Do alternative reproductive tactics facilitate evolutionary rescue? A comment on Knell & Parrett 2024

This contribution is a comment on a simulation study of Robert J. Knell and Jonathan M. Parrett (Evo. Lett. 8, 539-349, 2024). There is growing evidence that in ecological adaptation, sexual selection is a "double-edged sword"-it can fuel adaptation and population persistence, or hinder adaptation and lead to population extinction. Knell and Parrett explore this topic, using an individual-based model to investigate how alternative reproductive tactics (ARTs) affect adaptation to changing environments. They find that in the presence of ARTs, extinction can be averted, as fixed ARTs facilitate evolutionary rescue. While we appreciate their research question and approach, we question the generality of this result. First, some of their conclusions hinge on the parameter values chosen. In their model, individuals express one of two reproductive tactics (fighting or sneaking) depending on whether their condition exceeds a given threshold. We demonstrate that their conclusions rely strongly on this threshold value. For high values (i.e., when most individuals sneak), they observe evolutionary rescue-however, for values lower than those explored in K&P, fixed ARTs do not impact extinction. When we allow the threshold to evolve, it evolves to take low values, indicating that when fixed ARTs are adaptive, they do not promote evolutionary rescue. Second, K&P assume that the sneaking strategy results in considerably lower mating success than the fighting strategy. We show that, if the average mating success of the sneaking strategy is increased, fixed ARTs again do not cause evolutionary rescue. Finally, we show that varying the degree of influx of variation or the inheritance process similarly breaks the association between fixed ARTs and evolutionary rescue. Overall, we agree with K&P that ARTs may influence evolutionary rescue, but possibly in different contexts than those considered in their manuscript. Thus, whether and how ARTs shape extinction risk remains an open question.