Mutual benefit from exploitation of female foraging motivation may account for the early evolution of gifts in spiders

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Male exploitation of female sensory or motivational biases has been proposed to account for the early evolution of nuptial gift-giving behaviour. The hypothesis is supported if females of a species positioned early in a clade respond positively to sexual signals from males of more recent species in the clade, and if these signals are not included in the courtship repertoire of its conspecific males. We tested whether such a scenario may apply to the evolution of gift-giving behaviour in the spider family Pisauridae. Presumably, the Canarian endemic Cladycnis insignis diverged on an early branch from the clade that includes the well-known nuptial gift-giving species Pisaura mirabilis. We first showed that the natural courtship and mating in C. insignis does not include gift-giving behaviour. Second, by staging female C. insignis with gift-carrying males of P. mirabilis, we found that these females accepted the gift and allowed the males to attempt mating. The duration of heterospecific ‘matings’ was much longer than conspecific matings (45–50 min versus ca. 1 min). Thus, there is scope for exploitation of the females' foraging motivation through a behavioural switch from courting without a prey gift to courting with a prey gift. Such a switch would initially have brought huge fitness benefits to these males in terms of greatly increased mating duration (advantage in sperm competition) and protection against aggressive females (shield effect), and also a benefit to the females from increased food supply.