Sensitivity Of Fitness To Variation In Its Components In Drosophila Sturtevanti (Diptera, Drosophilidae)

12 Pages·1999·4.3 MB·English

by  Claudio Marcia Aparecida Carareto

SENSITIVITYOFFITNESSTOVARIATIONINITSCOMPONENTSIN
DROSOPHILASTURTEVANTI(DIPTERA,DROSOPHILIDAE)
ClaudiaMareiaAparecida Carareto'
MarceloFerreiraLourenço^
CelsoAbbadeMourão^
ABSTRACT
An evaluation was made oftotal fitness and the contribution ofVariation in fitness components on
total fitness offourstrainsandtheir 12 reciprocaicrossesofDrosophilasturtevantiDuda, 1927. The strain
from Brazil presents standard arrangement in all chromosomes and the otherthree (from Colômbia, Costa
RicaandMexico)present thesamefourhomozygousinversionsinchromosomesIIandIII.Foreachstrain
and its crosses 12 metric traits ofthe larval and the adult stages were studied. Data were used to compose
fitness Índices, proposed as representative of total fitness, and to estimate the effect of Variation in each
component on total fitness. The diversity of the fitness index values showed that the inversions and the
Standardarrangementhaddiiferentexpressionsinthecompositionoftotalfitness;italsoshowedthatequally
high total fitness values couldbe due tohigh value components forlarval oradult stages. The results also
demonstratedtheoccurrenceoftrade-offsintheexpressionoffitnesscomponents whichareconsideredas
adaptivestrategies.
KEYWORDS.Totalfitness,adaptivestrategies,lifehistorytraits,trade-offs.
INTRODUCTION
Many studies reportgenotype specific fitness or fitnesscomponentsconsidering
only one stage of the life cycle; studies that consider only a small number of fitness
components may overlook others that could be fundamental to the understanding of
genotypic differences relatingto total fitness.According toHedrick & Murray (1983),
thereisnoassurancethatagenotypewhichisfavoredastoonefitnesscomponentwillbe
1.DeparlamenlodeBiologia.InstitutodeBiociências,LetraseCiênciasExatas,UniversidadeEstadualPaulista.RuaCristóvãoColombo,2265.
15054-000-SãoJosédoRioPreto.SPBrasil.Fax:[phone]:e-mail:[email protected].
2.CentroUniversitáriodeRioPreto.RuaIveteGabrielAtique.45.15025-400.SãoJosédoRioPreto.SP.Brasil.
3.Inmemorian
Iheringia,Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999
38 Carareto;Lourenço&Mourão
similarly favored as to the another. Studies made with populations ofD. melanogaster
Meigen, 1830,suggestedVariationinfitnesscomponentsofthelarvalstage,toavariable
degree, to be less important than those ofthe adult stage, and that mating success or
fertiUtyhavemajorcontributions(Prout, 1971;Bundgaard&Christiansen, 1972).Also
Andersonetai. (1979), studying genetic load \nDmelanogaster, Brittnacher (1981),
studyinginversionsofchromosomelllin D.pseudoobscuraFrolova, 1929, andEHRMAN
& Parsons (1976), showed that male mating success largely determines lifetime
reproductivesuccessofmale.InanattempttoestablishtherelativeimportanceofVariation
infitnesscomponents indifferentstagesofthelifecycleofD. melanogaster, Hiraizumi
(1961) considered that lifetime reproductive success is most sensitive to Variation in
development rate and fertility, in the pre-adult and adult stages, respectively. But, as
shownbyBarnes&Merrell(1985),therelativeimportanceoflarvaloradultcomponents
couldbe subordinatedtothedegreeofadaptationtotheenvironmentconsidered.
Prediction of responses to natural selection requires the identification of many
characters whichtogethercomprise fitness, theirphenotypic and genetic variances and
covarianceswithfitnessandwitheachother.Thisstudyconsiderssuchaquestionproposing
thattheconstructionofanindexwouldenabletopredictnotonlythepopulationresponse
tonaturalselectionindifferenthabitats,inwhichtherelativeweightsofthecomponents
mayvary,butalsotheevolutionofthecomponentcharactersasacorrelatedresponse, as
proposedbyMackay(1985).TotalfitnessofD.sturtevantiDuda, 1927,wasfirstbroken
down into several metric components of pre-adult and adult stages, followed by the
combination oftheirmeasures in a Single value which is proposed as representative of
totalfitness.Thisproceduremakesitpossibletocomparethefourstrainsandalltypesof
offspringoftheircrossesaccordingtotheirtotalfitnessvalues.Italsomakespossiblethe
estimation oftotal fitness sensitivity to Variation in its components and to propose the
occurrenceoftrade-offs inthis Variationaspattems ofadaptive strategies.
