Invasive Species' Immune Systems Improve as They Spread, Study of Sparrows Suggests

Invasive species' immune systems improve as they push the boundaries of their habitat, a new study suggests.

Researchers from the University of South Florida looked at house sparrows in Kenya, the site of one of the bird's most recent invasions. The results, outlined in Proceedings of the Royal Society B, indicate that the best predictor of a bird's immune system was population age.

"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," researcher and biology Associate Professor Lynn Martin said in a statement. "In the range edge populations, sparrows' immune cells expressed a lot more of the surveillance molecule for microbe components than in old sites."

Based on this, Martin hypothesizes that the birds' immune systems are especially active in identifying harmful parasites in new areas "where parasites are more likely novel," giving them a competitive edge they otherwise would not have.

House sparrows quickly expanded their reach from Western Europe starting 150 years ago, moving across to North and South America, Australia and, more recently, Africa and Southeast Asia.

In many of its new territories, the animal is considered a pest, due in part to its insatiable appetite for grain. In the United States where eradication programs have sought to remove it, the house sparrow has been deemed responsible as well for the decline in other species as a result of its role in different disease cycles.

Ultimately, Martin hopes to better understand what gives invasive species a competitive advantage in their new environments, with the goal of one day enabling governments with the tools needed to counteract their potential harm.