A pheromone antagonist liberates female sea lamprey from a sensory trap to enable reliable communication Tyler J. Buchingera,1, Anne M. Scotta,1, Skye D. Fissettea, Cory O. Branta,2, Mar Huertasa,3,KeLia,4, Nicholas S. Johnsonb, and Weiming Lia,5 aDepartment of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824; and bHammond Bay Biological Station, US Geological Survey, Millersburg, MI 49759 Edited by John G. Hildebrand, University of Arizona, Tucson, AZ, and approved February 21, 2020 (received for review December 12, 2019) The evolution of male signals and female preferences remains a subsequent preference evolution precludes a full understanding central question in the study of animal communication. The sensory of how receiver biases shape communication. trap model suggests males evolve signals that mimic cues used Sea lamprey (Petromyzon marinus) are a useful model to track in nonsexual contexts and thus manipulate female behavior to the evolutionary trajectory of communication that originated via generate mating opportunities. Much evidence supports the sen- a sensory trap. Chemical cues and pheromones guide sea lam- sory trap model, but how females glean reliable information from prey behavior throughout their complex life history, especially both mimetic signals and their model cues remains unknown. We during the terminal reproductive phase (21). After parasitizing discovered a mechanism whereby a manipulative male signal guides fish in lakes or the Atlantic Ocean, prespawning sea lamprey reliable communication in sea lamprey (Petromyzon marinus). Mi- migrate into streams following chemical cues released by larvae gratory sea lamprey follow a larval cue into spawning streams; once residing in nursery habitats near spawning grounds. The larval sexually mature, males release a pheromone that mimics the larval cue consists, in part, of the steroidal compound 3-keto petro- cue and attracts females. Females conceivably benefit from the mi- myzonol sulfate (3kPZS), which is released by larvae into the metic pheromone during mate search but must discriminate against water (22) at rates sufficient to create detectable plumes (23) the model cue to avoid orienting toward larvae in nearby nursery and attracts prespawning males and females during their mi- habitats. We tested the hypothesis that spawning females respond gration (24, 25). Several weeks after entering streams, sea lam- to petromyzonol sulfate (PZS) as a behavioral antagonist to avoid prey become sexually mature (spermiated or ovulated) and EVOLUTION attraction to the larval cue while tracking the male pheromone de- exhibit behaviors markedly distinct from those of prespawning spite each containing attractive 3-keto petromyzonol sulfate (3kPZS). migrants. At this point, males construct nests in gravel beds and We found 1) PZS inhibited electrophysiological responses to 3kPZS release a multicomponent sex pheromone that attracts females and abated preferences for 3kPZS when mixed at the same or greater concentrations, 2) larvae released more PZS than 3kPZS whereas over long distances (26, 27). Interestingly, several lines of evi- males released more 3kPZS than PZS, and 3) mixtures of 3kPZS and dence implicate 3kPZS as the major component of the male sex PZS applied at ratios measured in larval and male odorants resulted in pheromone: 1) Spermiated males release 3kPZS at high rates via the discrimination observed between the natural odors. Our study elucidates how communication systems that arise via deception can Significance facilitate reliable communication. In many animals, males deceive females into mating using sexual selection | signal evolution | mimicry | receiver bias | traits that mimic cues of food, predators, preferred habitats, or chemical ecology offspring in need of care. However, if and how these deceptive signals guide reliable communication without females confus- n 1860, Darwin famously decried the perplexity of elaborate ing the mimic and the model remain unclear. We discovered Imale displays by claiming the sight of a peacock’s tail made him that female sea lamprey discriminate a nonsexual cue of pro- sick (1); today, the evolution of sexual signals continues to agi- ductive habitat from the deceptive male sex pheromone that tate the curiosity of biologists but also has implications for un- mimics it and identify a pheromone antagonist as the un- derstanding and conserving biodiversity in a time of dramatic derlying mechanism. Our results implicate a means by which environmental change (2, 3). As Darwin proposed (4), ex- females can detect and benefit from male deceit and could aggerated male traits are often the result of sexual selection via have applications for control of destructive populations of sea female choice (5). Classic models of sexual selection suggest lamprey in the Laurentian Great Lakes. female preferences for male signals arise per the benefits they Author contributions: T.J.B., A.M.S., and W.L. designed research; T.J.B., A.M.S., S.D.F., provide or indicate (6). Alternatively, receiver bias models pro- C.O.B., M.H., K.L., and N.S.J. performed research; T.J.B., A.M.S., S.D.F., C.O.B., and K.L. pose males manipulate female behavior using signals that target analyzed data; T.J.B., A.M.S., and W.L. wrote the paper; and W.L. coordinated the preexisting nonsexual responses (7). For example, some male overall study. signals mimic nonsexual cues of food (8), predation (9), pre- The authors declare no competing interest. ferred habitats (10), or offspring in need of parental care (11). This article is a PNAS Direct Submission. These signals, known as sensory traps (12, 13), elicit out-of- This open access article is distributed under Creative Commons Attribution-NonCommercial- context reactions that give males opportunity to mate females NoDerivatives License 4.0 (CC BY-NC-ND). and are inherently deceptive as females respond to the male sex 1T.J.B. and A.M.S. contributed equally to this work. signal as if it were a cue associated with nonsexual information 2Present address: Great Lakes Science Center, US Geological Survey, Ann Arbor, MI 48105. (14). A deluge of empirical data indicates that receiver biases 3Present address: Department of Biology, Texas State University, San Marcos, TX 78666. explain the origin of many signals (15). However, if and how 4Present address: Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, females adapt to resist manipulation by males (16, 17) or in- 264003 Shandong, China. corporate deceptive signals into reliable sexual communication 5To whom correspondence may be addressed. Email: [email protected]. remain the focus of much debate and theory (14, 18–20). As This article contains supporting information online at https://www.pnas.org/lookup/suppl/ male signals and female preferences represent an intertwined doi:10.1073/pnas.1921394117/-/DCSupplemental. coevolutionary unit, the narrow focus on signal origin but not www.pnas.org/cgi/doi/10.1073/pnas.1921394117 PNAS Latest Articles | 1of6 Downloaded by guest on September 30, 2021 specialized gill cells (28), 2) ovulated females orient toward Petromyzonol Sulfate Abates Olfactory and Behavioral Responses to 3kPZS in 2-choice flumes and large-scale in-stream assays (26, 27), 3kPZS. As we began our search for the mechanism underlying and 3) 3kPZS replicates the behavioral effect of the complete ovulated female indifference to larval odorants which in- male sex pheromone in attracting ovulated females to nests over clude 3kPZS, we noted previous indications that the larval bile long distances (26). Therefore, males signal with a compound that acid petromyzonol sulfate (PZS) is a potent odorant that reduces is a component of the larval cue females orient toward during their olfactory responses to 3kPZS (35–37). Therefore, we hypothe- prespawning migration. Interestingly, the nonsexual migratory sized that PZS in larval odor nulls ovulated female preference preference for 3kPZS likely originated before male signaling with for 3kPZS to prevent misguided orientation toward larvae during 3kPZS, as some other lamprey species respond to it as a compo- mate search. Accordingly, we predicted that PZS nulls the ol- nent of the larval cue but not as a sex pheromone (10). Taken factory and behavioral responses to 3kPZS. together, these observations support the hypothesis that males PZS reduced olfactory responses to 3kPZS across a wide range signal with a sex pheromone that partially mimics the nonsexual of concentrations (Fig. 2). We perfused the olfactory epithe- larval cue. lium with PZS and recorded the response to 3kPZS using We postulated that female sea lamprey discriminate between electroolfactogram (EOG) recordings. The olfactory response to − the model larval cue and the mimetic male pheromone to enable 3kPZS at 10 6 M decreased as the concentration of the PZS − − reliable sexual communication. A long-distance signal for lo- increased from 10 10 to 10 6 M(P < 0.001; Fig. 2B), whereas the cating mates conceivably benefits females, as they bear the onus −5 response to L-arginine (10 M) did not change across PZS ex- of mate search and have only a few days to a week to reproduce posure concentrations (P = 0.773; Fig. 2B). The olfactory re- − − before they die (29, 30). Indeed, evidence that communication sponse to 3kPZS at 10 6 M during exposure to PZS at 10 6 M with 3kPZS is mutually adaptive comes from observations that was 6.5 ± 4.2% (mean ± SE, n = 6) of the response to 3kPZS females evolved a sexual preference for 3kPZS in response to prior to exposure to PZS. At equal concentrations, saturating the sexual signaling by males; in sea lamprey and other lamprey olfactory epithelia with PZS resulted in a greater suppression of species, the nonsexual response to 3kPZS is nontargeted up- the 3kPZS responses than did saturating with 3kPZS to the PZS stream movement fit for navigation into streams, but the sexual − responses; exposure to 7.5 × 10 9 M PZS suppressed 50% of the response is a robust attraction to the point source fit for orien- B tation to a male’s nest (10, 22, 31).