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201309Apr17:07

Envi­ron­men­tal change trig­gers rapid evolution

Infor­ma­tion
pub­lished 09 April 2013 | mod­i­fied 19 March 2014
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Peacock miteEnvi­ron­men­tal change can drive hard-​wired evo­lu­tion­ary changes in ani­mal species in a mat­ter of gen­er­a­tions.

A Uni­ver­sity of Leeds-​led study, pub­lished online on 8 April in the jour­nal Ecol­ogy Let­ters, over­turns the com­mon assump­tion that evo­lu­tion only occurs grad­u­ally over hun­dreds or thou­sands of years.

Instead, researchers found sig­nif­i­cant genet­i­cally trans­mit­ted changes in lab­o­ra­tory pop­u­la­tions of soil mites in just 15 gen­er­a­tions, lead­ing to a dou­bling of the age at which the mites reached adult­hood and large changes in pop­u­la­tion size. The results have impor­tant impli­ca­tions in areas such as dis­ease and pest con­trol, con­ser­va­tion and fish­eries man­age­ment because they demon­strate that evo­lu­tion can be a game-​changer even in the short-​term.

Pro­fes­sor Tim Ben­ton, of the Uni­ver­sity of Leeds’ Fac­ulty of Bio­log­i­cal Sci­ences, said:

This demon­strates that short-​term eco­log­i­cal change and evo­lu­tion are com­pletely inter­twined and can­not rea­son­ably be con­sid­ered sep­a­rate. We found that pop­u­la­tions evolve rapidly in response to envi­ron­men­tal change and pop­u­la­tion man­age­ment. This can have major con­se­quences such as reduc­ing har­vest­ing yields or sav­ing a pop­u­la­tion head­ing for extinction.


Although pre­vi­ous research has implied a link between short-​term changes in ani­mal species’ phys­i­cal char­ac­ter­is­tics and evo­lu­tion, the Leeds-​led study is the first to prove a causal rela­tion­ship between rapid genetic evo­lu­tion and ani­mal pop­u­la­tion dynam­ics in a con­trolled exper­i­men­tal set­ting.

The researchers worked with soil mites that were col­lected from the wild and then raised in 18 glass tubes. Forty per­cent of adult mites were removed every week from six of the glass tubes. A sim­i­lar pro­por­tion of juve­niles were removed each week in a fur­ther six tubes, while no “har­vest­ing” was con­ducted in the remain­ing third of the tubes.

Lead author Dr Tom Cameron, a post­doc­toral Fel­low in the Fac­ulty of Bio­log­i­cal Sci­ences at Leeds at the time of the research and now based in Umeå Uni­ver­sity, Swe­den, said: “We saw sig­nif­i­cant evo­lu­tion­ary changes rel­a­tively quickly. The age of matu­rity of the mites in the tubes dou­bled over about 15 gen­er­a­tions, because they were com­pet­ing in a dif­fer­ent way than they would in the wild. Remov­ing the adults caused them to remain as juve­niles even longer because the genet­ics were respond­ing to the high chance that they were going to die as soon as they matured. When they did even­tu­ally mature, they were so enor­mous they could lay all of their eggs very quickly.”

The ini­tial change in the mites’ envi­ron­ment — from the wild into the lab­o­ra­tory — had a dis­as­trous effect on the pop­u­la­tion, putting the mites on an extinc­tion tra­jec­tory. How­ever, in every pop­u­la­tion, includ­ing those sub­jected to the removal of adults or juve­niles, the tra­jec­tory switched after only five gen­er­a­tions of evo­lu­tion and the pop­u­la­tion sizes began to increase. The researchers found that the lab­o­ra­tory envi­ron­ment was select­ing for those mites that grew more slowly. Under the com­pet­i­tive con­di­tions in the tubes, the slow grow­ing mites were more fer­tile when they matured, mean­ing they could have more babies.

Ecol­ogy and evo­lu­tion are intertwined

Dr Cameron said: “The genetic evo­lu­tion that resulted in an invest­ment in egg pro­duc­tion at the expense of indi­vid­ual growth rates led to pop­u­la­tion growth, res­cu­ing the pop­u­la­tions from extinc­tion. This is evo­lu­tion­ary res­cue in action and sug­gests that rapid evo­lu­tion can help pop­u­la­tions respond to rapid envi­ron­men­tal change.”

Short-​term eco­log­i­cal responses to the envi­ron­ment — for instance, a reduc­tion in the size of adults because of a lack of food — and hard-​wired evo­lu­tion­ary changes were sep­a­rated by plac­ing mites from dif­fer­ent treat­ments into a sim­i­lar envi­ron­ment for sev­eral gen­er­a­tions and see­ing whether dif­fer­ences per­sisted.

Pro­fes­sor Ben­ton said: “The tra­di­tional idea would be that if you put ani­mals in a new envi­ron­ment they stay basi­cally the same but the way they grow changes because of vari­ables like the amount of food. How­ever, our study proves that the evo­lu­tion­ary effect — the change in the under­ly­ing biol­ogy in response to the envi­ron­ment — can hap­pen at the same time as the eco­log­i­cal response. Ecol­ogy and evo­lu­tion are inter­twined,” he said.

Unpick­ing evo­lu­tion­ary change from eco­log­i­cal responses is par­tic­u­larly impor­tant in areas such as the man­age­ment of fish­eries, where human deci­sions can result in major changes to an entire population’s envi­ron­ment and life his­to­ries. The size at which cod in the North Sea mature is about half that of 50 years ago and this change has been linked to a col­lapse in the cod pop­u­la­tion because adult fish today are less fer­tile than their ances­tors.

“The big debate has been over whether this is an evo­lu­tion­ary response to the way they are fished or whether this is, for instance, just the amount of food in the sea hav­ing a short-​term eco­log­i­cal effect. Our study under­lined that evo­lu­tion can hap­pen on a short timescale and even small 1 to 2 per cent evo­lu­tion­ary changes in the under­ly­ing biol­ogy caused by your har­vest­ing strat­egy can have major con­se­quences on pop­u­la­tion growth and yields. You can’t just try to bring the envi­ron­ment back to what it was before and expect every­thing to return to nor­mal,” Pro­fes­sor Ben­ton said.



(Source: Uni­ver­sity of Leeds press release, 09.04.2013)

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