A parental care-mating dilemma? Potential risks for offspring in the Pholcid spider when egg-carrying females accept mating

Abstract

Many species face a trade-off between additional mating opportunities and the offspring benefits (viability, quality) provided by parental care. Female Holocnemus pluchei spiders must abandon their egg-sac, which they otherwise carry with their chelicerae, to copulate. This may involve risks for the offspring, such as predation and fungal infection. We assessed whether (1) males discriminate between egg-carrying females according to the egg development stage, (2) females are influenced by the egg development stage in regard to their proneness to mate, and (3) offspring are less likely to survive, due to high humidity and/or predation, in the absence of egg-carrying females. Apparently, males did not distinguish between females according to the developmental stage of the eggs they carried. However, females were more likely to mate when carrying relatively mature versus immature eggs (14–18 days and 3–6 days post-oviposition, respectively). All egg-sacs hatched successfully when guarded by egg-carrying females because this avoided both fungal infections (at high humidity) and cannibalism by conspecific spiders. Thus, H. pluchei females may face a trade-off between mating and parental care. Further research should clarify why egg-carrying females mate and how females prevent their egg-sacs from being infected by fungi.