Evolution of reduced pre-adult viability and larval growth rate in laboratory populations of Drosophila melanogaster selected for shorter development time

Abstract

Four large (n > 1000) populations of Drosophila melanogaster, derived from control populations maintained on a 3 week discrete generation cycle, were subjected to selection for fast development and early reproduction. Egg to eclosion survivorship and development time and dry weight at eclosion were monitored every 10 generations. Over 70 generations of selection, development time in the selected populations decreased by approximately 36 h relative to controls, a 20% decline. The difference in male and female development time was also reduced in the selected populations. Flies from the selected populations were increasingly lighter at eclosion than controls, with the reduction in dry weight at eclosion over 70 generations of selection being approximately 45% in males and 39% in females. Larval growth rate (dry weight at eclosion/development time) was also reduced in the selected lines over 70 generations, relative to controls, by approximately 32% in males and 24% in females. However, part of this relative reduction was due to an increase in growth rate of the controls populations, presumably an expression of adaptation to conditions in our laboratory. After 50 generations of selection had elapsed, a considerable and increasing pre-adult viability cost to faster development became apparent, with viability in the selected populations being about 22% less than that of controls at generation 70 of selection.

Correlates of sexual dimorphism for dry weight and development time in five species of Drosophila

“…Similarly, in another study carried out on related populations of D. melanogaster, the degree of sexual dimorphism in dry weight did not differ between treatments at high and low larval density, even though adult dry weights at eclosion were reduced by c. 20-33% in the high density treatment (Borash & Ho, 2001). A study on two strains of D. melanogaster that were completely unrelated to those used by Prasad et al (2000) and Borash & Ho (2001), however, showed that reduced food levels per larva led to a reduction in both dry weight and sexual dimorphism for dry weight (Bakker, 1961). It is not possible to pinpoint the cause of the differences between the results from these studies.…”

“…obs. ), although dimorphism in development time in these populations decreased as selection proceeded (Prasad et al, 2000). Indeed, the per cent reduction in dry weight in these populations, over the first 70 generations of selection, was slightly greater in males than in females, suggesting that, if anything, sexual size dimorphism might be increasing with an overall reduction in size in both sexes (Prasad et al, 2000).…”

“…), although dimorphism in development time in these populations decreased as selection proceeded (Prasad et al, 2000). Indeed, the per cent reduction in dry weight in these populations, over the first 70 generations of selection, was slightly greater in males than in females, suggesting that, if anything, sexual size dimorphism might be increasing with an overall reduction in size in both sexes (Prasad et al, 2000). Similarly, in another study carried out on related populations of D. melanogaster, the degree of sexual dimorphism in dry weight did not differ between treatments at high and low larval density, even though adult dry weights at eclosion were reduced by c. 20-33% in the high density treatment (Borash & Ho, 2001).…”

Correlated changes in life history traits in response to selection for faster pre-adult development in the fruit fly Drosophila melanogaster

“…Trade-offs are observed at phenotypic as well as genetic levels; hence assessment of trade-offs is necessary at both levels. Previous studies on flies selected for faster pre-adult development and early reproduction showed shortening of development time (Chippindale et al, 1994;Chippindale et al, 1997;Prasad et al, 2000) and trade-offs between development time and pre-adult viability (Chippindale et al, 1997;Prasad et al, 2000), adult weight (Chippindale et al, 2004), fecundity (Prasad et al, 2000;Chippindale et al, 2004) and adult lifespan (Chippindale et al, 1994). Populations selected for slower development and delayed reproduction showed increased pre-adult development time (Chippindale et al, 1994) and extended adult lifespan (Partridge and Fowler, 1992;Djawdan et al, 1996).…”

“…Studies examining the correlation between circadian clocks and pre-adult and adult fitness traits have always been carried out separately, often in different model organisms, under varying selection or maintenance protocols, yielding contradictory and inconclusive outcomes. For instance, studies on selection for faster pre-adult development (Chippindale et al, 1994;Chippindale et al, 1997;Prasad et al, 2000) were carried out in D. melanogaster under rhythm-abolishing laboratory conditions of constant light (LL) by imposing additional selection pressure on the age of reproduction [early life (Prasad et al, 2000) or very early (Chippindale et al, 1994;Chippindale et al, 1997)]. Such studies were also carried out under different LD cycles in the laboratory (Miyatake, 1997a;Miyatake, 1997b;Shimizu et al, 1997) or under natural conditions (Pijpe et al, 2006) on several insect species, such as melon flies and the butterfly B. anynana.…”