MATERIALANDMETHODS
The following four strains ofDrosophila sturtevantiDuda, 1927 were used: one with the standard
arrangementinallchromosomes(BRABRA)andtheotherthree(COLCOL,COSCOSandMEXMEX)with
the Standard X chromosome arrangement and the same four homozygous inversions (A, B, C and F) in
chromosomesIIandIII,comprising22%ofthegenome(Hosaki, 1986).ThestrainBRABRAwasprepared
with 18fliescollectedinMirassol (SRBrazil), in 1971, byW.J.Tadei.ThestrainMEXMEXwasprepared
with 40 females and nine males, collected in Veracruz (VER, Mexico), in 1975, by A.J. Gallo and V.M.
Salceda.Thestrains,herecalledCOLCOLandCOSCOShavebeenmaintainedsince 1967attheLaboratory
ofPopulations"Prof.Dr.CelsoAbbadeMourão" (DepartmentofBiology,IBILCE-UNESP,SãoJosédoRio
Preto), and were derived from stocks brought from the Genetics Foundation (University of Texas,Austin,
USA),respectivelylabeledas"H 193.3"(Villavicencio,Colômbia)and"Hl58.1"(Turrialba,CostaRica).
The four strains were intracrossed and intercrossed in all combinations to produce offspring with
threedifferentchromosomalconstitutions(tab.I)asfollows:(i)fourstructuralhomozygotes,withchromosomes
ofthesamegeographicorigin(parentalstrains 1 to4);(ii)sixstructuralheterozygotes(offspring5to 10)and
(iii)sixstructuralhomozygotesforinversionsbutheterozygotesforgeographicoriginofeachsetofchromosomes
(offspring 11 to 16).Fivegroupsof10coupleseach,fromeachcross,sevendaysold,wereputintovials(2crt)
diameterx 10cmheight)andobservedforsexualactivity.Thebestageforcrossesinthisspeciesisthe7 day,
beforewhichfewfliesareabletomate(Dobzhansky, 1944).AsD.sturtevantinormallypresentssinglemating
duringthetimeintervalconsideredforthisstudy, andcouplesremainstillinthesameplace,almostunmoving
duringthemating,wewereabletoobserve 10couplesatatimeover90minutes,at25°C.Foreachcouple,the
beginningandendofthematingwasrecorded.After90minutes,the lOcouplesofeachofthefivevialsfrom
eachparental strainsandtheirhybrids weretransferredtobottleswithfreshcom-wheat-arrowrootmedium.
fheringia,Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999
SensitivityoffitnesstoVariationinitscomponents. 39
Fiveothersimilarbottles.with 10couplesalsosevendaysoldwereprepared,totaling 10replicatesofmass
Grosses.Fliesweremaintained3.5daysinthesefirstbottlesforovipositionandthentransferredtonewbottles
twiceforanothertwoperiods3.5dayseach,resultingin30bottlesper parentalstrainandper eachhybrid.
Deadflieswerereplacedateachtransferwithotherstakenfromextrabottlespreparedatthesametimeand
exactlythesamewayastheexperimentalones.Thus,thedensityof10couplesatthebeginningofeachhalf
weekofovipositionperiodwasmaintained.Eachbottlewasdailyobservedandthedayoftheappearanceof
thefirstpupaandofthefirstimagowasrecorded. Flieswerecountedeveryhalfweekafteradultemergence
began;thelastcountingwasdonewhentheemergenceceasedoratthelateston35 dayafterthecrossdate.
Aftercounting, malesandfemales fromeachbottlewere separately weighed. Thepupae werealsocounted
(Carareto&MouRÀo, 1992).
TableI.Parentalandgeneticconstitutionsproducedbyintraandintercrossesamongfourparentalstrainsof
Drosophilasturtevanti(1 to 16asdefinedinMaterialandMethods).
