The Auk 116(1):64-72, 1999
EXOGENOUS
TESTOSTERONE
AND
THE
ADRENOCORTICAL
RESPONSE IN DARK-EYED JUNCOS STEPHANJ. SCHOECH, • ELLEND. KETTERSON, AND VAL NOLAN JR. Department of Biology andCenterfor theIntegrative StudyofAnimalBehavior, IndianaUniversity, Bloomington, Indiana 47405, USA
ABSTRACT.--Hormonal manipulations with implantsallow examinationof the costsand benefitsof behaviorsand physiologic statesmediatedby a givenhormone.As a part of ongoingresearchinto the effectsof the steroidhormonetestosterone (T) in Dark-eyedJuncos (Junco hyemalis), we measuredthe corticosterone (B, asteroidhormonesecretedby the adrenalin responseto stress) responseto the stressof captureandhandlingin malestreated with T (T-males)and in controlmales(C-males).AlthoughB may be essentialfor energy mobilization,chronicor repeatedexposureto elevatedlevelsof B canhavemanynegative effects.Because T mediatesmanybehaviorsthat may increasethe likelihoodthat an individual will encounterstressors, we predictedthat plasmaB wouldrise morerapidly in Tmalesthan in controls.In the first few minutespost-capture,the increasein B levelswas significantlyhigherin T-malesthan in controls.B levelsin samplescollected10, 30, and 60 min post-capture wereconsistently higherin T-malesthanin C-males;however,the differencewasnot statisticallysignificant.Because previousworkhasshownthatT-malesreduce their parentalcontribution,we comparedfemalesthat were matedto T-malesand C-males (hereafterT- and C-females).B levelsof T-femalesincreasedsharplyin the first few minutes post-capture, whereasin C-femalesthey did not;however,the responses werenot statisticallydifferent.Maleshadhigherinitial levelsanda greaterB-response to stressthanfemales whendatawerecomparedirrespectiveof treatment.Our resultssuggestthat thebehaviors or physiological changes inducedby T arepotentiallycostlyandthat suchcostsmayin part be incurredthroughelevatedB. Received 25 November 1997,accepted 5 May 1998.
IN MOSTNORTH-TEMPERATE BIRDS, circulating Otherstudiesof free-livinganimalswith exlevels of testosterone(T) in males are elevated perimentallyelevatedT have demonstrated
duringthe sexualphaseof thebreedingseason (i.e. territory establishment, pair formation, nest building, and copulation) and become lowerduringparentalcarewheneggsor young are present (Wingfield 1984, Ball 1991). Althoughrelativelyhigh levelsof T early in the breedingseasonmay be essentialfor the expressionof reproductivephysiologyand behaviors,it is thoughtthat the behaviorspromotedby T are incompatible with the careof young(seebelow).Accordingly, maleswith experimentallyelevatedlevelsof T (T-males)during the parentalphasecanbe expectedto reducetheir parentaleffort comparedwith control males (C-males).Indeed, the few studies thathaveartificiallyelevatedT duringincubation andbroodrearinghavefoundthattreated malesdecreasetheir parentaleffort (Silverin 1980;Hegner and Wingfield 1987;Oring et al. 1989; Ketterson et al. 1992, 1996; Saino and
Moller 1995;Schoechet al. 1998).
that additionalcostsmay be associated with maintaining elevatedtestosteronelevelsafter the time when levelstypically peak. For example, in mountain spiny lizards (Sceloporus jarrovi; Marler and Moore 1988, 1989) and Brown-headed Cowbirds(Molothrus ater;Dufty 1989),T-implantedmalessufferedhighermortality than controls.WhereasDufty (1989)attributedthemortalityto woundscausedby increasedaggressionin T-treatedcowbirds,Marler and Moore (1988, 1989) suspectedthat Tmales: (1) starved due to a reductionin the amountof time theyallocatedto feeding,and (2) sufferedhigher predationbecauseof increasedexposureand/or decreasedvigilance. Testosterone-treatedlizards also expended more energyas a result of an increasein territorial behavior(Marler et al. 1995).In contrast, field studiesof Dark-eyedJuncos(Junco hyetnalis) revealed no differencesin survival between T-implantedand controlbirds (Kettersonet al.
