Systematic Penguin Evolution

Contributed by: Oceana Hopkins, Arooj Khalid, Kevin Lu

The core idea of modern evolutionary theory is that all life is descended from a common ancestor. Though the theory garners much scrutiny and skepticism, it can be explained in part through the simple mechanism of natural selection. Natural selection takes advantage of the variability that exists within the genome. Random mutations that occur in the genome are behind these variations and sometimes change the fitness of an organism. Natural selection dictates that those with higher fitness survive and reproduce; thus, certain traits are selected for within the species. This process explains how gradual change occurs and how complex organisms arise from simplistic ancestors. A common misconception regarding evolution is that life evolved randomly, or by chance. This misconception could arise because of the random nature of mutations that promote variability. Though randomness is an important component to evolutionary theory, natural selection and survival of those who are more biologically fit make sure that the process is non-random.

Known for their characteristic black and white “tuxedos”, penguins are an aquatic, flightless bird found in both warm and cold climates. Because such a large part of their lives are spent in the water, certain species of penguins will only exit the water to shed their feathers or to mate. Spending nearly 75% of their lives in the water foraging for food, penguins have developed very specific traits optimized for swimming.  Utilizing their strong forelimbs to propel their large bodies through the water, penguins have undergone very specific evolutionary changes that allow this mechanism to run smoothly. As discussed in Michael Habib’s paper on structural evolution, the strength of the bones in the forelimbs are significantly greater than that of birds who do not exhibit aqua-flying behavior (2009). In conjunction with increased bone density, more muscle mass also developed and aided in keeping the penguins warm in their cold feeding environment.

Closer inspection of the features that aid water-feeding behavior provides more evidence that disputes the misconception that evolution is random. As seen in 2006 by Slack and colleagues, macroevolution within penguins based on their fossils and mitochondrial genes was tracked and recorded. The evidence showed that the penguins’ bodies gradually adapted to the cold feeding environment over many generations. Additionally, researchers Thomas and colleagues observed in 2010 that cold water penguins have a flow of heat along their wings that originates from the brachial artery called the humeral plexus.  This vascular countercurrent heat exchanger (CCHE) provides penguins the opportunity to forage in cold water by limiting heat loss through the flippers. Scientists identified this adaptation through fossil evidence and, upon further research, learned it evolved after penguins lost the ability of aerial flight. Researchers have proposed the CCHE evolved to help balance the energy costs of longer foraging times, since the oceans were significantly cooler than penguin body temperature. Ultimately, researchers have concluded that the humeral plexus was instrumental in allowing penguins to be water feeders in subaquatic environments.


To learn more:

Clarke, J. A., D. T. Ksepka, R. Salas-Gismondi, A. J. Altamirano, M. D. Shawkey, L. D’alba, J. Vinther, T. J. Devries, and P. Baby. “Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers.”Science 330 (2010): 954-57. Print

Fordyce, R. E. and Jones, C. M. 1990. The history of penguins, and new fossil penguin material from New Zealand. Pages 419-446 in Davis, L. S. and Darby, J. D. (editors), Penguin biology. Academic Press, San Diego. 467 p.

Habib, Michael. “The Structural Mechanics And Evolution Of Aquaflying Birds.” Biological Journal of the Linnean Society 99 (2009): 687-98. Print.

Stack, Kerryn E., Craig M. Jones, Tatsuro Ando, G. L. Harrison, R. Ewan Fordyce, Ulfur Arnason, and David Penny. “Molecular Biology and Evolution.” Early Penguin Fossils, Plus Mitochondrial Genomes, Calibrate Avian Evolution. Oxford Journals, Mar. 2006. Web. 13 Nov. 2015.

Subramanian S, Beans-Pico´n G, Swaminathan SK, Millar CD, Lambert DM. 2013 Evidence for a recent origin of penguins. Biol Lett 9: 20130748.

Thomas, D. B., D. T. Ksepka, and R. E. Fordyce. “Penguin Heat-retention Structures Evolved in a Greenhouse Earth.” Biology Letters 7 (2010): 461-64. Print.

From Lakes to Oceans: Speciation of Sockeye Salmon and Other Fishes

Contributed by Heng Cheng

When you go to a zoo, an aquarium, or a botanical garden, you may wonder how nature created countless species. In fact, nature did not “create” species—species arose from a common ancestor through a process called speciation. Speciation can occur through a number of mechanisms. Among these, one mechanism that is widely seen is that populations of the same species diverge from one another because they use different resources in the environment. We called this ecological speciation.  We are going to focus on ecological speciation here. Fishes in postglacial lakes provide excellent examples of how the use of different parts of the environment can lead to reproduction isolation then ultimately, speciation.

