Gender based disruptive selection maintains body size polymorphism in Drosophila melanogaster

Abstract

Darwinian fitness in holometabolous insects like the fruit fly Drosophila melanogaster is reported to be positively correlated with body size. If large individuals in a population have higher fitness, then one would expect directional selection to operate leading to uniformly large individuals. However, size polymorphism persists in nature and needs further probing. We assessed the effect of body size on some of the fitness and fitness-related traits in replicate populations of genotypically large, genotypically small and phenotypically small D. melanogaster flies. In this study, the time taken to attain reproductive maturity and copulation duration were independent of fly size. Fecundity and longevity of large females were significantly higher when they partnered genotypically small males than when they were with genotypically larger or phenotypically small males. The increased female longevity when in association with genotypically small males was not due to selective early death of males that would release the female partner from presumed cost of persistent courtship. On the contrary, the genotypically as well as phenotypically small males had significantly higher longevity than large males. The virility of the genotypically small males was not significantly different from that of genotypically large males. Our results clearly show that selection on body size operates in the opposite direction (disruptive selection) for the two genders, thus explaining the persistence of size polymorphisms in the holometabolous insect, Drosophila melanogaster.

Curcumin enhances parental reproductive lifespan and progeny viability in Drosophila melanogaster

“…The longevity of reproducing female and male F A , F B , F C , F D , and F E flies was assessed in mixed sex cultures (Handa et al 2014). The flies were sorted into vials containing ∼4 mL SM under light diethyl ether anesthetization.…”

Role of Critical Size on Adult life History Traits in Drosophila Melanogaster.

“…Although the selected populations are under the physiological trigger to complete development due to higher ecdysone levels throughout L3 38 they can accumulate adequate proteins and lipids to maintain their phenotypic integrity albeit emerge as small adults 13,38 . Despite small size due to curtailed post-critical duration their copulation latency (i.e., time to attain sexual maturity) and copulation duration were unaffected supporting the claim that sexual maturity and copulation duration are speciesspeci c traits 18 . However, copulation latency and duration were affected when Drosophila melanogaster was starved during early adult life 41 .…”

“…The differences in the two ndings might be due to diet restriction at different life stages ascertained in the two studies. Two studies in the past have reported decoupling of body size and copulation duration 18,42 .…”

“…Being an inhabitant of rotting fruits and vegetables, it is under direct selection for faster preadult development due to over-crowding and food limitation. Selection for faster pre-adult development is known to exhibit reduced development time and subsequently results in the smaller adult body size [13][14][15][16][17][18] .…”

“…Further, if the larval nutritional environment or developmental diet is rich then they tend to emerge with larger adult body size and attain reproductive maturity at an early age that has a positive implication on tness 11,25,26 . In general though not universal 18 "bigger is better" idea prevails with larvae spending more time in weight (equal to resource/energy) gain under good nourishment conditions, eventually emerging as larger adults with higher tness. Also 'silver spoon hypothesis 25 ' posits that individuals born in good conditions have tness or performance advantages in later life with many examples 25 and those born in poor conditions are at a permanent disadvantage 27 .…”