1996)exceptwhenimplantswere not removed priorto thewintersothattheprebasic moltwas
E-mail:
[email protected]
suppressed(Nolan et al. 1992). 64
January 1999]
Corticosterone inDark-eyed Juncos
65
Other research(Kettersonet al. 1991, 1992, lamic-pituitary-adrenal (HPA) axis,the cap1996;Raoufet al. 1998)suggests thatthemain- ture-stressparadigmof Wingfield(1994) altenance of elevated levels of testosterone lowsoneto gain additionalinformationabout throughoutthe breedingseasoncausesno the conditionof theHPA axisby samplingcapmarkeddisadvantages to malejuncos.As has tured individualsrepeatedly.Forexample,a Tamount been found for other species(see above),T- male that allocatesa disproportionate of time to sexual or aggressive behaviors while malesprovision offspringlessfrequently than behaviorsmight do C-males(Kettersonet al. 1996,Schoech et al. reducingself maintenance 1998).Possiblyas a resultof the reductionin havelessstoredenergy,or itsenergymightbe As a recare,the socialmatesof T-malesfledgefewer in a form that is not readily accessible. sult, a T-male might exhibit a more pronounced youngthan thoseof C-males(Ketterson et al. to a stressor thanwoulda C-male. 1996,Raoufet al. 1998).Thus, althoughone B response mightexpectT-malesto havelowerreproduc- Here, we comparethe stressresponseof TBecause females tive success than C-males,theydo not because and C-maleDark-eyedJuncos. T-malessiremoreyoungthroughextrapairfer- matedto T-maleswork harderat provisioning tilizations (EPFs)and sufferfewer lossesof pa- theiroffspringthanfemalesmatedto C-males et al. 1992),we alsocomparethe B ternityto EPFsin theirsocialmates.As a result, (Ketterson of thesetwo groupsof females(rethe net reproductivesuccessof T-malesdoes responses according to the not differ from that of C-males (Raouf et al. ferredto asT- andC-females, treatment of their mates). Moreover, because of 1998).Thesefindingssuggestthat the costs(if any) of experimentallyelevatedT in adult the relationshipbetweenbodyconditionandB thathasbeenfoundin otherspecies(Wingfield males are related more to their survival than to et al. 1994b, Schoechet al. 1997), we examine their reproductivesuccess. betweenbodymassandB. Forexample, T treatment canincrease thefre- the relationship quencyof aggressive interactions (Balthazart METHODS 1983;Wingfieldet al. 1987,1990)andlocomotor activity (Wada 1982, 1986) while decreasing Studysite and species.--The study populationof lipid storage(Wingfield1984,Kettersonet al. Dark-eyedJuncos(J.h. carolinensis) was locatedin 1991).Probably asa resultof changes in behav- and around the University of Virginia's Mountain ior andphysiology, malejuncostreatedwith T LakeBiologicalStationin westernVirginia (37ø22'N, increasethe size of their territory or home 80ø31'W)at 1,180melevation.The reproductivebirange(Chandleret al. 1994).A recentstudyof ology of this populationhas been under study by captivejuncos(S. Lynn unpubl. data) found Ketterson,Nolan, and colleaguessince 1983. The that T-malesincreasedthe time spentforaging data we report were collectedduring the breeding andmovinganddecreased thetimeallottedto seasons of 1995, 1996, and 1997. Mostof thejuncosin thestudyareahavebeencapself care comparedwith C-males.Clearly,reducingselfmaintenance whilesimultaneouslytured andbandedwith a uniquecombinationof U.S. Fish and Wildlife Servicealuminumbandsand plasincreasingaggression, territorialdefense,and tic colored bands. Almost all nests are located each other energeticallycostly behaviorsmight year,and the pair associated with eachnestis iden-
provestressful.
The well-established link between stress and the secretion of the adrenal steroid hormone
tified by intensivefield observations, allowingus to know the reproductivestageof all individuals. Testosterone treatment and blood collection.--Males
corticosterone (Harvey et al. 1974,Selye1979, werecapturedand implantedbetween15 April and Siegel1980,GreenbergandWingfield1987)led 15 May beforeor shortlyafterpair formation.Indi-
us to investigatewhethercirculatinglevelsof corticosterone(B) are elevatedin T-males.Two recent studies of Dark-eyed Juncos,one con-
ductedwith free-livingbirds and the other with captives,showedthatbasallevelsof B are higherin T-malesthanin C-males(Ketterson et al. 1991,Klukowskiet al. 1997).Althoughbasal levelsof B provideinformationaboutthecurrent (or immediatepast)stateof the hypotha-
vidualswereanesthetized by inhalationof metophane and implantedwith two 10-mmlong Silastictubes (1.44mm inner diameter,1.96mm outerdiameter) that were empty (C-males)or packedwith crystalline testosterone(T-males;seeWingfield and Farner 1983, Kettersonet al. 1991, Schoechet al. 1996). Al-
thoughwe did notmeasureT,T-implants of thesedimensions are known to elevate T to levels that are
similar to the early seasonmaximumof non-implanted males, after which it remains elevated
66
SCHOECH, KETTERSON, ANDNOLAN
throughoutthe breeding season(Kettersonet al. 1991, 1996;Enstromet al. 1997;Schoechet al. 1998).
In theprecedingstudies,T levelswereapproximately 3-foldhigherin T-malesthanin C-males.Implants werepositionedsubcutaneously alongthe left flank underthewing.Individualsthathadbeenbandedin earlieryearswere designatedastreatmentor control basedon the previousyear'streatment,i.e. birds were giventhe sametreatmentin subsequent years. Juncosthat were new to the studytract were randomly designatedas treatmentor control.In a few cases,we failed to capturea malebetweenthe dates pre-establishedfor implanting; these males were comparableto C-malesand were incorporatedinto the control data set.