Female
Male BRABRA COLCOL COSCOS MEXMEX
BRABRA BRABRA (5)BRAC0L BRAÇOS BRAMEX
(1) (7) (9)
COLCOL (6)COLBRA (2)COLCOL (11)COLCOS (13)C0LMEX
COSCOS (8)COSBRA (12)C0SC0L (3)COSCOS (15)C0SMEX
MEXMEX (lO)MEXBRA (14)MEXC0L (16)MEXC0S (4)MEXMEX
Theexperimentalprocedureenabledthestudyof12metrictraits,fromthreestagesoflifecycle, for
each strain and their 12 crosses. The 16 groups ofgenotypes are here called genetic constitutions (GCl to
GC16), The so-called Sexual Activity Stage (SA) was broken down into three traits related to the sexual
activityperformedby 10couples, in5 vials: (1) matingfrequency (MF); (2)durationofpre-copula(DPC),
takenasthetimeintervalbetweenthebeginningoftheObservationofthevialandeachcopula;(3)durationof
copula(DC),takenasthetimeintervalduringwhichthemaleremainedoverthefemale.TheProgenyStage
(P) was broken down into five traits related to the emerged individuais in each ofthe 30 bottles: (4) total
numberofimagines(NI);(5)numberofimaginesinthefirstcounting(NIFC);(6)numberofpupae(NP); and
(7) female individual biomass (FB), and (8) male individual biomass (MB), measured in milligrams. The
TimeofDevelopmentStage(TD),measuredindays,wasbrokendownintofourtraits:(9)egg-to-pupatimeof
development(EPTD);(10)egg-to-imagotimeofdevelopment(EITD);(11)pupa-to-imagotimeofdevelopment
(PITD);and(12)durationoftheemergenceperiod(DEP).Themeansandthestandarderrorsofthesetraits,
were publishedin Carareto& Mourào(1992). Here weare analyzing the meansofthese traits (tab. II)to
generate fitness indices representative oftotal fitness (W). We also aimto estimate the sensitivity oftotal
fitnesstothesevariousfitnesscomponents.
Toobtainfitnessindices,wecalculatedageometricmeanof the 16meanvaluesofeachtrait(tab.II)
thatwerefirstlytransformedtoalogarithmscale.Then,forthe 12traits, eachmeanvaluewascalculatedas
apercentageoftherespectivegeometricmean,asillustratedbelow.
>
u<iitl u>iit12 Uiiii1 Uüii12
xGCl xGCl 100(GC1)/G1=A1indexG^l-l AI indexGCl
^ 4
xGCI6 ¥ xGCló 100(0C16)yGl=Al index0(^16 A12indexGCl6
Geoiueuic meaiL1 012
(Ol)
Iheringia,Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999
40 Carareto;Lourenço&Mourão
TableII.Meansfor 12fitnesscomponentsoffourparentalstrainsofDrosophilasturtevantiandoffspringof
theirintercrosses, measuredat 25°C (MF, mating frequency; DPC, duration ofpre-copula; DC, duration of
copula; NI,numberofimagines;NIFC,numberofimaginesinthefirstcounting; NP,numberofpupae; FB,
female individual biomass; MB, male individual biomass; EPTD, egg-pupae time ofdevelopment, EITD,
egg-imagotimeofdevelopment,PITD,pupa-imagotimeofdevelopment;DERdurationofemergenceperiod;
biomassmeasuredinmilligrams;timeofdevelopmentmeasuredindays).
Conifoi« BRABRA coLca coscos MEXMEX BRACOL COLBRA BRAOK OSBRA BRAMEX MEXBRA coiros COSCOL COLMEX MEXCa CDSMEX MEXCOS
MF 25.0 34,0 37.0 55.0 31.0 38,0 40,0 38,0 39,0 37,0 40,0 39,0 47,0 39,0 45.0 49,0
DPC 19.0 37.8 15.6 24.6 35.1 11,0 27,1 15,1 22,4 19,2 12,2 31,7 26.0 30,4 13,2 11.0
DC 12.5 8.8 10.5 11.5 11.4 13,8 11,3 12,5 16,7 11,4 13,0 11,7 12,7 11,2 12,1 12,7
NI 252.0 254.0 318.0 242.0 357.0 339,0 307,0 346,0 274,0 257,0 312,0 304,0 272,0 303.0 237,0 253.0
NIFC 12.0 63.9 33.3 24.7 27.0 32,0 30,6 10,9 12,0 12,4 30,7 24,0 41,6 30,6 6,8 10.4
NP 272.0 316.0 437.0 395.0 430.0 452,0 477,0 580,0 468,0 479,0 533,0 537,0 458,0 501,0 563,0 540.0
FB 1.31 1.34 1.26 1.34 1.24 1,25 1,24 1,26 1,30 1,32 1,25 1,26 1,35 1,29 1,33 1.4
MB 0.93 1.03 1.01 1.08 0.88 0,89 0,99 0,96 0,98 0,97 0,97 0,99 1,04 1,00 1,06 1.11
EPTD 11.2 8.4 9.4 9.4 9.3 9,5 8,8 9,7 9,2 9,6 8,9 9,0 9,0 9,0 9,5 9,1
EITD 19.6 17.7 20.0 23.1 20,2 20,7 21,5 23,3 23,7 23,4 21,4 21,1 21,3 22,4 24,9 24,6
PITD 8.5 9.3 106 13.8 10.9 11,2 12,7 13,6 14,4 13,8 12,5 12,1 12,3 13,4 15,4 15,4
DEP 7.9 8.9 12.0 14.5 11,4 12,9 13,2 15,0 15,6 14,5 13,0 12,7 13,7 14,6 15,6 15,9
Thesevalues,denominatedAÍndices(tab.Ill),compareeachmeanvalueofeachtraittothegeometric
mean ofthe 16 genetic constitutions. Thus, mean value similar to the geometric mean originates A index
around100andmeanvaluesaboveorbelowthegeometricmeanoriginateíndices biggerorslowerthan 100,
respectively. These Índices were usedtocompose fitness índices, assumíng amultíplícatíveeffectfortraits
(SvEDetaL, 1967)W,toeachstage(SA",P',TD'índices)andtotheproposedtotalfitnessíndex(W).
