Natural history and behavior of Chymomyza mycopelates and C. exophthalma (Diptera: Drosophilidae), and allometry of structures used as signals, weapons, and spore collectors

Males of Chymomyza mycopelates Grimaldi and Chymomyza exophthalma Grimaldi battled at sites where females fed and mated (but did not oviposit). Both sexes in the two species waved their brightly marked front legs during aggressive interactions, and males used these legs to strike and grasp opponents forcefully. During intense battles, male C. mycopelates also butted or pushed with their heads, whereas male C. exophthalma used their more strikingly wide heads to threaten with stereotyped displays, during which they also held their front legs folded against the sides of their eyes. Courtship behavior by male C. mycopelates involved tactile and perhaps visual displays with the tips of their front legs. Both species also fed by sweeping their front legs over the surface of fruiting fungi and by removing the spores from their legs with their mouthparts. Although male head width in C. exophthalma showed positive allometry, portions of the front legs that were used as signals and as weapons did not, and thus were not in accord with theoretical predictions that weapons and display devices would have steeper allometries.