To assess stressresponses, all birdswerecaptured whentheirnestlingswerebetween8 and 11daysold. To controlfor possiblediel fluctuationsin corticosterone secretion,almostall sampleswere collectedbetween0700and 1tOO.Thefew samplescollectedlater in the day did not differ from the early samples,so all sampleswerecombinedfor analysis. Our protocolin measuringstressresponseswasas
[Auk, Vol. 116
1997 (n = 78) was 20.13 _+0.58 •L; recoverywas 84.5%,and intra-assayvariationwas12.0%.Inter-assay variation (n = 3) was 13.1%. Statisticalanalyses.--Although our goal had been to collectthe initial bloodsamplewithin oneminute after an individualenteredthenet, theprocedureoften took longer (f = 2.45 _+0.12 min, n = 81). Consequently,we usedregressionanalysisto relateB to
handlingtime.As a preliminaryanalysis,however, we used analysisof covarianceto test for homoge-
neityof slopes.Whenno yeareffectswerenotedin any category(T-males,F = 0.25,P = 0.79,n = 17;Cmales, F = 0.97, P = 0.40, n = 23; T-females, F = 0.83, P = 0.45, n = 24; C-females, F = 0.46, P = 0.64, n =
17),we combineddatafrom the threeyears.Wethen determinedwhetherthe B responsein the first few minutesof handling differed betweenT-malesand C-males and between T-females and C-females.
Data
from samplescollectedat t0, 30, and 60 minutepost-
capturein 1996 and 1997 were analyzedwith repeated-measures analysisof variance. To furtherexaminethe relationshipbetweenbody mass and B, and to control for differences in the time
requiredto obtainthe initial plasmasample,we calculatedthe rateof changein B levelsbetweentheinithenet and an initial bloodsamplecollected(to con- tial sample(B•)and the 10-minsample(B•0)for each trol for differencesin the time requiredto removein- individual and used that rate to extrapolatewhat dividualsfromthenet,we notedtheelapsedtimebe- eachjunco'sB levelwould havebeenat 1 min posttweenthe bird's first enteringthe net and collection capture.We assumeda linear changein B between of the initial sample);(3) the bird was held in the the timestheinitial sample(T0 and the 10-minsamhand until 10 min had passedfrom the time it had ple (T•0)were collectedand between1 min and the enteredthenet (duringwhichtime we tookstandard actual time of the initial sample.We calculatedthe morphometricdata);and (4) a secondsamplewas rate of changein B levelsbetweenthe initial and 10then collected. In 1996 and 1997, in addition to takmin sampleusingthe equation: ing the initial and 10-minsamples,we placedbirds (B•0- B0/(T•0 - T,) = X ng/min. (t) in looselywovenclothbagsandcollectedsamplesat 30 and 60 min. All blood sampleswere collectedin We then determined how much time an initial sammicrohematocrit tubes(50•L of wholeblood)follow- ple deviatedfrom the desiredcollectiontime of 1 ing punctureof the brachialvein with a 26-gauge min (i.e.T• - Y min = I min). Y wasthenmultiplied needle.Bloodsampleswere kept on ice until trans- by the aboverate,giving the numberof ng that B port to the laboratory,wheretheywere centrifuged would havechangedin the elapsedtime.This value and the plasma fraction harvestedand stored at wasthensubtractedfromB• to yield theextrapolated betweenbodymass -20øC until taken on dry ice to Bloomington,Indi- valueat 1 min.Therelationships follows: (1) a timer was started when the bird entered the net; (2) the individual was removedfrom
and extrapolatedB levelsat I min were then examana, for assay. Radioimmunoassay.--Direct assayof corticosterone ined with regressionanalysis.Data were transwas conductedaccordingto Wingfieldet al. (1992), formedasnecessaryto ensureequalvariance(Sokal
with the exceptionthat we usedanhydrousdiethyl and Rohlf 1981, Neter et al. 1985). ether rather than dichloromethane
to extract steroids
from plasma. Prior to extraction, approximately 2,000 cpm of radio-labeledB were added to each sampleand permittedto equilibrateovernight.This allowedcalculationof thepercentage of hormonerecoveredduring the process.Sampleswere run in a singleassayfollowingeachfield season.Mean plasma volumein the 1995samples(n = 86) was26.37+ SE of 0.64 •L; recoverywas 91.0% and intra-assay variationwas13.5%.Meanplasmavolumein 1996(n = 104) was 20.59 -+ 0.46 •L; recoverywas 80.11% andintra-assay variationwas16.5%.Meanvolumein
RESULTS
Initial levelsof corticosterone.--Initial samples from T-males
showed
a marked
increase in B
with time sincecapture(F = 17.63,n = 17, P = 0.001, r2 = 0.54; y = 10.66x + 0.05; Fig. 1). In contrast,the relationshipbetweenB and the time requiredto collectthefirstsamplewasnot significantin C-males (F = 0.08, n = 23, P = 0.79,r2 = 0.004;y = 0.65x + 16.46).The slopes
January 1999]
Corticosterone inDark-eyed Juncos
80 --*--
+
T-Males
T-Females
-o- C-Females o
70 -oC-Males ß
•
67
ß
60
o
40
u
20
o o o /•o •
o
o
_ v ................
.' "øoø
0 1
2
3
4
5
1
6
Corticosterone levels as a function of the
2
3
4
5
IntervalBetweenCaptureandInitialSample(min)
•te•al Be•een Cap.re •d Initi• Staple (min)
FIG. 1.
o
FIG. 2.
