Par­a­sitic worms ma­nip­u­lat­ing ants the fo­cus of U of L study

Prairie Post (East Edition) - - AGRICULTUR­E - Con­trib­uted

A new study co-au­thored by the Univer­sity of Leth­bridge’s Dr. Cam Goater and grad­u­ate stu­dent Dr. Brad van Pari­don (BSc ’10, PhD ’17) is be­gin­ning to un­lock the evo­lu­tion of one of the most cap­ti­vat­ing and com­plex par­a­site life cy­cles in na­ture.

In a paper pub­lished in this week’s is­sue of Pro­ceed­ings of the Na­tional Academy of Sciences (PNAS), Goater, van Pari­don , Dr. John Gil­leard (Univer­sity of Cal­gary) and col­lab­o­ra­tor Dr. Charles Criscione (Texas A&M Univer­sity) as­sess the ge­netic re­la­tion­ships of a par­a­sitic worm to help ex­plain how they take over the brains of ants, ef­fec­tively ma­nip­u­lat­ing them into zom­bies as they seek to com­plete their life cy­cle.

PNAS is widely con­sid­ered one of the top three science jour­nals in the world and Goater is quick to praise van Pari­don’s work dur­ing his PhD stud­ies as a driver of the lat­est re­search find­ings.

“His fo­cus on in­te­grat­ing ap­proaches in an­i­mal ecol­ogy, molec­u­lar bi­ol­ogy and evo­lu­tion­ary the­ory is re­ally what pushed this paper for­ward,” says Goater. “It’s a tes­ta­ment to the tal­ent of our grad­u­ate stu­dents and the high level of re­search be­ing done in our grad­u­ate pro­grams.”

The par­a­site, known as the lancet liver fluke, Di­cro­coelium den­driticum, is one of the most well­known and least un­der­stood par­a­sites in na­ture. It in­fects ants and causes them to cling to veg­e­ta­tion and wait to be eaten by an­i­mals, in­clud­ing cat­tle and sheep.

Con­sum­ing the par­a­site can cause the an­i­mals to de­velop liver dis­eases that are dif­fi­cult to di­ag­nose and treat, cost­ing farm­ers time and money.

They are preva­lent in the Cy­press Hills area of south­east­ern Al­berta and south­west­ern Saskatchew­an.

“When these ants in­gest lar­vae of the fluke, they crawl to the tops of flow­ers that are ad­ja­cent to their nests,” says Goater, a re­searcher in the Depart­ment of Bi­o­log­i­cal Sciences who has been study­ing the ants and ob­serv­ing their bizarre be­hav­iour for years. “Once they have set­tled on a flower, they firmly at­tach with their mandibles. A few hours later, if not eaten by a graz­ing mam­mal, the in­fected ants de­tach from the flower and re­turn to their nest. They re­peat the same at­tach/de­tach se­quence the very next day — of­ten on pre­cisely the same flower petal.”

The nat­u­ral world is ripe with ex­am­ples of hosts chang­ing their be­hav­iour and even ap­pear­ance at the be­quest of a par­a­site, but re­searchers still do not fully un­der­stand how par­a­sites cause these al­ter­ations or how they evolve.

Their paper, Clone­mate co­trans­mis­sion sup­ports a role for kin se­lec­tion in a pup­peteer par­a­site, em­pha­sizes that to un­der­stand the evo­lu­tion of this ab­surd ma­nip­u­la­tion, it is im­por­tant to un­der­stand how ants are ex­posed to these par­a­sites, their fate in­side an ant, and the ge­netic re­la­tion­ships be­tween in­di­vid­ual par­a­sites.

The life cy­cle starts as a mi­cro­scopic egg in the dung of a graz­ing mam­mal such as a cow or deer be­fore in­fect­ing and mul­ti­ply­ing in snails and be­ing re­leased in tiny slime balls. Ants love to eat these slime balls but when they do, they be­come ex­posed to myr­i­ads of mi­nus­cule lar­vae that pass into the ant’s ab­domen. Those in the ab­domen re­side there for the rest of the ant’s life, await­ing in­ges­tion by a cow. One lone lar­vae, how­ever, heads to the brain where it ini­ti­ates the zom­bie-like be­hav­iour — know­ing it will die upon in­ges­tion by a graz­ing mam­mal. Thus, the par­a­site in the brain sac­ri­fices its life for its mates that live in the ab­domen — a clas­sic case of al­tru­is­tic be­hav­iour.

“Un­like equiv­a­lent stages of sim­i­lar par­a­sites, there is a very close ge­netic re­la­tion­ship be­tween the par­a­site in the brain and those in the ab­domen. In fact, they tend to be per­fect clones,” says Goater. “This means that in sac­ri­fic­ing it­self, the ‘brain­worm’ fa­cil­i­tates the move­ment of close rel­a­tives into the next host where they can re­pro­duce.”

The evo­lu­tion­ary ex­pla­na­tion for why some an­i­mals ap­pear to sac­ri­fice them­selves for oth­ers is a sub­ject of much de­bate. The the­ory of kin se­lec­tion seeks to ex­plain al­tru­is­tic be­hav­iour as a mech­a­nism by which in­di­vid­u­als can in­crease the chance of their genes be­ing passed to the next gen­er­a­tion by im­prov­ing chances of sur­vival and re­pro­duc­tion of ge­net­i­cally re­lated fam­ily mem­bers.

“By demon­strat­ing the close ge­netic re­la­tions be­tween brain- and ab­domendwell­ing par­a­sites in ma­nip­u­lated ants, we’ve been able to demon­strate the key role of kin se­lec­tion in the evo­lu­tion of this pup­pet mas­ter par­a­site.”

Photo con­trib­uted

The at­tached photo shows Dr. Brad van Pari­don with a vial of in­fected ants.

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