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Voordouw, Maarten

Nom
Voordouw, Maarten
Affiliation principale
Fonction
Ancien.ne collaborteur.trice
Identifiants
https://libra.unine.ch/handle/123456789/375
_
0000-0001-9384-0436

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  • Publication
    Accès libre
    Rodent malaria-resistant strains of the mosquito, Anopheles gambiae, have slower population growth than -susceptible strains
    (2009)
    Voordouw, Maarten 
    ;
    Anholt, Bradley R.
    ;
    Taylor, Pam J.
    ;
    Hurd, Hilary
    Background
    Trade-offs between anti-parasite defence mechanisms and other life history traits limit the evolution of host resistance to parasites and have important implications for understanding diseases such as malaria. Mosquitoes have not evolved complete resistance to malaria parasites and one hypothesis is that anti-malaria defence mechanisms are costly.
    Results
    We used matrix population models to compare the population growth rates among lines of Anopheles gambiae that had been selected for resistance or high susceptibility to the rodent malaria parasite, Plasmodium yoelii nigeriensis. The population growth rate of the resistant line was significantly lower than that of the highly susceptible and the unselected control lines, regardless of whether mosquitoes were infected with Plasmodium or not. The lower population growth of malaria-resistant mosquitoes was caused by reduced post blood-feeding survival of females and poor egg hatching.
    Conclusions
    With respect to eradicating malaria, the strategy of releasing Plasmodium-resistant Anopheles mosquitoes is unlikely to be successful if the costs of Plasmodium-resistance in the field are as great as the ones measured in this study. High densities of malaria-resistant mosquitoes would have to be maintained by continuous release from captive breeding facilities.
  • Publication
    Accès libre
    Larval density and the Charnov–Bull model of adaptive environmental sex determination in a copepod
    (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.
  • Publication
    Accès libre
    Paternal inheritance of the primary sex ratio in a copepod
    (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.
  • Publication
    Accès libre
    Heritability of Sex Tendency in a Harpacticoid Copepod, Tigriopus californicus
    (2002)
    Voordouw, Maarten 
    ;
    Anholt, Bradley R.
    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 Tigriopus californicus. 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 T. californicus.
  • Publication
    Accès libre
    Environmental sex determination in a splash pool copepod
    (2002)
    Voordouw, Maarten 
    ;
    Anholt, Bradley R.
    The sex-determining mechanism has important demographic and genetic consequences by virtue of its effect on the population sex ratio. Here we investigate the effect of temperature dependent sex determination (TSD) on the primary sex ratio of the harpacticoid copepod, Tigriopus californicus. At the two experimental temperatures (15° and 22°C) used in this study, the primary sex ratio is almost always biased in favour of males. Higher temperatures induce masculinization and the change in sex ratio is not caused by differential mortality of the sexes. The mean level of TSD in the population is small (proportion of males increases by ~5% between 15° and 22°C) because only one-third of the families actually exhibit a significant sex-ratio response while the rest of the population is insensitive to temperature. A comparison of the primary sex ratio and the level of TSD between two locations reveals few differences among populations. Finally, individuals still exhibited TSD after having been maintained under constant temperature conditions in the lab for several generations. In addition the proportion of temperature-sensitive individuals remained unchanged. This suggests that the observed level of TSD is not an artefact of testing field-captured individuals in a novel laboratory environment. At this point the adaptive significance of temperature-dependent sex determination in T. californicus remains unknown.