Corticosterone levels as a function of the
interval between capture and collectionof initial interval betweencapture and collectionof initial matedto T-males blood samplesin testosterone-implanted (T-males) bloodsamplesin Dark-eyedJuncos (T-females)and matedto C-males(C-females). and control(C-males)Dark-eyedJuncos.
of the regression linesfor T- and C-malesdifferedsignificantly(F = 7.76,P = 0.008,Fig. 1). Inspection ofFigure1 suggests thatthetimerequiredto collecttheinitial samples differedbetweengroups,but this differencewasnot significant(t = -1.75, P = 0.09).To further addressthe possibilitythatdifferences in B were due to differencesin samplingtime, we comparedB levelsof a subsetof the two groups whosebloodsampleswerecollectedwithin 4 min of capture.Again,T-malesreactedrapidly to captureandhandling(F = 8.28,n = 14,P = 0.01,r2 = 0.41;y = 11.97x- 3.02),whereasCmales did not (F = 0.08, n = 23, P = 0.79, r2 = 0.004;y = 0.65x+ 16.46);the slopesof theregressionlinesdifferedsignificantly(F = 6.53, P = 0.02).
dividuals (F = 16.42, n = 16, P = 0.001, r2 =
0.54;y = -8.93x + 209.09),whereasthe two variableswere unrelated in C-males (F = 1.24, n = 23, P = 0.28,r2 = 0.056;y = -1.78x + 52.0;
Fig.3). Theslopesof the regression linesdifferedsignificantly(F = 7.28,P = 0.011). Surprisingly, the sameanalysisrevealeda
significant negative relationship between body massand extrapolatedbasallevelsof B in Cfemales(F = 5.38, n = 23, P = 0.03, r2 = 0.20; y = -5.91x + 134.86)butnotin T-females (F = 0.22, n = 16, P = 0.65, r2 = 0.02;y = -1.89x + 54.03;Fig.4). Theslopesof theregression lines werenot significantlydifferent(F = 0.79,P = 0.38).
Serialsampling ofcorticosterone.--B increased significantly with handlingtimein malessam-
T-females also showed an increase in B levels
with initial samplingtime (F = 9.99,n = 17, P = 0.006,r2 = 0.40;y = 9.83x- 4.89),whereas 70 C-femalesdid not (F = 0.88, n = 24, P = 0.36, • 60 r2 = 0.04;y = 2.36x + 12.36).However,the slopesof the regression lineswerenot signifi- • so cantlydifferentfor T- andC-females(F = 3.40, E 4o P = 0.07;Fig. 2). B levelsextrapolatedto 1 min post-capture • 30 shouldapproximate basallevels.Extrapolated • 2o basallevelsof B werehigherin T-males(24.18 lO o•: øo ß + 4.1 ng) thanin C-males(14.65+_1.8ng; t = -2.13, P = 0.04)but werenot significantly dif16 17 18 19 20 21 22 23 24 ferentbetweenT-females(16.41_+3.5 ng) and BodyMass(g) C-females(15.9-+ 2.6 ng; t = -0.13, P = 0.91). Bodymassandinitial levelsof corticosterone.-- FIG. 3. Corticosteronelevels extrapolatedto 1
In T-males,lighterindividualshadhigherex- min post-captureas a functionof body massin Ttrapolated basallevelsofB thandid heavierin- male and C-maleDark-eyedJuncos.
68
SCHOECH, KETTERSON, ANDNOLAN 60
• •
50
•
40
Males
T-Females o-
[Auk,Vol. 116
•
C-Females
T-Males
-C• C-Males
•o •0 o
20 10 0
17
lg
19
20
21
10
20
30
40
50
60
22 45
Females
BodyMass(g)
•
40
Fie. 4. Corticosteronelevels extrapolatedto 1 min post-captureasa functionof body massin T-female and C-femaleDark-eyedJuncos.
T-Females
35
_•• C-Fex
30
25
20 pled at 10, 30, and 60 min post-capture(re15 peated-measuresANOVA, F = 28.12, P < 0.001).Levelsappearedto behigherin T-males, 0 10 20 30 40 50 60 but treatmenthad no significanteffecton B (F Time After Capture (min) = 3.51,P = 0.08,Fig. 5). In contrast,the B responseof femalesshowedneitheran effectof FIG.5. Corticosteronelevelsfrom seriallycollecthandlingtime (F = 2.51,P = 0.10)noraneffect ed bloodsamplesin T- andC-male(upperpanel)and of the treatmentof their mates(F < 0.001,P = T- andC-female(lowerpanel)Dark-eyedJuncos. Val-
0.99).
ues are œ_+SE. Data at 1 min post-captureare ex-
The apparentlackof an adrenalresponse to trapolatedfor eachindividual usingthe rate of incaptureand handlingin femalesled us to in- creasefrom initial sampleto sampleat 10 min. corporate theextrapolated B valuesintotherepeated-measures model.Thisanalysisrevealed a markedB response to captureandhandling al. 1991,Klukowski et al. 1997).Interestingly, in females (F = 43.46, P < 0.001) and males (F our finding that the HPA axis of T-malesre= 80.15, P < 0.001). However,there were no spondsmorerapidly to captureand handling significantdifferencesattributableto treatment than that of C-males(Fig. 1) doesnot agree (males, F = 3.43, P = 0.08; females, F < 0.001, P = 0.99).