Toobtaín índex, theíndicesofeachstageweretransformedíntodecimais andthenmultiplíedas
director invertedratios,basedonthefollowingassumptions:(1)forSAfitnessindex:highmatingfrequency
andhighdurationofcopulaarebetterthanlowvaluesforthesecomponents,sincealargernumberoffemales
canyíeldprogenyandmoretimeisavailableformalegametetransfer;forthedurationofpre-copula,lower
valuesmeangreaterefficíency,i.e.,fastermating;(2)forP'fitnessíndex:highervaluesmeangreaterefficiency
becausetheycorrespondtomoreoffspringandmoreefficíencyinConvertingfoodíntovitalsubstance;(3)for
TD' fitness índex: lower values mean greater efficiency, that is, faster life-cycle, since a líneage could be
producedmorequíckly.Thus,thefitnesscomponentsnumberedas1 and4to8werecomputedasdirectratios
and ali the others as inverted ratios, so that: SA'=(MF)(1/DPC)(1/DC) (1); P'=(NI)(NIFC)(NP)(MB)(BF)
(2); TD'=(1/EPTD)(1/EITD)(1/PITD)(1/DIEP) (3);W'=(SA')(P")(TD') (4).
ToevaluatetheímportanceofVariationinfitnesscomponentstototalfitness (W"), weestimatedthe
contributiondegreeofeachcomponenttransformingíntodecimaisthe12AíndicesofeachgeneticConstitution,
summingthemintheirdirectorinvertedratios,duetotheassumptionsmentionedabove,andthen,Computing
each one as a percentage ofthe respective sum (tab. IV). These 192 values, denominated as B índices,
estimatetherelativedegreeas eachtraitcontributetocomposethetotalfitness(W),asillustratedbelow.
Correlatíon analysís between each pair ofthe 16 genetic constitutions was made, using the 12 B
Índicesofeachone, as aprocedure tocompareeach withone anotheras totherelative ímportance ofeach
trait's contribution to total fitness (W")composition. As we performed multiple linearcorrelatíon tests, the
criticai avalueusedwas0.0005,accordingtotheSequentialBonferroniCorrectionTechníque(Rice, 1989).
GCl GC1Ö GCl GC16
trait IAindex "^ trait 1 Aindex trait 1 Aitidex^'GCl sum •>trait IAindex/GClö sijm=
=B índex
1
^ " + + +
trait 12 Aindex ^ trait 12 Aindex trait 1 Aindex/GCl sum trait IAindesí/GCló sijm=
B12indes
GCl smn > GC12siun
Iheringia,Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999
SensitivityoffitnesstoVariationinitscomponents. 41
TableIII. AÍndicesfor12fitnesscomponentsoffourparentalstrainsofDrosophilasturtevantiandoffspring
oftheirintercrosses(MF,matingfrequency;DPC,durationofpre-copula;DC,durationofcopula;NI,number
ofimagines; NIFC, numberofimagines in the firstcounting; NR numberofpupae; FB, female individual
biomass; MB, male individual biomass; EFTD, egg-pupae time ofdevelopment, EITD, egg-imagotimeof
development,PITD,pupa-imagotimeofdevelopment;DEP,durationofemergenceperiod;biomassmeasured
inmilligrams;timeofdevelopmentmeasuredindays).
