Fall 2011 - the Department of Biology - Syracuse University

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are beautiful and are often cultivatedin gardens. Some yuccas are relativelyfamous; Joshua tree (Yucca brevifolia), forexample, is both the name of a nationalpark in California and a popular U2album.Yuccas are only pollinated by yuccamoths, and the relationships betweenthe moth and the plant has becomeextremely specialized during theirevolutionary history. During the daythe small white yucca moths benignlyrest inside yucca flowers, but at nightthey become bandits, stealthily flittingfrom yucca flower to yucca flower to layeggs and pollinate. The female yuccamoths deposit eggs inside of the flowers,hypodermically injecting them into thefloral tissue using a modified structurethat resembles a needle (similar to thestinger of a wasp). Just after laying anegg, a female will climb to the top of theflower and purposefully pollinate usinga bit of pollen that she carries in a ballunder her head. Females have specializedmouthparts used for collecting anddepositing pollen, and these mouthpartsare not found in any other insect. Suchactive pollination behavior is incrediblyrare, as nearly all pollinators accomplishthe task by accidentally brushing pollenonto the receptive surfaces of flowers. Bypurposefully pollinating the flower, thefemale yucca moth is ensuring a foodsource for her offspring, since the eggswill eventually hatch into small larvae thatfeed exclusively on yucca seeds. In theend, the plant generally comes out aheadbecause the moths pollinate more seedsthan the larvae destroy; thus, the plantgains an extremely effective pollinator bygiving up a few seeds.My Ph.D. project focused onhow cheaters evolve in mutualisticinteractions, and I took advantage ofa new discovery that Olle had madewhile conducting field research in thesouthwestern United States. When hebegan working on yucca moths, therewere only a few named species, andhis observations of the moth Tegeticulayuccasella led him to believe this entitywas actually a composite of severalunrecognized species. A combinationof DNA sequence analysis andmeasurements of the shape and size ofthe moths showed that Olle was right,Figure 1: Tegeticula yuccasella in a yucca flower. The female in the lower right is laying an egg,and the female on the left is actively pollinating.and revealed that T. yuccasella consistedof at least 14 distinct species. The trulyexciting finding was that two of thesenew species were “cheaters,” or mothsthat avoided pollination and laid eggsdirectly into developing fruit. Cheaterscapitalize on the efforts of the pollinatormoths, and their larvae feed on yuccaseeds in competition with pollinatormoth larvae. In theory, cheaters shouldoverexploit the mutualistic partners byeating all the seeds, and the final resultwould be extinction of all three species.Yet, a quick look at the evolutionaryhistory of the cheaters shows thatthey have happily coexisted with themutualistic moths for upwards of twomillion years; clearly, cheaters are notdestabilizing the mutualism. Duringthe course of my Ph.D. work, I usedbehavioral studies of the moths, fieldobservations, and molecular analyses ofthe evolutionary histories of the pollinatorand cheater moths to examine howcheaters might have evolved. Althoughthe evidence remains thin, our bestguess is that cheaters may come intoexistence when a mutualistic interactionis more complex than the simple scenarioof two interacting partners. That is, incircumstances when multiple pollinatormoth species coexist on a singleyucca species, there is an evolutionaryopportunity for one pollinator speciesto cheat because the other pollinator isstill providing a benefit to the plant. Weare still exploring this hypothesis andare learning more about how mutualistscan turn to the dark side and becomecheaters.This idea about how communitycomplexity might lead to cheating drewme to think more deeply about how themultitude of interactions present in acommunity could influence the pair-wiseinteraction between mutualist partners.We often think of mutualisms as existingin isolation of their surroundings andignore the effects of other species. Partof the reason for doing so is one ofsimplification; species often interact withhundreds of other species, and tryingto study even just the direct effects of afew interactions can be challenging. Forinstance, a typical pollination mutualismwill involve a focal plant species that hasOlle PellmyrS12 THE DEPARTMENT OF BIOLOGY AT SYRACUSE UNIVERSITY
