Correlated response in reproductive and life history traits to selection on testis length in Drosophila hydei

Flies in the genus Drosophila have undergone striking evolutionary divergen ce in the size and number of sperm produced. Based on comparative studies o f sperm length, testis length, and other reproductive and life history trai ts, including body size, age at first reproduction, and the number of sperm produced, macroevolutionary trade-offs resulting from the need to produce high-investment testes have been postulated. To understand better the micro evolutionary processes underlying these interspecific patterns, we imposed replicated bidirectional selection for testis length for 11-12 generations on D. hydei, a species with 23.5 mm-long sperm and 30 mm-long testes. Testi s length exhibited realized heritabilities ranging from 0.45 to 0.72. Follo wing selection, traits were assayed for correlated responses. Thorax length , testis mass, sperm length, egg-to-adult development time, and posteclosio n maturation time showed consistent positive correlated responses. Numbers of sperm produced and transferred to females, male longevity, female egg pr oductivity, and seminal receptacle length did not show consistent correlate d responses to selection on testis length. The pattern of correlated respon ses to testis length reveal the potential for the evolution of reproductive strategies to alter important life history attributes.