Voordouw, Maarten

2008, Voordouw, Maarten, Stebbins, Gabe, Robinson, H. Eve, Perrot-Minnot, Marie-Jeanne, Rigaud, Thierry, Anholt, Bradley R

Hypothesis: Genetic variation for the primary sex ratio is widespread in a copepodwith polygenic sex determination. Cytoplasmic sex ratio distorters (e.g. Wolbachia andmicrosporidians) influence the primary sex ratio in this copepod.
Organism: The intertidal copepod, Tigriopus californicus; six populations from VancouverIsland, British Columbia.
Study site: Quantitative genetics experiment in the laboratory. PCR and antibioticsexperiment to test for the presence of cytoplasmic sex ratio distorters.
Results: Genetic variation for the primary sex ratio was found in five of the six populationssurveyed. The primary sex ratio was paternally transmitted. There was no evidence thatWolbachia or microsporidians influenced the primary sex ratio of T. californicus.

2005, Voordouw, Maarten, Robinson, H. Eve, Stebbins, G., Albert, A. Y. K., Anholt, Bradley R.

2005, Voordouw, Maarten, Robinson, H. Eve, Stebbins, Gabe, Albert, Arianne Y.K., Anholt, Bradley R.

Charnov et Bull avancent que la variation de la taille adulte induite par le milieu en combinaison avec les différences sexuelles de fitness peut sélectionner l'évolution de la détermination sexuelle adaptative due au milieu (ESD). Dans notre étude, nous déterminons si la densité larvaire affecte la détermination sexuelle chez le copépode Tigriopus californicus (Baker, 1912) comme le prédisent Charnov et Bull. Les individus élevés à densités faibles se développent plus rapidement et sont significativement plus grands que leurs frères et soeurs élevés à forte densité. Chez ces individus élevés en laboratoire, la sélection sexuelle faite sur la taille corporelle des mâles est plus forte que la sélection reliée à la fécondité sur la taille corporelle des femelles; mais ce pattern de sélection relié au sexe est inversé en nature. Des différences de disponibilité de nourriture (chez les femelles) et le mode de compétition (chez les mâles) peuvent peut-être expliquer les résultats contradictoires au laboratoire et en nature. Nous avons observé un faible effet de la densité larvaire sur la détermination sexuelle dans une expérience préliminaire, mais aucun effet dans une seconde expérience plus puissante. Bien que la densité larvaire n'affecte pas le sex-ratio chez T. californicus, nos estimations de la sélection spécifique au sexe de la taille corporelle adulte affecteront les modèles futurs de ESD adaptative chez cette espèce et chez les autres copépodes, Charnov and Bull suggested that environmentally induced variation in adult body size coupled with sex-specific differences in fitness can select for the evolution of adaptive environmental sex determination (ESD). In this study we determine whether larval density affects sex determination in the copepod Tigrioptis californicus (Baker, 1912), as predicted by Charnov and Bull. Individuals reared at low densities developed faster and were significantly larger than siblings reared at high densities. For these laboratory-reared individuals, sexual selection on male body size was stronger than fecundity selection on female body size. but this sex-specific pattern of selection was reversed in the field. Differences in food availability (for females) and the mode of competition (for males) may account for the conflicting results between laboratory and field. We found a weak effect of larval density on sex determination in a pilot experiment but no effect in a second, more powerful experiment. While larval density did not affect the sex ratio of T. californicus. our sex-specific estimates of selection on adult body size will inform future models of adaptive ESD in this species and other copepods.

2005, Voordouw, Maarten, Robinson, H. Eve, Anholt, Bradley R.

Uniparentally inherited genetic elements are under strong selection to manipulate sex determination in their host and shift the host sex ratio towards the transmitting sex. For any sex-ratio trait, lineage analysis and quantitative genetics are important tools for characterizing the mode of inheritance (biparental vs. maternal vs. paternal) thereby narrowing the field of possible sex-determining mechanisms (e.g. polygenic, sex chromosomes with meiotic drive, cytoplasmic microorganisms). The primary sex ratio of the harpacticoid copepod, Tigriopus californicus is often male-biased and is highly variable among full sib families. We found that this extra-binomial variation for the primary sex ratio is paternally but not maternally transmitted in T. californicus. Paternal transmission of the primary sex ratio has been well documented in the haplo–diploid hymenoptera but is relatively rare in diplo–diploid organisms. If the sex-ratio trait is paternally transmitted in other closely related harpacticoid copepods it would explain why male biased primary sex ratios are so common in this group.