BRABRA COUXX. COSCOS MEXHEX BRACOL COLBRA BRAMEX MEXBRA COLMEX MEXCOL COSMEX MEXCOS
107I
143.7
1027
iO70
EPTD
EITD
PITD
TableIV. Bindicesfor 12fitnesscomponentsoffourparentalstrainsofDrosophilasturtevantiandoffspring
oftheirintercrosses(MF,matingfrequency;DPC,durationofpre-copula;DC,durationofcopula;NI,number
ofimagines; NIFC, numberofimagines in the firstcounting; NP, numberofpupae; FB, female individual
biomass; MB, male individual biomass; EPTD, egg-pupae timeofdevelopment, EITD,egg-imagotimeof
development,PITD,pupa-imagotimeofdevelopment;DEP,durationofemergenceperiod;biomassmeasured
inmilligrams;timeofdevelopmentmeasuredindays).
COSCOS MEXMEX MEXBHA COLCOS MEXCOL COSMEX MEXajS
102O
14,<)7
BM
EPTD
EITD
PITD
DEP
RESULTS
W
The scores,proposedasfitnessindices, showedstrikingdifferencesamongthe
indices oflife stage for the same genetic Constitution, or among constitutions forWthe
same life stage (tab. V). The strains COLCOL and COSCOS presented the higheWst
values, andBRAMEXandCOSMEX, the lowestones. ThehighestCOLCOL's isa
consequence ofelevated P' and TD' fitness indices which were up to four times larger
than the indices ofthe others. These high values are aresult ofits NIFC'sA index and
EPTD'sA index,respectively.These values, associatedwithasmallerSA index, shows
COLCOLasaverydifferentiatedstrain.Asinthecaseoftheparentalstrain,theoffspring
ofCOLCOLcrossesareingeneralassociatedwiththehighestP' andTD' indicesandthe
slowestSA,particularlyiftheCOLchromosomecomplementcomesfromtheirmothers.
OnthecontraryoftheSituationshowedbyCOLCOLstrainandtheiroffspring,the
Iheringia,Sér.Zool.,PortoAlegre, (87); 37-48, 18denovembrode 1999
42 Carareto;Lourenço&Mourão
strain MEXMEX and its offspring are associated with the lowest P' and TD' indices,
except when the MEX and COL chromosomes are combined. The highest SA' index
amongtheparental strains are associatedwithCOSCOS andMEXMEX. The samecan
beobservedinoffspringofCOSandMEX reciprocaicrosses;however,theirSA'indices
are almost twice the parental strains. Nevertheless, when intercrossed with BRA and
COL,theindexvaluesareveryvaried.
TableV. Fitness indicesofSexualActivity (SA'),Progeny (P')andTimeofDevelopment(TD')stagesand
TotalFitness(W)offourparentalstrainsoiDrosophilastitrtevantiandoffspringoftheirintercrosses.
W
Genetic Slages
Conslitulion SA' P- TD- Absolute Relative
BFLABRA 0,659 0,280 2,195 0.405 0,122
COLCOL 0.639 1,978 2.629 3.325 1.000
COSCOS 1.413 1,645 1.353 3.146 0.946
MEXMEX 1.216 0,955 0.745 0.865 0.260
BRACOL 0.485 1.264 1,386 0.849 0.255
COLBRA 1.566 1.524 1.139 2.718 0.817
BRAÇOS 0.817 1,537 1.020 1.281 0.385
COSERA 1.260 0.739 0.702 0.653 0.196
BRAMEX 0.652 0,548 0.661 0.236 0.071
MEXBRA 1.058 0,546 0.720 0.416 0.125
COLCOS 1.578 1,730 1.045 2.853 0.858
COSCOL 0.658 1,365 1.109 0.996 0.300
COLMEX 0.891 2.033 1.002 1.813 0.545
MEXCOL 0.717 1.674 0.820 0.984 0.296
COSMEX 1.76.1 0,357 0.569 0.359 0.108
MEXCOS 2,194 0.617 0.590 0,799 0.240
To compare the contribution degree ofeach component to total fitness, B indices
werecalculated(tab. IV).Twocomponentsaredistinguishedamongthosewithfrequent
highVariation accordingtothedistributionoftheB indices: durationofpre-copulaand
numberofimaginesinthefirstcounting. Consideringthe 12Bindices,linearcorrelation
analyses between all pairs ofgenetic constitutions were made. Absence ofcorrelation
was considered as indicating different expressions ofthe array ofthe traits to the total
fitnessbetween two pairs. Positive correlation was considered asproportionality in the
degreeofcontribution,andnegativecorrelationwasconsideredasinverseproportionality
inthecontributiondegreeofthe 12metrictraitsbetweentwogeneticconstitutions.From
the 120rvalues(tab.VI), 15 wereconsideredasastrongassociation:thecriticaiavalue
usedwas0.0005 (r=0.850),accordingtotheSequentialBonferroniCorrectionTechnique
(Rice, 1989). Among these, seven pairs had positive strong values, and eight pairs
presentednegativestrongvalues. Fromthesevenpositivecorrelations,fivearebetween
pairsofConstitutionwithchromosomesproceedingfromColômbiaorbetweenColômbia
and Costa Rica, and two are between pairs with chromosomes proceeding only from
Brazil, CostaRica andMexico (fig. 1). Chromosomes proceeding from Colômbia are
present in sevenoutoftheeightpairsofgenetic constitutions negatively correlatedand
onlyinonepairtherearenoCOLchromosomesassociatedwith: COSCOS vsBRAMEX
(fig.2).Thescatterdiagramsofthese 12Bindicesof pairsofgeneticconstitutionsshow
that fitness components such as duration ofpre-copula and numberofimagines in the
firstcountingaremostlyresponsibleforthesignificanceofthecorrelation.
