Plasticity in reproductive effort of male dung flies (Scatophaga stercoraria) as a response to larval density

1. Explaining variation in reproductive effort is fundamental to understand ing diversity in male mating and life-history strategies, although relative ly little is known about environmental influences on such variation and ass ociated trade-offs, 2, Plasticity in reproductive effort was examined in male Yellow Dung Flies (Scatophaga stercoraria) reared under two larval density treatments. Relat ive testis size, thorax size and mate-searching effort were compared, and r elationships between these traits examined to look for correlational eviden ce of predicted trade-offs in gonadal and mate-searching expenditure. 3, Males reared under high larval density conditions developed relatively l arger testes than those reared at low density but no evidence was found for a corresponding reduction in mean mate-searching effort at the population level. 4. A negative relationship was found between testis size and mate-searching activity among males within the high larval rearing density treatment but not among those reared at low density. 5, Willingness to engage in struggles for possession of females increased i n relation to body size among males reared at high larval density, and the opposite relationship was found among those reared at low density. 6, Plasticity in male reproductive effort in relation to environmental cond itions be more widespread among insects than has previously been appreciate d.