October 1982]
Short Communications
767
EnlargedSex Chromosomesof Woodpeckers(Piciformes)
GE•LD F. SmELDS,GORDONH. J.•a•cc, .•ND ECXZ.•B•Trt
R•DRV•'•'•
Instituteof ArcticBiologyandDivisionof Life Sciences,
Universityof Alaska,
Fairbanks, Alaska 99701 USA
The evolutionof sexchromosomes
in birdsis poorly terize not only woodpeckersbut alsoother piciform
understood.In part, this is becausethe W chromo- families.
some in most speciesresemblesmicrochromosomes,
Collectionof specimensfor this study has been
which are lessthan 2/x in length and thereforedif- piecemeal in that, for the most part, we have ana-
ficultto characterize.
Autoradiographic
studiesof the
chickenby Schmid(1962)indicatedthat the W chro-
lyzed the karotypesof variouswoodpeckersas the
birds becameavailable.The Torontospecimenswere
taken as adultsor eggs,and at leastthree malesand
three femalesof eachspecieswere used. All karyotypes of thesebirds were preparedfrom acetoorceinstainedslidesof culturedkidney cellsgrownin CMRL
1415+15% fetalcalfserum.We verifiedthe presence
(C-) heterochromatin
on W chromosomes
of birdsby of enlargedZ chromosomesin AlaskanHairy Wood(3 femaleand
C-banding establishedanother procedurefor iden- peckersand flickers.Thesespecimens
tification of the W chromosome(Stefosand Arrighi 2 male Hairy Woodpeckersand 3 femaleand 3 male
1971).Neither of thesetechniqueshasbeenusedex- flickers)were taken as embryosand culturedin estensively, however. The Z chromosomeof birds ap- sentiallythe sameway as the Torontobirds.
Adult lesser Spotted Woodpeckers(3 females, 1
pearsto have been conservedin evolutionto the extent that it consistently comprises 8-9% of the male), 2 female Greater Spotted Woodpeckers(D.
chromatinof the entire genome,that it is typically major), and a male Black Woodpecker(Dryocopus
wereshotnearAs, Norwayandprocessed
the fourth or fifth largestchromosomeof the com- martius)
plement,and that the centromereis consistentlyme- as above.
diocentric (Ohno et al. 1964, Ohno 1967). Ohno has
The tentativeidentificationby the Torontogroup
referred to this, and a similar chromosome in adof an enlargedW chromosomein femaleflickersfrom
vanced snakes,as the "original Z" to emphasize its the Torontoareamadethis speciesthe logicalchoice
conservative evolution.
for autoradiographicidentification of the W chroWe describea deviationfrom Ohno'soriginalZ in mosome.Nestlingsof both sexeswere used. Kidney
somewoodpeckers(Piciformes:Picidae)and believe cultureswere labelledwith tritiatedthymidine(2
that this phenomenon is widespread within the ml, 2,233/xC//xM), and treatment was continuous to
group. Our interestin woodpeckersexchromosomes fixationat 4, 43/4,and 51/2h. The cellswere pretreated
was stimulated by the unpublished observationsof with colchicine(1 /xg/ml) for 2 h. Metaphase cells
with
Drs. E. Sexsmith, E. Redrupp, and B. Thorneycroft were photographedand then autoradiographed
in the laboratoryof ProfessorK. H. Rothfelsof the KodakAR-10 strippingfilm. After 26 h exposure,the
showed8-400 grains,dependDepartment of Botany, University of Toronto from labelledmetaphases
1965-1967. These researchers studied chromosomes
ing on the time spentsynthesizingDNA in the presof the CommonFlicker (Colaptesauratus),the Yel- enceof the isotope.All metaphasecellspreviously
werescoredfortotalgrains,grainsover
low-belliedSapsucker
(Sphyrapicus
varius),the Hairy photographed
and the two pairsof metacenWoodpecker (Picoidesvillosus), and the Downy the sexchromosomes,
Woodpecker(P. pubescens).
