Does High Adult Mortality Explain Semelparity in the Spider Stegodyphus lineatus (Eresidae)?

Abstract

In life history theory, low adult survival is considered to favour the evolution of semelparity. Low adult survival could result from intrinsically high costs of reproduction or from high mortality due to extrinsic causes such as predation. In a field experiment, we removed females of the spider Stegodyphus lineatus from their young and induced a second breeding event to test these hypotheses. These semelparous spiders normally die after producing a single clutch, while the young are still in the nest. However, females that lose their brood will produce a second clutch. Experimental females that were protected from predation were capable of laying a second clutch and raising the young of two clutches. During the same time, the survival of unprotected females in the field was extremely low due to predation. When females were removed experimentally, growth and survival of first broods were reduced. None the less, a model revealed that only a small increment in adult survival would favour a second breeding attempt. We conclude that high predation pressure resulting in low adult survival selects for a single reproductive event in these spiders.