Abstract
BackgroundMales of many species adjust their reproductive tactics with regard to their condition and status. For example, large males may develop weapons and fight for access to females, whereas small or undernourished males do not express costly weapons or ornaments and sneak copulations. Different condition-dependent reproductive tactics may be associated with unequal average fitness, but the tactic chosen by a given male under given circumstances is thought to result in the highest possible fitness return.The ant species Cardiocondyla obscurior exhibits an environment-controlled polymorphism of docile, winged males and aggressive "ergatoid" males. Ergatoid males, which can replenish their sperm supply throughout their lives, engage in lethal fighting, and attempt to monopolize all female sexuals available in their nests, were previously assumed to gain higher lifetime reproductive success than the peaceful, winged males, which disperse to mate away from the nest and whose spermatogenesis is limited to the first days of adult life. However, precise data on male mating success have as yet not been available.Here, we compare the average mating success of the two male morphs, taking the high mortality rate of immature ergatoid males into account. Because individuals in insect societies may have opposing interests about their own development, we also investigate whether the interests of male larvae coincide with those of the workers and the rest of the society.ResultsWhen the survival probability of males is taken into account, winged males are more likely to mate multiply and in consequence have a higher estimated average mating success than ergatoid males. Therefore, male larvae are expected to prefer developing into winged instead of ergatoid adults.ConclusionThough male larvae can expect a higher average mating success when developing into winged males, most colonies produce only ergatoid males under standard conditions. This might point at a novel type of potential kin conflict within the social insect colony. Because workers in insect societies usually control male larval development, ergatoid male production under normal conditions probably reflects the optimal allocation strategy of workers to maximise their inclusive fitness.
Highlights
Males of many species adjust their reproductive tactics with regard to their condition and status
When the survival probability of males is taken into account, winged males are more likely to mate multiply and in consequence have a higher estimated average mating success than ergatoid males
Though male larvae can expect a higher average mating success when developing into winged males, most colonies produce only ergatoid males under standard conditions
Summary
Males of many species adjust their reproductive tactics with regard to their condition and status. Males of many animal species have evolved different ways of increasing their reproductive success Such "alternative reproductive tactics" are often associated with differences in body size or different expression of morphological traits, such as weapons or ornaments, which again are controlled either by a genetic polymorphism or the environment during a certain life stage. Older ergatoid males use their mandibles to puncture the not yet sclerotised cuticle of freshly eclosed ergatoids, and may grasp with their mandibles adult ergatoid rivals that somehow have survived the sensitive phase directly after emergence to daub them with hindgut secretions Such besmearing elicits worker aggression, which results in the elimination of the contaminated male [6]. Frequent mating is possible because, in contrast to males of all other social Hymenoptera, the testes of ergatoid Cardiocondyla males persist throughout their whole lives, resulting in a permanently replenishable sperm supply [9,10]
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