Inspectionof thesedataled us to compare males and femalesirrespectiveof treatment. Maleshad significantly higherB thanfemales (F = 43.09, P < 0.001;Fig. 6), and B increased significantly with handlingtime (F = 15.56,P < 0.001).Furthermore, whenthe extrapolated B datawereincorporated, significantdifferences again were attributableto sex (F = 22.67,P < 0.001)and handlingtime (F = 131.40,P < 0.001).
70
o
50
õ
•
Males
-O-Female•
4o 'E 30 2O
10 0
DISCUSSION
10
20
30
40
50
60
TimeAfterCapture(min)
FIG. 6. Capture-stressresponsesof male and fe-
Initial levelsof corticosterone.---Our findings male Dark-eyed Juncosirrespectiveof treatment.
that T-maleshavehigherbaselinelevelsof B than do C-males is consistent with results of
otherstudiesof Dark-eyedJuncos (Ketterson et
Valuesareœ_+SE.Data at 1 min post-captureareextrapolatedfor eachindividual usingthe rate of increasefrom initial sampleto sampleat 10 min.
January1999]
Corticosterone in Dark-eyed Juncos
69
with the studyby Klukowskiet al. (1997),who
fort. If femalejuncoswork harder to compensatefor theirmates'reducedpaternalcare,they with handling time, despite T-maleshaving may have lesstime to devoteto self maintehigherbasalB levels.However,Dark-eyedJun- nance and, as a result, may be more sensitive coshousedin individual cageswith accessto to stressors.This suggestionis supportedby adlibitumfoodare not exposedto the full spec- Silverin (1983), who found that female Pied trum of environmental conditions and social Flycatchersthat raised nestlingsunaided by interactionsthat free-livingindividualswould their mateshad higherlevelsof B than did feexperience.Consequently,the absenceof an ef- malesthat were assistedby their mates. fect of T on the stressresponses of captivejunThe higher baselinelevels of B in T-males cosobservedby Klukowski et al. (1997) is not than in controlsmay reflectchronicallyelevatsurprising. ed B. The well-documentedgluconeogenic acOur data support the hypothesisthat the tionsof B arethoughtto beessentialfor themoHPA axisis stimulatedby chronicallyelevated bilization of energy stores,and this function testosterone to havean increasedsensitivityto may be especially important in facilitating stressors and/ or an increasedsecretoryability. short-termresponses to stressors by increasing If the responseinducedby the capture-stress availableglucoseto fuel the fight-or-flightreprotocolis comparableto the natural response sponse.However,becauseB preferentiallymeto acutestressors encountered by juncos,then diatesthe breakdownof proteins,in the longthe highly responsiveadrenocortical reaction term it can causeseveremusclecatabolism(Sein T-malesmay reflecta costof elevatedT that lye 1979).Sapolsky(1992) listed severalcomhas not been documentedbefore. Compared ponentsof the stressresponse,in additionto with controls,T-malesare known to: (1) in- gluconeogenesis, that can result in pathology, creasethe size of their homerange (Chandler e.g. suppressionof digestion,growth,immuet al. 1994);(2) increasetheir songrate (Ketter- nity, and reproduction.In addition,Wingfield son et al. 1992);and (3) decreasethe amountof (1994)postulatedthat elevatedB caninducebewith the completionof retime spentpreeningand sleeping(S. Lynn un- haviorsinconsistent publ. data). It seemsthat increasingactivity productiveeffort (see below). If, as our data while reducingself-careresultsin increased suggest,experimentallyelevatedT sensitizes adrenocorticalsensitivityto stressors. the HPA axisand causes chronicallyelevatedB, found
no difference
in the rate of B increase
Our data on females are less consistent and,
then it follows that a bird with
elevated T is
therefore,more difficult to interpret.The ex- more likely to suffer from one or more of the trapolatedB data,whichrevealedno differenc- abovepathologies. If so,maintaininghighT for es in baseline B between T- and C-females, a prolonged period may be disadvantageous agreewith an earlier reportby Kettersonet al. and, thus, could be expectedto be selected (1991). However,the increasein initial B with against. Serial samplingof corticosterone.--Although time required for sample collectionin T-femalessuggeststhat T-femalesare more sensi- our data from repeatedsamplingof B did not tive to stressorsthan are C-females(Fig. 2). In differ significantlyaccordingto treatment,TDark-eyed Juncos,T-femalesmust feed their males tended to have higher B than did CyoungmorefrequentlythanC-femalesbecause males(Fig. 5). Furthermore,the levelsof B extheir mates come to the nest less often and trapolatedto 1 min werehigherin T-males,and bring lessfood (Kettersonet al. 1992).Similar B rosemorerapidlyin T-malesthanin C-males compensatory feedingby matesof T-maleshas (Fig.1). DespitethefactthatT-females showed been reported for HouseSparrows(Passerdo- a significantearly increasein B in responseto mesticus; HegnerandWingfield1987),PiedFly- captureand handling,whereasC-femalesdid catchers (Ficedula hypoleuca; Silverin1980),Barn not (Fig. 2), B levels of the two treatment Swallows (Hirundo rustica;Saino and Moller groupsdid not differ (Fig.5). Giventhe poten1995), and Lapland Longspurs(Calcariuslap- tial negativeeffectsof B describedabove,the ponicus; Hunt et al. 1998).Furthermore, when datafrom serialsamplingfurthersuggestthat Wolf et al. (1990)removedmalesfrom pairs of elevatedT has costs,especiallyfor males. The clear differencein the B responsesof juncos,femalescompensated for the absence of theirmatesby increasingtheirownparentalef- male and femalejuncosto the capture-stress
