Variance components of sex determination in the copepod <i>Tigriopus californicus</i> estimated from a pedigree analysis

How sex chromosomes evolve compared to autosomes remains an unresolved question in population genetics. Most studies focus on only a handful of taxa, resulting in uncertainty over whether observed patterns reflect general processes or idiosyncrasies in particular clades. For example, in female heterogametic (ZW) systems, bird Z chromosomes tend to evolve quickly but not adaptively, while in Lepidopterans they evolve adaptively, but not always quickly. To understand how these observations fit into broader evolutionary patterns, we explore Z chromosome evolution outside of these two well-studied clades. We utilize a publicly available genome, gene expression, population, and outgroup data in the salmon louse Lepeophtheirus salmonis , an important agricultural pest copepod. We find that the Z chromosome is faster evolving than autosomes, but that this effect is driven by increased drift rather than adaptive evolution. Due to high rates of female reproductive failure, the Z chromosome exhibits a slightly lower effective population size than the autosomes which is nonetheless to decrease efficiency of hemizygous selection acting on the Z. These results highlight the usefulness of organismal life history in calibrating population genetic expectations and demonstrate the value of the ever-expanding wealth of publicly available data to help resolve outstanding evolutionary questions.

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Genetic drift drives faster-Z evolution in the salmon louseLepeophtheirus salmonis

Mongue,

Baird

2023

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Sex chromosome evolution is a particularly complex sub-field of population genetics and there are still unresolved questions about how quickly and adaptively these chromosomes should evolve compared to autosomes. One key limitation to existing knowledge is an intense focus on only a handful of taxa in existing literature, resulting in uncertainty about whether observed patterns reflect general processes or are idiosyncratic to the more widely studied clades. In particular, the Z chromosomes of female heterogametic (ZW) systems tend to be quickly but not adaptively evolving in birds, while in butterflies and moths Z chromosomes tend to be evolving adaptively, but not always faster than autosomes. To understand how these two observations fit into broader evolutionary patterns, we explore, for the first time, patterns of Z chromosome evolution outside of these two well-studied clades. We utilize a publicly-available high quality genome, gene expression, population, and outgroup data for the salmon louseLepeophtheirus salmonis, an important aquacultural pest copepod. We find that the Z chromosome is faster evolving than the autosomes, but that this increased effect is driven by drift rather than adaptive evolution. This faster-Z effect seems to be a result of a very low effective population size of the Z chromosome, as well as high rates of female reproductive failure contributing to decreased efficiency of hemizygous selection acting on the Z. These results highlight the usefulness of organismal life history in calibrating population genetic expectations and demonstrate the usefulness of the ever expanding wealth of modern publicly available genomic data to help resolve outstanding evolutionary questions.

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Variance components of sex determination in the copepod Tigriopus californicus estimated from a pedigree analysis

Cited by 3 publications

References 55 publications

Yes, polygenic sex determination is a thing!

Yes, polygenic sex determination is a thing!

Genetic drift drives faster-Z evolution in the salmon louse Lepeophtheirus salmonis

Genetic drift drives faster-Z evolution in the salmon louseLepeophtheirus salmonis

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