Response of terrestrial isopods, Armadillidium vulgare and Porcellio laevis (Isopoda: Oniscidea) to the ant Tetramorium caespitum: morphology, behavior and reproductive success.

摘要

Little is known about the effects of predatory stress on reproduction in terrestrial isopods (Crustacea: Oniscidea). We studied the direct and indirect influences of predatory ant T. caespitum (Hymenoptera: Formicidae) on the behaviour and reproduction of two terrestrial isopods, A. vulgare and P. laevis. A. vulgare females were more cryptic than P. laevis females in both the presence and absence of the ant, but in both species the control animals were more cryptic than the experimental animals exposed to the ant. This likely resulted from increased movement in the presence of the ant. Both species also avoided ventilated enclosures containing the ant, but the control animals not previously exposed to the ant remained significantly further away. P. laevis also remained significantly further from the ant than A. vulgare, suggesting that P. laevis more actively avoids potential predators. This is consistent with morphological differences between the two species: A. vulgare can roll into a sealed ball whereas the morphology of P. laevis permits swift locomotion. Furthermore, mortality rates of P. laevis were greater than A. vulgare when both were directly exposed to the ant in the laboratory, and P. laevis suffered significantly more attacks than A. vulgare under experimental conditions. However, the length of the brooding period in A. vulgare was shorter in the ant-exposed females than in the controls, whereas the experimental and control P. laevis females showed no such difference. This could be an adaptive trade-off for A. vulgare because in the late brooding period the distended marsupium can prevent rolling into a closed ball for protection. The results underscore the relationships between morphology, behaviour and reproductive success..