Crepitation, Pair Formation, and Female Choice in Chortophaga viridifasciata (DeGeer) (Orthoptera: Acrididae)

Abstract

-After the relative roles played by males and females in pair formation were determined in the field, the mating preferences of females were examined in more detail in the laboratory. Males of the oedipodine grasshopper, Chortophaga viridifasciata (De Geer), spent 48% of their time perched on vegetation that offered an unobstructed view of areas where social interactions took place, patches with less than 20% cover. Male-male interactions were of short duration. Both males silently raised and then lowered hindlegs, (femur tipped or flicked) before separating. The first male to enter a patch was usually the first male to leave, and males produced sound while flying (crepitation) to new patches. Thus, a male signaled his arrival in an area with crepitation. The frequency of crepitation flights was more influenced by social than climatic factors. Receptive females also crepitated while flying. Local clusters of crepitating males resulted when numbers of males followed moving females, as females crepitated, flew silently, or walked from patch to patch. Males were unresponsive to crepitation by other males in the absence of female activity and if the view of the flyer was unobstructed. Females played an active role in initiating, and the dominant role in maintaining, pair formation in interactions terminating in copulation. Females would femur tip or flick, sometimes waving or moving the legs so that the stripes on the inside of the femur opposite the male were most conspicuous. Males responded by attempting to mount. Young females in the laboratory mated, after interacting with two to five males sequentially, with the next male who was heavier than the first male allowed to mount. Mated males did not differ from unmated males in size (such as femur or body length) or behavior (such as activity level or the number of interactions initiated). Females believed to be carrying eggs were less choosy, and often mated with the first male encountered. Females struggled less if mounted by heavy males. Also more heavy males than light males transferred complete spermatophores. In the laboratory, but not in the field, males approached copulating pairs and tried to displace the mating male. Heavy males were more successful. Females may have incited some displacements and when females re-mated, they did so with heavy mates. Thus, females exhibited active mate choice before, during, and after mating. In nature, receptive females were uncommon, relative to the number of males searching for mates. Males in the field avoided interacting with other males, instead devoting most of their time and energy into maximizing the probability of contacting females.