About 15000 years ago, lakes formed after ice disappeared over the northern part of North America and Eurasia. These lakes were mainly freshwater lakes. Some lakes connected to the ocean, which provided the opportunity for some fishes to go to the ocean. However, fish had different degrees of salt-tolerance–not all the fish were able to live in high salt concentrated ocean water. Only salt-tolerant fish were able to get to the ocean. From this point, fish utilized different habitats. Some used fresh water and some used salted water. This happened in the yummy sockeye salmon. One kind of sockeye salmon, anadromous sockeye salmon, spend their first two years in the lakes then swim to the ocean. In the ocean, they grow into a very big size. Another kind, kokanee salmon, stay in the lakes forever and remain a much smaller size. These two kinds of sockeye salmon are genetically distinct. DNA analyses demonstrate that kokanee salmon evolved from anadromous salmon. This sockeye salmon speciation was an example of sympatric speciation. They lived in the same place but they did not mate with each other.

Another example of ecological speciation can been seen in the European whitefish (Coregonus lavaretus) in Scandinavian lakes. Similar to the sockeye salmon, whitefish utilize different areas of the lakes that were ecologically different. To the extreme, some lakes have up to five ecologically different areas. As a result, whitefishes in these lakes developed into five different species: they have different sizes, consume different resources, and have different spawning sites and times, which lead to reproductive isolation, just like the sockeye salmon.

To read more, see:

Schluter, Dolph. 1996. Ecological Speciation in Postglacial Fishes. Philosophical Transaction of The Royal Society B.Biological Sciences 351(1341): 807-814.

Fahlman, Johan. 2014. Size selective predation of pike on whitefish: The effects on resource polymorphism in Scandinavian whitefish populations. Umeå University. 13p.

Hummingbirds Debunk Misconceptions in Evolution

by Randolf Lee and Nick Mirza
humminbird2What are some of the things that come to mind upon hearing the word “fitness?” The immediate reaction is to think of how fitness applies to humans – strength, speed, and agility are commonly associated with fitness. These traits constitute a rather narrow definition of fitness; in the context of biology, fitness takes on a much broader definition to include any traits that increase reproductive success. In practice, fitness appears in an incredibly wide variety of forms, many of which defy the common conceptions of what it means to be fit.

Hummingbirds are an excellent example of organisms whose evolution contradicts conventional notions of what it means to be “fit”. The blazing fast speeds at which hummingbirds flap their wings give them remarkable flying abilities. This comes at a high cost: hummingbirds have a huge metabolic demand relative to their size. In other words, a huge amount of energy is needed to sustain hummingbird flight. It might seem that the high metabolic demand caused by hummingbirds’ flight mechanics would favor the evolution of slower wing speeds. This does not appear to be the case. Instead, one of the ways that hummingbirds compensate for the high metabolic demand of their wing flapping is by reducing metabolic demand in an entirely different realm: DNA. Current research suggests that natural selection has favored smaller genome sizes in hummingbirds (and other avian species). Smaller genomes require less energy during replication and maintenance, meaning precious resources can be used by flight muscles. This budgeting of energy consumption allows hummingbirds to maintain their stunning flight abilities without sacrificing other physical abilities or raising their already high caloric demand. The reduction of genome size is probably not among the first things that come to mind when thinking about evolutionary adaptation and fitness. One commonly held belief regarding evolution is that complexity and fitness go hand-in-hand; it would therefore be assumed that large and highly complex genomes would result in higher fitness. Hummingbirds demonstrate that this is not the case, and that fitness is manifested in a variety of ways.

Hummingbird evolution is also an excellent example of speciation caused by isolation of populations from one another. There are about 350 identified hummingbird species, all of whom live in the Americas. A considerable number of these species are found in the Andes Mountains. Contemporary research suggests that as parts of the Andes gradually rose in elevation (due to tectonic shifting), hummingbird populations were forcibly separated, which eventually led to speciation. More specifically, the genus Adelomyia split into several species due to uplift in the northern reaches of the Andes.

For more information see:

Chaves, J. A., Weir, J. T., & Smith, T. B. (2011). Diversification in Adelomyia hummingbirds follows Andean uplift. Molecular Ecology, 20,21.

Chaves, J. A., & Smith, T. B. (2011). Evolutionary patterns of diversification in the Andean hummingbird genus Adelomyia. Molecular Phylogenetics and Evolution, 60,2.

Gonzlez, C., Ornelas, J. F., & Gutierrez-Rodriguez, C. (2011). Selection and geographic isolation influence hummingbird speciation: Genetic, acoustic and morphological divergence in the wedge-tailed sabrewing (Campylopterus curvipennis). BMC Evolutionary Biology, 11, 1.

Kirchman, J. J., Witt, C. C., McGuire, J. A., & Graves, G. R. (2010). DNA from a 100-year-old holotype confirms the validity of a potentially extinct hummingbird species. Biology Letters, 6, 1, 112-5.

Parra, J., McGuire, J. A., & Graham, C. (2010). Incorporating clade identity in analyses of phylogenetic community structure: an example with hummingbirds. The American Naturalist, 176, 5.

Wright, N. A., Gregory, T. R., & Witt, C. C. (2014). Metabolic ‘engines’ of flight drive genome size reduction in birds. Proceedings of the Royal Society of Biological Sciences, 281.