Biomedical subjects

Amitabh Joshi

Publications and source records attributed to Amitabh Joshi.

22 records · Page 2Linked to original sources

PubMed2003

Variation in adult life history and stress resistance across five species of Drosophila.

Dry weight at eclosion, adult lifespan, lifetime fecundity, lipid and carbohydrate content at eclosion, and starvation and desiccation resistance at eclosion were assayed on a long-term laboratory population of Drosophila melanogaster, and one recently wild-caught population each of four other species of Drosophila, two from the melanogaster and two from the immigrans species group. The relationships among trait means across the five species did not conform to expectations based on correlations among these traits inferred from selection studies on D. melanogaster. In particular, the expected positive relationships between fecundity and size/lipid content, lipid content and starvation resistance, carbohydrate (glycogen) content and desiccation resistance, and the expected negative relationship between lifespan and fecundity were not observed. Most traits were strongly positively correlated between sexes across species, except for fractional lipid content and starvation resistance per microgram lipid. For most traits, there was evidence for significant sexual dimorphism but the degree of dimorphism did not vary across species except in the case of adult lifespan, starvation resistance per microgram lipid, and desiccation resistance per microgram carbohydrate. Overall, D. nasuta nasuta and D. sulfurigaster neonasuta (immigrans group) were heavier at eclosion than the melanogaster group species, and tended to have somewhat higher absolute lipid content and starvation resistance. Yet, these two immigrans group species were shorter-lived and had lower average daily fecundity than the melanogaster group species. The smallest species, D. malerkotliana (melanogaster group), had relatively high daily fecundity, intermediate lifespan and high fractional lipid content, especially in females. D. ananassae (melanogaster group) had the highest absolute and fractional carbohydrate content, but its desiccation resistance per microgram carbohydrate was the lowest among the five species. In terms of overall performance, the laboratory population of D. melanogaster was clearly superior, under laboratory conditions, to the other four species if adult lifespan, lifetime fecundity, average daily fecundity, and absolute starvation and desiccation resistance are considered. This finding is contrary to several recent reports of substantially higher adult lifespan and stress resistance in recently wild-caught flies, relative to flies maintained for a long time in discrete-generation laboratory cultures. Possible explanations for these apparent anomalies are discussed in the context of the differing selection pressures likely to be experienced by Drosophila populations in laboratory versus wild environments.

Adaptation, Physiological↗

PubMed2003

Entrainment of eclosion rhythm in Drosophila melanogaster populations reared for more than 700 generations in constant light environment.

In this paper, we report the results of our extensive study on eclosion rhythm of four independent populations of Drosophila melanogaster that were reared in constant light (LL) environment of the laboratory for more than 700 generations. The eclosion rhythm of these flies was assayed under LL, constant darkness (DD) and three periodic light-dark (LD) cycles (T20, T24, and T28). The percentage of vials from each population that exhibited circadian rhythm of eclosion in DD and in LL (intensity of approximately 100 lux) was about 90% and 18%, respectively. The mean free-running period (tau) of eclosion rhythm in DD was 22.85 +/- 0.87 h (mean +/- SD). Eclosion rhythm of these flies entrained to all the three periodic LD cycles, and the phase relationship (psi) of the peak of eclosion with respect to "lights-on" of the LD cycle was significantly different in the three periodic light regimes (T20, T24, and T28). The results thus clearly demonstrate that these flies have preserved the ability to exhibit circadian rhythm of eclosion and the ability to entrain to a wide range of periodic LD cycles even after being in an aperiodic environment for several hundred generations. This suggests that circadian clocks may have intrinsic adaptive value accrued perhaps from coordinating internal metabolic cycles in constant conditions, and that the entrainment mechanisms of circadian clocks are possibly an integral part of the clockwork.

Animals↗

PubMed2002

Locomotor activity rhythm in Drosophila melanogaster after 600 generations in an aperiodic environment.

The locomotor activity rhythm of flies from four populations of Drosophila melanogaster, maintained under constant light for more than 600 generations, was recorded in continuous light (LL) and continuous darkness (DD) using four different protocols. The main objective behind these experiments was to estimate the proportion of flies exhibiting circadian rhythm of locomotor activity in LL, and to investigate whether this could be increased by subjecting the flies to various light regimes. About 26% of the flies exhibited a circadian rhythm of locomotor activity in LL, and the proportion increased to about 48% after an exposure to 12 h of darkness. About 77% of the flies exhibited a circadian locomotor activity rhythm in DD. Persistence of circadian locomotor activity rhythm in a considerable proportion of these flies suggests an intrinsic adaptive value to possessing circadian rhythmicity, derived, perhaps, from the need to synchronise various processes within the organism.

Animals↗

PubMedDate not supplied

What have two decades of laboratory life-history evolution studies on Drosophila melanogaster taught us?

A series of laboratory selection experiments on Drosophila melanogaster over the past two decades has provided insights into the specifics of life-history tradeoffs in the species and greatly refined our understanding of how ecology and genetics interact in life-history evolution. Much of what has been learnt from these studies about the subtlety of the microevolutionary process also has significant implications for experimental design and inference in organismal biology beyond life-history evolution, as well as for studies of evolution in the wild. Here we review work on the ecology and evolution of life-histories in laboratory populations of D. melanogaster, emphasizing how environmental effects on life-history-related traits can influence evolutionary change. We discuss life-history tradeoffs - many unexpected - revealed by selection experiments, and also highlight recent work that underscores the importance to life-history evolution of cross-generation and cross-life-stage effects and interactions, sexual antagonism and sexual dimorphism, population dynamics, and the possible role of biological clocks in timing life-history events. Finally, we discuss some of the limitations of typical selection experiments, and how these limitations might be transcended in the future by a combination of more elaborate and realistic selection experiments, developmental evolutionary biology, and the emerging discipline of phenomics.

Adaptation, Physiological↗