Contributed by Francesca Abramson, Sydney Bunshaft, Rebecca Pankove, and Justin Elsey
Have you ever thought about why some animals fly while others swim or run? For instance, take a look at the differences at a puffin versus a penguin. Both are black and white and have a love for fish, yet a puffin can wander the skies while penguins majestically dart through the water to collect fish. This occurs because populations adapt to their environment. There are many ways this can occur such as migration, random genetic changes, or mutation, but perhaps the more fundamental method is natural selection. Evolution by natural selection is a theory that dates back to the days of Charles Darwin’s Origin of Species, which explains natural selection as a driving force of evolution that non-randomly selects for certain types of individuals that have favorable traits. This selection for favorable traits leads to higher fitness (having more offspring). This then influences the next generation’s genotypes (genes) and phenotypes (appearance).
Natural selection, however, does not continuously select for more perfect organisms, it fluctuates just as the environment does. The change of selection pressures in the environment can either drive a population to adapt to it, leave, or perish, and penguins are a great example of this because of the trade-offs made over the course of their evolution. But we did not understand its evolutionary significance until recently.
Research done in the Department of Zoology at the University of Manitoba reveals the evolutionary origin of flightlessness in penguins, and why flight was selected against- in favor of a strong swimming ability. By comparing the energy costs of flying and diving in another wing-propelled diving bird, the thick-billed murre (Uria lomvia), scientists deduced that the energy costs of flightless diving birds is significantly lower than that of birds who can both fly and swim. Thus, it is more advantageous, due to their higher energy efficiency, to excel at swimming and diving than be subpar at both swimming and flying.
Penguins are also physiologically incapable of flying due to their reduced wingspan, large wing bones, large body mass and slow wing-beat frequency. These characteristics, however, provide penguins with the endurance and reduced drag to reach food sources at higher depths in the water. The adaptive evolution of a population to suit the environment can be seen in the various organisms that inhabit the planet. It is this natural selection and adaptive evolution that shapes the life around us.
To learn more about the flightlessness of penguins, see the interview with Bronx Zoo penguin expert, Nancy Gonzalez below.
To read more:
Elliott, K. H., Ricklefs, R. E., Gaston, A. J., Hatch, S. A., Speakman, J. R., & Davoren, G. K. (2013). High flight costs, but low dive costs, in auks support the biomechanical hypothesis for flightlessness in penguins. Proceedings of the National Academy of Sciences Proc Natl Acad Sci USA, 110(23), 9380-9384.
Olson-Manning, C. F., Wagner, M. R., & Mitchell-Olds, T. (2012). Adaptive evolution: Evaluating empirical support for theoretical predictions. Nat Rev Genet Nature Reviews Genetics, 13(12), 867-877.
Li, C., Zhang, Y., Li, J., Kong, L., Hu, H., Pan, H., . . . Zhang, G. (2014). Two Antarctic penguin genomes reveal insights into their evolutionary history and molecular changes related to the Antarctic environment.GigaScience Giga Sci, 3(1), 27. doi:10.1186/2047-217x-3-27
McNab, B. K.(1994). Energy Conservation and the Evolution of Flightlessness in Birds. The American Naturalist, 144(4), 628–642.
Wang, Xia, and Julia A. Clarke. “Phylogeny and Forelimb Disparity in Waterbirds.” Evolution 68.10 (2014): 2847-860. Academic Search Alumni Edition. Web. 13 Nov. 2015.
Hui, Clifford A. “Maneuverability of the Humboldt Penguin ( Spheniscus Humboldti ) during Swimming.” Can. J. Zool. Canadian Journal of Zoology 63.9 (1985): 2165-167. Web.