E.O.B.U.: Evolutionary Biology Laboratory

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About Evolution About Population Ecology

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Our Research in Evolutionary Genetics

Our Research in Population Ecology

OUR RESEARCH IN EVOLUTIONARY GENETICS

BACKGROUND & RATIONALE

"Evolution is a study of the very dynamics of life" (Theodosius Dobzhansky)

"Any variation that is not inherited is unimportant" (Charles Darwin)

 

Evolutionary biology, taken in the broadest sense, is today a vast field encompassing many different areas, and utilizing many different methodologies. Unlike many areas in sub-organismal biology, evolutionary biology rests upon a very well developed and mathematically sophisticated substratum of theory, deduced from the axioms of the principles of Mendelian inheritance. This feature makes it different from many other areas in biology in that it permits a kind of rigorous feedback between theory and experiment, reminiscent more of the "hard science" picture of physics than of what most people think about when they consider biology. Within evolutionary biology itself we can delineate four broad areas of research which differ considerably in the issues they address, and the methodology they use.

Palaeontology and, today, molecular systematics, are primarily concerned with understanding patterns of biological diversity in time: the focus here is on reconstructing past events. Understanding spatial patterns in the diversity of extant life forms constitutes the domain of biogeography, nowadays often called biodiversity. Many evolutionary biologists concern themselves with trying to understand why and how extant traits in species may have evolved. The focus here is on extant populations or species as products of evolution, and possible fitness consequences of extant traits are the principal object of study. For want of a better label, and in order to contrast it with the fourth area of evolutionary biology research, I will call this broad approach evolutionary ecology. Finally, there is evolutionary genetics wherein the major interest is in the dynamics of the evolutionary process. Here, one is not typically interested in a particular extant trait or species per se, but is rather trying to elucidate broad principles of how adaptive evolution occurs in response to certain clearly defined selection pressures.

 

 

 

The evolutionary trajectory of a population is a resolution of the force of natural selection acting on it, the genetic structure of the population, its past selection history and ancestry, and chance in the form of genetic drift. The approach used by our laboratory, and many other practitioners of evolutionary genetics, is to work with well characterized laboratory systems where one can simplify and control the selection pressures, allow for and quantify historical effects, and circumvent the problems of chance by working with replicated populations. In such studies, the logic of one’s approach is to study the evolutionary trajectory of a well characterized set of populations under a certain set of selection pressures and use this information to draw inferences about the genetic architecture of fitness in the population.

BRIEF OUTLINE OF RESEARCH

Evolutionary genetics research in our laboratory is focussed primarily on life-history evolution, and uses fruit flies of the genus Drosophila as a model system. The life-history of an organism refers primarily to the timing of events important to reproduction (Darwinian fitness) such as time from birth to sexual maturity, distribution of offspring, time to cessation of reproduction etc. How life-histories evolve under different scenarios is a major area of interest in evolution, because the life-history is, in a sense, the interface through which the total phenotype of the organism is ultimately related to fitness. At this time, we are mainly working on the evolution of (a) developmental rates, (b) patterns of life-time offspring production, and (c) rates of ageing under different kinds of selection pressures. Our lab is also interested in density-dependent selection and the evolution of competitive ability, as well the evolution of resistance to stresses such as starvation and desiccation. In order to study these issues, we use methodology drawn from population and quantitative genetics, as well as physiology, and in the very near future we hope to augment this work with molecular genetics and field ecological approaches. Most of what we know about life-history tradeoffs in Drosophila is based upon studies with D. melanogaster. We have recently begun studying life history and stress resistance variation in D. malerkotliana, D. ananassae (Sub-genus Sophophora, Species group Melanogaster), and D. nasuta nasuta, D. sulfurigaster neonasuta (Sub-genus Drosophila, Species group Immigrans), with an intention of examining the generality of life-history trade-offs in the genus, as well as trying to link up trade-offs revealed in laboratory selection studies to selection pressures in wild populations. We are also interested in the evolution of life-histories under conflicting selection pressures: this work is being done in collaboration with Dr. Mallikarjun Shakarad of the Poornaprajna Institute of Scientific Research, Bangalore.

 

In collaboration with the Chronobiology Laboratory at JNCASR we are engaged in studies of adaptation to different periodic and aperiodic environments in lab populations of D. melanogaster, with the intention of investigating the evolutionary genetics of circadian organization. We are also collaborating with the Chronobiology Laboratory at JNCASR in trying to understand the possible involvement of biological clocks in timing of life-history events in D. melanogaster.

Some other research interests which are presently on back-burner are (a) evolutionary maintenance of sexual reproduction, (b) adaptation to different temperatures, and (c) evolutionary genetics of host-habitat specialization.

Some recent research highlights

     

    • Successful development of populations of D. melanogaster that develop about 40-45 hours faster than control ancestral populations. This represents a reduction of about 25% in development time from egg to adult, and these populations are the fastest developing D. melanoagster in the world.

     

     

    • Studies of these populations have revealed that the duration of the first and third larval instars, and of the pupal phase, has been reduced by selection, but not that of the second larval instar. Why exactly this is so is not yet clear. It is also seen that the faster developing populations have evolved a syndrome of reduced energy expenditure, exhibiting reduced larval feeding rates, pupation heights, and levels of foraging activity compared to control populations.

     

     

    • Contrary to a fairly widely held view, the faster developing populations do not exhibit increased competitive ability: on the contrary, they are far poorer competitors than controls.

     

 

 

 

OUR RESEARCH IN POPULATION ECOLOGY

BRIEF OUTLINE OF RESEARCH

The major themes of interest in population ecology in our laboratory are

  1. demographic stochasticity and the dynamics of small populations
  2. development and analysis of realistic models of population growth that explicitly incorporate various density-dependent feedback loops across different life-history stages
  3. ecological factors promoting population stability
  4. evolution of population dynamics parameters as a by-product of individual selection on life-history traits
  5. the interaction of sub-population dynamics and migration in metapopulation dynamics

We have been studying these issues using a combination of theoretical work involving model building and simulation, assessing model fitting techniques and approaches using simulated data sets, and experimental studies on laboratory populations and metapopulations of Drosophila.

We have experimentally verified the predictions of a Drosophila specific model of population dynamics (Mueller, 1988) for very small populations, and ruled out sex-ratio fluctuations as a major contributor to demographic stochasticity.

In collaboration with Larry Mueller of Univ. of California, Irvine, a heuristic model of population dynamics in life-stage structured populations was developed, emphasizing the importance of the relative mapping onto the ontogeny of life-stages acting as triggers and targets, respectively, for density-dependent regulatory processes.

We have shown that incorporating random spatial variation in population density into simple models of population growth greatly stabilizes their dynamics over very large parts of the parameter space.

In the first experimental study of its kind, we showed that migration in metapopulations stabilizes sub-population dynamics by damping, but also destabilizes metapopulation dynamics by bringing fluctuating sub-populations in phase.

 

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   Last modified date: 07-05-2010