Ivermectin resistance in dung flies.

Avermectins are potent and popular veterinary pharmaceuticals used globally to fight parasites of livestock and humans. By disturbing ion channel transport through the membrane, avermectins are effective against endo- and ectoparasitic round- and horsehair worms (Nematoida), insects or ticks (Arthropoda), but not against Plathelminthes, including flatworms (Trematoda) and tapeworms (Cestoda), or segmented worms (Annelida).

Unfortunately, excreted avermectins have strong non-target effects on beneficial arthropods such as the insect community decomposing livestock dung, ultimately impeding this important ecosystem function to the extent that regulators mandate standardized eco-toxicological tests of dung organisms worldwide.

Figure 1 from Puniamoorthy et al. 2014

Traditional (top) and new (bottom) phylogenetic hypotheses for the ancient relationships between invertebrate taxa (adapted from Burda et al. 2008). The pattern of ivermectin sensitivity (red = sensitive and green = nonsensitive bars) more parsimoniously agrees with the most recent phylogenomic hypothesis.

By phylogenetic comparisons we show that the deep pattern and qualitative mechanism of avermectin sensitivity is conserved and compatible with most recent phylogenetic hypotheses grouping the Nematoida with the Arthropoda as Ecdysozoa (moulting animals).

At the species level, we demonstrate phylogenetic clustering in the ivermectin sensitivities of 23 species of sepsid dung flies (Diptera: Sepsidae). This clustered 500-fold quantitative variation in sensitivity may indicate recent lineage-specific responses to selection, but more likely reflects pre-existing genetic variation with pleiotropic effects on eco-toxicological responses to pollutants. Regardless, our results question the common practice in eco-toxicology of choosing single test species to infer detrimental effects on entire species communities, which should ideally assess a representative phylogenetic taxon sample.

For more information see

Puniamoorthy et al. 2014 Evol. Appl.

Blanckenhorn et al. 2013 Ecotox. Envir. Safety