Next Cen­tury May Bring Doom To Many Par­a­sites, and Hosts

One in three par­a­site species may go ex­tinct in the next cen­tury.

Paper Boy - - Life / Style - By CARL ZIM­MER­MAN

Sci­en­tists who stud­ied what cli­mate change may do to the world’s par­a­sites came to a star­tling con­clu­sion: one in three species may go ex­tinct in the next cen­tury.

As global warm­ing raises the planet’s tem­per­a­ture, the re­searchers found, many species will lose ter­ri­tory in which to sur­vive. Some of their hosts will be lost, too.

“It still ab­so­lutely blows me away,” said Colin J. Carlson, lead au­thor of the study and a grad­u­ate stu­dent at the Univer­sity of Cal­i­for­nia, Berke­ley. He knows many peo­ple may re­act to the news with a round of ap­plause.

“Par­a­sites are ob­vi­ously a hard sell,” Mr. Carlson said.

But as much as a tape­worm or a blood fluke may dis­gust us, par­a­sites are cru­cial to the world’s ecosys­tems. Their ex­tinc­tion may ef­fect en­tire food webs, per­haps even harm­ing hu­man health.

Par­a­sites typ­i­cally live in or on their hosts, but that does not pro­tect them from cli­mate change. Ris­ing air tem­per­a­tures can harm them. Ticks, for in­stance, risk bak­ing in the heat as they wait in the grass for their next vic­tim. Hook­worm lar­vae re­quire damp soil to sur­vive be­fore slip­ping into some­one’s foot.

Some par­a­sites won’t lose much in a warm­ing world, the study found. For in­stance, thorny-headed worms are likely to be pro­tected be­cause their hosts, fish and birds, are com­mon and wide­spread.

But other types, like fleas and tape­worms, may not be able to tol­er­ate much change in tem­per­a­ture; many oth­ers in­fect only hosts that are fac­ing ex­tinc­tion, as well.

In all, roughly 30 per­cent of par­a­sitic species could dis­ap­pear, Mr. Carlson con­cluded. The im­pact of cli­mate change will be as great or greater for these species as for any oth­ers stud­ied so far.

Mr. Carlson said cli­mate change would do more than just drive some species ex­tinct. Some par­a­sites would move into new ter­ri­tory.

Deer ticks, for ex­am­ple, spread Lyme dis­ease, and cli­mate change mod­els sug­gest they have a rosy fu­ture as they ex­pand north­ward. “We’re not wor­ried about them go­ing ex­tinct,” said Mr. Carlson.

Mi­grat­ing par­a­sites like these will ar­rive in ecosys­tems where other par­a­sitic species are dis­ap­pear­ing. With less com­pe­ti­tion, they may be able to wreak more havoc — and not just on an­i­mal hosts. Many hu­man dis­eases are the re­sult of par­a­sites and pathogens jump­ing from an­i­mal species to our own.

“If par­a­sites are keep­ing dis­ease down in wildlife, they might also be in­di­rectly keep­ing them down in hu­mans,” Mr. Carlson said. “And we might lose that.”

PAUL FETTERS FOR THE SMITH­SO­NIAN IN­STI­TU­TION

Spec­i­mens from the Na­tional Par­a­site Col­lec­tion, which holds more than 20 mil­lion par­a­sites. Though re­viled, par­a­sites play a sig­nif­i­cant role in main­tain­ing the world’s ecosys­tems.

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