Differences in energy source storage in eye stalks between two species of stalk-eyed flies, Sphyracephala detrahens and Cyrtodiopsis dalmanni

Some diopsid flies have sexually dimorphic eye stalks that are assumed to require considerable nutrition for growth but are advantageous in competition and courtship. According to the handicap theory, the eye span in some dimorphic species serves as a reliable signal of individual quality to an opponent. However, it is not well understood how well eye span represents energy source storage. In this study, we focused on two species: Sphyracephala detrahens, which has weak dimorphism, and Cyrtodiopsis dalmanni, which has moderate dimorphism. We found that the eye stalks of the former species contained more fat bodies than those of the latter species. When the flies were starved, the fat body cells in the eye stalks underwent autophagy. A strong positive correlation was consistently found between eye span and starvation tolerance for S. detrahens, while a weak correlation was found for C. dalmanni. Furthermore, starvation decreased the contest winning rate between S. detrahens pairs with similar eye spans. These findings suggest that the presentation of resource holding potential may be larger than the actual storage ability and that the fidelity of nutritional storage signaling varies; the signal presented by S. detrahens is more reliable than that presented by C. dalmanni.

Automated summary

This study investigates the relationship between eye span and energy storage in two species of diopsid flies. The results show that the eye stalks of Sphyracephala detrahens contain more fat bodies compared to Cyrtodiopsis dalmanni. Additionally, there is a strong positive correlation between eye span and starvation tolerance for S. detrahens, while a weak correlation is found for C. dalmanni. Starvation also decreases the contest winning rate for S. detrahens pairs with similar eye spans. These findings indicate that the presentation of resource holding potential may be larger than the actual storage ability, and the reliability of nutritional storage signaling varies between species.