Life history trade-offs imposed by dragline use in two money spiders

Abstract

Trade-offs among life history traits are central to understand the limits of adaptations to stress. In animals, virtually all decisions taken during life are expected to have downstream consequences. To which degree rare, but energy demanding, decisions carry-over to individual performance is rarely studied in arthropods. We used spiders as a model system to test how single investments in silk use –as for dispersal or predator escape- affect individual performance. Silk produced for safe lines and as threads for ballooning is of the strongest kind and energetically costly, especially when resources are limited. We induced dragline spinning in two species of money spider at similar quantities as under natural conditions and tested trade-offs with lifespan and egg sac production under unlimited prey availability and a dietary restriction treatment. We demonstrate strong trade-offs between dragline spinning and survival and fecundity. Survival trade-offs were additive to the ones imposed by the dietary treatment, but a reduction in eggs produced after silk use was only prevalent under conditions where food was deprived during the spider's life. Because draglines are not recycled after their use for dispersal or predator escape, its spinning induces incurs substantial fitness costs in dispersal, especially in environments with prey limitation. Rare but energetically costly decisions related to dispersal or predator escape may thus carry-over to adult performance and explain phenotypic heterogeneity in natural populations.