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The ecology and behavior of the sand wasp Steniolia nigripes (Hymenoptera: Crabronidae): natural history, resource utilization, and reproductive tactics

Abstract

Differences in reproductive strategies are often hypothesized as the adaptive result of frequency-dependent and condition-dependent selection. However, conventional explanations of mating systems based on ecology do not include the fitness effects of interactions between the sexes. Ecological factors, phenotypic variation, and intersexual interactions must all be examined in order to understand the evolution of reproductive behavior. I investigated the natural history, ecology, and behavior of the sand wasp Steniolia nigripes (Hymenoptera: Crabronidae), using both field observations and controlled behavioral trials. The sand wasps (Bembicinae) are a large, highly diverse group of wasps with extensive variation in male and female reproductive behavior across species. Steniolia nigripes shows reversed sexual size dimorphism and a previously undescribed resource-based territorial strategy in males. The results of this research indicate that the distribution of S. nigripes is determined primarily by the availability of prey used to provision offspring. Seasonal changes and social environment also affect the distribution and behavior of both male and female wasps. A small minority of male wasps hold territories consisting of plants that females visit for prey and nectar. These territorial males are significantly larger and more aggressive than other males, indicating that body size may be important to male competitive success. However, there is no clear evidence of female mating preferences based on either the size or the behavior of males, despite the frequent harassment of females by territorial males in the field. This species thus demonstrates unusual and highly variable morphological and behavioral phenotypes. Studying unique species such as Steniolia nigripes provides a rich opportunity for a comparative understanding of the evolution of body size and reproductive tactics.

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