MATING STRATEGIES BASED ON FORAGING ABILITY - AN EXPERIMENT WITH GRASSHOPPERS

Female mate choice and the benefits of this behavior are critical aspe cts of Darwinian sexual selection, but they are seldom documented beca use it is difficult to identify the male trait(s) that females may be seeking. We conducted experiments with grasshoppers (Melanoplus sangui nipes: Orthoptera, Acrididae) to examine this behavior. Males that fee d more intensively and select a diet mix that permits greater food int ake (food intake per body mass per time) in laboratory trials were pre ferentially selected by females. These better foraging males on averag e provide greater paternal investment (greater spermatophore mass) to the female, which increases her reproductive rate (eggs produced per b ody mass per time). However, paternal investment may not entirely expl ain female choice of better foraging males, because these males were s till selected even if they had their food intake restricted or had bee n allowed to recently mate, which reduces spermatophore production. Fu rthermore, males change their mating strategy in response to female ch oice and the foraging abilities of surrounding males. Poorer foraging males attempt forcible copulation rather than displaying and allowing female choice. A male will facultatively switch between these strategi es depending on the foraging abilities of the surrounding males. While females attempt to reject forcible copulation, forcible copulation re duces the frequency with which females successfully copulate with bett er foraging males. Therefore, males that are less ''attractive'' to fe males adopt alternative mating strategies to counter female choice whi ch would exclude them from mating.