70
SCHOECH, KETTERSON, ANDNOLAN
paradigm (seeFig. 6) may reflecta sexdifferencein the ability to modulatethe adrenocortical response to stress. Mounting evidence suggests thatsomespecies of birdscandampen their stressresponseduring the breedingseason(seebelow).Thisability may minimizethe negativeeffectsof B upon the reproductive axis.Alternatively,it may suppressforagingor irruptivebehavior,bothof whicharepromoted by B, and both of which would interferewith parentalcare(Silverin1986,Wingfieldand Silverin 1986,Wingfield et al. 1990,Astheimeret al. 1992).Wingfield(1994)positedthattheability to reducethe stressresponseis an adaptation to minimize nestabandonmentduring periods of environmentalperturbations.Indeed, desertspeciessuchasBlack-throated Sparrows (Amphispizabilineata),CactusWrens (Campylorhynchus brunneicapillus), Curve-billedThrash-
[Auk, Vol. 116
Hudman,TraceyKast,Erin Kennedy,SharonLynn, MicheleRosenshield, EricSnajdr,Andy Stoehr,Jen Zaebst,andCharlesZiegenfus. WealsothankHenry Wilbur, Director of Mountain Lake BiologicalStation, and his staff who facilitated our research in
many ways. We are also grateful to Mountain Lake
Hotelfor allowingaccess to theirproperty.Thisresearchwassupportedby the NationalScienceFoundation (BSR 87-18358, BSR 91-11498, IBN 94-408061)
andtheDepartmentof BiologyandCenterfortheIntegrativeStudy of Animal Behaviorat Indiana University. Thanks also to Sarah Kistler, Hubert Schwabl,JohnWingfield,and an anonymous referee for helpfulcommentson the manuscript. LITERATURE
CITED
ASTHEIMER,L. B., W. A. BUTTEMER,AND J. C. WINeFIELD. 1992. Interactions
of corticosterone
with
feeding, activity and metabolismin passerine birds. Ornis Scandinavica
23:355-365.
ers (Toxostoma curvirostre),and Abert'sTowhees BALL,G. E 1991. Endocrine mechanismsand the evo-
(Pipilo aberti) have significantlylower B re-
lution of avian parental care. Pages984-991 in
Acta XX Congressus InternationalisOrnitholosponsesto captureand handlingduring the gici(B.D. Bell,Ed.).Christchurch, NewZealand, breedingseasonthan during the nonbreeding 1990. New Zealand Ornithological Congress season(Wingfield et al. 1992). Additionally, Trust Board,Wellington. arctic-livingCommonRedpolls(Carduelisfiam- BALTHAZART, J. 1983. Hormonal correlatesof behavmea)alsomodulatetheir stressresponseduring ior. Pages221-365 in Avian biology,vol. 7 (D. S. breeding(Wingfieldet al. 1994a).UnfortunateFarner,J. R. King, and K. C. Parkes,Eds.). Aca-
ly, our data do not permit us to determine demic Press, New York. whetherfemalejuncosvary seasonallyin their CHANDLER, C. R., E. D. KETTERSON,V. NOLAN, JR., AND C. ZIEGENFU$. 1994. Effects of testosterone adrenocorticalresponse.Interestingly,both on spatial activity in free-ranging male Darkadultandhatching-year femaleWhite-throated eyedJuncos, Juncohyemalis. Animal Behaviour Sparrows(Zonotrichia albicollis), whichare eco47:1445-1455. logicallycomparableto juncos,had a greater DUFTY, A.M., JR. 1989. Testosterone and survival: A stressresponsethanmaleswhentestedduring costof aggressiveness? Hormonesand Behavior the fall (Schwabl1995). 23:185-193. In summary,relativeto controls,malejuncos ENSTROM,D. A., E. D. KETTERSON,AND V. NOLAN, JR. treatedwith testosterone have:(1) higherbase1997. Testosterone and mate choice in the Darkline levels of corticosterone;(2) a more rapid eyedJunco.Animal Behaviour54:1135-1146. corticosteroneresponse;and (3) a tendencyto- GREENBERG,N., AND J. C. WINGFIELD. 1987. Stress andreproduction: Reciprocal relationships. Pagward higherlevelsof corticosterone in repeated es 461-505 in Hormones and reproduction in samples,all of whichsuggestpossiblecoststo fishes,amphibians andreptiles(D. O.Norrisand the maintenanceof high levelsof testosterone. R. E. Jones,Eds.). Plenum Press,New York. Additionally,differencesin the adrenocortical HARVEY, S., J. G. PHILLIPS,A. REES,AND t. R. HALL. responseof males and femalesthat we docu1974. Stressand adrenal function. Journal of Exmentedare provocative,especiallyin light of perimentalZoology 232:633-645. seasonaland sexual differencesreported for HEGNER,R. E., AND J. C WINGFIELD. 1987. Effects of otherspecies. experimentalmanipulation of testosteronelevels on parental investmentin male HouseSparACKNOWLEDGMENTS
rows.
