Reduced fitness in losers of leg-biting male combat compared to uncontested males in Zophobas atratus

Sexual dimorphism and male combat are observed in many species. Often, the outcome of male combat affects the outcome of subsequent combats, mating success, number of sperm, and fitness of the male’s offspring. Also, the quantity and quality of sperm may be regulated by winning or losing, depending on species ecology and mating system. However, very few studies have experimentally examined the influence of fight outcomes on male offspring fitness. We studied male combat in the giant mealworm (Zophobas atratus) in which males bite each other’s hind legs. We hypothesized that subsequent fitness could differ between winners and losers in the escalated male combat of this species. We measured several fitness traits including the number of eggs laid by mated females, and the number of hatches sired by uncontested males, winners, and losers in escalated and non-escalated combat, and compared the fitness of each winner and loser to that of an uncontested male. We also measured mating duration. The numbers of eggs and the percentages of hatched eggs of losers in the escalated combat were significantly reduced compared to that of the uncontested males. This reduction may be due to injuries from escalated leg- biting fights and a result of the sperm amount of the uncontested males being greater than that of the loser males.