dozens of pollinator species all of whichalso interact with dozens of other plantspecies. The picture becomes even morecomplex when the diverse community ofherbivores and predators is added. Butone of the great qualities about the yuccastudy system is its inherent simplicity. Incontrast to other mutualisms, the yuccayuccamoth interaction typically has onlya single pair of mutualists (one plant andone moth species) and they interact witha small handful of other species—fromspiders that sit and await prey in flowersto beetles that feed on yucca flowers.When I arrived at Syracuse Universityin 2005, I decided to use the yuccasystem to ask how community complexityaffects the mutualism between theplants and moths. My colleagues andI are focusing on the plant side of thestory, trying to understand how all ofthe direct and indirect interactions withthe community impact seed production.At the outset, we thought the resultswould be straightforward: communitymembers that fed on the plants shouldharm seed production and those thategravesfed on the herbivores should improveseed production. That’s not quite whatwe found. Instead, we learned that someherbivores could increase seed set. Inparticular, we found that plants beingfed on by a small flower-feeding beetle(Hymenorus) produced more seeds thanplants lacking the beetle. Althoughthe obvious direct effect of the beetles(destroying floral tissue) is bad for theplants, we found that the beetles alsoproduce a strong indirect effect. Not onlydo they consume plant tissue but theyalso incidentally eat yucca moth eggs. Bydoing so, they are reducing the number ofmoth larvae feeding within fruit and thisincreases seed set. So, counter-intuitively,we’ve shown that a flower-feeding insectcan benefit plants.Our next step in this project involvesdetermining how the community ofinsects interacting with the plants andmoths might influence pollen movementamong yuccas. Yucca plants arehermaphrodites—single flowers produceboth pollen (sperm) and eggs—meaningthat a given plant can pass on its genesby serving as either a mother (producingseeds in fruit) or as a father (siringseeds in fruit of other plants). So far,our analyses have only focused on howwell a plant fares as a mother, and doesnot include the plant’s performance as afather. To remedy this, we are currentlyusing molecular tools similar to theones used in human paternity tests toassess the number of seeds an individualplant has sired. We expect that the maleperspective of the plant may differsubstantially from the female perspective.For instance, we’ve shown that the flowerfeedingbeetles improve seed set fromthe female perspective, but since thesebeetles can also quickly consume all ofa plant’s pollen, we’re betting that theydecrease the ability of a plant to sireseeds. If the pollen is removed beforea moth can collect it, then that plantwill not sire any seeds. Consequently,the benefits gained through femalereproduction may come at a cost to malereproduction. In the end we hope to painta full picture of the effects of a number ofinsects that interact directly and indirectlywith yuccas and their pollinator moths tounderstand more about how these typesof mutualisms are shaped in naturalcommunities.As the yucca project draws to a close,I’ve decided to return to my work on theHeuchera system to learn more about howvariation in the number of chromosomesimpacts interactions between species.Rather than focusing exclusively oninsects, I’m working with the soil fungithat inhabit the roots of Heuchera. Theinteraction between the plants andfungi is thought to be mutualistic as thefungi forage for critical plant nutrientsthat they then trade with the plant forcarbohydrates. I’m interested in the tiesbetween DNA content and the nutrientrequirements of plants and how thesefactors in turn affect interactions withthe mutualistic fungi. Since many ofour crop plants also have extra sets ofchromosomes (e.g., bananas, wheat, andstrawberries), knowing more about theseinteractions that can help plants growin nutrient-depleted environments maybe useful in agriculture. I find it excitingthat my research might help us engineerbetter crops, and I look forward to thediscoveries to come.Figure 2: Hymenorus densus beetles feeding on yucca flowerFALL 201113
Page 2: 4DeanGeorge M. LangfordEditorErnest
Page 11 and 12: UC San Francisco; three are attorne
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Page 17 and 18: Figure 1: Sperm pairing in Graphode
Page 19 and 20: Figure 1: Fruiting body development
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Page 23 and 24: UNDERGRADUATE STUDENT PROFILE:Emily
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Page 27 and 28: Muslim world as in westernsocieties
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Page 35 and 36: Who, What, When, WherePeter V.N. Bo
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Page 39 and 40: GIVINGTOBIOLOGYAT SU:In this issue

Fall 2011 - the Department of Biology - Syracuse University

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