Adaptive radiation is seen when the stickleback fish is exposed to a new niche that has no predators

Gene-environment interactions play an extremely important role in the adaptation of any species to a new or (rapidly) changing environment. For any living organism to colonize a new habitat or niche –– often it must rapidly adapt to multiple environmental challenges (this is called ‘multifarious’ divergent selection). This is most dramatic in adaptive radiations, where rapid successions of niche and habitat shifts take place within a lineage. However, most adaptive radiations started thousands of generations ago; thus, no one knows whether major phenotypic and genomic adaptation might occur within the first few generations of colonizing a new habitat, or over much longer time scales.

An excellent example of an “evolutionary bloom” is the secretoglobin gene group (SCGB) [Hum Genom 2o11; 5: 691-702]. If one compares the human and mouse genomes, the human genome has 11 SCGB genes and five pseudogenes, whereas the mouse genome contains 68 Scgb genes –– four of which are highly orthologous (similar in DNA/protein sequence) to human SCGB genes; the remainder (64 genes) represent an ‘evolutionary bloom’ and make up a large gene family having similarities to only six of the human SCGB counterparts. Such a “bloom” occurs by (rapid?) gene-duplication events, to create many genes in tandem, each protein of which then diverges to “handle” some new environmentally adverse signal. This “bloom” is evidence of a dramatic adaptive radiation required by the mouse ancestor (during the past 70 million years) to some (unknown) adverse environmental challenge(s) with which the human ancestor was not challenged..!!

Authors [see attached] decided to test whether rapid adaptation is possible –– in the adaptive radiation of threespine stickleback fish on the Haida Gwaii archipelago (in Western Canada). In a selection experiment that ONLY took 19 years, authors allowed stickleback fish from a large blackwater lake to evolve in a small clear-water pond that had no apparent vertebrate predators. Authors then compared 56 whole genomes from the experimental group and 26 whole genomes from natural populations. Authors found that adaptive genomic change was rapid in many small genomic regions and encompassed 75% of the change between 12,000-year-old ecotypes (which are distinct forms, or races, of a plant or animal species, occupying a particular habitat). Genomic change was as fast as phenotypic change in defense and trophic morphology, and both were largely parallel between the short-term selection experiment and long-term natural adaptive radiation. (Yes, even “living without predators” can represent a “new, shocking environmental adverse event”!) This really cool exciting experiment therefore shows that (functionally relevant) standing genetic variation can persist in derived radiation members –– thereby allowing adaptive radiations to unfold (evolutionarily) very rapidly..!!

Nature Ecol Evol July 2o18; 2: 1128–1138

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