Wings of changeButterflies shed light onorganisms’ ability to adjust totheir environment
What does it take to thrive in achanging world? Being able toalter one’s developmentaltrajectory in response to theenvironment can be a big boon.But such “plasticity” may alsocome with a cost – such as lowerreproductive rates. Improving ourunderstanding of how organismsmeet the demands of changingworld is more important thanever today, as human actionscreate new and unusual habitats.
Emilie Snell-Rood, assistantprofessor in the Department ofEcology, Evolution and Behavior, isdoing just that, using butterfliesas research subjects. Whybutterflies? “There are a lot ofgood natural history recordsbecause people love to watchbutterflies,” she explains.Butterflies also exhibit a largeamount of variation amongspecies and reproduce quickly. 3
One trait that has been linked tosurvival in shifting environmentsis brain size. 5
Changes in diet over the last 2million years may havecontributed to the evolution oflarge brains in humans. Is diet agenerally important driver inbrain evolution? To answer thisquestion, Snell-Rood is looking atbrain size across more than 40species of butterflies that feed ondifferent plants as caterpillars. Forinstance, this Rocky MountainParnassian uses stonecrop(Sedum) as a host plant, whileother caterpillars feed oncabbage, milkweed, pine, grass,or even other insects! 6
Junior scientist Anne Espesetspends a lot of time dissectingand then measuring brains ofhundreds of butterflies. 7
With the help of undergraduateresearch assistant Ihab Mikati, thelab is also measuring eye size (aproxy for brain volume) inmuseum specimens of more than60 butterfly species and lookingat how it relates to the quality ofthe species’ known diets. 8
A better understanding ofnutritional ecology can shed lighton whether a species might thrivein a changing environment.“Some species can deal withmuch more variable diets, so theyhave more resilience to change,”Snell-Rood says. “Understandingadaptations to low-quality andhigh-quality diets could inform alot of human health questions.” 9
In addition to exploring whyspecies might differ in cognitiveresponses to new environments,Snell-Rood is also studyingresponses to these environmentsdirectly – for example, responsesto changing nutrient dynamicscaused by human use of fertilizeron crops and lawns. 10
Snell-Rood’s lab is looking at thelink between nutrition and abilityto choose the fittest mates. Incabbage white butterflies, thebrightness of a male’s wings isassociated with the amount ofnitrogen they’ve gotten fromtheir environment – a measure ofthe survival value they canprovide to their offspring. Thiscue provided females butterflies acue about relative fitness whennitrogen was scarce. But does itstill today, when farm fertilizermakes it abundant? 11
To find out, Snell-Rood is raisingnormal and genetically inferiormale cabbage whites on low-nitrogen and high-nitrogen diets,then watching how they pair upwith females. “Is the female’sability to distinguish betweenlow- and high-quality malesdisrupted when we flood thesystem with nitrogen?” she asks. 12
In a follow-up study, Snell-Roodalso plans to compare the abilityto survive on different nitrogendiets for cabbage whites collectedin North Dakota, where nitrogenfertilizer is common, and thosefrom populations with lessfertilizer use, such as northernWisconsin. “We predict butterfliesfrom areas with less fertilizer usewill retain the ability to survive ona low-nitrogen diet,” she says. Incontrast, she suspects the loss of“honest” signals of mate qualityin butterflies from high-nitrogenareas will make it less likely theiroffspring can cope with lownitrogen. 13
Snell-Rood is also studying yetanother dimension of human-induced change. She’s comparingcabbage white populations fromenvironments with diversevegetation with others collectedfrom canola monocultures inNorth Dakota. 14
By raising the capturedbutterflies’ young on various dietsin the lab, she seeks to learn howfood specialization (for instance,on an agricultural crop) mightaffect fitness. 15
Snell-Rood hopes improvedunderstanding of how livingthings adjust to a shiftingenvironment will shed light onhow we can help nature thrive inthe face of human-inducedalterations to habitat. “Given thecurrent rate of environmentalchange, we may not have a lot oftime,” she says. 16
Mary Hoff, writer Jonathan Pavlica, photographer Stephanie Xenos, editor Katie Hoffman, productionCopyright 2012University of MinnesotaCollege of Biological Sciences 17
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