Microchromosome fusions underpin convergent evolution of chameleon karyotypes
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2023-07-17
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2021-04-01
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chromosome evolution
cytogenetics
molecular phylogenetics
ancestral state estimation
cytogenetics
molecular phylogenetics
ancestral state estimation
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Evolutionary shifts in chromosome compositions (karyotypes) are major drivers of lineage and genomic diversification. Fusion of ancestral chromosomes is one hypothesized mechanism for the evolutionary reduction of the total chromosome number, a frequently implied karyotypic shift. Empirical tests of this hypothesis require model systems with variable karyotypes, known chromosome features, and a robust phylogeny. Here we used chameleons, diverse lizards with exceptionally variable karyotypes ($2n=20\text{-}62$), to test whether chromosomal fusions explain the repeated evolution of karyotypes with fewer chromosomes than ancestral karyotypes. Using a multidisciplinary approach including cytogenetic analyses and phylogenetic comparative methods, we found that a model of constant loss through time best explained chromosome evolution across the chameleon phylogeny. Next, we tested whether fusions of microchromosomes into macrochromosomes explained these evolutionary losses using generalized linear models. Multiple comparisons supported microchromosome fusions as the predominant agent of evolutionary loss. We further compared our results to various natural history traits and found no correlations. As such, we infer that the tendency of microchromosomes to fuse was a quality of the ancestral chameleon genome and that the genomic predisposition of ancestors is a more substantive predictor of chromosome change than the ecological, physiological, and biogeographical factors involved in their diversification.
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Marcello Mezzasalma, Jeffrey W Streicher, Fabio M Guarino, Marc E H Jones, Simon P Loader, Gaetano Odierna, Natalie Cooper, Microchromosome fusions underpin convergent evolution of chameleon karyotypes, Evolution, Volume 77, Issue 9, September 2023, Pages 1930–1944, https://doi.org/10.1093/evolut/qpad097
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Copyright ©The Author(s) 2023. Published by Oxford University Press on behalf of The Society for the Study of Evolution (SSE). This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. The linked file is the published version of the article.
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0014-3820
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1558-5646