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More than a colour change: insect melanism, disease resistance and fecundity
Proceedings of the Royal Society B: Biological Sciences, Volume: 280, Issue: 1763, Pages: 20130584 - 20130584
Swansea University Authors: Miranda Walker, Tariq Butt , Carolyn Greig
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DOI (Published version): 10.1098/rspb.2013.0584
A “dark morph” melanic strain of the Greater wax moth, Galleria mellonella, was studied for its atypical, heightened resistance to infection with the entomopathogenic fungus, Beauveria bassiana. We show that these insects exhibit multiple intraspecific immunity and physiological traits that distingu...
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A “dark morph” melanic strain of the Greater wax moth, Galleria mellonella, was studied for its atypical, heightened resistance to infection with the entomopathogenic fungus, Beauveria bassiana. We show that these insects exhibit multiple intraspecific immunity and physiological traits that distinguish them from a non-melanic, fungus-susceptible morph. The melanic and non-melanic morphs were geographic variants that had evolved different, independent, defence strategies. Melanic morphs exhibit a thickened cuticle, higher basal expression of immunity and stress-management related genes, higher numbers of circulating haemocytes, upregulated cuticle phenoloxidase activity concomitant with conidial invasion, and an enhanced capacity to encapsulate fungal particles. These insects prioritize specific augmentations to those front-line defences that are most likely to encounter invading pathogens or to sustain damage. Other immune responses that target late-stage infection, such as haemolymph lysozyme and phenoloxidase activities, do not contribute to fungal tolerance. The net effect is increased larval survival times, retarded cuticular fungal penetration and a lower propensity to develop haemolymph infections when challenged naturally (topically) and by injection. In the absence of fungal infection, however, the heavy defence investments made by melanic insects result in a lower biomass, decreased longevity and lower fecundity in comparison with their non-melanic counterparts. Although melanism is clearly correlated with increased fungal resistance, the costly mechanisms enabling this protective trait constitute more than just a colour change.
Accepted in principle for Publication; no doi assigned yet; currently in final proof stage for imminent publication.
Faculty of Medicine, Health and Life Sciences