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Researchers identified 22 chromosomal inversions in guppy populations from three Trinidadian rivers with varying predation levels, finding these inversions are ancient (1-6 million years old) and predate river colonization. Three inversions showed associations with adaptation to different predation environments, while seven others were maintained across all populations without clear adaptive benefits. The study reveals that sexual selection, particularly female preference for novel male color patterns, likely contributes to maintaining these genetic inversions at higher levels than would be expected from natural selection alone.
Why it matters
This research demonstrates how sexual selection can preserve genetic diversity over millions of years, providing insights into how complex traits evolve and are maintained in wild populations. The findings help explain the mechanisms behind balanced polymorphisms in nature and the interplay between different selective pressures in shaping genome evolution.
Understand the Science
by Yuying Lin, Wouter van der Bijl, Judith E. Mank
Understanding the distribution, frequency, and long-term persistence of chromosomal inversions in natural populations is key to understanding population evolution and adaptive processes. Inversions often span multiple genes, are subject to strong selective pressures and can affect complex traits. Here, we used an unbiased method to identify inversions in guppies from three different Trinidadian rivers with paired high- and low-predation populations which differ in a wide range of morphological, behavioural and life-history traits. We identified 22 inversions, ranging in age from 1 to 6 million years, which are widespread across the genome and predate the colonisation of each river. We were able to verify the breakpoints for all but one of these inversions using linked reads. We find three inversions that are significantly associated with local adaptation syndromes in high- versus low-predation populations, however, none are reciprocally fixed throughout all three replicate rivers. Additionally, we observe seven additional inversions maintained in all three rivers without evidence of local adaptation. Simulations reveal that the level of inversion polymorphism that we observe is far greater than expected under a neutral model. We observed a significant overlap between polymorphic inversions and loci previously implicated in male ornament pattern variation in guppies, suggesting that negative frequency-dependent selection due to female preference for male pattern novelty might explain the maintenance of inversion polymorphism. Overall, our results show the role of sexual selection in the long-term maintenance of inversion polymorphisms, and an interplay between sexual and natural selection in frequency dynamics.