Convergent Evolution

Contributed by Greg Fricker and Geoffrey Welch

Have you ever thought how similar butterflies and bats are in taking to the skies? Looking around, we see that both of these creatures use wings for flight; however, butterflies are insects, and bats are mammals, like you and me. If we imagine the tree of life, these organisms would be on distant branches, having distinct lineages, but they have similar characters. Convergent evolution is this phenomenon where similar characters evolve independently in multiple lineages. This seems like a counter-intuitive process initially, as similar features are often associated with relatedness. As evolution is all about favorable hereditary traits being passed on to future generations, how then do the same traits arise in completely separate lineages?

The answer lies in the selection pressures organisms face. When a certain trait is so remarkably important for organisms in a particular environment, it can be expected to arise in multiple different species. For example, consider underwater foraging birds. Cormorants, penguins, puffins, and gannets, each with minimal relatedness to the others, have evolved to have a “pygostyle” tail, which is straight and elongated.  This pygostyle tail is vitally important to these birds, as it acts like a “rudder,” allowing for enhanced steering in water, just like the rudder on a sailboat. This rudder is so beneficial for these underwater foraging birds in finding food–and thus surviving and having offspring–that we see it arise multiple times. When the random mutations occurred separately in these four species, the advantage provided by this “rudder” tail ensured that the pygostyle phenotype would be passed along to future generations.

Yet another example can be seen in echolocation, or the ability of an animal to use vocalizations to locate objects and better “see” its environment.  It might be easy to dismiss instances of convergence within the birds previously stated due to the fact that all four cases are aquatic birds, and thus seem as though they would be at least somewhat related. In that case, consider bats and dolphins. Despite the fact that they are both mammals, bats and dolphins would be expected to share little in common, as they both evolved in drastically different environments.  However, both utilize echolocation. Not only did they both evolve the same physical trait, but it has been determined that the two groups converged on a genetic level as well. Three separate genes that play a role in echolocation, including a protein associated with inner ear hair formation, have been shown to have converged among three separate groups–dolphins and two groups of bats. Echolocation provided such a substantial fitness benefit in the two separate environments of caves and marine life that natural selection drove the evolution of it in these rather unrelated lineages.

For more information, check out the video below:

Also, check out some of the recent research on convergence:

Parker et al. 2013. Genome-wide signatures of convergent evolution in echolocation mammals.  Nature. 502: 228-231.

Shen et al. 2012. Parallel evolution of auditory genes for echolocation in bats and toothed whales.  PLoS Genetics.  8(6): e1002788.

Liu et al. 2010. Convergent sequence evolution between echolocating bats and dolphins. Current Biology. 20 (2): 53-54.

Jones, G and MW Holderied.  2007.  Bat echolocation calls: adaptation and convergent evolution.  Proceedings of the Royal Society B. 274: 905-912.

Felice, RN and PM O’Connor. 2014. Ecology and caudal skeletal morphology in birds: the convergent evolution of pygostyle shape in underwater foraging taxa. PLoS One.  9(2): e89737.

Alerstam et al. 2011. Convergent patterns of long-distance nocturnal migration in noctuid moths and passerine birds. Proceedings of the Royal Society B. 278(1721): 3074-3080.

Gleiss et al. 2011.  Convergent evolution in locomotory patterns of flying and swimming animals.  Nature Communications. 2: 352.