But the parasite escape is still somewhat surprising when considering the types of parasites that infect the whelks. "We discovered that the whelks are mostly intermediate hosts for tapeworms and roundworms said Hopper. "These parasites eventually end up maturing and reproducing in sharks and rays."
"These sharks and rays, they can move around," said Hechinger. "And they should be able to move the parasites around. It's been a few decades since the whelks moved up north. Why haven't sharks and rays brought parasites from south to north to let the parasites catch up with the whelks?"
A likely reason is a phenomenon called "site fidelity."
"It turns out that many of the sharks and rays that are potential hosts for the whelk parasites do not move up and down the coast a lot," said Hechinger. Thus, although free to wander, the sharks and rays likely do not regularly make the trek from southern to northern California.
"Also important is that the hosts in the expanded range are at lower densities than in the historical range so, even if some parasites got to the north, it's hard for them to be transmitted under those conditions," said Kuris, UCSB professor of zoology.
According to Hechinger and Kuris, the evidence from this study suggests that perceived fallout from global warming in terms of the fears of the spread of infectious disease associated with global warming-induced range expansions is not as foregone a conclusion as many may think. At least for marine parasites such as the ones that live in the Kellet's whelk, the evidence indicates that range expansion for the host does not mean the same for its parasites.
In fact, a trend of parasite escape for expanded-range species might signal a different phenomenon altogether: the spread of host species that are missing their natural enemies and are thus not as impacted by parasites as they would be in their natural, historical environm
|Contact: Sonia Fernandez|
University of California - Santa Barbara