Differences in transmission and ploidy between sex chromosomes and autosomes drive divergent evolutionary trajectories, with sex chromosomes generally evolving faster. Because sex-linked genes are transmitted less frequently, they are under less efficient selection. Conversely, exposure of recessive mutations on haploid sex chromosomes creates more efficient selection. In most systems, these effects occur simultaneously and are confounded. The fly families Sciaridae (fungus gnats) and Cecidomyiidae (gall midges) have X0 sex determination, but males transmit only maternally inherited chromosomes. This phenomenon results in equal transmission of the X and autosomes, allowing the effect of haploid selection to be studied in isolation. We discover that, unlike well-studied systems, X chromosomes diverge more slowly than autosomes in these flies. Using population genomic and expression data, we show that despite the X evolving more adaptively, stronger purifying selection explains slower divergence. Our findings demonstrate the utility of non-Mendelian inheritance systems for understanding fundamental evolutionary processes.

Department of Biology and Ecology Faculty of Science University of Ostrava Ostrava Czech Republic

Department of Entomology and Nematology University of Florida Gainesville Florida USA

Institute of Ecology and Evolution University of Edinburgh Edinburgh UK

RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences RIKEN Wako Japan

School of Biology University of St Andrews St Andrews UK

Whitehead Institute for Biomedical Science and Howard Hughes Medical Institute Cambridge Massachusetts USA

Zobrazit více v PubMed

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