Our research focuses on understanding behavioral, life history, physiological and genetic bases of adaptive evolution. Much of it involves experimental evolution, i.e, studying in real time the evolutionary responses of replicated populations to controlled selection regimes, using the fruit fly Drosophila melanogaster as the study system. This approach allows for direct testing of evolutionary hypotheses. We currently focus on cognitive traits, such as learning ability, including in a sexual context, and on tolerance to chronic malnutrition. However, we have also recently followed up on our discovery of cannibalism in Drosophila larvae with experiments aiming to understand its adaptive significance.
Evolutionary biology of learning
One set of projects aims to understand learning ability and memory as products of biological evolution. It is usually assumed that learning is beneficial in terms of survival and reproduction, and concrete benefits of learning have been demonstrated under natural settings e.g. in birds or bees. However, if learning is beneficial, why do most animals show rather limited learning and memory? One possibility is that evolution of improved learning ability is limited by lack of genetic variation. We have demonstrated that this is not that case for Drosophila by breeding within several dozen generations flies with substantially improved associative learning ability. Rather, learning is a costly adaptation, as we have demonstrated in several experiments, and these costs rather than genetic variation may limit the evolution of better learning. See this New York Times article on our research on this subject.
Almost all research on learning in fruit flies, including our own, has been done in the laboratory. We are currently also exploring flies' ability to learn in semi-natural settings, with the ultimate goal of understanding the ecological significance of learning in non-social insects in nature. We are also carrying out an evolutionary experiment to address the relationship between cognitive and demographic aspects of aging.
Role of sexual selection in the evolution of cognitive abilities
While some specialized forms of learning (e.g., song learning in birds) are clearly important in acquiring mates, sexual selection is not usually considered a major force driving the evolution of cognitive abilities. However, mate choice and mate attraction involve acquiring, processing and acting upon information. To address the role of sexual selection in the evolution of those skills, we study cognitive performance of fruit flies that evolved for over 100 generations under enforced monogamy, a regime that virtually eliminates sexual selection. Our preliminary results indicate that males evolved under monogamy are less adept at focusing their courtship effort on receptive females in complex social environments and also show some impairment in olfactory learning outside of the sexual context. This suggests that sexual selection is a major force maintaining cognitive abilities in fruit fly males.
Adaptation to chronic malnutrition
It has been increasingly recognized that responses to nutritional stress during development may have far-reaching consequences for adult life, including aging processes. At the same time, mechanisms of responses to nutritional environment seem highly conserved. Thus, understanding how evolution shapes these responses is likely to throw light on early-life determinants of human aging and metabolic disease. We work with flies which, in the course of over 100 generations, evolved improved tolerance to an extremely poor larval food, on which non-adapted populations show 30 % reduction in viability, three-fold longer larval development, and adult size reduced by half. We aim to understand the life history, physiological, behavioral, and genomic traits that mediate the evolutionary adaptation to this chronic nutritional stress in our experimentally evolved populations. We also address the costs of this adaptation. Recent results indicate that the malnutrition-tolerant populations are more susceptible to intestinal bacterial pathogens despite having an apparently higher expression of immune defense genes. Ongoing experiments aim to detect the underlying causes of this apparent trade-off, focusing on the double role of the gut in extracting resources from food and defense against ingested pathogens.
Genomic approaches to experimental evolution
The advent of low-cost high-throughput genomic technologies opens new possibilities to understand the genetic and molecular bases of evolutionary change. We are applying this approach to experimental evolution, aiming to identify candidate molecular mechanism of tolerance to malnutrition and genes under sexual selection, as well as to study the signature of sexually antagonistic selection in gene expression patterns.
Adaptive and ecological significance of cannibalism
Through serendipity, we recently discovered that Drosophila larvae engage in predatory cannibalism, whereby younger larvae pursue, attack and consume fully-grown larvae as the latter prepare for pupation. Behavioral experiments revealed that this phenomenon has hallmarks of a coordinated adaptive behavior rather than an opportunistic byproduct of accidental encounters. Furthermore, nutrients derived from cannibalism allow larvae to complete their development in the absence of other food, and populations that evolved under chronic larval malnutrition (see above) have become more efficient cannibals. Hear Roshan Vijendravarma (the lead researcher on this project) talk about this work on the BBC and see videos of cannibalism on Roshan's website. Currently, Roshan is trying to identify some of the chemical cues that trigger cannibalism – we know that cannibals are attracted to injured potential victims.