AboutZoos, Since 2008


Brain size tracks human-​induced changes to the envi­ron­ment in some species

pub­lished 23 August 2013 | mod­i­fied 28 June 2014

Does adapt­ing to envi­ron­ments shaped by humans make ani­mals smarter? A paper from the lab of Emi­lie Snell-​Rood, a behav­ioural and evo­lu­tion­ary biol­o­gist with the Col­lege of Bio­log­i­cal Sci­ences of the Uni­ver­sity of Min­nesota, sug­gest that ani­mals are show­ing com­plex cog­ni­tive responses to both urban and rural areas with cra­nial capac­ity track­ing human-​induced change in some cases. In other words, for some species the answer is yes and for oth­ers it is no.

It [the study] reminds us of the fact that pop­u­la­tions adapt, and that at least some species are track­ing human-​induced envi­ron­men­tal change
Emi­lie Snell-​Rood, behav­ioural and evo­lu­tion­ary biol­o­gist, Col­lege of Bio­log­i­cal Sci­ences, Uni­ver­sity of Minnesota »

White footed mouse“Which species are going to be able to deal with 100 per­cent con­ver­sion of prairie to agri­cul­ture?” she says. “Which species are going to be able to deal with forests being sup­planted by cities?” Ulti­mately, says the researcher, being able to under­stand which species are going to be able to cope with that kind of human-​induced change will pro­vide vital con­text when pri­ori­tis­ing con­ser­va­tion objectives.

Pre­vi­ous research across bird species sug­gests a link between brain size and abil­ity to adapt to urban envi­ron­ments, but doesn’t address the ques­tion of whether cities select for increases in cog­ni­tion within species. That’s where Snell-​Rood and under­grad­u­ate stu­dent Naomi Wick come in. Their find­ings are pub­lished on 21 August in the jour­nal Pro­ceed­ing of the Royal Soci­ety B.

“We wanted to find out if deal­ing with a new envi­ron­ment is just a mat­ter of species sort­ing (in which a par­tic­u­lar species is “pre-​adapted” for suc­cess in a par­tic­u­lar envi­ron­ment) or actu­ally changes going on within species in addi­tion to that species-​level vari­a­tion,” says Snell-​Rood.

The researchers turned to the Bell Museum of Nat­ural His­tory col­lec­tions to find out. Draw­ing on spec­i­mens dat­ing back to the early 20th cen­tury, Snell-​Rood and Wick exam­ined the cra­nial capac­ity of 10 species, includ­ing vari­eties of shrews, voles, bats, and squir­rels, along with a mouse and gopher, from loca­tions in and around the Twin Cities metro. They found that the urban pop­u­la­tions of two of the species did, in fact, pos­sess sig­nif­i­cantly greater cra­nial capac­ity. They also pre­dicted that if more smarter species were favoured in urban envi­ron­ments cra­nial capac­ity should also increase over time. “We didn’t see cra­nial capac­ity increases over time in the urban spec­i­mens,” she says. “And, actu­ally, for two species we see a decline over time, while the bats and shrews show an increase in cra­nial capac­ity in rural populations.”

While there are a num­ber of fac­tors that could account for this such as the time frame in which the spec­i­mens were col­lected, Snell-​Rood points out that cities aren’t entirely unpre­dictable. “Things are laid out in a reg­u­lar fash­ion. There are cer­tain resources that might be exploitable. There’s a reduc­tion in preda­tors and the new preda­tors are fol­low pre­dictable patterns.”

Learn­ing is costly, says Snell-​Rood. “Neural tis­sue is incred­i­bly expen­sive meta­bol­i­cally. There are trade-​offs in invest­ing in brains and invest­ing in repro­duc­tion, which may be why we see a reduc­tion in cra­nial capac­ity over time in two of the species — larger brains may be favoured just dur­ing the ini­tial coloni­sa­tion of the city.” More­over, humans are chang­ing rural envi­ron­ments in ways that could be just as chal­leng­ing as cities, result­ing in the changes in cra­nial capac­ity over time seen in bats and shrews.

While the researchers can’t say for cer­tain whether the changes are evo­lu­tion­ary or devel­op­men­tal, evi­dence sug­gests the for­mer. “We tended to not see changes in body size which sug­gests it’s not just nutri­tional, but rather an evo­lu­tion­ary response,” says Snell-​Rood. And while the study raises as many ques­tions as it answers, she con­sid­ers the find­ings cause for some opti­mism. “It reminds us of the fact that pop­u­la­tions adapt, and that at least some species are track­ing human-​induced envi­ron­men­tal change.”

For fur­ther read­ing, expla­na­tion and dis­cus­sion Carl Zimmer’s writ­ing in the col­umn ‘Mat­ter’ in The New York Times you may find inter­est­ing. Espe­cially rec­om­mended is the stream of com­ments to Zimmer’s tweet.

(Source: Uni­ver­sity of Min­nesota news release, 22.08.2013)

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