Secret Behind Invasive House Sparrow Success: Sharpening Immune Cells

House sparrows are some of the most successful invasive species in the world. Originally heralding from Europe, they've spread throughout the United States. Now, scientists have discovered that something in a sparrow's biology may help with this proliferation. It turns out that adjustments in the sparrow's immune system may aid its spread.

About 150 years ago, the English sparrow spread rapidly across North and South America as well as Australia. The species further spread into Africa and Southeast Asia. With an aggressive nature, these birds can crowd out native species and can carry diseases that can cause native bird populations to decline.

In order to learn a bit more about this bird, the researchers focused on Kenya's sparrow population. More specifically, they examined how interactions between hosts and parasites influenced the success of the host species' introductions and range. They found that on the molecular level, the immune systems of house sparrows at the edge of the species' range in Kenya were more attuned to finding dangerous parasites than birds from older sites in the same country.

"A major function of the immune system is distinguishing self from non-self, and immune cells do this with special receptors that look for molecules made by microbes that animal cells don't make," said Lynn Martin, one of the researchers, in a news release. "In the range edge populations, sparrows' immune cells expressed a lot more of the surveillance molecule for microbe components than in old sites. So perhaps their immune systems are more attuned to finding particularly harmful parasites in new regions where parasites are more likely novel."

So why do house sparrows have this adaptation? It's possible it's meant to keep the invading birds from becoming sick in new areas where pathogens are more likely to be novel.

The findings are important for better understanding how these birds were so successful in their spread. This could, in turn, help government agencies focus resources on eradicating species with the most potential to do damage to natural environments.

The findings are published in the journal Proceedings of the Royal Society B: Biological Sciences.