Do polyandrous pygmy grasshopper females obtain fitness benefits for their offspring?

Abstract

Explanations for polyandry in insects invoke material and genetic benefits that enhance female fitness via the production of more viable or more variable offspring. Here we use the color polymorphic pygmy grasshopper, Tetrix subulata, to evaluate effects of male quality, mate color morph resemblance (a proxy for compatibility), and polyandry on offspring performance. We experimentally mated females with different numbers and color morph combinations of males and reared offspring under either sun-exposed or shaded conditions using a split-brood design. We find a significant male identity effect on egg hatchability, consistent with the hypothesis that males vary in paternal quality. Offspring viability posthatching varied in a complex manner with solar regime, mating treatment, and parental resemblance. The effects of parental color morph resemblance on offspring performance suggest a potential role of compatibility and offspring variability. Monandrous females produced more viable offspring than polyandrous females (under shaded conditions) and we suggest as a hypothesis that the expected positive influence of polyandry on offspring performance may have been outweighed by more intense competition and antagonistic interactions among half-siblings. That an effect of mating treatment was evident under shaded but not under sun-exposed conditions suggests that great care is called for when making inferences from studies that show negative results.