Ifwe are notextremely strict and adoptthe commonly usedO.Ol criticaiavalue.
Iheringia,Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999
—
1
SensitivityoffitnesstoVariationinitscomponents. 43
15 - 20
12 -
S P°°
rf
ff^
G
0*
3- 1 I 1 1 1 T—1 r-T—1— I I I II
8 10 12 14 6 8 10 12 9 12 15 18 21
COSMEX COLCOL
I I I II II
3 6 9 12 1S 18 21
COLCOL
Fig 1.ScatterdiagramsamongBindicesofthe 12metrictraitssiiowingpositiveassociationbetweengenetic
constitutionsoffourstrainsoiDrosophilasturtevanti(2:DPC,5: NIFC).
the significantvalueof rdropsto0.708. In suchacasethereare 35 significantrvalues:
from 18positivevalues, 10arebetweenpairsthathaveCOLchromosomes(fourofthem
have also COS chromosome associated), two are between pairs wit—h COL and COS
chromosomesandsixofthemhavenoCOLchromosomescombined theassociation
isbetweenBRAandMEX.Fromthe 17negativelyassociatedpairs, 13arebetweenCOL
andnonCOLchromosomes(BRAandMEXinparticular)andfiveassociatingnonCOL
chromosomes(COSCOSandBRAMEX).TheparentalstrainsBRABRAandMEXMEX
areneverassociatedwiththeiroffspring.
DISCUSSION
This study has its experimental procedure devised in function of the following
idea: the greater number ofgenotypes used in measuring the expression ofthe greater
numberoffitnesscomponents,thegreaterprobabilityofrevealingpattemswhichidentify
components and permit the establishment ofthe relative importance ofits Variation to
totalfitness.
In the present study, fitness indices, considered as representative oftotal fitness,
wereestimatedbycombiningthefitnessindicesofSexualActivity,Progeny andTimeof
W,
Development life stages. The total fitness indices (relative tab. V) disclosed the
parental strain COLCOL as the most efficient in transmitting their genes to future
Iheringia.Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999
44 Carareto;Lourenço&Mourão
M
I I I II II I I II II I I
3 6 9 12 15 18 21 9 12 15 18 21 9 12 15 18 21
COLCOL COLCOL COLCOL
32 °1
" o
o o
-
o °öO
-
5o
I Tt-l-TTItTI I I M I1 1
3 6 9 12 15 18 21 6 8 10
COLCOL BRACOL
Fig2.ScatterdiagramsamongBíndicesofthe 12metrictraitsshowingnegativeassociationbetweengenetic
constitutionsoffourstrainsoiDwsophilasturtevanti(2:DPC,5:NIFC).
generations, followed by COSCOS, COLCOS and COLBRA. In contrast, BRAMEX,
followedbyCOSMEX,BRABRA,MEXBRAconstitutionswereshowntobetheworst.
AlthoughCOSMEXandMEXCOShaveshowngreaterefficacyforSexualActivityand,
COLCOLandBRABRAthegreaterfortheTimeofDevelopmentstage,thecomponents
ofP' andTD' Índices,withrespectivelyveryhighandlowvalues, whichareconsidered
to be favorable to gene transmission to the next generation, according to ourpremises,
wereresponsibleforthehighertotalfitnessofCOLCOL,exactlythelessefficientstrain
forSexualActivity.DifferentgeneticconstitutionspresentinghigherÍndicesfordifferent
fitness stages were arecurrent Situation. However, the high fitness values ofCOSCOS,
COLCOS andCOLBRAwereduetoarelativebalanceofhighvaluesforalifractions.
