Lifetime spermatophore investment in natural populations of two closely related bush-cricket species (Orthoptera: Tettigoniidae: Poecilimon)

Male bush-crickets transfer a substantial spermatophore to females during copulation. The spermatophore comprises a large spermatophylax and a sperm-containing ampulla which is consumed by the female while the ejaculate transfers into her. Spermatophores are costly to produce and investment trade-offs are expected to occur between the ejaculate, sperm and spermatophylax. While models of ejaculate allocation predict strategic allocation between current and potential reproductive rates, no comparative studies to date have analysed interspecific spermatophore component variation between bush-cricket species over the entire mating season. Here we compare field data from two bush-cricket species (Poecilimon) that differ in spermatophore investment. While Poecilimon thessalicus invests heavily in spermatophore production and was variable in body mass and spermatophylax size over the season, they consistently produced similar-sized ampullae and transferred constant numbers of sperm. In contrast, the ampulla size of the less investing species, P. veluchianus minor, varied considerably over the season, yet the body, spermatophylax mass and sperm number remained constant. Differences between the two species reflect within-species adjustments that male bush-crickets make to specific spermatophore components as conditional strategies in order to maximize reproductive output.