©Copyright 2018 GEOSCIENCE RESEARCH INSTITUTE
11060 Campus Street • Loma Linda, California 92350 • 909-558-4548
Franchini, P, P Xiong, C Fruciana, RF Schneider, JM Woltering, CD Hulsey, A Meyer. MicroRNA gene regulation in extremely young and parallel adaptive radiations of crater lake cichlid fish. Molecular Biology and Evolution 36(11):2498-2511. https://doi.org/10.1093/molbev/msz168
Summary. Cichlid fish are well-known for their diversity in East African Rift lakes, but they are also present in Central America and other places. In Nicaragua, two volcanic crater lakes, Lake Xiloá and Lake Apoyo, have multiple cichlid species that apparently differentiated in a short time and without geographic separation. Each lake has an elongated “limnetic form” and more than one high-bodied “benthic form.” The lakes are believed to have formed relatively recently, raising the question of how these fish could diverge so rapidly, since there has not been enough time for mutations to accumulate. The answer seems to be that rapid changes in microRNA sequences have affected gene expression by reducing the activity of mRNA. This seems to be an important factor in the rapid changes in the morphology of these cichlid species.
Comment. Many examples are known of species that have apparently changed much more rapidly than can be accounted for by conventional estimates of mutation rates. This has been puzzling, since neo-Darwinian orthodoxy postulates that species evolve through accumulation of mutations of long periods of time, despite evidence that harmful mutations would accumulate more rapidly than beneficial mutations. Discoveries such as this, along with epigenetic effects, help explain the mechanism behind some of the rapid changes. Rapid changes can be due to changes in gene regulation, as shown in this study. These mechanisms might explain changes that result in minor modifications of existing structures. However, they cannot explain the origins of new morphological structures because they apparently affect only the amounts of gene products and do not produce anything new.
Elmer, KR, S Fan, H Kusche, ML Spreitzer, AF Dautt, P Franchini, A Meyer. 2014. Parallel evolution of Nicaraguan crater lake cichlid fishes via non-parallel routes. Nature Communications 5.5168. Doi: 10.1038/ncomms6168
 E.g., see Brand, LR and LJ Gibson 1993. An interventionist theory of natural selection and biological change within limits. Origins 20(2):60-82; Gibson, LJ. 2019. Genetic similarity does not necessarily mean common inheritance; Frequently Asked Questions on Speciation.