Dragline silk reveals female developmental stage and mediates male vibratory courtship in the nuptial gift‐giving spider Pisaura mirabilis

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AbstractMale mate choice likely occurs when costs are associated with courtship or mating. For example, when males produce continuous vibrational signals, provide nutritious nuptial gifts, or are likely killed during mating, they should assess female developmental and reproductive state. Substrate‐borne vibratory courtship signals are very common in spiders serving species recognition, suppressing the female's aggression towards the male, or signalling individual quality. Males of the nursery web spider, Pisaura mirabilis, usually offer a prey item wrapped in silk as a nuptial gift to the female; the gift is commonly produced prior to female contact. When touching dragline silk deposited by a female, males tremulate their opisthosoma presumably reacting to chemical cues. Courtship energy expenditure and resource transfer should select for selective male mating decisions in this species. We hypothesized that male P. mirabilis differentiate between developmental stages of the female (sub‐adult vs. adult). Differential courtship towards virgin and mated females was not expected since females forage for nuptial gifts and might continuously signal receptivity. To test this, vibrational courtship signals of male spiders towards draglines of sub‐adult, adult unmated and mated females were recorded with a Laser Doppler Vibrometer. We found that males were less likely to perform vibrational courtship and produced less pulses when contacting silk of sub‐adult females, compared to silk produced by adult females, while their reaction towards silk of unmated and mated adult females did not differ. Reduced courtship in response to sub‐adult female silk seems beneficial since it reduces energy expenditure in the face of a not yet reproductive female. When vibratory courtship occurred, the temporal patterns and dominant frequencies of the males' vibratory signals were similar, regardless of female developmental stage or mating status. Such stable patterns suggest a role in species recognition already at a distance without direct physical contact and in reducing female aggression.