Highly Conserved Is Relative

When discussing some aspect of biology, we often want to know how common is the gene, pathway, structure, interaction, or other phenomenon we are interested in. This can be important in two distinct manners: 1. if we find our gene, pathway, etc. is maintained in many different types of organisms, this suggests that our gene, pathway, etc. likely plays an important or fundamental role in some level of biology; 2. if we find our gene, pathway, etc. is not found in different types of organisms, this suggests our gene, pathway, etc. likely can tell us something about the unique biology of what we are studying.

To discuss this phenomenon of commonality, we say that something is conserved (or not). Of course saying a gene, pathway, etc is conserved doesn't tell us much by itself, because we need to know the level of conservation. Is the gene, pathway, etc. conserved among sister species? within a class? a phyla? a kingdom? The answer to this question tells us a lot about whether we are looking at a fundamental process or at the level of specificity of the process. In the seminars and papers I read, I generally see a short-hand approach to discuss conservation where the speaker or author uses a superlative or adverb to suggest the level of conservation.

For example, I recently heard a talk where the presenter stated that a protein was 'highly conserved, being found in both mammalian systems and yeast.' That sounds pretty impressive. But I immediately thought of eukaryotic phylogeny (mammals and yeast are both eukaryotes), and this figure I borrowed from Lab Rat a former FoS blogger who blogs at Scientific American. This is a figure my Eukaryotic Microbiology students see every week in class (the bacteria and archaea are not included in this figure).

I want to draw your attention to the Opisthokonts over at ~4:00. This is the supergroup of eukaryotes containing the metazoa (animals) and fungi. If we blow up this area of the figure, the last common ancestor of animals and fungi is indicated by the red arrow. (FYI humans, including you, are indicated by the green arrow.)

Now look at the first picture and think about all the eukaryotic diversity absent from the Opisthokont group! Is something found in both mammals and yeast highly conserved? I suppose so, since that last common ancestor lived ~1 billion years ago. But mostly I suppose not, because the vast amount of eukaryotic diversity lacks it.

A tangential point, but it's probably worth pointing out that the eukaryotic kingdoms we mostly hear about: animals, fungi, and plants represent little of eukaryotic diversity. Animals and fungi are contained within the Opisthokonts and plants are contained within the embryophytes at ~1:00. Everything else on this wheel represent non-animal, non-fungal, non-plant eukaryotes.