Environmentally driven variability in size-selective females’ mating frequency of bush-cricket Pholidoptera griseoaptera

Abstract

Reproduction in less favourable conditions requires genetic adaptation and/or behavioural plasticity of the organism. In order to determine the effects of these mechanisms on environment-associated variability in polyandry, a phenomenon related to reproductive success, we explored the frequency of copulations in females of nuptial gift-giving bush-cricket Pholidoptera griseoaptera (Orthoptera: Tettigoniidae) using a laboratory experiment. In a factorial design, we reared two populations originating from contrasting altitudes in two temperature treatment conditions. After 3 weeks for possible copulations in established mating groups, females (n = 108) contained between 0 and 15 spermatodoses (a proxy for the number of copulations) in their spermatheca. The mean number of spermatodoses per female did not differ either between lowland and highland populations or between warm and cold treatments. Thus, we did not observe main effects of these two factors on adaptation or plasticity. In contrast, the frequency of copulations was significantly affected by female size as log(number of spermatodoses) increased by 0.41 ± 0.27 per each 0.1 mm of pronotum length. However, interactions between the body size (the trait that predicts females’ quality for reproduction) with environmental factors revealed that larger females originating from the highland population and larger females reared in cold treatment copulated more often than smaller ones, whereas females’ size did not affect copulation frequency in the lowland population or in warm treatment. It suggests stronger competition among females in harsher environmental conditions, whereas effect sizes of interaction terms showed that observed mating behaviour expressed a similar extent of genetic and plastic responses to female size. This first observation of environment-associated body size-dependent mating behaviour suggests the interplay of sexual and natural selection in a nuptial gift-giving species.