Competitive tapeworms fight to control shared host

Two tapeworms infecting the same host may actively sabotage each other in a competition to seize control if they find themselves at cross-purposes, a new research suggests.
Researchers at the Max Planck Institute for Evolutionary Biology in Germany infected small crustaceans called copepods with multiple Schistocephalus solidus tapeworms.
These live in copepods and then move to fish for their next life-cycle stage.
Researchers Nina Hafer and Manfred Milinski found that when two tapeworms in the same copepod were ready to move hosts, they combined to make the copepod even more active than a single parasite would, 'nature.Com' reported.
But when an older tapeworm was sharing a host with a younger one, the older animal always won out.

The younger tapeworms failed to influence their hosts at all when in conflict with their older brethren, and did not lower the activity compared with hosts infected with only one parasite.

The activity of the host does not reach an intermediate level as a result of the two competing parasites, researchers said.
This suggests that the older parasite is "sabotaging" the younger one's activity because "we don't expect the non-infective parasite to stop what it's doing," said Hafer.
The older parasite even won out when it was in competition with two younger individuals.