POLLUTION AS A PROBE OF LIFE-HISTORY ADAPTATION IN ASELLUS-AQUATICUS (ISOPODA)

Habitat classification schemes attempt to predict the types of life-history patterns that should be selected for in particular habitats. Several such schemes have been proposed, all of which are based on habitat characteristics relating to productivity, disturbance and/or biotic interactions. As environmental pollution may impact one or all of these habitat characteristics, it should act as a selection pressure resulting in life-history modification and could therefore be used to test predictions arising from life-history theory. Two populations of the freshwater isopod, Asellus aquaticus (L.), separated by an effluent discharge from a disused coal mine, were studied to investigate whether they had adapted to the pollution by modifying their life history in accordance with the predictions of life-history theory. Using the classification scheme proposed by Sibly and Calow it was predicted that asellids below the discharge should invest less in reproduction and allocate this investment into fewer, larger offspring than asellids at the site above the discharge. Both these predictions were supported by field observations. Laboratory studies indicated that the observed differences in reproductive biology had a genetic basis and were therefore due to adaptation and not acclimation.