New research con­ducted at the NRS’s Motte Rim­rock Reserve shows that evo­lu­tion – genetic changes in pop­u­la­tions over time – can occur so rapidly in organ­isms that its impact on pop­u­la­tion num­bers and other aspects of biol­ogy can be seen within just a few generations.

The research, pub­lished online Aug. 9 in Ecol­ogy Let­ters, the high­est ranked jour­nal in the field of ecol­ogy, can improve sci­en­tists’ abil­ity to pre­dict the growth and spread of endan­gered species, inva­sive species, and dis­ease epidemics.

Work­ing on aphids, con­sid­ered the world’s most impor­tant crop pest, the researchers exper­i­men­tally tested the impact of rapid evo­lu­tion on wild pop­u­la­tions within a sin­gle crop-growing sea­son. To accom­plish this, the researchers set up an exper­i­ment that pre­vented evo­lu­tion by nat­ural selec­tion from occur­ring in some aphids while allow­ing it in oth­ers. They then com­pared the rate at which the non-evolving and evolv­ing pop­u­la­tions grew.

Each fall, aphids undergo one gen­er­a­tion of sex­ual repro­duc­tion. The fol­low­ing spring, they begin mul­ti­ple gen­er­a­tions of asex­ual repro­duc­tion. Dur­ing this period mul­ti­ple clonal lin­eages com­pete, lead­ing to changes in gene fre­quen­cies and mean trait val­ues in the pop­u­la­tion in the process.

In their field exper­i­ment, the researchers com­pared repli­cated aphid pop­u­la­tions that were non-evolving (sin­gle clone, thus genet­i­cally iden­ti­cal) to aphid pop­u­la­tions that were poten­tially evolv­ing (two clones genet­i­cally dif­fer­ent from each other and with dis­sim­i­lar growth rates).

As the pop­u­la­tions grew, the researchers tested whether the mixed pop­u­la­tions evolved. Count­ing aphids repeat­edly, they found that clones rapidly changed in fre­quency, within 30 days or 4–5 aphid gen­er­a­tions. They then tested the impact of this evo­lu­tion­ary change on the ecol­ogy of the aphids. They found that evolv­ing pop­u­la­tions grew in num­ber up to 42 per­cent faster than non-evolving populations.

“This shows that even with­out human inter­fer­ence nat­ural selec­tion act­ing on aphid pop­u­la­tions causes rapid evo­lu­tion,” said Mar­tin M. Tur­cotte, who led the research as a grad­u­ate stu­dent in ecol­ogy, evo­lu­tion and organ­is­mal biol­ogy at UC River­side. “Even stronger effects might be expected when pes­ti­cides are in use. For decades, evo­lu­tion was deemed too slow and, hence, it was not con­sid­ered when study­ing pop­u­la­tion growth – an over­sight that needs to be cor­rected. Ignor­ing this evo­lu­tion, as is not cur­rently uncom­mon, can lead to pre­dic­tions that greatly under­es­ti­mate pest den­si­ties and outbreaks.”

Rapid evo­lu­tion could have impor­tant untested impacts in many other applied areas. For exam­ple, rapid evo­lu­tion is impor­tant in fish­eries where intense fish­ing causes fish to evolve traits that let them escape fish­ing nets. Antibi­otic resis­tance and increased vir­u­lence in pathogens are exam­ples where rapid evo­lu­tion impacts human health.

The study was con­ducted at the Uni­ver­sity of Cal­i­for­nia Motte Rim­rock Reserve where the researchers col­lected mul­ti­ple clonal lin­eages from a wild aphid pop­u­la­tion feed­ing on mus­tard plants. They iden­ti­fied clones and char­ac­ter­ized their intrin­sic per capita growth rates in a green­house at UCR.

Tur­cotte grad­u­ated with a doc­toral degree in biol­ogy from UCR this year. Cur­rently a post­doc­toral scholar at the Uni­ver­sity of Toronto at Mis­sis­sauga, Canada, he uses exper­i­men­tal evo­lu­tion to study fun­da­men­tal ques­tions about the ecol­ogy and evo­lu­tion of plant-herbivore interactions.

He was joined in the research by his co-advisors at UCR: David N. Reznick, a pro­fes­sor of biol­ogy, and J. Daniel Hare, a pro­fes­sor of ento­mol­ogy. A few UCR biol­ogy under­grad­u­ate stu­dents also assisted the research team.

Tur­cotte was funded by grants from the Nat­ural Sci­ences and Engi­neer­ing Research Coun­cil of Canada; Fonds de Recherche du Québec and the Uni­ver­sity of Cal­i­for­nia Nat­ural Reserve Sys­tem. Grants from the U.S. National Sci­ence Foun­da­tion sup­ported Reznick and Hare in the study.

— Iqbal Pit­tawala, UC River­side Office of Strate­gic Communications