The effects of predation risk on mate signaling and choice in the waxmoth Achroia grisella Christopher Edomwande and Flavia Barbosa1 Department of Biology, Lake Forest College, Lake Forest IL [email protected] Introduction Results • Male waxmoths attract females with ultrasonic signals consisting of an incessant pulse pair train (fig. 1). • Males signal from leks, which receptive females orient and walk towards. Females prefer calls with faster Solitary males are more likely to exhibit a silence Females are more likely to choose the low PR call pulse‐pair rate1 (fig. 2). response than those calling in a lek. in the presence of the predator signal. • Several mating behaviors make waxmoths vulnerable to predators: male signals attract both females and **p<0.001 *p=0.03 bats, thus creating a tradeoff. Females are more vulnerable when moving towards males. *p=0.014 p=0.06 20 Continuous callingSeries2 12 • Both sexes may respond to bat calls by freezing, and calling males exhibit a silence response. More attractive 2 Chose low PR call males exhibit shorter silence responses2‐4 . 15 8 Silence responseSeries1 9 8 Chose high PR call 13 10 Cochran Q test: 6 13 17 2 Fig. 1 – Oscillogram of a X2 = 15.1667, p<0.001. McNemar test: X = 4.5 5 11 3 typical male call. Males Number of males 5 6 Pairwise comparisons: typically produce 0 McNemar test, Number of females 0 between 70 to 110 pulse Silence Low PR lek High PR lek Bonferroni adjusted No predator Predator pairs s‐1, at 70–130 kHz. Treatment alpha = 0.016. Treatment Female response (distance moved toward stimulus) Solitary males exhibit longer silence Male attractiveness did not responses than those calling in a lek. affect silence response length. ‐1 ***p<0.0001 Call PR (pulse pairs s) 120 SLS univariate model with **p<0.01 p=0.18 male ID as a random effect: Fig. 2‐ Female preference function for pulse pair ))))) 100 Source F Ratio P rate. From Barbosa and Greenfield (in prep) 80 treatment 8.63 <0.001 Pulse pair 3.42 0.08 60 rate treatment*PR 1.77 0.18 Hypotheses 40 Calling males exposed to a bat signal… 20 (1) will be more likely to exhibit a silence response when solitary than when calling in a lek. Silence response length (s) 0 (2) will exhibit a longer silence response when solitary than when calling in a lek. Silence response length (s) Silence Low PR lek High PR lek 60 70 80 90 100 (3) will exhibit a shorter silence response when calling in a lek containing attractive competitors. Treatment Pulse pair rate (pulse pair s‐1) Receptive females presented to calls of different pulse rates… (1) Will be more likely to choose a higher PR call in the absence of bat signals. Discussion (2) Will be more likely to choose a lower PR call in the presence of a bat signal associated with a higher PR call. Summary and implications • Bat signals pressure males into protective measures, though sexual competition pressures these males into forgoing these measures and taking risks Methods • A previous study found that more attractive males have shorter silence responses due to high chances of 1- Male risk-taking successful mating2. We did not find the same result, but found a similar trend. (a) • While lekking males respond to bat signals, the likelihood that they will exhibit a silence response varies with lek attractiveness. Individuals are faced with more competition in leks with high PR mles, being under higher 200 pressure to spend more time calling1. 120O 100 • Females have a preference for higher pulse rates. However, the presence of a predator may cause females to 5 1 2 50 disregard these preferences and select mates based on predation safety . Frequency (KHz) • The tradeoff between sexual selection and natural selection explains the complex nature of the male and ♂ ♂ 0 0.1s female responses. Future Studies 3 treatments per male (n=19): (1) silence; (2) Low PR (b) • Increase sample size for both tests, especially female choice. call (60 pulse pairs –s); (3) High PR call (85 pulse pairs –s) • Test different PRs for to incorporate more levels of male attractiveness. • Test other environmental factors that can influence male and female responses. 2- Female choice under predation risk Silence response Acknowledgements Fig. 3 – (a) Oscillogram and spectrogram of bat stimulus used in experiments, The authors thank Bob Danka and Bob Cox at the USDA for collecting the individuals used to start our laboratory representing the searching phase call of population, Madison Martell at LFC for assistance with data collection and Michael Greenfield at the Institut de 1 2 the greater horseshoe bat Rhinolophus Recherche sur la Biologie des Insectes for supplying bat stimuli. This work was supported by Lake Forest College. ferrumequinum gleaning 1m away. A 2‐s ♀ ♀ stimulus was used in both experiments. In experiment 1, the bat stimulus was played References 20s into a calling bout of the test male (b), and we measured the length of his silence 1. Brunel‐Ponz et al. The complex auditory scene at leks: Balancing antipredator behaviour and competitive signalling in an acoustic moth. Animal behaviour 81 (2011): 231‐239. response if he exhibited one, as well as his 2. Cordes N et al. Sexual signaling under predation: attractive moths take the greater risks. Behavioral Ecology 2014. 25:409–414. L/R side of high PR stimulus alternated among tests. 3. Cordes N et al. Risk‐taking behavior in the lesser wax moth: disentangling within‐ and between‐individual variation. Behavioral Ecology and Sociobiology 67.2 (2013): 257‐264 call PR (fig. 3b is not to scale). 4. Greenfield M and M Baker. Bat Avoidance in Non‐Aerial Insects: The Silence Response of Signaling Males in an Acoustic Moth. Ethology 2003 109:427–442. n=13 females 5. 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