Researchers find natural section favors parasite fitness over host health

May 12, 2008

Why do parasites harm their hosts? Classic evolutionary theory predicts that parasites become more virulent because they must transmit themselves between hosts, yet scientists have found little data to support this idea, until now.

Led by Emory University researcher Jacobus de Roode, PhD, a team of scientists has uncovered evidence that natural selection selects for harmful parasites by maximizing parasite fitness.

De Roode and co-authors Andrew Yates, PhD, Emory University; and Sonia Altizer, PhD, University of Georgia, studied monarch butterflies Danaus plexippus infected with parasite Ophryocystis elektroscirrha and observed that higher levels of replication within the host resulted in both higher virulence and greater transmission of the parasite.

The study will be published online in the Proceedings of the National Academy of Sciences.

"A fundamental evolutionary question is why parasites that depend on their hosts for their own survival and fitness hurt or even kill them," says de Roode. "According to theory, parasites face a trade-off between the benefits of increased replication, the transmission to new hosts and the costs of host mortality, resulting in the highest fitness at intermediate parasite replication. During the past 30 years there has been very little experimental evidence that this trade-off actually exists. This is one of the first demonstrations that really shows that this trade-off model applies.

"These findings support the idea that selection for parasite transmission can favor parasite genotypes that cause substantial harm," he says.

In natural populations, D. plexippus become infected as caterpillars after they ingest spores of O. elektroscirrha that are scattered onto eggs or host plant leaves by adult butterflies. The parasites then penetrate the gut wall and replicate, forming spores around the scales of the developing butterflies.

"Greater parasite replication reduced host survival to the adult stage, with fewer monarchs emerging successfully from their pupal cases," says de Roode. "Among female monarchs that survived to the adult stage, higher parasite loads reduced mating success, in part by reducing the female lifespan.

"Harmful effects from the parasites on the host may appear maladaptive," says de Roode. "But high parasite loads were necessary to increase transmission."

Because the parasites affect the butterflies' lifespan, their ability to fly, and whether they can migrate and reproduce, de Roode says he and his colleagues are now studying how the parasites' virulence level varies among monarch populations and whether migration patterns and length affect the parasites' virulence level.

Source: Emory University

Explore further: Japanese scientist resigns over stem cell scandal

add to favorites email to friend print save as pdf

Related Stories

Ancient wisdom boosts sustainability of biotech cotton

Dec 15, 2014

Advocates of biotech crops and those who favor traditional farming practices such as crop diversity often seem worlds apart, but a new study shows that these two approaches can be compatible. An international ...

Nanotechnology against malaria parasites

Dec 09, 2014

Malaria parasites invade human red blood cells, they then disrupt them and infect others. Researchers at the University of Basel and the Swiss Tropical and Public Health Institute have now developed so-called ...

What makes Toxoplasma gondii so unpredictable?

Dec 01, 2014

Toxoplasma gondii is a common parasite often spread by cats. Most people who are infected in Europe or North America show no symptoms at all, and only a few suffer from encephalitis or ocular toxoplasmosis, ...

'Sleeping dogs' threaten the genome as we age

Dec 05, 2014

The genomes of many organisms, humans included, are littered with repetitive sequences of DNA called retrotransposons. In a new "Perspective" in the journal Science, four biologists write that while most r ...

Recommended for you

Japanese scientist resigns over stem cell scandal

23 minutes ago

A researcher embroiled in a fabrication scandal that has rocked Japan's scientific establishment said Friday she would resign after failing to reproduce results of what was once billed as a ground-breaking study on ...

'Hairclip' protein mechanism explained

14 hours ago

Research led by the Teichmann group on the Wellcome Genome Campus has identified a fundamental mechanism for controlling protein function. Published in the journal Science, the discovery has wide-ranging implications for bi ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

Ragtime
1 / 5 (2) May 12, 2008
If such mechanism wouldn't work, then the predation and the whole human civilization couldn't appear. The humans are parazites of Earth biosphere in certain extent. The parasite formation is sort of phase transition, followed by spontaneous symmetry breaking. The increasing of complexity leads to the better exploatation of sources, which increases the complexity even more.
AJW
not rated yet May 13, 2008
One:
"This is one of the first demonstrations that really shows that this trade-off model applies."
Two:
"These findings support the idea that selection for parasite transmission can favor parasite genotypes that cause substantial harm," he says.

So, which is it,
'trade-off applies'
or 'favor parasite genotypes'?

Was anything show or did the summarizer get it wrong?
PPihkala
not rated yet May 27, 2009
The title 'Researchers find natural section favors parasite fitness over host health' has a typo in it. 'section' should be 'selection'.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.