Auk
104:462-469.
HUNT, K., t. P.HAHN, ANDJ. C. WINGFIELD.1998. En-
We thank the many peoplewho have been involvedin thejuncoproject,especiallythefieldassistantsand colleagues who helpedcollectdatapresentedin this paper:Shan Bentz,JoeCasto,Steve
docrine influenceson parental care during a short breeding season:Testosteroneand male
parentalcarein LaplandLongspurs. Behavioral Ecologyand Sociobiology43: In press.
January 1999]
Corticosterone in Dark-eyed Juncos
71
(Aves:Juncohyetnalis). Proceedings of the Royal G. PARKER, ANDC. ZIEGENFUS. 1996.Phenotypic Societyof LondonSeriesB 246:1599-1603. engineering:Using hormonesto explore the SAINO, N., AND A. P. MOLLER. 1995. Testosterone-induceddepressionof male parentalbehaviorin mechanisticand functionalbasesof phenotypic variation in nature. Ibis 138:70-86. the Barn Swallow:Femalecompensationand efKETTERSON,E. D., V. NOLAN, JR., L. WOLF, AND C. fectson seasonalfitness.BehavioralEcologyand ZIEGENFUS. 1992. Testosterone and avian life hisSociobiology 33:151-157. R. M. 1992.Neuroendocrinology of the tories:Effectsof experimentallyelevatedtestos- SAPOLSKY, terone on behavior and correlates of fitness in stress-response. Pages287-324in Behavioralendocrinology(J. B. Becker,S. M. Breedlove,and the Dark-eyedJunco(Junco hyetnalis). American Naturalist 140:980-999. D. Crews, Eds.). MIT Press,Cambridge,MassaKETTERSON, E. D., V. NOLAN, JR.,M. J. CAWTHORN,P.
KETTERSON,E. D., V. NOLAN, JR., L. WOLF, C. ZIEGENFUS,g. M. DUFTY, G. E BALL, AND t. S. JOHNSEN. 1991. Testosterone
and avian life histories:
The effect of experimentallyelevatedtestosterone on corticosteroneand body mass in the Dark-eyedJunco(]uncohyernalis). Hormonesand Behavior
chusetts.
SCHOECH,S. J., R. L. MUMME, AND J. C. WINGFIELD.
1996. Delayed breeding in the cooperatively breedingFlorida Scrub-Jay(Aphelocoma coerulescens):Inhibition or the absenceof stimulation?
BehavioralEcologyand Sociobiology 39:77-90. SCHOECH,S. J., R. L. MUMME, AND J. C. WINGFIELD.
25:489-503.
KLUKOWSK1,L.A., J. M. CAWTHORN,E. D. KETTERSON,
AND V. NOLAN, JR. 1997. Effects of experimentally elevatedtestosteroneon plasmacorticoste-
rone and corticosteroid-bindingglobulin in Dark-eyedJuncos(Junco hyetnalis). Generaland ComparativeEndocrinology108:141-151. LACK,D. 1968.Ecologicaladaptationsfor breedingin birds. Methuen, London. MARLER, C. g., AND M. C. MOORE. 1988. Evolution-
1997. Corticosterone,reproductive status, and
bodymassin a cooperative breeder,the Florida Scrub-Jay(Aphelocoma coerulescens). Physiological Zoology 70:68-73. SCHOECH,S. J., E. D. KETTERSON,V. NOLAN, JR., P. J.
SHARP,AND J. D. BUNTIN.1998. The effect of ex-
ogenous testosterone onparentalbehavior,plasma prolactin, and prolactin binding sites in Dark-eyedJuncos.Hormonesand Behavior34: 1-10.
ary costsof aggressionrevealedby testosterone SCHWABL,H. 1995. Individual variation of the acute manipulationsin free-living male lizards. Beadrenocortical responseto stressin the WhitehavioralEcologyand Sociobiology 23:21-26. MARLER, C. g., AND M. C. MOORE. 1989. Time and
energy costs of aggressionin testosterone-im-
plantedfree-livingmalemountainspinylizards (Sceloporus jarrovi). PhysiologicalZoology 62: 1334-1350.
MARLER, C. A., G. WALSBERG,M. L. WHITE, AND M.
MOORE.1995.Increasedenergyexpendituredue to increased
territorial
defense in male lizards
throatedSparrow.Zoology(Jena)99:113-120. SELYE, H. 1979.The stressof my life. Van NostrandReinhold, New York.
SIEGEL,H. S. 1980. Physiologicalstressin birds. BioScience
30:529-534.
