The energetics of reproduction and parental care in the terrestrial isopod Porcellio laevis

Parental care is a behavioral strategy that contributes to increased fitness of progeny. Among terrestrial arthropods, many isopods provide extensive parental care. Few studies have quantified the underlying cost of parental care in terms of energy. We used the terrestrial woodlouse Porcellio laevis (Latreille) as a study model to examine how energetic acquisition and expenditure in females is affected during the incubation period and how parental care affects energy balance in this species. We determined the basic reproductive biology (i.e. fecundity, reproductive output, egg volume, egg loss), energy expenditure (i.e. metabolic rate), and energy acquisition (i.e. food consumption, digestibility) of ovigerous females in different stages of embryonic development. Non-ovigerous females were used as the control group. Our results show that P. laevis displays variability in life-history traits compared with populations from other zones around the world. Ovigerous females exhibited a lower ingestion rate and lower digestibility than control females, thus indicating a lower capacity for energy acquisition. Furthermore, energy expenditure was higher in ovigerous females when compared to non-ovigerous females. In particular, females in early embryonic development stored 5.1-fold less daily energy than females without eggs. The results presented here show that the parental care provided by female P. laevis is energetically costly. Overall, our work brings us much closer to understanding the proximate mechanisms of the costs of parental care in terrestrial isopods. Both proximal mechanisms and consequences of providing care on future reproduction, should be considered in explaining the evolution of parental care.