Flight muscle allocation diverges between two moth families with distinct flight strategies

Muscle morphology and volume in two closely related moth families, wild silkmoths (Saturniidae) and hawkmoths (Sphingidae), show a divergence that aligns with their distinct flight strategies. Both families rely on similar muscles to power and steer their flight, but they allocate muscle volume differently to prioritize unique functions.

The researchers hypothesized that hawkmoths, which have higher wingbeat frequencies and maneuverable flight, would have larger flight power muscles and that these muscles would increase in proportion with wingbeat frequency. They also expected some individual muscles to diverge in proportional volume and area to support distinct wing control strategies.

Using CT scans, the team quantified volumes and geometries of six flight muscle pairs in twenty bombycoid moth species. As anticipated, flight power muscle proportions did indeed correlate positively with wingbeat frequency, and these muscles were generally larger in hawkmoths. Two of the three steering muscles also showed substantial differences in relative volume and area between families.

In general, muscles in silkmoths were longer, while hawkmoths had greater cross-sectional area. The most intriguing finding was the exceptional size and morphology of the dorsal oblique (DO) muscle, which was highly developed in hawkmoths and either smaller or absent in silkmoths. This difference suggests that the DO muscle, previously underappreciated, plays an important role in flight control, possibly by shaping indirect strain propagation in the elastic thorax.

The study demonstrates that muscle volume distribution in bombycoid moths corresponds with their divergent flight strategies, highlighting how muscle allocation can adapt for specialized functional goals.