We are addressing two major issues under life-history evolution-
Evolution of adult traits in response to larval crowding:
For animals, such as fruit flies, with a distinct larval stage, larval crowding is one of the most important environmental factors that affects nutritional intake and increases exposure to toxic metabolic wastes. Larval crowding has been very well studied and the evolution of various larval traits in response to crowding have been reported such as larval tolerance to toxic waste products, pre-adult development time, survival rate and adult body size. Larval crowding alters the relative investment between reproduction and somatic maintenance. Hence, it is very likely that adaptation to larval crowing could potentially affect rates of aging through correlated selection for environmental stress resistance and/or its effects on adult body size.
We address this issue by studying a set of large, out-bred populations of Drosophila melanogaster, experimentally evolved for adaptation to larval crowding for more nearly 150 generations in laboratory conditions. We have found that the selected populations have evolved increased longevity when compared to the control populations when grown in crowded condition but had comparable longevity under non-crowded condition. Additionally, we have found that reproductive behaviour of males and females as well as reproductive investment by females has evolved in these populations. Further experiments are underway.
Adaptation to Environmental Stress:
Ability to resist temperature shock is an important component of fitness in insects and other ectotherms. Cold shock is known to affect adult fitness by inducing mortality. Interestingly, cold shock can affect reproduction (without inducing mortality) by reducing sperm number and egg number as well as reproductive behaviour. However, not much is known about the effects of cold-shock on the evolution of adult fitness components, especially, reproductive behaviour. We selected replicate populations of Drosophila melanogaster for resistance to cold shock. The selected populations could recover from cold shock faster and lay more number of fertile eggs than the control populations. Interestingly, the selected populations had higher mating frequency both with and without cold shock. After being subjected to cold shock, males from the selected populations successfully mate with significantly more number of non-virgin females and sired significantly more number of progeny compared to control males. Thus, our results document the evolution of reproductive behaviour and egg viability in response to selection for cold shock resistance in D. melanogaster. We are now studying the mechanisms by which selected populations achieve greater reproductive fitness in the face of cold shock. We are also analysing the evolution of behaviour, biochemistry and gene expression in the selected populations.