Saturday, September 22, 2012

Evolutionary contingency (in the lab)

Bount et al (2012) describes a very interesting study of the appearance (evolution) of the ability of the common gut bacteria, E. coli, to utilize citrate in the presence of O2, something that E. coli normally cannot do. This work was based on the original observation that described the evolutionary origin of citrate utilizing E. coli (Bount et al., 2008).  The Lenski lab has been growing (and freezing) samples of this population for over 40,000 generations (here is an interesting paper on how these populations have been used to study competition within a population (Le Gac et al., 2012).  

The evolution of the ability to utilize citrate in the presence of O2 in E. coli involved "potentiating mutations", which occurred in one specific lineage somewhere around the 20000th generation of the experiment.  These mutations have no (as yet discovered) overt phenotype on their own. 

Later on in this lineage, around the 31,000th generation, there was a mutation that involved the duplication and generation of a novel fusion protein derived from the citrate-succinate antiporter (a membrane-transport protein of a type we discuss generically here in biofundamentals).  This mutation allows the cell's carrying it to import and grow (albeit) poorly on citrate.  Subsequent mutations improve the efficiency of citrate metabolism.  

What is interesting is that because they had "frozen ancestors", Blout et al could "replay" their evolution, and ask, when new citrate utilizing lines arose (which they did), whether they had similar (although not identical) mutations to that found in the originally identified lines.  Interestingly, they did.  

Now it becomes an interesting question whether, given that E. coli is usually defined in part by its inability to grow on citrate under aerobic conditions, whether the appearance of cells, derived from E. coli, but able to grow on citrate in the presence of O2 represents a new species or not.  

Saturday, September 15, 2012

Evolutionary thinking and "just so" stories

It is all to easy to tell satisfying stories about how various traits have come to be:  here Anthony Gottlieb in the New Yorker writes about just so stories about the origins of human behavior (and consciousness).

The essay makes a number of points that I have tried to emphasize in class and is worth reading.

Thursday, September 13, 2012

Thinking about sexual dimorphism (again)

Well, here is a particularly dramatic example of sexual dimorphism, a new species of monkey identified in the Congo (and described in the NYT) and an interesting quote, "And adult males have a huge bare patch of skin in the buttocks, testicles and perianal area,” said John A. Hart, the researcher who described the coloring. “It’s a brilliant blue, really pretty spectacular.”" Now I wonder why?

Monday, September 10, 2012

Out of Africa, Mitochondrial Eve and Nuclear Adam

  Here is an article by CAMPBELL & MISHKOFF (2008) on genetic diversity in Africa and a current view on human migration out of African that you might find interesting.

The video is a cleaned up version of the original video, so as to remove (most) gratuitous insults.