Finding more examples of convergent evolution is something evolutionary biologist seek to discover. How about examples of convergence even more deeply ingrained - for example evolutionary convergence at the genetic level. Though not as easy to explain as the wing example (the reason wings are used to illustrate the concept in Biology 101) discovery of these pathways would be an exciting development in our understanding of how genetic traits evolve, core to understanding evolution and biology in general.
A recent publication in Science (Oct 2016) has illustrated just this, that different species took separate genetic pathways to similar end points.
The endpoint (trait) is increased oxygen affinity by hemoglobin. This trait would be very helpful to species that live in high altitudes since oxygen concentration in the air is lower. Jay Storz, from The University of Nebraska Lincoln, and colleagues looked at birds living in the Andes to see how high and low altitude species differed. High altitude birds, as expected, had more efficient hemoglobin. The surprise (in truth I don’t actually know if the researchers were surprised but doesn’t it sound good that way) was that the high altitude birds with more functional hemoglobin didn’t all get the ‘better’ hemoglobin in the same way, different genetic pathways lead to the final results.
Let me try to explain a possible mode for this by taking not from Biology 101 but from Genetics 101. A concept of introductory genetics called epitasis can be used to explain how this might occur.
In epistasis genes interact with each other so a single gene mutation in species 1 might cause different effects in species 2. Brief Genetics 101 tangent; Genes are illustrated with symbols A or a, for example. We have two of every gene so a genotype of the ‘A’ gene might be illustrated AA, or Aa, or aa. These forms of genes are called alleles. Further, if we add the ‘B’ gene the genotype for this individual might be AABb, or Aabb, or aaBB. Lets not worry about the other Genetic 101 idea about what uppercase or lowercase letters designate except to say that they are different forms (alleles) of the gene.
Consider two related species with four genes all with the same alleles that somehow influence hemoglobin function.
Species 1, genotype: aa bb dd ee
Species 2, genotype: aa bb dd ee
Species 3, genotype: aa bb dd ee
Over time mutations occur and divergence of species occurs. In species 1 the first mutation causes a change in the ‘A’ gene so its genotype is now AA bb dd ee. In species 2 and 3 a similar mutation occurs but in the ‘E’ gene, they are now aa bb dd EE.
Now these three species are under low oxygen pressure, high altitude species, so mutation that increase oxygen delivery efficiency would be very beneficial. A second mutation in species 1 (this time the ‘B’ gene) allows better oxygen delivery - its genotype is now (AA BB dd ee). The ‘A’ gene and ‘B’ gene work together to allow better oxygen delivery. Species two has the same mutation in the ‘B’ gene but due to its differing genotype, (aa BB dd EE) doesn’t reap the same effects. Species 3 meanwhile has a different mutation, this time in its ‘D’ gene. Its genotype is now (aa bb DD EE). The ‘D’ and ‘E’ genes work in concert allowing this species to gain better oxygen delivery via its hemoglobin. Now we have two species that have more efficient oxygen delivery (species 1 and 3), an adaptation to high altitude living, but they arrived at the more efficient system by different genetic routes.
Resultant structures, again, that come about via convergent evolution are called analogous structures, thus these are analogous genetic outcomes.
In this scenario the same mutation would not necessarily work for different species due to the differing genetic makeup of each species. Not only did the researches discover different pathways to better oxygen delivery but they found the same pathway would not necessarily work among different species, just as suggested by my simplified epistasis example.
Damn this evolution stuff is awesome.
Details about the paper:
Title: Predictable convergence in hemoglobin function has unpredictable molecular underpinnings. Authors: Chandrasekhar Natarajan, Federico G. Hoffmann, Roy E. Weber, Angela Fago, Christopher C. Witt, Jay F. Storz. Journal: Science 21 Oct 2016: Vol. 354, Issue 6310, pp. 336-339. DOI: 10.1126/science.aaf9070
Find it here: http://science.sciencemag.org/content/354/6310/336
or here: http://digitalcommons.unl.edu/bioscistorz/65/
Further reading:
Storz, JF. 2013. Causes of molecular convergence and parallelism in protein evolution. Nature Review Genetics. 17: 239-250.