All roommate jokes aside, UCSB researchers have determined that moving an animal to a non-native habitat decreases the number of parasites that species carries.

The findings, published in the Feb. 6 issue of Nature, conclude that invasive plant or animal species are healthier than the native species they sometimes overtake because many of the parasites that restrict reproductive success for the invader do not survive transport from one habitat to another. UCSB assistant research biologist Mark Torchin is credited as first author on the paper.

Researchers used European green crabs (Carcinus maenas) to study how the number of parasitic barnacles changed between crabs found in their native European home and crabs currently invading the coasts of the United States, Australia, Japan, Tasmania and South Africa.

“Since the newly introduced crabs have less parasites, it’s like the native crabs are fighting with one claw tied behind their back,” Armand Kuris, co-author of the research and UCSB professor of biology, said.

Invading species grow bigger in host habitats and are allowed to flourish unchecked without the parasites from their native habitats, Kuris said.

Torchin said on average an animal has 16 parasites at home, but brings less than three of them to new areas that it invades. In the new region, parasites are not well matched to novel hosts, and only about four parasites will successfully attack an invading species.

“This is just the tip of the iceberg,” Kuris said in a statement. “We’ve demonstrated that introduced species don’t have the parasites, but we still haven’t nailed down how much of an effect those parasites have. Our larger body of research is trying to figure out what role parasites and infectious diseases have on ecosystems.”

The research team for this initial study and for ongoing research includes Kevin Lafferty, an assistant adjunct professor of biology at UCSB and a marine ecologist with the U.S. Geological Survey; ecology, evolution and marine biology graduate student Valerie McKenzie; and Princeton University ecology and evolutionary biology Professor Andrew Dobson.

The National Science Foundation and the National Center for Ecological Analysis and Synthesis funded the research.