Reproductive Allocation in the Terrestrial Isopods Porcellio scaber and Oniscus asellus in a Metal-Polluted Environment

Abstract

1. Terrestrial isopods (woodlice) exposed to toxic concentrations of metals can suffer early mortality and reduced body size, suggesting that the cost of metal detoxification causes trade-offs in resource allocation. This study investigates whether woodlice from populations that persist in sites heavily polluted with metals have a level of reproductive success different from that of woodlice from less polluted sites. 2. Two species of woodlice, Porcellio scaber Latreille and Oniscus asellus L., were collected from eight sites at different distances from an industrial smelting works at Avonmouth, England. The sites represented a continuum of concentrations of Zn, Cd, Pb and Cu in the woodlice, from background concentrations to a grossly contaminated site close to the smelter. Gravid females were reared in the laboratory until the release of the brood. 3. For both species there was no significant difference among sites in the number of live offspring per adult mass, the degree of brood-pouch mortality in affected adults, or the reproductive allocation. 4. Significant differences were found among sites in the proportion of adults experiencing some degree of brood-pouch mortality, and in the mean dry mass of offspring per adult mass. However, these differences could not be attributed to contamination by metals. 5. Females of both species that survive to reproduce in the most polluted sites around the smelter show no evidence of detrimental effects on reproduction. However, high concentrations of Zn at these sites causes early mortality of woodlice and therefore reduces the size of the breeding population.