Alternative reproductive tactics and evolutionary rescue

Alternative reproductive tactics (ARTs), whereby males within a species exhibit qualitatively different behaviours in their pursuit of matings, are common throughout the animal kingdom. Here, using an individual-based modelling approach, we consider the possible impacts on adaptation and evolutionary rescue arising from one class of ARTs, those expressed through condition-dependent polyphenism such that high-quality, well-adapted males compete aggressively for mates and low-quality, poorly adapted males attempt to acquire matings via other, non-aggressive behaviours. When the ART is simultaneous, meaning that low-quality males do engage in contests but also pursue other tactics, adaptive capacity is reduced and evolutionary rescue, where a population is able to adapt to a changing environment, becomes less likely. This is because the use of the ART allows low-quality males to contribute more maladaptive genes to the population than would happen otherwise. When the ART is fixed, however, such that low-quality males will only use the alternative tactic and do not engage in contests, we find the opposite: adaptation happens more quickly and evolutionary rescue when the environment changes is more likely. This surprising effect results from an increase in the mating success of the highest quality males who face many fewer competitors in this scenario--counterintuitively, the presence of males pursuing the ART increases reproductive skew towards those males in the best condition.