An investigation of genetic heterogeneity in a biological sentinel species (Lumbricus rubellus)

  • Robert Donnelly

    Student thesis: Doctoral Thesis


    Studies have indicated the existence of several possible sources of genetic heterogeneity within the sentinel species Lumbricus rubellus that could compromise its suitability for ecotoxicological assessment. The species appears to consist of two genetically divergent cryptic lineages and has been demonstrated to display genetic adaptation towards contaminants within some populations.

    In order to investigate the cryptic lineages of L rubellus further a combined morphological and DNA barcoding approach was undertaken, with both the mitochondria! COI gene being sequenced and external morphological characters being assessed. Combined barcoding and morphological analysis confirmed the existence of the previously described genetic lineages of L. rubellus and highlighted a potential lineage-specific morphological trait. The effectiveness of this trait in field identification of the two lineages was tested in a blind trial. This indicated that the trait may be particularly effective in successfully identifying the individuals of one of these lineages.

    The two cryptic lineages were also analysed in a second study featuring cross-amplifying microsatellite loci. Both the sequencing and fragment analysis of these microsatellite loci strongly supported the existence of a high degree of reproductive isolation between the two lineages.

    Finally microsatellite markers were applied to test the hypothesis of genetic adaptation within L. rubellus populations located along an aerially-deposited nickel contamination gradient. No support was obtained for the existence of genetic adaptation within these populations. This could indicate that the most heavily contaminated sites represent demographic 'sinks' into which individuals immigrate from adjacent less-contaminated regions.

    The general implications of these studies are that the two lineages of L rubellus should be treated as separate species in future ecotoxicological trials given their high degree of genetic differentiation. An implication of the nickel study is that L. rubellus may display a greater capacity for tolerating toxic metals through phenotypic plasticity than previous studies have indicated.
    Date of AwardSep 2011
    Original languageEnglish

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