Evolutionary capacitance

Previously, I took issue with John Avise’s abrupt description of alternative splicing as having “some advantage,” as alternative splicing may play a crucial role in the evolution of metazoans by shielding sequence from selection, allowing minor variants to emerge and grow before being put to the full test of selection. It’s such shielding that might be required to expand a more complex state. One way to think of alternative splicing is as an evolutionary capacitor. I’ll let the Masel group describe what that means:

Biological systems have a tendency to become robust or canalized to perturbation during evolution. This leads to a buildup of cryptic genetic variation. Cryptic genetic variation may not be 100% hidden, and low residual levels of selection may act as a form of pre-screening. This removes the most deleterious alleles and leaves the remaining variation pre-enriched for potential adaptations (Masel 2006). This enrichment means that the majority of adaptations are likely to stem from cryptic genetic variation, making it of fundamental importance in evolution. Evolutionary capacitors provide a window into cryptic genetic variation, facilitating its study.

Evolutionary capacitors are molecular mechanisms that are able to tap into stocks of cryptic genetic variation. Just as an electronic capacitor stores and releases charge, an evolutionary capacitor stores and releases genetic variation. Examples include the yeast prion [PSI+], regulators of alternative splicing, phase variation and gene conversion. In fact, any complex network can have evolutionary capacitance properties, so capacitance is likely to be widespread.

6 responses to “Evolutionary capacitance

  1. What is cryptic genetic variation?

  2. “Cryptic genetic variation (CGV) is defined as standing genetic variation that does not contribute to the normal range of phenotypes observed in a population, but that is available to modify a phenotype that arises after environmental change or the introduction of novel alleles.” – Greg Gibson and Ian Dworkin

  3. “The major difference is that the eukaryotic RNAP has two components not seen in the archaeal version – Rpb 8 and 9.”

    I couldn’t find the essay you pulled together on the subject, Mike Gene. Something about ribosomes.

    I’m sure its one of those duck/rabbit things, but the most significant difference that I immediately noticed between the two tinker-toy diagrams was not the addition of elements, but in the number of triangles.

    You’ve illustrated an increase in evolutionary capacity.

  4. Still can’t quite get my head around this. Is CGV conserved, or is it more like a secretary pool – you might get lucky and get a girl who can type 100 wpm just at the right moment when you have to produce a 1200 page report by noon but she might not be there tomorrow?

    Sorry for the lame analogy but I’m having trouble visualizing this concept.

  5. Speaking of “rationality”—What would be the design rationale for retaining in memory information (charging a capacitor) that does not does not serve an immediate purpose or serves as a the basis of prediction (pre-adaptation?)?

    What saves the assertion from being a triviality? Whenever you say anything does something it amts to saying it has that capacity, to do whatever it is it does (evolve, e.g.)?

    Every material object and process has a memory or capacity, after all.

    [William Bialek and one of his students, whose name I’ve forgetten, have published a very interesting paper on predictive information. I recall (but check me) that they assert that there is in fact no other rationale for retaining info (memory, capacitance) than prediction. And how does “cryptic variation” and prediction relate to “junkDNA”?]

  6. Someone has just told me that the “design rationale” for hoarding “junk” is the uncertainty (inherent to info) of its future utility.

    Interesting theory?!

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