More interesting than the whole concept of natural selection, which is indeed astounding and amazing and interesting in its own right, is that right now, we are in the midst of a very large experiment along the those lines.
You may have gotten the memo, or at least you stole a glance at it on Kendra’s desk, that the earth is warming. This has to do with the large amount of gases we have expelled into our atmosphere. The one with most of the press is carbon dioxide. Along with the warming, is an increase in carbon dioxide dissolving into water, which lowers the pH. There are direct consequence of a warmer and more acidic environment; many organisms will undoubtedly die, many populations will be wiped out, species may go extinct.
Organisms all over the planet are experiencing unprecedented changes to their surroundings. Among the organisms effected are the phytoplankton. In the worlds ocean phytoplankton are responsible for the majority of the productivity, not to mention oxygen production, that allow us to inhabit this planet. Will these microscopic algae manage to persist in our warmer more acidic world? This question is not a new question, and several researches have already attempted to tackle this, and related questions. It is an important question, because if they do not survive, neither will we.
Marine phytoplankton are single celled organisms with fast reproduction. This probably gives them adaptive potential. That is a fancy, but descriptive, word to describe the genetic variation that exists within a population, that allows a selective response to environmental change. Organisms that reproduce quickly, produce lots of young, the more you produce, the more potential variation exists. Single celled organisms, however, make a direct copy of themselves, and therefore a population might not hold as large amount of genetic variation as expected.
A quick aside: These organism, though single celled may go through a period of sexual reproduction as well. Diatoms, one of the major phytoplankton groups, do this periodically.
Back to the big question: Do marine phytoplankton have enough variation within populations to suffer the slings and arrows of the outrageous fortune of climate change? Another, related question, is that if…okay, when, huge numbers of a population die-off due to climate changes, will the resulting population maintain enough variation to handle other environmental fluxes? When lots of a population die-off one of the potential consequences is known as a genetic bottleneck; another descriptive terms that just means only a few individual fit through the narrow part of the bottle and survive, these few only carry with them a small portion the genetic diversity that existed within the original population.
Some good news:
In a review, Collins and her colleagues (referenced below) found that gene diversity is pretty high among most of the phytoplankton examined. Gene diversity, as reported, was a measure of heterozygosity based on unique genotypes: Maybe time for a quick genetics refresher?
Genetics/DNA Refresher side note:
At a location on the DNA, called a loci in genetics speak, exists a nucleotide, one of four abbreviated by the first letters A, T, C, or G. An individual with a heterozygote loci is one where, for example, most of the population has a G at that locations, while this individual has an A. That’s the very basic idea anyway. It is a measure of genetic diversity that is one of the easier to determine, but also not one of the more precise.
Genetic diversity (heterozygosity) ranged, among several groups studied, from 0.39 to 0.88. WTH does this mean? It’s basically the change that a gene, drawn randomly I guess, is different than the “regular” population. Heterozygosity of humans is slightly lower than the phytoplankton in these studies.
This is good news: Much of the marine phytoplankton appear to have a high degree of genetic diversity. This bodes well for these population in managing to survive the changes that are rushing in. However, on the bad news front, modeling of the biodiversity of phytoplankton shows a decrease in overall diversity and thus resilience of these communities. (See Henson et al below)
Let’s take a step back. These conclusions, above, are drawn from single studies, sometimes with a little backup enhancement. I mentioned that heterozygosity may not be the most precise was to measure genetic diversity, and the biodiversity modeling is just that, modeling. Basically, keep your salt shaker handy.
Okay step forward again: Changes are happening, plenty of bad things will occur, and some interesting stuff too. Keep your hats on, your eyes open, and watch with me as the world changes.
*Something about bubbles.
Reference and further readings
Collins S, Rost B, Rynearson TA. 2014. Evolutionary potential of marine phytoplankton under ocean acidification. Evolutionary Applications 7:140–155. doi: 10.1111/eva.12120
Henson SA, Cael BB, Allen SR, and Dutkiewics S. 2021. Future phytoplankton diversity in a changing climate. Nature Communications 12: 1–8. https://doi.org/10.1038/s41467-021-25699-w
Rudan, I., Carothers, A., Polasek, O. et al. Quantifying the increase in average human heterozygosity due to urbanisation. European Journal of Human Genetic 16:1097–1102 (2008). https://doi.org/10.1038/ejhg.2008.48
Shakespeare W. 1881. Hamlet, Prince of Denmark. New York: Harpers and Brothers.
I just must put a note here, the official way to cite Shakespeare appears to be to cite the copy you have handy, although I see the point, it also seems a bit strange. Hamlet was written in 1609 (or first performed then anyway), shouldn’t we be citing that one? But of course I do not have that one handy, so maybe it makes sense to cite a handy copy: It turns out my copy is damn old, but not that old. On the other hand I should probably have not put this reference here at all to see who could pick out the bow to WS.