Plasticity of vibratory courtship in response to nuptial gift quality in male Pisaura mirabilis

Abstract Courtship is often a multimodal process involving several signals of different modalities occurring simultaneously. Male nursery web spiders (Pisaura mirabilis) perform substrate-borne vibrations while offering a nuptial gift (a nutritional donation which also serves as a visual and olfactory signal) as they court females. The nuptial gift, consisting of a prey item wrapped in silk, is a considerable investment for the male, and vibration is also likely an energetically costly signal. In this study, we investigate how these 2 expensive mate attraction tactics interact in order to explore how investment might be partitioned between them. We conducted behavioral experiments where male P. mirabilis were provided with nuptial gifts in 3 treatments—no gift, medium gift, large gift—and recorded their courtship vibrations in repeated trials (once with each nuptial gift treatment). We found that calling duration (the total amount of time spent signaling) is longer when males have a nuptial gift vs. when they do not, but the duration is not plastic in response to the mass of the gift. Pulse rate is not affected by the quality of the nuptial gift. In trials where a gift is present, only pulse interval consistency changes based on gift quality, with intervals becoming more consistent (putatively more attractive) as gifts increase in mass. Our results suggest that male spiders do adjust their investment in vibratory courtship signals at a general level, though the plasticity is slight.