They observedthat the tric autosomes.These chromosomeswere easily
Z chromosomes
of thesespeciesare extremelylarge, identifiedand were divided into three or four segnearly twice the size of Z chromosomesof the ma- ments for counting. C-banding of Lesser Spotted
jority of other birds. Additionally, they demonstrat- Woodpeckercellswas doneby the methodof Summosomeis the last to incorporatetritiated thymidine
during the synthesisphase of the cell cycle. Thus,
late replication of the DNA of the W chromosome
characterizes
this elementin the karyotype.More recently, the stainingof large amountsof constitutive
ed that the W chromosome
of the flicker could be
ner (1972).
Partial karyotypes of the four North American
identifiedby its late replicationpattern.
studiedare shownin Fig. 1. ChromoWe havenow verified the presenceof largeZ chro- woodpeckers
mosomesin Alaskanflickersand Hairy Woodpeck- somesof femalesare arrangedin descendingorder
of malesof eachspecies
ers. Additionally, we have observedlarge Z chro- of size, and Z chromosomes
mosomesin three speciesof Europeanwoodpeckers are inset.
and have identified the W chromosome of the Lesser
(a) CommonFlicker(Colaptes
auratus):The Z chroSpotted Woodpecker (Dendrocoposminor) by mosomes have an arm ratio of 1:3.5. The second and
C-banding. Enlarged Z chromosomesmay charac- fourth pairs of chromosomesare metacentric. The
probablediploid numberfor this speciesis 90, with
the fundamental
number(totalnumberof arms)being
• Presentaddress:Departmentof BiologicalSciences,University of
Western Ontario, London, Ontario, Canada.
96. Late labellingof centromeres
was not observed
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[Auk,Vol. 99
9
10....4 5.46
Cß111ptes
Illlrlltlls 21l:9ß,f.L:96
!
w
Picoidesvillßsus 211:92,[11.:96
it II IIIItl,,,..,,,,,......
P.pubescerts2U:92, f.U.=96
lW
Sphyrapicus
vllrius 211--92,f.
11.-lO6
Fig. 1. Partialkaryotpyesof femalewoodpeckers
showingenlargedZ chromosomes.
PairedZ chromosomesof malesof each speciesare inset.
in the flicker.
The W chromosome
was late to label
in both the shortand long arm, but this effectwas
not as pronouncedas in mammaliancells(e.g. late
X in Chinese hamster). DNA replication of the Z
chromosomesin both sexeswas synchronouswith
the autosomes. There was no difference between la-
(d) Yellow-bellied Sapsucker(Sphyrapicusvarius):
The Z chromosomes have an extreme arm ratio of 1:
5, and the secondpair of chromosomesis almost exactly metacentric.This i• iollowed by five sets of
chromosomeshaving various centromerelocations.
The diploadnumber appearsto be 92, with the fun-
belling patternsof the two Z chromosomes
in males. damental number of 106.
(b) Hairy Woodpecker (Picoidesvillosus):the Z
Partial karyotypesof the three Europeanwoodchromosomeof this specieshas a median centromere peckersare shown in Fig. 2.
with an arm ratio of 1:1.5. The karyotypeis alsodis(e) LesserSpotted Woodpecker (Dendrocopusmitinguishedby the presenceof a secondlarge chro- nor): the Z chromosome
of this speciesis again the
mosomepair (number 2) with a sub-median centro- largestof the complement,its arm ratio being 1:1.4.
mere (arm ratio 1:2.5). The remainder of the
The W chromosome
is conspicuously
largeand has
chromosomesare acrocentric. The dipload number
an arm ratio of 1:1.8. The secondpair of chromoappears to be 92, with the fundamental number of somesis sub-metacentric,
while the remainingpairs
96.
appearacrocentric.The entire chromosomecomple(c) Downy Woodpecker(P. pubescens):
the Z chro- ment of this speciesis shownin Fig. 3a. The dipload
mosomeof this speciesis the largestof the comple- number appears to be 108 while the fundamental
ment, beingalmosttwicethe sizeof the next largest number is 112.Figure 3b showsa C-banded cell from
pair. The Z has an arm ratio of 1:2. Exceptfor the the same bird. The W chromosome is heterochrometacentricfourth pair, all other chromosomesare matic, while the negativelystainingZ chromosome
acrocentric.The diploadnumber appearsto be 92 and is unpaired in the complement.
the fundamental
number 96.
