PUB - Publikationen an der Universität Bielefeld

The seminal fluid proteins (SFPs) transferred to mating partners along with sperm often play crucial roles in mediating post-mating sexual selection. One way in which sperm donors can maximize their own reproductive success is by modifying the partners' (sperm recipient's) post-copulatory behavior to prevent or delay re-mating, thereby decreasing the likelihood or intensity of sperm competition. Here, we adopted a quantitative genetic approach combining gene expression and behavioral data to identify candidates that could mediate such a response in the simultaneously hermaphroditic flatworm Macrostomum lignano. We identified two putative SFPs - Mlig-pro46 and Mlig-pro63 - linked to both mating frequency and 'suck' frequency, a distinctive behavior, in which, upon ejaculate receipt, the worm places its pharynx over its female genital opening and apparently attempts to remove the received ejaculate. We, therefore, performed a manipulative experiment using RNA interference-induced knockdown to ask how the loss of Mlig-pro46 and Mlig-pro63 expression, singly and in combination, affects mating frequency, partner suck propensity and sperm competitive ability. None of the knock-down treatments impacted strongly on the mating frequency or sperm competitive ability, but knock-down of Mlig-pro63 resulted in a significantly decreased 'suck' propensity of mating partners. This suggests that Mlig-pro63 may normally act as a cue in the ejaculate to trigger recipient suck behavior, and - given that other proteins in the ejaculate have the opposite effect - could be one component of an on-going arms race between donors and recipients over the control of ejaculate fate. However, the adaptive significance of Mlig-pro46 and Mlig-pro63 from a donor perspective remains enigmatic. This article is protected by copyright. All rights reserved.