BIOL 1070 Midterm 1
Unit 1 Online
• Thewater hasbecomemuchclearer asthequantity of particulatematter in thewater column hasbeengreatly
reduced.This is oneof thebyproductsof thehugeabundanceof zebramussels, whosefilter-feeding activities
cycle massiveamountsof water every day.
• Zebramusslesareableto attachto just about any solid surfacehasmadethemareal menaceasthey clog pipes
andcover industrial equipment, docks, andboats.
• It hasbeenestimatedthat theeconomic damageby zebramusselsandtheefforts to control themhavealready
cost billionsof dollars
Herearethequestionsabout zebramusselsthat struck measbeing important:
o Wheredid zebramusselscomefrom?
o Whenandwheredid they first arrive, andhow havethey spreadsoquickly?
o What impactsarethey having onthenative faunaandecosystem?
o Why havethey beensosuccessful atspreading into new lakesandrivers?
Peer-reviewed scientific publications, also known as the “primary literature” are the means by which scientists
share their results with other researchers. As members of the University of Guelph, you have access to an
extraordinary number of peer-reviewed journals through the library, most of them with electronic access. Search
engines such as Google Scholar, PubMed, and Web of Science can all be used to locate papers on any topic.
• Thezebramussel (Dreissenapolymorpha) is native to eastern Eurasia, specifically theBlack Seaand
• Modeof transport acrosstheAtlantic wasin theballast water of anoceanliner.
• First reportedin NorthAmericain 1988in LakeSt. Clair, in apeer-reviewedpaper by Hebert etal. (1989).
o Prof. Hebert is theDirector of theBiodiversity Instituteof Ontario hereat theUniversity of
• This is not thefirst timethezebramussel hasinvadednewenvironments— it alsoinvadedwestern Europe
in thelate1700sandearly 1800s
• Therehassincebeenasecondinvasion by arelatedmussel, thequaggamussel (Dreissenarostriformis)
In Ontario, thenative musselsareall membersof thefamily Unionidae, but within thisthereareseveral distantly
Zebramusselsandother factors(especially agricultural practices) arehaving asignificant impact onthenative
Freshwater musselsareamongthemost endangeredorganismsin NorthAmerica.
Unionidsareparticularly interesting becauseof their complex life cycle, which includesacomponent of obligate
parasitism (i.e., they must parasitizeahost atsomestageto completetheir reproductive cycle). Most of thespeciesin Ontario aredioecious(“two houses”), meaning that they haveseparatemalesandfemales.
o Malesreleasetheir sperm into thewater through their exhalant siphon, which arethentakenupby females
downstreamthrough their inhalant siphon. Fertilization is internal (i.e., insidethefemale’sbody), andthe
embryosdevelop insidemodified pouchesof thefemale’s gills called amarsupium.
o Theembryosmatureinto specializedlarvaecalled glochidia (singular glochidium), andit is thesethat
represent theparasitic life stage.
o Glochidia must attachto thegills of afish in order to continuetheir development.
o Themantle tissueactsasa“lure” that resemblesafish or invertebrateprey that attractsthehost.
Key Pointsin Unit 1
1. Theinvasivezebramussel (Dreissenapolymorpha) hashadanenormouseconomic, aesthetic, andbiological
impact ontheGreat Lakeswatershed. It originatedfrom eastern Eurasiaandis thought to havebeentransportedby
2. Peer-reviewedprimary literatureis thestandard meansby which scientistssharetheir researchfindings. It is
typically awell regulatedsystemwheretwo or moreexternal refereesreadandcritiquethemanuscript providing a
recommendation to thejournal editor to publish or reject thestudy.
3. Thereare41native freshwater musselsin Ontario, many of themareendangered. Unionidsareobligateparasites
whereglochidia (larvae) arereleasedandmust attachto thegills of afish host to completetheir development.
4. Native andinvasive mussel speciesarestudiedby avariety of different people: undergraduates,graduates,
professorsandgovernment scientists. Thesepeopleexploremussel diversity, adaptations, distribution,
Phyla (singular: Phylum) - Mollusca(mollusks)
Genera(singular: Genus) - Homo(humansandextinct relatives, e.g., Neanderthals)
Species(singular is alsospecies, not specie) - sapiens(humans)
Biologistsusetheword “diversity” to refer to thenumber of speciesin ataxonomic groupor ageographical area.
DifferencesWithin Species: Sexual Dimorphism andAge
Eachspecieshasmorphological (physical) traitsthat canbeusedto distinguishit from other mussels. Our
development — what biologistscall “ontogeny” — involvessignificant changesin morphology from youth to old
age.This is alsotrueof mussels!
Like humans,musselsmay exhibit clear differencesamongindividualswithin speciesdueto sexual dimorphism (in
somespecies) andage.Finding gravid femalesandjuvenilesis agood sign that recruitment (production of thenext
generation) is succeeding
Femalemusselshaveawider posterior while malescometo apoint.
DifferencesWithin SpeciesII: Morphology
Thescientific nameconveysimportant information about thespeciesitself- .Dreissenapolymorpha(zebra mussel),
is onesuchexample: “polymorpha” means“many forms”.