(f) GreaterSpottedWoodpecker:(D. major):the Z
October1982]
ShortCommunications
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Dendrocopos
minor
Z
Z
4
5
6
769
7
8
9
10
W
W
D. major
Z
Z
D__ryocopos martius
Fig.2. Partialkaryotypes
of threespecies
of woodpeckers.
Enlarged
Z chromosomes
arethelargest
of
the complements.
chromosome
is largebut with a differentarm ratio embryowhosesexwaseitherdifficultor impossible
(1:2.5)than the Z of the LesserSpottedWoodpecker. to determine. If the individual were a male, chroThe remainderof the karyotypeis similarto that of mosomesidentified by Hammar as Z and W might
be paired with a number of autosomeswhose structhe LesserSpottedWoodpecker.
(g)BlackWoodpecker
(Dryocopus
martius):a single ture is similar. As Hammar's descriptiondid not inmale of this specieswas analyzed, so we cannot un- cludeautoradiographyor C-bandingand as, accordof his
equivocally
identifytheZ chromosomes.
Because
the ing to our scheme,the largestchromosomes
Z chromosomes
are the largestchromosomes
in the karyotypearesimilarto the Z chromosomes
of other
otherspecies,
however,it is likelythatthelargestchro- woodpeckers,we proposethis alternativeinterpremosomesin the BlackWoodpeckerare also the Z tation.
chromosomes; their arm ratio is 1:4.0. The second
The absence of C-bands
in the Z chromosome
of
pair in thisspecies
is nearlymetacentric
(1:1.1).This the LesserSpottedWoodpeckerindicatesthat enpair is followedby anothernearlymetacentric
(1:1.2) largementof this chromosomehas not been accombut smallerpair and by three other pairs that are plished by the addition of C-heterochromatin.We
submetacentric.
The remainingchromosomes
are ac- intend to determine whether or not G- (Giesma)
rocentric.The diploidnumberappearsto be 88, with banding sequencesin original Z chromosometypes
the fundamentalnumber being 98.
also occurin enlargedZ chromosomes
of Alaskan
Table 1 summarizesthe available karyotypic data
for piciformbirds. All speciesof Picidae,exceptthe
Green Woodpecker(Picusviridis) discussedbelow,
possessZ chromosomes
that are the largestof the
complements.
Barbets
(Capitonidae)
alsopossess
large
Z chromosomes.Other piciform families have trot
been studied.
woodpeckers.
While the size of Z chromosomesin woodpeckers
is generallyuniform (Table 1), the positionof the
centromereis not. Even speciesof the same genus
(P. villosusand P. pubescens
aswell asD. minorand
D. major)haveZ chromosomes
thatdifferin position
of the centremere.This variability is probably the
resultof intrachromosomal
rearrangement(e.g. peri-
That large Z chromosomes
were describedindependentlyby severalresearchers
studyingdiversetaxa centric inversions or centric shifts).
supportsour contentionthat largeZ chromosomes The enlargedZ chromosomeis not unique to Picharacterizeall woodpeckers.The karyotypeof the ciformes.The karyotypesof 20 speciesof the family
GreenWoodpeckeris a possibleexception.Hammar Accipitridae (Falconiformes)have been described
(1970:44) describesthe Z and W chromosomes
from (Takagi and Sasaki1974, de Boer 1976, Misra and
this speciesas acrocentric
and as being the fourth Srivastava 1976, Williams and Benirschke 1976), and
and tenthlargestin size, respectively.
