Facultative polyandry protects females from compromised male fertility caused by heatwave conditions

Why is polyandry such a common mating behaviour when it exposes females to range of significant fitness costs? Here, we investigated whether protects against reduced male fertility caused by thermal stress from heatwave conditions. Sperm production and function are vulnerable heat, conditions forecast increase as our climate warms, so examined these effects on female reproduction in the flour beetle, Tribolium castaneum, promiscuous ectotherm model which damaged environmental warming. We tested polyandrous matings, or sperm stores, protect conditions, flexibly adjust their remating enable rescue. found that protected fertility: monogamous matings with males exposed halved offspring production, but opportunities mate five allowed normal reproductive output. By contrast this improvement following opportunities, there was no protective benefit for already carrying stores multiple males, suffered similar damage within tract stores. Importantly, flexible condition, showing greater motivation remate new if previous had been exposure, enabling rapid Our results reveal enables rescue compromised phenomenon may become more prevalent under change.