposed in situ to genotoxic pollution

We hypothesized that populations exposed to chronic levels of genotoxins for many generations in situ will accumulate latent heritable genetic damage leading to increases in mutational load and decreased population fitness. Common pulmonate snails (Lymnaea stagnalis) were collected from three sites that differed in pollution level [Manitoulin Island (reference), Beauharnois (moderate pollution), and Varennes (highly polluted)]. These organisms have a rapid generation time and are capable of self-fertilization. Fitness indicators were clutch size, survival (hatching to day 30) and growth (length from hatching to day 90). Recessive deleterious mutations that have accumulated through time are masked as snails preferentially outcrossed, but are expressed when snails self-fertilize. Results obtained by comparing fitness components of snails derived from selfing and outcrossing experiments showed that in sites with higher levels of pollution inbreeding depression increased for clutch size and survival. Results for growth rate were similar to those for clutch size and survival in the two least polluted sites, but not for the most polluted site, due possibly to biased mortality of smaller snails at this site. After correction for size biased mortality, the growth estimates showed patterns similar for the two polluted sites when compared to the reference site. This study suggests that long-term in situ exposure to genotoxic pollution may effect population fitness due to the accumulation of latent heritable genetic damage