Asthe 16geneticconstitutionswereproducedbycombining,throughhybridization^
fourstrains, three ofthemcarrying the same chromosomal arrangement, we concluded
thatthesearrangementsandthestandardone,whichhasnoinversions(BRA),provedto
be highly differentiated as to their genetic content and respective expressions in the
compositionoftotal fitness. Itis noteworthythat, accordingtoourresults,thesegenetic
Contents, through interaction, are expressed differently, resulting in greatly diversified
fitnessvalues.Notwithstanding,constanteffectsofthesegeneticmateriaiscanbeobserved:
the higher fitness índices always correspond to chromosomes COL and COS and the
lowest to MEX when associated with BRA or COS chromosomes. The expression
variabilityofthefitnesscomponentsreflectsthegeneticvariabilítyofthegenepoolstudied.
Iheringia,Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999
SensitivityoffitnesstoVariationinitscomponents... 45
TableVICorrelationcoefficients(r)between therespectiveBindicesofallpairsofgeneticconstitutionsof
fourstrainsofDwsophilasturtevanti(p=0.0005tor=0.850;df- 10,accordingtothe Bonferronisequential
correction;andp=O.Ol tor=0.708;df= 10)
BRABEÍA COLCOL COSCOS MEXMEX BRACOL COLBRA BRAÇOS COSERA BRAMEX MEXBRA CÜLCOS COSCOL COLMEX MEXCOL COSMEX
COLCOL -oow
COSCOS -00«) 0722
MEXMEX -0,475 0,290 -0055
BRACOL 0,123 0650 0271 0.U3
COLBRA 00*5 0,L54 0,747 -0,2.58 -0,258
BRAÇOS -04'« 0850 0466 0399 0,700 0069
COSBRA -0OH •0,906 -0440 -0,493 -0,586 0,137
BRAMEX 0,048 -0,854 -0,856 -0,101 -0488 -0,347
MEXBRA OLi; -0890 -0,699 -0,257 -0654 -0,291 0,674
COLCOS -0266 136 0,685 -0188 -0,347 0,953 -0,294 -0,240
COSCOL -0,295 0418 0,153 0186 725 -0,602 0128 -0392
COLMEX •0490 0872 0603 543 4,35 0190 -0618 0,871
MEXCOL 0600 0,750 0,346 0,410 0,639 0165 0,493 0,683 0,847
COSMEX -0,0L5 -0,883 -0,490 -0168 -0,903 0,089 0,655 0,877 0,731 -0,747
MEXCOS -0,077 -0769 0,267 -0118 0,951 0,345
Theseexpressionsshowpositiveandnegativeextremeeffectsinthecompositionoftotal
fitness. Although the strains have been maintained in the laboratory under essentially
identical conditions, for almost 200 (BRABRA and MEXMEX) or as much as 400
(COLCOLandCOSCOS)generations,theoriginalgeneticvariabilityhasbeenpreserved,
at least in sufficient degree to permit differWent responses to the conditions to which the
Wflieshavebeenexposed. Thepattemofthe values,thatsWhowsinalmostallcasesthat
relativeofeachstraincrossedwithitselfishigherthan relativeofcrossesofthe
same strain with any another, argues against Inbreeding depression due to long time
maintenanceinlaboratory.
Ourresults contributeto understand the followingquestion: which component is
more important to determine total fitness, those ofthe pre-adult, or those ofthe adult
stages(Prout, 1971;Ehrman&Parsons, 1976),orboth(Hiraizumi, 1961;Polivanov&
Anderson, 1969; Sved &Ayala, 1970; Sved, 1971;Tracey &Ayala, 1974; Barnes &
Merrell, 1985)?ConsideringthattheSA'indexiscomposedonlybycomponentsofthe
adult stage; thatTD'index iscomposedby larvalcomponentsexclusively, andthatthe
P' iscomposedbybothlarval andadultfitnesscomponents, wefoundthatequallyhigh
total fitness values might be due to high values of traits for the larval or adult stage,
dependingon thegenetic Constitution. This assumption has been also demonstratedfor
onlythreegeneticconstitutions(Carareto&Mourão, 1991a,b)inDwsophilaprosaltans
Duda, 1927.ToMueller&Ayala(1981)"itisreasonabletoassumethatallthebiological
processesareimportantinthedeterminationofreproductivesuccess;however,therelative
importance ofeach to net fitness is not clear, not even whetherone orfew components
haveamajorimportance".Cararetoetal. (1992)foundsignificantcorrelationbetween
fitnesscomponentsandtotalfitnessinD.prosaltans;theanalysisresultsoftheprincipal
componentsshowedadifferentialimportanceofcomponentsassociatedwithnumberof
offspring.
