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Interactions Between Density-Dependent and Age-Specific Selection in Drosophila melanogaster

L. D. Mueller, J. L. Graves and M. R. Rose
Functional Ecology
Vol. 7, No. 4 (Aug., 1993), pp. 469-479
DOI: 10.2307/2390034
Stable URL: http://www.jstor.org/stable/2390034
Page Count: 11
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Interactions Between Density-Dependent and Age-Specific Selection in Drosophila melanogaster
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Abstract

1. Density-dependent natural selection and age-specific natural selection are important determinants of life-history evolution. A variety of laboratory populations of Drosophila melanogaster have been created to study the effects of these selection mechanisms. 2. Two types of populations have been selected for reproduction early (B) and late (O) in life. These have exhibited changes in life span and resistance to stresses, such as desiccation, starvation, ethanol vapours and flying to exhaustion. 3. Similarly, two types of populations have been selected at high adult and larval densities (K) and low adult and larval densities (r). These have exhibited changes in characters like larval feeding rates, pupation height and minimum food required for successful pupation. 4. To study whether age-specific and density-dependent selection act on the same traits either directly or through indirect effects, such as pleiotropy or linkage, we have examined the B and O populations for the traits that have become differentiated in the r and K populations and vice versa. 5. In general, there is a lack of similar response, except for starvation resistance which is greater in the K populations than the r populations. 6. We have 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 and this difference does not depend on density. In contrast, the K populations are able to resist the decline in longevity caused by increasing density much more effectively than are the r populations. 7. Lastly, a new set of populations, called CU, has been derived from the B populations and is maintained by crowding the larval life stage but raising adults under low densities. The 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.

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