Sir2, an evolutionarily conserved NAD(+)-dependent deacetylase, has been implicated as a key factor in mediating organismal life span. However, recent contradictory findings have brought into question the role of Sir2 and its orthologs in regulating organismal longevity. In this study, we report that Drosophila Sir2 (dSir2) in the adult fat body regulates longevity in a diet-dependent manner. We used inducible Gal4 drivers to knock down and overexpress dSir2 in a tissue-specific manner. A diet-dependent life span phenotype of dSir2 perturbations (both knockdown and overexpression) in the fat body, but not muscles, negates the effects of background genetic mutations. In addition to providing clarity to the field, our study contrasts the ability of dSir2 in two metabolic tissues to affect longevity. We also show that dSir2 knockdown abrogates fat-body dFOXO-dependent life span extension. This report highlights the importance of the interplay between genetic factors and dietary inputs in determining organismal life spans.
BackgroundInterlocus conflict predicts (a) evolution of traits, beneficial to males but detrimental to females and (b) evolution of aging and life-span under the influence of the cost of bearing these traits. However, there are very few empirical investigations shedding light on these predictions. Those that do address these issues, mostly reported response of male reproductive traits or the lack of it and do not address the life-history consequence of such evolution. Here, we test both the above mentioned predictions using experimental evolution on replicate populations of Drosophila melanogaster. We present responses observed after >45 generations of altered levels of interlocus conflict (generated by varying the operational sex ratio).ResultsMales from the male biased (high conflict, M-regime) regime evolved higher spontaneous locomotor activity and courtship frequency. Females exposed to these males were found to have higher mortality rate. Males from the female biased regime (low conflict, F-regime) did not evolve altered courtship frequency and activity. However, progeny production of females continuously exposed to F-males was significantly higher than the progeny production of females exposed to M-males indicating that the F-males are relatively benign towards their mates. We found that males from male biased regime lived shorter compared to males from the female biased regime.ConclusionF-males (evolving under lower levels of sexual conflict) evolved decreased mate harming ability indicating the cost of maintenance of the suit of traits that cause mate-harm. The M-males (evolving under higher levels sexual conflict) caused higher female mortality indicating that they had evolved increased mate harming ability, possibly as a by product of increased reproduction related activity. There was a correlated evolution of life-history of the M and F-males. M-regime males lived shorter compared to the males from F-regime, possibly due to the cost of investing more in reproductive traits. In combination, these results suggest that male reproductive traits and life-history traits can evolve in response to the altered levels of interlocus sexual conflict.
In naturally polygamous organisms such as Drosophila, sperm competitive ability is one of the most important components of male fitness and is expected to evolve in response to varying degrees of male-male competition. Several studies have documented the existence of ample genetic variation in sperm competitive ability of males. However, many experimental evolution studies have found sperm competitive ability to be unresponsive to selection. Even direct selection for increased sperm competitive ability has failed to yield any measurable changes. Here we report the evolution of sperm competitive ability (sperm defense-P1, offense-P2) in a set of replicate populations of Drosophila melanogaster subjected to altered levels of male-male competition (generated by varying the operational sex ratio) for 55-60 generations. Males from populations with female-biased operational sex ratio evolved reduced P1 and P2, without any measurable change in the male reproductive behavior. Males in the male-biased regime evolved increased P1, but there was no significant change in P2. Increase in P1 was associated with an increase in copulation duration, possibly indicating greater ejaculate investment by these males. This study is one of the few to provide empirical evidence for the evolution of sperm competitive ability of males under different levels of male-male competition.
Maintenance and deployment of the immune system are costly and are hence predicted to trade-off with other resource-demanding traits, such as reproduction. We subjected this longstanding idea to test using laboratory experimental evolution approach. In the present study, replicate populations of Drosophila melanogaster were subjected to three selection regimes-I (Infection with Pseudomonas entomophila), S (Sham-infection with MgSO4 ), and U (Unhandled Control). After 30 generations of selection flies from the I regime had evolved better survivorship upon infection with P. entomophila compared to flies from U and S regimes. However, contrary to expectations and previous reports, we did not find any evidence of trade-offs between immunity and other life history related traits, such as longevity, fecundity, egg hatchability, or development time. After 45 generations of selection, the selection was relaxed for a set of populations. Even after 15 generations, the postinfection survivorship of populations under relaxed selection regime did not decline. We speculate that either there is a negligible cost to the evolved immune response or that trade-offs occur on traits such as reproductive behavior or other immune mechanisms that we have not investigated in this study. Our research suggests that at least under certain conditions, life-history trade-offs might play little role in maintaining variation in immunity.
When the cost of reproduction for males and variance in female quality are high, males are predicted to show adaptive mate choice. Using Drosophila melanogaster, we test this prediction and show that sperm limited males preferentially mated with young and/or well fed females. The preferred females had higher reproductive output – direct evidence of adaptive precopulatory male mate choice. Our most striking finding is the strong positive correlation between the degree of mating bias showed by the males and the variance in the fitness of the females. We discuss the possible mechanism for such adaptive male mate choice and propose that such choice has important consequences with respect to the existing understanding of the mating system and the evolution of aging.
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