Raw data and R code for statistical analyses from: Sensory trap leads to reliable communication without a shift in nonsexual responses to the model cue

The sensory trap model of signal evolution suggests that males manipulate females into mating using traits that mimic cues used in a nonsexual context. Despite much empirical support for sensory traps, little is known about how females evolve in response to these deceptive signals. Female sea lamprey (Petromyzon marinus) evolved to discriminate a male sex pheromone from the larval odor it mimics and orient only towards males during mate search. Larvae and males release the attractant 3-keto petromyzonol sulfate (3kPZS), but spawning females avoid larval odor using the pheromone antagonist, petromyzonol sulfate (PZS), which larvae but not males, release at higher rates than 3kPZS. We tested the hypothesis that migratory females also discriminate between larval odor and the male pheromone and orient only to larval odor during anadromous migration, when they navigate within spawning streams using larval odor before they begin mate search. In-stream behavioral assays revealed that, unlike spawning females, migratory females do not discriminate between mixtures of 3kPZS and PZS applied at ratios typical of larval versus male odorants. Our results indicate females discriminate between the sexual and nonsexual sources of 3kPZS during but not outside of mating and show sensory traps can lead to reliable sexual communication without females shifting their responses in the original context.

Methods
All behavioral data was collected using passive integrated transponder technology during in-stream behavioral assays (see Methods section for specific details). All statistical analyses were conducted in R v3.5.1 (Team 2018). The proportions of migratory females entering each sub-channel were analyzed using a mixed-effects logistic regression model with a binomial distribution. A separate model was run for each treatment, and all models evaluated the effect of odor on which sub-channel a migratory female entered and tested for channel bias. All analyses used the lme4 (Bates et al. 2015) and car (Fox et al. 2012) packages with type III sums of squares (α = 0.05). For all treatments, only migratory females that swam upstream from the release point and entered a sub-channel were included in statistical analyses. For the negative control, a “treatment” side was randomly assigned for the first trial and alternated across subsequent trials. Quantification of chemical components present in LE and SMW was conducted using liquid chromatography tandem mass spectrometry (LC-MS/MS).