Genetic variation for plasticity in physiological and life-history traits among populations of an invasive species, the terrestrial isopod Porcellio laevis

Background: Evolutionary interpretations of life-history as well as physiological patterns require distinction between genotypic variations and environmentally induced phenotypic variation. Problem: We investigate the extent to which variation in life history and metabolism have an environmental or a genetic basis in an invasive species. Methods: We used the widely distributed isopod, Porcellio laevis, as a model. To examine the effects of latitudinal gradients in temperature and photoperiod on life-history and physiological traits, we studied three populations located along a latitudinal gradient. We performed two common garden experiments using 20 families from each population. Treatments were: (1) 12°C, 12/12 h light/dark and (2) 20°C, 14/10 h light/dark. Measurements of metabolic rate and life-history traits were performed on females from the F₁ generation. Conclusions: (1) Differences in life-history and metabolic traits among populations mimic the natural pattern of latitudinal variation in a cold environment, where offspring size and reproductive output increase towards higher latitudes and metabolic rate increases towards lower latitudes. (2) There is genetic variation for plasticity in response to the environment, which may be acted upon by natural selection. (3) Our results support the hypothesis that phenotypic plasticity itself is an adaptive response to environmental heterogeneity.