Bromadiolone resistance does not respond to absence of anticoagulants in experimental populations of Norway rats.
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Resistance to anticoagulant rodenticides in Norway rats (Rattus norvegicus) is documented to be associated
with pleiotropic effects, notably with an increased dietary vitamin K requirement. The aim of this study was to quantify
these effects in small populations of Norway rat in Denmark and to see how bromadiolone-resistant phenotypes are
manifested when bromadiolone selection is absent. Experimental populations were established under semi-natural
conditions with wild rats trapped at two Danish farms. The individuals caught on each of the two farms were divided
into two experimental groups. One group was regularly exposed to bromadiolone whereas the other group was
untreated. The level of bromadiolone resistance in the experimental populations was followed for two years. The
results presented here are those results obtained in the absence of bromadiolone selection.
The pleiotropic selection against resistance in the two non-treatment populations was found to be insignificant.
Thus, absence of anticoagulant, under the environmental conditions provided, did not lead to a selection favouring
anticoagulant-sensitive rats. However, we found some evidence of selection against presumed homozygous resistant
rats under non-anticoagulant conditions. Haemorrhagic symptoms are not only observed in sensitive rats exposed to
anticoagulants, but are also a symptom for severe vitamin K deficiency in resistant rats. This suggests that bromadiolone
resistance leads to loss of fitness, albeit that the cost is not strong enough to reduce the phenotypic resistance
level or minimise the effect of random genetic drift.
|Title of host publication||Rats, Mice and People: Rodent Biology and Management|
|Editors||G.R. Singleton, L.A. Hinds, C.J. Krebs, D.M. Spratt|
|Place of Publication||Canberra|
|ISBN (Electronic)||1 86320 357 5|
|Publication status||Published - 2003|
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