We calculatedB indices aiming toevaluate the importance ofeach metric traitor
its Variation to total fitness. We also intended to compare genetic constitutions, pure or
withtheirgeneticmaterialcombined,searchingforapattemthatcoulddifferentiatethem
accordingtothewaytheirfitnesscomponentsareassociatedtocomposethetotalfitness.
Iheringia,Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999
46 Carareto;Lourenço&Mourão
The Crossing manipulation enabled us to show that the strain from Colômbia, the one
W,
with the highest is very differentiated according to the pattem thatits 12 traits are
associatedtocomposeitstotalfitness. SimilartoCOLCOListhestrainfromCostaRica,
W.
the secondhighest Thesetwostrainshavethelargernumberof positivecorrelation
between them (tab. V). On theotherhand, the strainsfrom Brazil andfromMexico are
verydifferentiatedconcemingthepattemastheir 12traitscomposetotalfitness;compared
toeachotherandtotheothertwo,asindicatedbythenegativecorrelationbetweengenetic
constitutionscarryingCOL,BRAandMEXchromosomes.Assumingrelativeimportance
oftraitsastheabilitytobevariable,ourstudyshowedtimeofpre-copulaandnumberof
imaginesinthefirstcountingtobeamongthemostrelevantcomponentstotheVariation
oftotalfitness inD. sturtevantistrains.
TheCrossingmanipulationprovidedinterestingInformationaboutdifferentfitness
pattemcomponentsbeingcombinedtocomposetotalfitness.Trade-offsareknowninD.
melanogasterbetweenearlyfertilityandlongevityandbetweenearlyandlatefecundity
forfemale (Rose & Charlesworth, 1981a,b; Luckinbill et ai., 1984; Rose, 1984) and
betweenearlycompetitivemafingsuccessandlongevityandlatesuccess(Service, 1993).
Stearns (1992)estimatedthatatleast45 trade-offshavebeenestablishedinlifehistory
studiesandChippindaleetai. (1996)presentedevidenceforanewtrade-off,manifested
betweenlarvalgrowthrateandpre-adultviabilityin D. melanogaster.Weareawarethat
theoccurrenceoftrade-offsatthephenotypicleveidoesnotnecessarilymeanthatthere
isanunderlyingantagonisticpleiotropy(Reznick,1985;Reznicketai. 1986);otherwise,
we believe that important Information on trade-offs can be gathered from phenotypic
manipulation,asalsoconsideredbyBell(1984a,b),Partridge&Farquhar(1981)and
Partridgeetai. (1987).Itseemsthatour hybridcrossesallowedustocharacterizeanew
trade-off,betweendevelopmentrateandmating speed, whichisproposedas reflecting
possiblepatternsofadaptive strategies (figs. 1, 2).
Thescatterdiagramsshowsonlypairsofgeneticconstitutionsstronglycorrelated
according to their B Índices. It is noteworthy that two pairs (fig. 1) formed by three
genetic constitutions (BRAMEX, COSMEX, andMEXCOS) express asingle adaptive
strategy, with the perfect condition corresponding to the COSMEX-MEXCOS pair:
chromosomes proceeding from Brazil and Mexico are associated with component that
reflecthighmatingspeed(shortDPC)withagreatercontribufiontototalfitness,andalso
with component that reflect a greater development rate (small NIFÇ), with a smaller
contribution tototal fitness. Ifwe were nottoo strictin adopting theavalue, following
thecommonlyused a=0.01 wefindthesameassociafionintwomoregeneticconstitutions
,
(MEXBRA and COSBRA). An adaptive strategy seems to exist in relation to these
chromosomes: a slower speed ofdevelopment could be balanced by a greater mating
speed.Ontheotherhand,theoppositeisrelatedtoCOLchromosome:fasterdevelopment
rateassociatedtoaslowermatingspeed. Severalpairsofgeneticconstitutions(fig.1)are
positivelycorrelatedaccordingtotheVariationoftheirBÍndicesmainlyduetothegreatest
contribution to total fitness ofNIFC and the smallest contribution ofDPC (COLCOL,
BRACOL,BRAÇOS,COLMEX,MEXCOL).Thisassociationisalsoillustrated(fig. 2)
by genetic constitutions COLCOL, BRACOL, COLMEX, BRAMEX, MEXBRA,
COSBRA, COSMEX and MEXCOS. These pairs have a common characteristic: the
negative character ofthe association between COL and non-COL genetic Constitution
duetothesametwoextremepoints(DPC withthesmallestcontribution andNIFCwith
Iheringia,Sér.Zool.,PortoAlegre, (87): 37-48, 18denovembrode 1999