Experimental Evolution


The Fruit Fly (Drosophila melanogaster)

The fruit fly has been a model organism for documenting evolution in real time.

Organisms don’t have it easy. Environments change over the course of minutes to years, and these changes threaten what organisms do to survive and reproduce. To endure, species must evolve one of two solutions: they either tolerate a wide range of conditions or adjust their tolerance when conditions change. Adjusting to change, which biologists call plasticity, provides a superior benefit when the environment changes slowly and predictably. In such a situation, an organism can continuously tune its body to the current environment.

Flies laying eggs in a chamber

To study adaptation, we measure the performance of flies at different temperatures

We have tested this evolutionary theory with populations of fruit flies evolving in the laboratory. The fruit fly, with its small size and rapid development, has become a model organism for studying evolution in real time. Within a few years, you can actually see populations diverge genetically! By manipulating temperature while controlling other factors, we can isolate the cause of adaptation.

Our experiments have focused on populations exposed to either constant or fluctuating temperatures. Temperatures fluctuated slowly and predictably, switching between 16°C and 25°C once per generation. If the theory is correct, populations at fluctuating temperatures should have evolved greater plasticity than did populations at constant temperatures. As predicted, flies from fluctuating temperatures exhibit enhanced plasticity—tuning their cells according to their body temperature early in life. As a result of this plasticity, flies reproduce better over a wide range of temperatures.

Still, adaptation comes at a cost. Our recent studies suggest that the evolution of greater plasticity reduced a fly’s ability to tolerate extreme heat. When a species gives up one ability to acquire another, biologists say that a tradeoff has occurred. Tradeoffs explain why only certain populations evolve the ability to acclimate. After all, why should an organism pay for an ability that it doesn’t need?

 

Want to learn more? Read our recent publications about evolution:

Alton, L. A., C. Condon, C. R. White, and M. J. Angilletta. 2017. Colder environments did not select for a faster metabolism during experimental evolution of Drosophila melanogaster. Evolution 71: 145-152. 

Adrian, G.J., M. Czarnoleski, and M. J. Angilletta. Flies evolved small bodies and cells at high or fluctuating temperatures. Ecology and Evolution 2016: 1-6. 

Le Vinh Thuy, J., J. M. VandenBrooks, and M. J. Angilletta. 2016. Developmental plasticity evolved according to specialist-generalist tradeoffs in experimental populations of Drosophila melanogaster. Biology Letters 12: 20160379.

Condon, C., A. Acharya, G. J. Adrian, A. M. Hurliman, D. Malekooti, P. Nguyen, M. H. Zelic, and M. J. Angilletta. 2015. Indirect selection of thermal tolerance during experimental evolution of Drosophila melanogaster. Ecology and Evolution 5: 1873-1880.

Angilletta, M. J. 2014. Biochemical and Physiological Adaptations. Pp. 282-287 in The Princeton Guide to Evolution (J. Losos, ed.). Princeton University Press, Princeton.

Condon, C., B. C. Cooper, S. Yeaman, and M. J. Angilletta. 2014. Temporal variation favors the evolution of generalists in experimental populations of Drosophila melanogaster. Evolution 68: 720-728.

Cooper, B. C., J. M. Tharp, I. I. Jernberg, and M. J. Angilletta. 2012. Developmental plasticity of thermal tolerances in temperate and subtropical populations of Drosophila melanogaster. Journal of Thermal Biology 37: 211-216.