Interactions between density-dependent and age-specific selection in Drosophila melanogaster

Two types of populations were selected for reproduction early (B) and late (O) in life. These exhibited changes in life span and resistance to stresses, such as desiccation, starvation, ethanol vapours and flying to exhaustion. Similarly, two types of populations were selected at high adult and larval densities (K) and low adult and larval densities (r). These exhibited changes in characters like larval feeding rates, pupation height and minimum food required for successful pupation. The authors examined the B and O populations for the traits that have become differentiated in the r and K populations and vice versa. In general, there is a lack of similar response, except for starvation resistance which is greater in the K populations than the r populations. They tested, for the first time, longevity in all four types of populations as a function of adult density. The O populations show greater longevity than the B populations at all densities; this difference does not depend on density. The K populations can resist the decline in longevity caused by increasing density much more effectively than can the r populations. A new set of populations (CU) were derived from the B populations and maintained by crowding the larval life stage but raising adults under low densities. CU populations have evolved increased feeding rates, pupation height and larval viability at high density relative to the B populations. These changes parallel the changes seen in the r and K populations and demonstrate the importance of crowding in the larval stages for much of the evolution seen in the r and K populations. -from Authors