Date of this Version
Bickner, Bridget. Hydraulic recruitment and entrapment as a mechanism of sperm transfer and potential cause of spontaneous male death in the Dark Fishing Spider. Undergraduate Honors Thesis. University of Nebraska-Lincoln.
Sexual selection theory predicts that males will adopt polygynous reproductive strategies to maximize their reproductive outputs. However, monogyny, or male monogamy, has been documented in diverse lineages throughout the animal kingdom, indicating that monogyny can be an adaptive reproductive strategy under some conditions. Coincident with these examples of monogyny are often novel male reproductive morphologies and/or behavior; the current function of which remain unknown and explored. In Dolomedes tenebrosus, an obligately monogynous species, males spontaneously die following sperm transfer. Immediately upon inflating their hematodochal sac for sperm transfer, the male’s body curls up and as he hangs from the female his heart slowly stops beating. Additionally, the male’s hematodochal sac unusually remains inflated. The unique reproductive morphology and behavior associated with D. tenebrosus mating has been hypothesized to play an important role in increased sperm transfer and potentially in the spontaneous death of all males. In this study, we aimed to investigate (1) if D. tenebrosus males transfer more sperm during copulation than other spiders represented in the sperm transfer dynamics literature, (2) the role of extended copulation duration in sperm transfer, and (3) the role of hydraulic recruitment to secondary sperm transfer organs in sperm transfer. We found that male D. tenebrosus transfer more sperm during a single copulation than any other spider currently represented in the literature, and that the difference in sperm transfer appears to be caused by increased sperm loading in secondary sperm transfer organs rather than increased proportion of sperm transferred. Secondly, we found that copulation duration does not predict total or proportion of sperm transferred, and extended copulation duration is likely not an adaptive component of males’ terminal investment strategy. Lastly, we found a positive relationship between hydraulic recruitment and sperm transfer efficacy. Further, empirical data support our hypothesis that hydraulic recruitment is constrained by circulating haemolymph and is the most likely the cause of spontaneous male death following copulation. In conclusion, D. tenebrosus males maximize their reproductive outputs through unique sperm loading and novel sperm transfer mechanisms that exemplify an extreme form of paternal investment through self-sacrifice.