Investment in sensory structures, testis size, and wing coloration in males of a diurnal moth species: trade‐offs or correlated growth?

Abstract

For dioecious animals, reproductive success typically involves an exchange between the sexes of signals that provide information about mate location and quality. Typically, the elaborate, secondary sexual ornaments of males signal their quality, while females may signal their location and receptivity. In theory, the receptor structures that receive the latter signals may also become elaborate or enlarged in a way that ultimately functions to enhance mating success through improved mate location. The large, elaborate antennae of many male moths are one such sensory structure, and eye size may also be important in diurnal moths. Investment in these traits may be costly, resulting in trade-offs among different traits associated with mate location. For polyandrous species, such trade-offs may also include traits associated with paternity success, such as larger testes. Conversely, we would not expect this to be the case for monandrous species, where sperm competition is unlikely. We investigated these ideas by evaluating the relationship between investment in sensory structures (antennae, eye), testis, and a putative warning signal (orange hindwing patch) in field-caught males of the monandrous diurnal painted apple moth Teia anartoides (Lepidoptera: Lymantriidae) in southeastern Australia. As predicted for a monandrous species, we found no evidence that male moths with larger sensory structures had reduced investment in testis size. However, contrary to expectation, investment in sensory structures was correlated: males with relatively larger antennae also had relatively larger eyes. Intriguingly, also, the size of male orange hindwing patches was positively correlated with testis size.

Evolution of male antennal size in moths (Lepidoptera): a comparative test of potential trade‐offs and correlated growth in Australian species

“…The vertical diameter of the eye at its widest was taken as the measurement of eye size (Shiel et al . ; Fig. d).…”

“…In keeping with previous work (Shiel et al . ; Rogers et al . ), testis area was used as a measure of testis size, measuring the largest polygonal area of the testis (Fig.…”

“…b; Shiel et al . ); and the count of the number of lateral branches on the antenna. Pectinate antennae are rare in females (Scoble ).…”

“…For example, Shiel et al . () found no association between the two traits in the painted apple moth ( Teia anartoides ), a monandrous species. However, most moth species are polyandrous to at least some extent (Drummond ; Torres‐Vila et al .…”

“…Contrary to this expectation, Shiel et al . () found a positive association between these two sensory traits in T. anartoides (Lymantriidae), which they suggested may result either from individuals with larger eyes and antennae having greater capacity to extract resources from the environment or from both sensory structures sharing development from the same imaginal structures.…”