Effects of two seminal fluid transcripts on post‐mating behavior in the simultaneously hermaphroditic flatworm Macrostomum lignano

Weber M, Patlar B, Ramm SA. Effects of two seminal fluid transcripts on post‐mating behavior in the simultaneously hermaphroditic flatworm Macrostomum lignano. Journal of Evolutionary Biology. 2020;22(5): jeb.13606.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