Pollution-, temperature- and predator-induced responses in phenotypically plastic gastropod shell traits

Phenotypically plastic traits adopt different appearances in different environments. Researchers routinely investigate environmental variables such as humidity and temperature as influential factors, but predation also can influence phenotype. Gastropods include well-known examples where predation, even if only perceived, can produce shell morphology changes. We conducted a quantitative descriptive study to investigate how apple snail (Pomacea bridgesii) shells changed in response to red-clawed crab (Perisesarma bidens) predator presence when snails were forced to cope with increased pollution levels in water from an industrialised bay in Lake Ontario (Hamilton Harbour, Ontario, Canada). Compared to snails in unpolluted predator-free water, snails in unpolluted predator-containing water grew large thick shells with small apertures; shape differences were produced with relatively tightly coiled, elongated shell apertures. Snails in highly polluted predator-containing water produced thick shells that, contrastingly, changed from relatively short and wide to relatively long and narrow during growth. Antipredator responses that are evoked by waterborne chemical signals thus can be altered by environmental pollutants.