The possibil- these speciespossessenlarged Z and W chromo-
ity existsthat the karyotypewaspreparedfrom an
somes. The Z chromosomes resemble those of the
770
ShortCommunications
[Auk, Vol. 99
Fig. 3(a). Entirekaryotypeof a femalelesserspottedwoodpecker.Z and W sexchromosomes
are indicated
by arrows.(b) C-banded(constitutive
heterochromatin)
karyotypeof a femaleLesserSpottedWoodpecker.
The heavilystainedW chromosome
is obviousas is the unpairedZ chromosome.
woodpeckersin that they, too, are the largestof the
complement.Moreover, Bulatova(1973)reported enlargedZ chromosomes
in three speciesof lark (Alaudidae) near Novosibirsk, USSR. We know of no case
in birdsin whichthe Z chromosome
is enlargedwhile
the W is not. This suggeststhat a mechanismfor
enlargement operateson both sex chromosomesin
birds. While Ohno's original Z hypothesischaracterizes perhapsthe majority of avian lineages, derived conditions,such as describedhere, may be
common.Stockand Mengden(1975)did not describe
homologybetweenavian Z chromosomes
and chromosomesof bold snakes,a primitive family without
dimorphic sexchromosomes.
The apparentabsence
of dimorphic sex chromosomesin ratites (Takagi et
al. 1972) and in all but the advancedophidian reptiles complicatesOhno's interpretation of a homologousZ chromosomein these separateclasses.
We thank Prof. Klaus H. Rothfelsof the Depart-
ment of Botany,University of Torontoand his students,BruceThorneycroftand ElizabethSexsmith,
for bringing their observationson enlargedsexchromosomesin woodpeckersto our attention. Also, we
thank all of theseresearchersfor allowing us to cite
and describetheir unpublisheddata. Leonard Pey-
ton locatedand helped collecteggsand young of
Alaskanwoodpeckers.Hans Staalandand Knut Rudd
helpedcollectthe Norwegianwoodpeckers.
Finally,
TABLE1. A stunmaryof sex-chromosome
morphologyand chromosome
numbersin Piciformes.
Species
Z•
Zb
Wc
2n
f.n.
Reference
Picoides
pubescens
P. villosus
P. mahrattensis
Dendrocopos
minor
D. major
Picusviridis
Dryocopusmartius
Dinopiumbenghalense
Colaptesauratus
Sphyrapicus
varius
23.3
15.6
16.0
19.1
18.0
9.2?
19.7
14.8
17.1
21.7
1:2.0
1:1.5
1:3.1
1:1.4
1:2.5
n.r. a
1:4.0
1:3.0
1:3.5
1:5.0
10.8
10.0
5.1
12.0
9.6
6.3?
?
?
11.7
6.4
92
92
84
108
108
94
88
92
90
92
96
96
98
112
112
102
98
94
96
106
This paper
This paper
Kaul and Ansari (1978)
This paper
This paper
Hammar (1970)
This paper
Kaul and Ansari (1978)
This paper
This paper
15.6
17.3
1:2.6
1:2.5
10.7
2.9
96
90
126
106
Kaul and Ansari (1979)
Kaul and Ansari (1978)
Picidae
Capitonidae
Megalaimazeylanica
M. haemacephala
Relativelength of Z chromosomein relation to total macrochromosome
length.
Ratioof the lengthof the longarm of the chromosome
to the lengthof the shortarm of the chromosome.
Relativelengthof W chromosome
in relationto total macrochromosome
length.
n.r.--not reported.
October 1982]
Short Communications
we thank the Governmentof Norway for financial --,
support,tissueculturematerials,and laboratoryspace
during the seniorauthor'sstay there.
771
C. StENIUS, L. C. CI4RIStI.•N, W. BEc.•c, &
M. L. BECAme.
1964. Chromosomaluniformity
in the avian
subclass Carinatae.
