Madrid faces a new challenge in urban pest management: the emergence of “super rats” on Spanish streets. This involves the appearance of genetic mutations in brown rats that could be linked to the pressure of the urban environment.
According to the research published in Ecotoxicology and Environmental Safety, variants of the Vkorc1 gene associated with anticoagulant resistance were detected in Rattus norvegicus populations.
Within this discovery, two mutations were identified in the exon 3 of the gene, one already known in the city (S149I), and another found for the first time in Spanish brown rats (E155K), in addition to the emergence of specimens with double mutations.
For this, the researchers analyzed about 120 fecal samples collected in 21 one-square-kilometer quadrants, distributed in 17 neighborhoods of the Spanish capital, which revealed an uneven distribution of these mutations. In this regard, the S149I variant was detected in the south of Madrid, the E155K in the north, and the double mutations in the center.
The gene that divides the city
The distribution of the gene led researchers to propose the existence of differentiated patterns within the city, as the mutations could be the result of unequal selective pressure scenarios. This would explain why rat populations evolve differently, depending on the environmental conditions and the use of rodenticides.
The presence of the Vkorc1 gene is key to understanding the mechanism of action of anticoagulant rodenticides, which are used for human rodent control. According to the research, the mutations can alter the sensitivity of the VKORC1 protein, which would help reduce the efficacy of the compounds and favor their survival.
Waste management: a possible genetic modifier?
While one of the most relevant results of the study is the absence of a significant statistical correlation between the presence of mutations and population density, the use of bromadiolone or the generation of urban solid waste, the analysis suggests there might be a greater presence of mutations in areas with higher waste accumulation.
In these areas, the continued use of anticoagulants is common, which favors the phenomenon known in evolutionary biology as selection by chemical pressure. This is because the chemicals eliminate the more sensitive individuals, while carriers of resistant mutations survive and transmit those characteristics to subsequent generations.
For this reason, experts warn that traditional methods could lose effectiveness in certain urban areas, so strategies based on prevention, improved waste management, or fertility control of rodent populations should be considered.
Genetic mutations with environmental impact
The brown rat has a great capacity for adaptation, which is enhanced when mutations occur in its genetic material. Besides favoring its survival, it also contributes to a possible uncontrolled expansion, increasing the pressure on fragile ecosystems.
However, the changes not only affect its genetics but also its reproductive or feeding behavior, intensifying its impact on native species. This translates into greater predation of birds, reptiles, and invertebrates, as well as competition for resources with local fauna. Additionally, its ability to transmit pathogens may expand, affecting both wildlife and humans.
Furthermore, from an ecological perspective, these genetic changes can modify entire ecological dynamics. By altering trophic chains and dispersion processes, brown rats contribute to environmental imbalances that require more complex and sustainable management strategies.
