Contest vs. scramble competition and androgen responsivenesss of males pursuing fixed and plastic alternative reproductive tactics (#163)
Reproductive investment and aggression patterns typically diverge between individuals pursuing alternative reproductive tactics (ARTs). Evolutionary theory predicts that the relative frequencies of alternative male genotypes in a population are stabilized by negative frequency dependence, implying that competition is greatest between males pursuing the same tactic. Males of the cichlid fish Lamprologus callipterus exhibit three ARTs involving both fixed and plastic alternative behaviours. Large bourgeois males defend territories and construct nests of empty snail shells in which females breed. In contrast, males pursuing the genetically fixed dwarf tactic do not court but enter shells surreptitiously during spawning in order to obtain fertilizations. Finally, males pursuing a plastic and conditional sneaker tactic enter nests during spawning to opportunistically steal fertilizations from nest owners. In an experiment we exposed males pursuing divergent ARTs to rivals of same and different tactics and intensities of reproductive competition. The prediction of tactic specific aggression was confirmed in bourgeois nest males. In contrast, parasitic males exhibit scramble competition, as rapid responses to upcoming opportunities for parasitic reproduction are apparently selected. The differences between males pursuing fixed and plastic ARTs is reflected also in the control of reproductive and competitive behaviour by androgens. Interestingly, males pursuing the genetically fixed parasitic dwarf male tactic exceeded other males both in 11-ketotestosterone and testosterone levels. The former is the major active androgen controlling reproduction in male teleosts, whereas the latter has more varied functions in the regulation of fish behaviour. Experimental variation in competition and social context affected androgen levels only in bourgeois males, and their experimentally triggered androgen responses correlated significantly with the expression of aggressive behaviour. These data reveal that reproductive and aggressive behaviours respond differently to social challenges in a species with fixed and plastic ARTs, which is reflected by divergent regulation of behaviour by androgens.