title: Sex-ratio adjustment in response to local mate competition is achieved through an alteration of egg size in a haplodiploid spider mite.
abstract: Sex-ratio adjustments are commonly observed in haplodiploid species. However, the underlying proximate mechanisms remain elusive. We investigated these mechanisms in Tetranychus urticae, a haplodiploid spider mite known to adjust sex ratio in response to the level of local mate competition (LMC). In this species, egg size determines fertilization probability, with larger eggs being more likely to be fertilized, and thus become female. We explored the hypothesis that sex-ratio adjustment is achieved through adjustment of egg size. By using spider mites from a large population, we found that females produced not only a higher proportion of daughters under high levels of LMC, but also larger eggs. Moreover, in populations experimentally evolving under varying levels of LMC, both the proportion of females and the egg size increased with LMC intensity. These results suggest that sex-ratio adjustment in spider mites is mediated by egg size, although the causal relationship remains to be tested.
authors.affiliation: Université Montpellier 2, CNRS, IRD, UMR 5554, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France.
authors.forename: Emilie
authors.initials: E
authors.lastname: Macke
authors.forename: Sara
authors.initials: S
authors.lastname: Magalhães
authors.forename: Fabien
authors.initials: F
authors.lastname: Bach
authors.forename: Isabelle
authors.initials: I
authors.lastname: Olivieri
mesh_terms: D000818:Animals; D003163:Competitive Behavior; D005260:Female; D008297:Male; D010063:Ovum / Q000166:cytology; D011156:Population Density; D011157:Population Dynamics; D012744:Sex Ratio; D012726:Sexual Behavior, Animal; D040102:Tetranychidae / Q000235:genetics / Q000502:physiology*