Media Releases

Natural selection enables purple loosestrife to invade northern Ontario

October 17, 2013

Invasive plant thrives because it adapts quickly to local climates

TORONTO, ON — Uni­ver­si­ty of Toron­to research has found that pur­ple looses­trife – an inva­sive species that com­petes with native plants for light and nutri­ents and can degrade habi­tats for wildlife – has evolved extreme­ly rapid­ly, flow­er­ing about three weeks ear­li­er as it has spread to north­ern Ontario. This has allowed pop­u­la­tions of the species to thrive in the cold­er cli­mate with a more than 30-fold increase in seed pro­duc­tion.

“The abil­i­ty of inva­sive species to rapid­ly adapt to local cli­mate has not gen­er­al­ly been con­sid­ered to be an impor­tant fac­tor affect­ing spread,” said Dr. Rob Colaut­ti, who con­duct­ed the research as a Ph.D. stu­dent in U of T’s Depart­ment of Ecol­o­gy & Evo­lu­tion­ary Biol­o­gy under the super­vi­sion of Pro­fes­sor Spencer Bar­rett.

“Instead, fac­tors such as escape from nat­ur­al ene­mies includ­ing her­bi­vores, preda­tors, pathogens or par­a­sites were thought to explain how species become inva­sive. We found that the evo­lu­tion of local adap­ta­tion to cli­mate in pur­ple looses­trife increased repro­duc­tion as much as or more than escap­ing nat­ur­al ene­mies. Under­stand­ing that species can evolve rapid­ly to local cli­mates is impor­tant for pre­dict­ing how inva­sive species spread and how native and non-native species alike will respond to cli­mate change.”

To deter­mine whether pop­u­la­tions have evolved local adap­ta­tion, the sci­en­tists col­lect­ed seeds from three dif­fer­ent cli­mat­ic regions (north, south and inter­me­di­ate lat­i­tudes in east­ern N. Amer­i­ca) and then grew them at three sites span­ning the dis­tri­b­u­tion of the species to see if there were dif­fer­ences in sur­vival and repro­duc­tion, i.e. fit­ness. They found that ‘home’ plants col­lect­ed from lat­i­tudes most sim­i­lar to each com­mon gar­den loca­tion always had high­er fit­ness than the ‘away’ plants. For exam­ple, plants col­lect­ed from north­ern lat­i­tudes had the high­est fit­ness when grown at the north­ern site in Tim­mins, Ontario but the low­est fit­ness when grown at a south­ern site in north­ern Vir­ginia rel­a­tive to plants col­lect­ed from south­ern lat­i­tudes.

The team’s pre­vi­ous work showed that north­ern pop­u­la­tions flower about 20 days ear­li­er but at half the size of south­ern pop­u­la­tions when both were grown in the same ‘com­mon gar­den’ exper­i­ment. They won­dered whether these genet­ic dif­fer­ences could account for the obser­va­tion of local­ly adapt­ed pop­u­la­tions. So in the next phase of the research, they direct­ly mea­sured Dar­win­ian nat­ur­al selec­tion on flow­er­ing time at each of the com­mon gar­den sites. They found that ear­ly flow­er­ing was adap­tive at the most north­ern site, because ear­ly-flow­er­ing plants pro­duced the most off­spring while plants with delayed flow­er­ing began repro­duc­tion near the end of the grow­ing sea­son, when pol­li­na­tors were scarce and flow­ers were prone to frost dam­age. But lat­er flow­er­ing was favoured by nat­ur­al selec­tion at more south­ern sites because delayed repro­duc­tion allowed plants to grow larg­er and pro­duce more seeds when the grow­ing sea­son is longer. Remark­ably these dif­fer­ences have evolved over the past 50 years as the species moved north­wards, fol­low­ing its ini­tial intro­duc­tion to the east coast of the USA.

The research was fund­ed by grants from the Nat­ur­al Sci­ences and Engi­neer­ing Research Coun­cil of Cana­da. The paper “Rapid adap­ta­tion to cli­mate facil­i­tates range expan­sion in an inva­sive plant” will appear in Sci­ence Octo­ber 18. The research team includ­ed over 30 Uni­ver­si­ty of Toron­to under­grad­u­ate stu­dents and part of the research was con­duct­ed at the Uni­ver­si­ty of Toronto’s Kof­fler Sci­en­tif­ic Reserve.


For more infor­ma­tion, con­tact:

Rob Colaut­ti
NSERC Bant­i­ng Post­doc­tor­al Fel­low, Botany Depart­ment
Uni­ver­si­ty of British Colum­bia

Spencer Bar­rett
Depart­ment of Ecol­o­gy & Evo­lu­tion­ary Biol­o­gy
Uni­ver­si­ty of Toron­to

Kim Luke
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to