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.