Heritability of Sex Tendency in a Harpacticoid Copepod, <i>Tigriopus californicus</i>

Systems with genetic variation for the primary sex ratio are important for testing sex-ratio theory and for understanding how this variation is maintained. Evidence is presented for heritable variation of the primary sex ratio in the harpacticoid copepod <i>Tigriopus californicus</i>. Variation in the primary sex ratio among families cannot be accounted for by Mendelian segregation of sex chromosomes. The covariance in sex phenotype between full-sibling clutches and between mothers and offspring suggests that this variation has a polygenic basis. Averaged over four replicates, the full-sibling heritability of sex tendency is 0.13 ± 0.040; and the mother-offspring heritability of sex tendency is 0.31 ± 0.216. Genetic correlations in the sex phenotype across two temperature treatments indicate large genotype-by-temperature interactions. Future experiments need to distinguish between zygotic, parental, or cytoplasmic mechanisms of sex determination in <i>T. californicus</i>.