Preliminary investigations into the causes for alternative routes to the evolution of competitive ability in populations of drosophila selected for adaptation to larval crowding

Abstract

Natural selection, as first independently conceptualized by Darwin (1859) and Wallace (Darwin and Wallace 1858), aimed to explain the evolutionary changes in biological populations by differential survival and reproduction among individual organisms. The principle of natural selection has also provided insights into how life-histories themselves evolve, in addition to focusing attention on the life-history as the interface between organismal phenotypes and fitness (Roff 1992; Stearns 1992, 2000). The life-history is determined by the process of development, age of attaining reproductive maturity, lifespan, and the number and probability of survival of offspring (Reznick and Travis 1996). Life-history theory attempts to predict the evolution of optimization of the schedule of survival and reproduction in a given ecological scenario (Stearns 1992, 2000; Roff 1992). In an evolutionary utopia, life-histories should evolve to maximize overall fitness i.e. organisms would start reproducing soon after birth, producing very large numbers of offspring and survive infinitely. Such a scenario, however, is not possible due to resource limitation, manifested as trade-offs among fitness-related traits. The understanding of the evolution of life-history, thus, requires identification of main fitness-related traits and the genetic correlations among them in the ecological scenario of interest. In this regard, laboratory selection experiments on life-history related traits have been extremely useful in investigating the genetic architecture for fitness-related traits in a well defined and controlled ecology (reviewed in Prasad and Joshi 2003). In particular, such studies on Drosophila melanogaster have provided important insights into the manner in which ecology and genetics interact to shape trajectories of adaptive evolution (reviewed in Prasad and Joshi 2003).