Male reproductive competition and sexual selection in the field cricket Gryllus integer




Cade, William Henry

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Male reproductive competition and sexual selection were studied in the field cricket Gryllus integer in central Texas. Male acoustical insects typically contribute little parental investment to their offspring, a situation resulting in intense male competition for females, female mate choice, and potentially high male reproductive success (RS). In male acoustical insects, expenditures of reproductive effort (RE) largely take the form of attracting females by acoustical signaling, or silently locating females. A general consideration of RE expenditure, suggests that as RE increases, survival probability decreases because of increased vulnerability to predation, and to attacks by conspecific males. An optimal RE, in terms of net individual RS, should be a function of survival probability and the maximum RS obtainable. The following behaviors, apparently representing expenditures of RE, were observed within spatial aggregations: the regular production of calling song over a wide range of intensities; irregular production of calling song; occasional fights between calling males; walking or remaining stationary by non-calling males at short distances from calling males; courtship of females by non-calling males which infrequently resulted in mating; physical attacks by non-calling males on calling males; and the commencement of calling by previously non-calling males, often after a nearby male stopped calling. The above behaviors were time and density specific: large numbers of males call in the hours just before dawn, often at low sound intensities; and non-calling males, as well as spatial aggregations, tended to be more common during periods of high population density. Observations and the results of experiments are discussed in the context of contributions to individual RS, by the various patterns of male reproductive behavior. This information suggests that: larviparous female tachnid flies, Euphasiopteryx ochracea, selectively prey upon calling males; some male aggressive interactions are characteristic of territoriality and influence spacing patterns; phonotaxis by flying males and females to conspecific song, results in the formation of mating aggregations; female crickets are capable of preferential mate choice; non-calling aggressive males influence acoustical behavior in other males; and that females are more mobile than males. It is concluded that differential rates of parasitism, male-male aggression, and female mate choice are possible parameters of male RS.