Sperm limitation erases fecundity advantages of large female size in an extremely size-dimorphic spider

Fecundity selection is widely invoked to explain female-biased sexual size-dimorphism (SSD), yet tests based on lifetime reproductive output remain scarce. We quantified lifetime fecundity and age-dependent reproduction in the size-dimorphic spider Nephilingis cruentata , in which mating plugs restrict females to sperm from one/two copulations. We found no support for ongoing fecundity selection. Female body mass was positively associated with mean mass of viable egg-sacs but negatively with their number, so that total viable egg-sac mass did not increase with body size. Furthermore, maternal size effects on offspring survival were sex-specific: sons of larger females less likely reached maturity, whereas daughters were unaffected. Reproductive trajectories featured production of several viable egg-sacs followed by a terminal phase of non-viable egg-sacs. This pattern, and a decline in egg-sac viability with time since mating, support sperm depletion/deterioration as the primary constraint on fecundity, with weak evidence for reproductive senescence and none for adaptive restraint or terminal investment. Females that copulated twice showed no fecundity advantage but had shorter lifespans. We show that larger females do not achieve higher lifetime reproductive success and that sperm limitation may erase fecundity advantages of large female, questioning the generality of fecundity selection as a driver of female-biased SSD.