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The evo­lu­tion of city life: the effect of the con­crete jungle

pub­lished 29 August 2018 | mod­i­fied 29 August 2018

New research con­ducted by evo­lu­tion­ary biol­o­gists world­wide paints cities as evo­lu­tion­ary “change agents,” says a trio of biol­o­gists from the Uni­ver­sity of Toronto who selected and edited the studies.

Burrowing owlsBur­row­ing owls in South Amer­ica.
A Ger­man study on bur­row­ing owls found that sep­a­rate groups native to var­i­ous South Amer­i­can cities had devel­oped sim­i­lar genetic responses, even though there was no cross-​breeding between the pop­u­la­tions.
Image credit Jakob Mueller.

A com­pi­la­tion of 15 new research papers, pub­lished as a spe­cial issue of Pro­ceed­ings of the Royal Soci­ety B, con­firms that cities fre­quently alter evo­lu­tion by nat­ural selec­tion and species are adapt­ing to cities world­wide. As well, new com­men­sal species — those that live along­side humans — have arisen in response to the envi­ron­men­tal demands and chal­lenges imposed by urbanization.

These are the same evo­lu­tion­ary mech­a­nisms first iden­ti­fied by Charles Dar­win more than 150 years ago and the find­ings from these stud­ies will be increas­ingly impor­tant as more and more of the world’s pop­u­la­tion flocks to urban environments.

Marc John­son, co-​author and co-​editor, Depart­ment of Biol­ogy, Depart­ment of Ecol­ogy and Evo­lu­tion­ary Biol­ogy and Cen­tre for Urban Envi­ron­ments, Uni­ver­sity of Toronto Mis­sis­sauga, Ontario, Canada

These papers greatly advance our knowl­edge of urban evo­lu­tion­ary biol­ogy,” adds Marc John­son, an asso­ciate pro­fes­sor of biol­ogy at Uni­ver­sity of Toronto Mis­sis­sauga and direc­tor of the Cen­tre for Urban Envi­ron­ments. “It’s pretty remark­able. For years, biol­o­gists ignored cities, see­ing them as ‘anti-​life’ — and only recently biol­o­gists began to realise that cities are agents of change, dri­ving evo­lu­tion of organ­isms liv­ing around us and even some liv­ing on us.”

John­son co-​edited the project with two PhD can­di­dates in ecol­ogy and evo­lu­tion­ary biol­ogy, James San­tan­gelo and Ruth Rivkin. San­tan­gelo also con­tributed a study to the com­pi­la­tion, devel­op­ing the first the­o­ret­i­cal mod­els that pre­dict evo­lu­tion­ary out­comes in urban environments.

The spe­cial issue con­tains many other stud­ies that also illus­trate its key evo­lu­tion­ary find­ings. For exam­ple, a Bel­gian study of Daph­nia magna, a type of zoo­plank­ton of fresh­wa­ter ponds and lakes, demon­strates that cities fre­quently alter nat­ural selec­tion. Leu­ven researcher Kristien Brans and her col­leagues col­lected Daph­nia from ponds in both urban and rural loca­tions and put them into hold­ing tanks in the lab. They ele­vated the water tem­per­a­ture in the tanks and by mea­sur­ing their pro­tein metaboli­sa­tion and devel­op­ment were able to deter­mine that the urban Daph­nia were able to han­dle the stress of warmer tem­per­a­tures more eas­ily than their rural coun­ter­parts. Given that cities are warmer than rural areas, this abil­ity to adapt to a warmer and often more stress­ful cli­mate is essen­tial, John­son notes.

Par­al­lel evo­lu­tion­ary changes in diverse urban loca­tions is shown by a study of bur­row­ing owl pop­u­la­tions in South Amer­ica, a project led by Jakob Mueller in Ger­many. He and his col­leagues deter­mined that sep­a­rate groups of bur­row­ing owls native to var­i­ous South Amer­i­can cities had devel­oped sim­i­lar genetic responses, even though there was no cross-​breeding between the pop­u­la­tions. Urban envi­ron­ments share numer­ous fea­tures that likely account for these sim­i­lar changes.

The issue also illus­trates how urban areas influ­ence the evo­lu­tion of inva­sive species and pests; in many cases, humans become agents for the dis­per­sal and move­ment of their genes. For instance, Tina Arredondo and her col­leagues at Port­land State Uni­ver­sity in Ore­gon stud­ied the spread of an inva­sive grass species, Brachy­podium syl­vaticum, across urban-​rural bound­aries and dis­cov­ered that humans were actively involved in its spread, unwit­tingly car­ry­ing seeds as they pur­sued recre­ational activ­i­ties on local waterways.

We are facil­i­tat­ing the dis­per­sal and expan­sion of the plant’s range to new areas,” says Rivkin. “Humans are com­plicit in alter­ing the genetic dis­tri­b­u­tion of a vari­ety of species.”

mexico city urban jungleThe spe­cial issue of Pro­ceed­ings of the Royal Soci­ety B addresses some of the most press­ing gaps in our under­stand­ing of urban evo­lu­tion­ary ecol­ogy and points the way for­ward for fur­ther study.

Read the research

This issue marks the begin­ning of a very impor­tant area of research,” John­son says. “It will allow us to under­stand evo­lu­tion­ary biol­ogy more gen­er­ally and to realise how impor­tant it is for humans and the envi­ron­ment in which we live. It also has impor­tant impli­ca­tions for under­stand­ing how organ­isms persist.

San­tan­gelo notes that addi­tional research into urban evo­lu­tion­ary biol­ogy can also help us become bet­ter stew­ards of our urban environments.

Under­stand­ing how cities shape the evo­lu­tion of urban pop­u­la­tions can facil­i­tate design­ing man­age­ment strate­gies for urban pests and help min­i­mize the impact of humans on the spread of inva­sive species,” he says.

There’s lots to explore,” John­son adds. This is just the start of a long and inter­est­ing road of sci­en­tific discovery.”

(Source: Uni­ver­sity of Toronto news release, 22.08.2018)

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