On most Sundays, I won’t be around to post, except in the evening, half-brain dead from ISL class. Anyhow, I’m a day off to recuperate from last week, so I have time to post my very first “Monday Organism”, and a day early, at that!
Since this is the first weekly organism, I think it’s appropriate to explain why there is, in fact, a weekly organism. Since this blog is about biology, it’d be mighty improper unless it had periodical items about animals, don’t you think? I mean, come on, it’s no use running a blog about biology without fluffy animals in it (or angry wobbly ones or, well, extremely tiny ones).
Also, the Monday Organism is sometimes going to be about higher taxa as well (usually very high taxa, mainly to illustrate an interesting point about evolutionary biology)
The first Monday Organism is actually not an Organism, but a Phylum: Cyanobacteria.
Cyanobacteria literally means “blue bacteria”, but they’re actually called “blue algae” in Hebrew. The wiki on Cyanobacteria states that the taxonomy of Cyanobacteria is under revision, which is no surprise. In class, this group was even (I think most appropriately) called “Cyanophyta”, meaning “blue algae”.
Cyanobacteria are a fascinating group, and their existence is sound evidence for various evolutionary theories, the most important one is probably the evolution of the chloroplast organelle, the organelle in plant cells in which photosynthesis occurs.
The truly amazing thing about Cyanobacteria is the fact that they’re actually prokaryotes (having no distinct cell nuclei), and yet, they have photosynthetic pigments in their cells which are used to produce organic material by absorbing light energy from the sun. This means, in effect, that Cyanobacteria are the evolutionary precursor for the eukaryotic plants.
While it is obvious that all algae are commonly related, the truly interesting characteristics of Cyanobacteria are the ones that point out to the evolution of plant organelles. When I first learnt about Endosymbiont theory, I was plainly told that “endosymbiont bacteria eventually became permanent organelles”. Now these endosymbiont bacteria have a name: Cyanobacteria. In fact, the evidence shows that the Cyanobacteria themselves evolved into the chloroplast, and it is quite possible that every plant cell is, in a way, a symbiotic colony of eukaryotes and prokaryotic photosynthetic bacteria!
Obviously, the radiation of photosynthetic taxa is prolific enough to rule out such a simplistic story, but the evidence shows similar genetic and biochemical traits in modern day chloroplasts and in the makeup of Cyanobacteria. Since this isn’t an encyclopedic article and I rather focus only on one interesting concept at the time, I’ll give just one example for “evidence” of the common descent of CB and chloroplasts : the genetic makeup of chloroplast DNA (yes, they have their own DNA and they replicate on their own!) is similar to Cyanobacteria DNA. This alone is solid evidence for common descent for the two.
There’s lots of special cases of endosymbiosis that show not-so-common descent, but rather “common descents”, but I’ll leave that to the avid reader.
The main point of this post is not so much to tell about CB anatomy (warning: other posts might deal with interesting anatomy and physiology!), rather it is to illustrate classic tools in evolutionary research: genetic, anatomical, biochemical and physiological comparison as instruments for detecting common descent. It’s a crucial way of thinking in all of biology, and it highlights the sometimes elusive practical value in evolutionary theory: knowing the genetic relationship between different taxa can be critical in any biological endeavor. If one seeks to find antibiotic weaponry against infection and disease, knowing the culprit’s phylogeny can be of tremendous use, and phylogeny is best derived from the comparative tools I’ve briefly illustrated here.