Evolution: Cichlid fish variations (Evolution)

by David Turell , Wednesday, December 02, 2020, 21:05 (1450 days ago) @ dhw

QUOTE: "Evolutionary theorists have two models for how adaptive radiation might play out. In one, rapid diversification in some aspect of body morphology produces a burst of new species at first, and then speciation slows as the available niches fill up. In the other model, differences in species emerge in stages as a lineage cracks open opportunities available to it, which means that the rate of speciation can both rise and fall over time. Evolutionary biologists have turned up only limited evidence to bolster either of these theories.
This difference in genetic diversity across branches could be explained by hybridization, in which different cichlid species interbreed and introduce more genetic diversity into a genome.

DAVID: True speciation is in the eye of the beholder, be he splitter or grouper. This does not help us understand the huge gaps Gould noted.

dhw: Of course it does. But I see no reason why the authors don’t combine all three theories. When niches fill up, or when new opportunities arise, the cichlids adapt themselves accordingly. And the new forms can still interbreed with the surviving older forms. The gaps in speciation are caused by the gaps between changes to the environment or the gradual exhaustion of existing niches, which would require exploitation of different niches.

Gould's gaps were huge changes in phenotype and physiological processes. These are tiny variations in a family of fish.