SILVERIN, B. 1980.Effectsof long-actingtestosterone treatmenton free-living Pied Flycatchers,Fice-
dulahypoleuca, duringthe breedingperiod.Animal Behaviour
28:906-912.
afterphenotypicmanipulation.BehavioralEcol- SILVERIN, B. 1983. Populationendocrinologyof the ogy and Sociobiology 37:225-231. femalePiedFlycatcher, Ficedula hypoleuca. Pages NEWER,J., W. WASSERMAN,AND M. H. KUTNER. 1985. 388-397 in Hormonesand behaviorin higher Applied linear statisticalmodels:Regression, vertebrates(J.Balthazart,E. Pr6ve,and R. Giles, analysisof variance,and experimentaldesigns.
Irwin Inc., Homewood, Illinois. NOLAN, V., JR., E. D. KETTERSON,C. ZIEGENFUS,D. P. CULLEN, AND C. R. CHANDLER. 1992. Testoster-
one and avian life histories:Effectsof experimentally elevatedtestosteroneon prebasicmolt and survivalin male Dark-eyedJuncos.Condor 94:364-370.
corticosterone during the breedingperiod in PiedFlycatchers, Ficedula hypoleuca. Generaland ComparativeEndocrinology64:67-74. SOKAL, R. R., ANDE J.ROHLF.1981.Biometry,2nded. W. H. Freeman, New York.
ORING, L. W., A. J. FIVIZZANI, AND M. E. EL-HALAWANI. 1989. Testosterone-induced
Eds.). Springer-Verlag,Berlin. SILVERIN,B. 1986. Corticosterone-bindingproteins and behavioraleffectsof high plasmalevelsof
inhibition
of
incubationin the SpottedSandpiper(Actitistnacularia).Hormonesand Behavior23:412-423. RAOUF, S. A., P. G. PARKER, E. D. KETTERSON,V. NOLAN, JR., AND C. ZIEGENFUS.1998. Testosterone
SYSTAT.1996. Systat 6.0 for Windows: Statistics. SPSS,Inc., Chicago. WADA,M. 1982.Effectsof sexsteroidson calling,locomotoractivity,and sexualbehaviorin castrat-
edmaleJapanese Quail.Hormones andBehavior 16:147-157.
affectsreproductivesuccessby influencingex- WADA,M. 1986.Circadianrhythmsof testosteronedependentbehaviors,crowing, and locomotor tra-pair fertilizationsin male Dark-eyedJuncos
72
SCHOECH, KETTERSON, ANDNOLAN activity in male JapaneseQuail. Journalof Com-
parativePhysiologyA 158:17-25. WINGFIELD,J. C. 1984. Androgens and mating sys-
tems: Testosterone-induced polygyny in normally monogamous birds.Auk 101:665-671.
[Auk, Vol. 116
WINGFIELD, J. C., R. E. HEGNER, A.M.
DUFTY, JR.,
ANDG. F. BALL.1990.The "challengehypothesis":Theoreticalimplicationsforpatternsof testosteronesecretion,mating systems,and breeding strategies.AmericanNaturalist136:829-846.
WINGFIELD,J. C. 1994. Modulation of the adrenocortical responseto stressin birds.Pages520-528in Perspectivesin comparativeendocrinology(K. G. Davey,R. E. Peter,and S.S. Tobe,Eds.). Na-
WINGFIELD,J. C., AND B. SILVERIN.1986. Effects of
tional Research Council of Canada, Ottawa. WINGFIELD,J. C., G. F. BALL, A. M. DUFTY• JR., R. E. HEGNER, AND M. RAMENOFSKY.1987. Testoster-
WINGFIELD,J. C., R. SUYDAM,AND K. HUNT. 1994b.
one and aggressionin birds. AmericanScientist 75:602-608.
WINGFIELD, J. C., P. DEVICHE, S. SHARBAUGH,L. B. ASTHEIMER,R. HOLBERTON,R. SUYDAM, AND K.
corticosterone on territorial
behavior of free-liv-
ing male SongSparrows,Melospizamelodia. Hormones and Behavior 20:405-417.
The adrenocorticalresponsesto stressin Snow Buntings (Plectrophenax nivalis) and Lapland Longspurs(Calcariuslapponicus) at Barrow,Alaska. Comparative Biochemistry andPhysiologyC 108:299-306.
WINGFIELD, J. C., C. M. VLECK, AND M. C. MOORE.
1992.Seasonalchangesof the adrenocortical reHUNT. 1994a.Seasonalchangesof the adrenosponseto stressin birdsof the Sonorandesert. corticalresponsesto stressin Redpolls,Acanthis Journalof ExperimentalZoology264:419-428. fiammea,in Alaska.Journalof ExperimentalZoWOLF, L., E. D. KETTERSON,AND V. NOLAN, JR. 1990. ology 270:372-380. Behaviouralresponseof female Dark-eyedJunWINGFIELD,J. C., AND D. S. FARNER.1983. Endocricosto the experimentalremovalof their mates: nology of reproductionin wild species.Pages Implicationsfor the evolutionof male parental 163-327 in Avian biology,vol. 9 (D. S. Farner,J. R. King, and K. C. Parkes,Eds.).AcademicPress, New York.
care. Animal Behaviour 39:125-134.
Associate Editor:M. E. Murphy