DifferencesWithin Species: Cryptic Variation
To beevolutionarily relevant, variation amongindividualsmust beheritable. In other words, theremust beagenetic
basisfor theobservedtrait suchthat it will bepassedonin similar form to offspring.
Casesin which thesameset of genes(genotype) canresult in differing features(phenotype) according to
environmental conditionsareknown as“phenotypic plasticity”.
Abundancevs.Variation vs. Diversity vs. Disparity
Morphological and genetic variation (differencesamong individuals within aspecies)
diversity (number of species)
Whereasdiversity is ameasureof thenumber of different species,disparity refersto how physically different those
speciesarefrom eachother. We areall Related
You areamember of alineageof ancestorsanddescendantsthat hasnever oncebeenbrokenin morethan3.8
billion yearsof life onEarth.
Waysin which living thingsarerelatedto oneanother through their commonancestors: afield known as
Theclosest relativesdescendedfrom asingle recent ancestor areeven
called “sister taxa” — again, thereareimportant parallels between
This order of branching, what biologistscall “topology”, reflectsthe
ancestor-descendant relationships, andthat is themost important
information containedin atreediagram.
Theancestorsanddescendantsonaphylogeny areusually species.
Theroot (commonancestor sharedby all speciesdepicted), branches
(connectionsbetweenancestorsanddescendants), and“tips” (or
“terminal nodes”). Theterminal nodesusually represent living species,
whereasinternal nodesareusually extinct ancestors.
Theapproachto classification that is basedstrictly onevolutionary
relationshipsis known as“cladistics”, andtheevolutionary groupsthat it
considersworthy of naming arecalled “clades”.
A cladeis any groupof speciesthat includesthelast ancestor that they sharedandall its descendants.
Valid clades,which includethelast sharedancestor andall its descendants, areknown as“monophyletic” groups
Whenoneof thedescendantsis left out, which createswhat cladistscall a“paraphyletic” group. For example, the
term “reptile”, which includeslizards, snakes,turtles, andcrocodilesbut not birdsis aparaphyletic group. It is not a
clade,becauseit leavesout birds.
Musselsinhabiting fast-moving riversexhibit avariety of adaptationsto remaining anchoredin thesubstrateatthe
bottom. This includesvariousconfigurationsof bumps, ridges,or wings.
This sort of featurehasevolved morethanoncein independent lineagesasasimilar adaptation under similar
environmental pressures,aprocessknown as“convergent evolution”.
Sharing ancestral traits is called “homology”, whereashaving traits that aresimilar but evolved independently is
called “homoplasy” (convergent evolution).
Mutation (theorigin of newgenetic variation)
Genetic drift (changesdueto chance, specifically founder effectsandpopulation bottlenecks)
Geneflow (movement of genesamongpopulations)
Natural selection: Non-randomdifferencesin survival and/or reproduction amongindividual entitiesonthebasisof
Adaptation: 1) acharacteristic that enhancesthesurvival and/or reproduction of organismsthat bearit, relative to
alternative (especially ancestral) character states; 2) aphysical, physiological, behavioural, or other characteristic
evolved through natural selection.Adaptation is NOT thechangeundergoneby anindividual organismduring its
lifetimein responseto external conditions.
Population: for sexual species, agroupof interbreeding individualsandtheir offspring.
Alleles: alternate(i.e., different andmutually exclusive) formsof agene.e.g., “B” (brown eyes)versus“b” (blue
Genotype: thesetof genespossessedby anorganism.
Phenotype: thephysical expression of thegenotype(in combination with theenvironment).
Frequency: theproportional representation of aphenotype, genotype, gamete,or allelein apopulation. e.g., 6out of
10haveblueeyes= 60% = afrequency of 0.6.
The BasisOf Natural Selection Whenit comesspecifically to adaptive changesamongspeciesandthetraitsof organismsthat allow themto survive
successfully in their environments, natural selection is indeedtheonly known mechanismthat canprovidea
1. Individualswithin populationsarevariable.
That not every individual is identical in apopulation is obviousfor humans
2.This variability amongindividuals is atleast partly heritable.
Offspring tend to look morelike their parentsthanlike unrelatedmembersof thepopulation
3. Not everyonesurvivesandreproduces,andsomeindividualsaremoresuccessful thanothers.
Many moreoffspring areproducedin eachgeneration thancould possibly survive, aphenomenonknown as
4.Thedifferential survival andreproduction of individuals is associatedwith theheritablevariation among
individuals (i.e., it is non-random).
This is thekey to natural selection, that theindividuals who domanageto reachadulthoodandhaveoffspring of
their own are, onaverage,better suitedto surviving andreproducing in their particular environment becauseof traits
that they inherited from their parents.
10Thingsabout Natural Selection
1. Natural selection by itself does not create new traits, it only changes the proportion of variation that is already present in the
population. Most often, natural selection reduces the amount of variation in a population because some variants are eliminated.
2. Mutation, not natural selection, is the source of new variation. The repeated twostep interaction of mutation and natural
selection is what leads to the evolution of new adaptive features.
3. Mutation is random with respect to fitness — that is, it occurs without regard for what happens to the organism. It is simply a
genetic error. Natural selection is, by definition, nonrandom with respect to fitness. This means that, ove