Male Investment in Nuptial Gifts in Pisaura mirabilis (Clerck, 1757) Differs Between Light Conditions

Sexual signalling is influenced by environmental conditions, but limited focus has been given to the influence of light conditions on mating strategies in spiders. The males of Pisaura mirabilis (Clerck, 1757) produce nuptial gifts by wrapping the dead prey with silk, and female mate choice relies on complex signals involving visual, behavioural, vibratory, and chemical cues. Considering the former, we first examined the natural illumination conditions experienced by Pisaura mirabilis in their natural habitat. Specifically, we compared the light levels of spiders situated on leaves to those found within the denser vegetation where they typically reside. In the laboratory, we manipulated the visual conditions during courtship and mating using white (high visibility) and red (low visibility) light, and we blocked male spinnerets with dental silicone to assess the impact of males' ability to produce silk on mating success. The aim of the study was to examine the effect of visual conditions on male investment in nuptial feeding. The places where spiders spend time outside of vegetation in the wild were 40 times brighter than habitats inside vegetation. The mating success was not significantly dependent on light conditions, but males under red lights invested more effort in the production of nuptial gifts than males under white lights. Males with blocked spinnerets had a lower mating success than silk-intact males. The blocked males under red light, although unable to produce silk, also invested more time in attempts to wrap the gift with silk compared to the silk-intact males or silk-blocked males under white lights. These results suggest that gift production is influenced by an interplay between female behaviour and light conditions, highlighting the significance of taking into account visual conditions in spider mating behaviour research.