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    Sex ratios and sex-biased infection behaviour in the entomopathogenic nematode genus Steinernema


    Alsaiyah, Mohamed A.M. and Ebssa, Lemma and Zenner, Annemie N.R.L. and O'Callaghan, Kathryn M. and Griffin, Christine (2009) Sex ratios and sex-biased infection behaviour in the entomopathogenic nematode genus Steinernema. International Journal for Parasitology, 39. pp. 725-734. ISSN 0020-7519

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    Abstract

    In experimentally infected insects, the sex ratio of first generation nematodes of five species of Steinernema was female-biased (male proportion 0.35-0.47). There was a similar female bias when the worms developed in vitro (0.37-0.44), indicating that the bias in these species is not due to a lower rate of infection by male infective juveniles (IJs). Experimental conditions influenced the proportion of males establishing in insects, indicating that male and female IJs differ in their behaviour. However, there was no evidence that males are the colonising sex in any species, contrary to what has previously been proposed. Time of emergence from the host in which the nematodes had developed influenced sex ratios in experimental infections. In three species (Steinernema longicaudum, Steinernema glaseri and Steinernema kraussei), early emerged nematodes had a higher proportion of males than those that emerged later, with the reverse trend for Steinernema carpocapsae and Steinernema feltiae. In a more detailed in vitro study of S. longicaudum, the proportion of males was similar whether or not the nematodes passed through the developmentally arrested IJ stage, indicating that the female bias is not due to failure of males to exit this stage. The sex ratio in vitro was independent of survival rate from juvenile to adult, and was female-biased even when all juveniles developed, indicating that the bias is not explained by failure of males to develop to adults. The female-biased sex ratio characteristic of Steinernema populations appears to be present from at least the early juvenile stage. We hypothesise that the observed female bias is the population optimal sex ratio, a response to cycles of local mate competition experienced by nematodes reproducing within insect hosts interspersed with periods of outbreeding with less closely related worms following dispersal.

    Item Type: Article
    Keywords: Sex ratio; Male colonisation; Female-biased; Entomopathogenic nematode; Steinernema species; Nematoda;
    Academic Unit: Faculty of Science and Engineering > Biology
    Item ID: 7522
    Identification Number: https://doi.org/10.1016/j.ijpara.2008.11.003
    Depositing User: Dr. Christine Griffin
    Date Deposited: 18 Oct 2016 14:59
    Journal or Publication Title: International Journal for Parasitology
    Publisher: Elsevier
    Refereed: Yes
    Funders: Irish Research Council for Science Engineering and Technology (IRCSET), Science Foundation Ireland (SFI)
    URI:

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