Cohort dependent life-history traits in a wolf spider (Araneae: Lycosidae) with a bimodal life cycle

Abstract

Life-cycle polymorphism within single populations has been reported in a variety of arthropods including insects and spiders. Most individuals within polymorphic populations overwinter in a species-specific stage, which plays an important role in synchronizing the life cycle within a population. Here, we report the first case of a life-cycle polymorphism in spiders that differs in the overwintering stages between two coexisting cohorts, and test if the variation in timing of these two cohorts (autumn and spring maturing) results in expected differences between key life-history characteristics, namely size at maturity, adult survival and reproductive output. A 3-year mark and recapture study in the floodplain of the Avon River, south-east Australia, allowed the calculation of adult survival and recapture probability (Jolly–Cormack–Seber model) for the two cohorts in three consecutive generations of the riparian wolf spider Venatrix lapidosa (McKay). In the autumn maturing cohort, adult survival was time dependent with high survival rates during the winter months, but there was no difference between sexes. In contrast, survival was constant over time in the spring maturing cohort, but was higher for females than for males. Males and females of the autumn maturing cohort were significantly larger than those of the spring maturing cohort. More adverse conditions in the juvenile development of spring maturing cohort are likely to account for this difference. In addition, earlier maturation and reproduction of females of the spring maturing cohort in comparison to the winter maturing spiders may increase the survival of larger offspring during the upcoming winter. Propensity to oviposit was significantly lower in females of the autumn maturing cohort than in the spring maturing cohort, as spiders of the autumn maturing cohort are exposed to adverse winter conditions before reproduction. The life-cycle control of both cohorts seems to be governed by different mechanisms: diapause control of reproduction through delayed vitellogenesis of the ovaries in the autumn maturing cohort, and diapause control of juvenile development in the spring maturing cohort. Both mechanisms have previously been suggested for wolf spiders but have not been reported for the same species.