Evidence of a Slower-Z effect in Schistosoma japonicum

preprint Evidence of a Slower-Z effect in Schistosoma japonicum draft Andrea Mrnjavac author 353FAC84-AE61-11E9-8BFC-00D3E5697425 Beatriz Vicoso author 49E1C5C6-F248-11E8-B48F-1D18A9856A870000-0002-4579-8306 BeVi department Sex-linked and autosomal loci experience different selective pressures and evolutionary dynamics. X (or Z) chromosomes are often hemizygous, as Y (or W) chromosomes often degenerate. Such hemizygous regions can be under greater efficacy of selection, as recessive mutations are immediately exposed to selection in the heterogametic sex (the so-called Faster-X or Faster-Z effect). However, in young non-recombining regions, Y/W chromosomes often have many functional genes, and many X/Z-linked loci are therefore diploid. The sheltering of recessive mutations on the X/Z by the Y/W homolog is expected to drive a Slower-X (Slower-Z) effect for diploid X/Z loci, i.e. a reduction in the efficacy of selection. While the Faster-X effect has been studied extensively, much less is known empirically about the evolutionary dynamics of diploid X or Z chromosomes. Here, we took advantage of published population genomic data in the female-heterogametic human parasite Schistosoma japonicum to characterize the gene content and diversity levels of the diploid and hemizygous regions of the Z chromosome. We used different metrics of selective pressures acting on genes to test for differences in the efficacy of selection in hemizygous and diploid Z regions, relative to autosomes. We found consistent patterns suggesting reduced Ne, and reduced efficacy of purifying selection, on both hemizygous and diploid Z regions. Moreover, relaxed selection was particularly pronounced for female-biased genes on the diploid Z, as predicted by Slower-Z theory. https://creativecommons.org/licenses/by-nc-nd/4.0/ 2024 eng bioRxiv10.1101/2024.07.02.601697 https://research-explorer.ista.ac.at/record/19370 https://research-explorer.ista.ac.at/record/18531 Mrnjavac A, Vicoso B. Evidence of a Slower-Z effect in Schistosoma japonicum. bioRxiv, <a href="https://doi.org/10.1101/2024.07.02.601697">10.1101/2024.07.02.601697</a>. A. Mrnjavac, B. Vicoso, BioRxiv (n.d.). Mrnjavac, A., & Vicoso, B. (n.d.). Evidence of a Slower-Z effect in Schistosoma japonicum. bioRxiv. <a href="https://doi.org/10.1101/2024.07.02.601697">https://doi.org/10.1101/2024.07.02.601697</a> Mrnjavac, Andrea, and Beatriz Vicoso. “Evidence of a Slower-Z Effect in Schistosoma Japonicum.” BioRxiv, n.d. <a href="https://doi.org/10.1101/2024.07.02.601697">https://doi.org/10.1101/2024.07.02.601697</a>. Mrnjavac A, Vicoso B. Evidence of a Slower-Z effect in Schistosoma japonicum. bioRxiv. doi:<a href="https://doi.org/10.1101/2024.07.02.601697">10.1101/2024.07.02.601697</a> A. Mrnjavac and B. Vicoso, “Evidence of a Slower-Z effect in Schistosoma japonicum,” bioRxiv. . Mrnjavac, Andrea, and Beatriz Vicoso. “Evidence of a Slower-Z Effect in Schistosoma Japonicum.” BioRxiv, doi:<a href="https://doi.org/10.1101/2024.07.02.601697">10.1101/2024.07.02.601697</a>. 185492024-11-13T09:12:08Z2026-09-11T22:31:10Z