There’s no way I can back this up at all

14 01 2007

Lately I’ve been enthralled by all things large and mammalian that live(d) in Africa, indulging myself with the Alan Turner/Mauricio Anton books Evolving Eden, Big Cats and Their Fossil Relatives, and Relentless Enemies by Derek & Beverly Joubert. The “charismatic megafauna” of Africa is so interesting to me, especially given the variation in behavior and appearance across the continent. Relentless Enemies is a wonderful example of this, showing lions that have specialized in eating the dangerous Cape Buffalo and have learned to cope with the swampy Okovango Delta habitat. Lions normally aren’t big fans of water, but these lions quickly take to it, only really getting upset when their whiskers touch the surface (I assume because, other than perhaps wanting to keep their whiskers dry, this means they’re in water too deep to feel the bottom).

In any event, although there have been big cats, giraffes, antelope, elephant, hippos, and other extant varieties present for millions of years, they took some rather odd forms and were generally more “pointy” (more horns, teeth, etc) than their living counterparts. This got me wondering about evolution in general and convergence; if you have two animals that have arrived at the same form via two different lineages how different are they going to be genetically? The example that came to my mind first involved flight, bats having their wing made from membrane between their fingers and the extinct pterosaurs having their wings made of a membrane stretched from an elongated 4th digit to their body. Would both these groups have similar genes for making the membranes that allow them to fly? Perhaps not, the actual membrane differing in the way its attached and probably composition, but alas, there is likely no way to tell being we won’t ever be able to faithfull reconstruct a pterosaur genome for lack of material.

Even so, it makes me wonder. I thought about the oft cited similarity between chimpanzees and humans as well (the estimate of similarity going from 98% to 95% recently, if I remember correctly), but I think this implies a flase ancestor/descendant relationship at times. Surely, we are most closely related to chimpanzees out of the extant great apes, but we didn’t evolve from them; at best we shared a recent common ancestor and we’ve both evolved along seperate lineages for at least 2 million years. During the divergance of lineages later leading to humans and then to chimpanzees, what was the ancestor like? What adaptations or novel structures/functions/behaviors have chimps picked up since the split? Since we are related, if we both independantly evolved similar features how would these features be expressed in the genome; would it essentially show up as a “false positive” suggesting that we both inherited a feature that was evolved independantly by both groups?

Unfortunately for me, the areas in which I excel are the more “traditional” areas associated with zoology, mostly being anatomy, behavior, etc. and microbiology/genetics often makes my head spin (as much as I would love to have a natural aptitude for it). Still, I can’t help but wonder if some of the results of phylogenetic studies that don’t match up with the fossil record are because of convergence. In the Big Cats book, it’s mentioned that as a result of phylogenetic study that extant lions were suggested to be descendants of saber-toothed cats, but we know this not to be true (they are sister groups, both on different “brances” of the Tree of Life [or bush, or coral, if you prefer], sharing a common ancestor) because of fossil evidence. Is it possible that because both animals developed similar features independantly, resulting in convergent evolution, they appear to share more genetic material than they actually do? This problem may not be anything new to those who specialize in genetics, but they will have to forgive me for being slow. What if we could genetically figure out the results of convergent evolution, being able to better pinpoint relationships and what occurred during the history of life? If no one has tackled it yet, perhaps I’ll have to buy some genetics books and get cracking.


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2 responses

14 01 2007
Neil

Just stumbled across your weblog Brian, nice stuff.

Genetics are surely an incredibly powerful tool for reconstructing evolutionary patterns and relationships. As you note there is much to be worked to be done integrating what we’ve learned from the fossil record, and what can be revealed with genetic investigation.

Genetic “convergence” often takes a somewhat different form than morphological convergence. One example is the clustering of some parasitic plants on gene-based cladograms, not because they are closely related, but because they have all deleted formerly diagnostic sequences (related to photosynthesis for example), erasing their connections to their respective parent groups and making them appear superficially similar.

Like you I am no geneticist, but I find this stuff equally fascinating!

14 01 2007
laelaps

Hi there Neil, and thanks for the information! I figured that genetic “convergence” would show up differently, and we know from evodevo that you can have changes in phenotype without changes in genotype, but I do want to look further into seeing how a structure would be coded in various organisms, i.e. a wing in a bird, pterosaur, and bat since they’re all derived from tetrapods. Most likely the genes would be different, all relying on different structures, but all the crazy insertions, deletions, frame shifts, etc. that have occurred over time continue to pique my interest; I just wish I was better at understanding it all!đŸ™‚ Best regards,

Brian

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