Drift and Directional Selection Are the Evolutionary Forces Driving Gene Expression Divergence in Eye and Brain Tissue of Heliconius Butterflies.

Autor:	Catalán A; Department of Evolutionary Biology, Evolutionary Biology Centre (EBC), Uppsala University, 75236, Sweden ana.catalan@gmail.com sebastian.hoehna@gmail.com.; Division of Evolutionary Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried 82152, Germany., Briscoe AD; Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697., Höhna S; Division of Evolutionary Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried 82152, Germany ana.catalan@gmail.com sebastian.hoehna@gmail.com.; Department of Earth and Environmental Sciences, Paleontology and Geobiology, 80333 Munich, Germany.; GeoBio-Center, Ludwig-Maximilians-Universität München, 80333 Munich, Germany.
Jazyk:	angličtina
Zdroj:	Genetics [Genetics] 2019 Oct; Vol. 213 (2), pp. 581-594. Date of Electronic Publication: 2019 Aug 29.
DOI:	10.1534/genetics.119.302493
Abstrakt:	Investigating gene expression evolution over micro- and macroevolutionary timescales will expand our understanding of the role of gene expression in adaptation and speciation. In this study, we characterized the evolutionary forces acting on gene expression levels in eye and brain tissue of five Heliconius butterflies with divergence times of ∼5-12 MYA. We developed and applied Brownian motion (BM) and Ornstein-Uhlenbeck (OU) models to identify genes whose expression levels are evolving through drift, stabilizing selection, or a lineage-specific shift. We found that 81% of the genes evolve under genetic drift. When testing for branch-specific shifts in gene expression, we detected 368 (16%) shift events. Genes showing a shift toward upregulation have significantly lower gene expression variance than those genes showing a shift leading toward downregulation. We hypothesize that directional selection is acting in shifts causing upregulation, since transcription is costly. We further uncovered through simulations that parameter estimation of OU models is biased when using small phylogenies and only becomes reliable with phylogenies having ≥ 50 taxa. Therefore, we developed a new statistical test based on BM to identify highly conserved genes ( i.e. , evolving under strong stabilizing selection), which comprised 3% of the orthoclusters. In conclusion, we found that drift is the dominant evolutionary force driving gene expression evolution in eye and brain tissue in Heliconius Nevertheless, the higher proportion of genes evolving under directional than under stabilizing selection might reflect species-specific selective pressures on vision and the brain that are necessary to fulfill species-specific requirements. (Copyright © 2019 Catalán et al.)
Databáze:	MEDLINE
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