Chromosoma
15: 280-288.
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BOER, L. E.M.
1976. The somatic chromosome
complementsof sixteenspeciesof Falconiforrnes
(Aves) and the karyologicalrelationshipsof the
order. Genetica
46: 77-113.
BULATOVA,
N. S. 1973. Unusually large sex chro-
Scream, W. 1962. DNA replication patternsof the
heterochromosomes
in Gallusdomesticus.
Cytogenetics 1: 344-352.
S•EFOS, K., & F. ARR•½I4I. 1971. Heterochromatic
natureof the W chromosome
of birds. Exp. Cell.
Res. 68: 228-231.
STock, A.D.,
mosomes in some larks (Aves: Alaudidae).
Mammal.
Chromos.
Newsl.
14: 150.
H•a•aAR, B. 1970. The karyotypes of thirty-one
birds.
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D., & H. A. A•SARi.
1978.
Chromosome
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Genetica
48: 193-196.
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Barbet, Megalaimazeylanicacaniceps(Franklin)
(Piciforrnes:Aves). Genetica 49: 1-5.
MISRA, M., & M.D.
L. SRIVAStAVA. 1976.
The
karyotypesof two speciesof Falconiforrnes.
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OI4•O, S. 1967. Sex chromosomes and sex-linked
genes.New York, Heidelberg, Berlin, SpringerVerlag.
& G. ME•½VE•.
1975. Chromosome
bandingpatternconservatismin birds and nonhomologyof chromosomebanding patternsbetween birds, turtles, snakesand amphibians.
Chromosoma
50: 69-77.
SU•a•ER,A. T. 1972. A simple techniquefor demonstrating centromeric heterochromatin. Exp.
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study of bird karyotypes. Chromosoma(Berlin)
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M. Itoi4, & M. SASA•C•. 1972. Chromosome
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Received
22 October1981,accepted
18 February1982.
Individuality of Vocalizationsin Dunlin: a PossibleAcousticBasisfor
Recognitionof Parentby Offspring
MYRON CI4ARLES BA•ER
Department
of ZoologyandEntomology,
Colorado
StateUniversity,
Fort Collins, Colorado 80523 USA
Calls of parentscan be recognizedby the young "purring" vocalization.The purr vocalizationis also
in severalspeciesof the avian order Charadriiformes given by a parent when gatheringup its young for
(Beer 1970a,b; Evans 1970a,b). It can be predicted brooding.As the chickswander over the prime feedthat parent-offspringvocal recognitionmay evolve ing areas,two or more broodsmay mingle and sepin precocial specieswith the potential of young of arate.
Observationsat this time indicatethat adultsgive
differentparentagebecomingmixed during foraging
activities.
purr callsalmostconstantlyand the young move toIn the eastern Canadian Arctic, I made tape re- ward an adult that is producing these calls. These
cordings of breeding Dunlin (Charadriiformes, observations raise questions about the possible
Scolopacidae, Calidris alpina). From these I at- acousticbasis for recognition of the correctparent.
tempted to establish the acousticproperties of a It is possibleto discountthe importanceof visual
certain vocal signal that may allow young chicks
to recognizetheir parents.
The precocialyoung Dunlin leave the nest cup
within a few hoursafterhatchingand beginpecking
at small adult Diptera resting on vegetation.In the
first two or three days, a parent broodsits offspring,
particularlyin cold or rainy times. One or both of
the parentsaccompanies
the young, often "leading"
them by walking aheadand emiting a low-intensity,
recognition,becausethe uneventerrainusuallyprevents the tiny chicksfrom seeingthe parentafter a
few metersof separation.I did not verify the occurrenceof vocalrecognitionwith individuallymarked
birds, but I assumedthat the young re-assortwith
the correctparent. This assumptionis parsimonious
and logical from an evolutionarypoint of view.
Broodingspaceunder an adult is limited, and the