Predator experience overrides learned aversion to heterospecifics in stickleback species pairs

Abstract

Predation risk can alter female mating decisions because the costs of mate searching and selecting attractive mates increase when predators are present. In response to predators, females have been found to plastically adjust mate preference within species, but little is known about how predators alter sexual isolation and hybridization among species. We tested the effects of predator exposure on sexual isolation between benthic and limnetic threespine sticklebacks (Gasterosteus spp.). Female discrimination against heterospecific mates was measured before and after females experienced a simulated attack by a trout predator or a control exposure to a harmless object. In the absence of predators, females showed increased aversion to heterospecifics over time. We found that predator exposure made females less discriminating and precluded this learned aversion to heterospecifics. Benthic and limnetic males differ in coloration, and predator exposure also affected sexual isolation by weakening female preferences for colourful males. Predator effects on sexual selection were also tested but predators had few effects on female choosiness among conspecific mates. Our results suggest that predation risk may disrupt the cognitive processes associated with mate choice and lead to fluctuations in the strength of sexual isolation between species.

Keywords: hybridization; learning; plasticity; predation; sexual isolation; sexual selection.

Figure 1.

Female mate preference within species and predator exposure. Least-squared means ± s.e. shown for measure of preference in trials with conspecific mates (sexual selection). Benthic and limnetic female species combined. Filled symbols indicate control exposure, open symbols predator exposure. (a) Latency to respond; (b) follows per lead; and (c) preference score.

Figure 2.

Female mate preference between species and predator exposure. Least-squared means ± s.e. shown for measures of preference in trials with heterospecific mates (sexual isolation). Benthic and limnetic female species combined. Filled symbols indicate control exposure, open symbols predator exposure. Left panel shows all females; right panel shows females from the achromatic dataset (benthic females plus limnetics females who saw dull males). (a,b) Latency to respond; (c,d) follows per lead; (e,f) preference score. Significance of comparisons between trials (within treatments) indicated immediately to the right of symbols, significance of comparisons between treatments in second trials indicated next to the vertical line. ***p < 0.0001, **p < 0.01, *p < 0.05, ^†p ≤ 0.10.