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Variance Components of Sex Determination in the copepod Tigriopus californicus estimated from a pedigree analysis.
  • Jean Richardson,
  • Heather Alexander,
  • Bradley Anholt
Jean Richardson
University of Victoria

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Heather Alexander
Bamfield Marine Sciences Centre
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Bradley Anholt
University of Victoria
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Strong theory exists regarding population sex ratio evolution that predicts equal sex ratio (when parental investment is equal). In most animals, sex chromosomes determine the sex of offspring, and this fixed genotype for sex has made theory difficult to test since genotypic variance for the trait (sex) is lacking. It has long been argued that the genotype has become fixed in most animals due to the strong selection for equal sex ratios. The marine copepod Tigriopus californicus has no sex chromosomes, multiple genes affecting female brood sex ratio and a brood sex ratio that responds to selection. The species thus provides an opportune system in which to test established sex ratio theory. In this paper we further our exploration on the possibility that T. californicus has polygenic sex determination using an incomplete diallel crossing design and the “animal model” for analysis of the variance components of sex determination in the species. Our data confirm the presence of extra-binomial variance for sex, further confirming that sex is not determined through simple Mendelian trait inheritance. In addition, our crosses and backcrosses of isofemale lines selected for biased brood sex ratios show intermediate phenotypic means, as expected if sex is a threshold trait determined by an underlying “liability” trait controlled by many genes of small effects. Finally, we estimate heritability of an individual to be male or female on the observed binary scale as 0.09 (95% CI: 0.034-0.14). This work furthers our accumulating evidence for polygenic sex determination in T. californicus.
20 Dec 2022Submitted to Ecology and Evolution
21 Dec 2022Submission Checks Completed
21 Dec 2022Assigned to Editor
17 Jan 2023Reviewer(s) Assigned
17 Feb 2023Review(s) Completed, Editorial Evaluation Pending
20 Feb 2023Editorial Decision: Revise Minor
19 Mar 20231st Revision Received
21 Mar 2023Submission Checks Completed
21 Mar 2023Assigned to Editor
21 Mar 2023Review(s) Completed, Editorial Evaluation Pending
24 Mar 2023Editorial Decision: Accept