KARYOTYPES
NORTH
OF SIX SPECIES
AMERICAN
OF
BLACKBIRDS
(ICTERIDAE: PASSERIFORMES)
HOLLYH. HOBART,
1 SCOTTJ. Gu•q•q,
2 A•qVJoH•qW. BICKI4AM
Departmentof Wildlife and FisheriesSciences,TexasA&M University,
CollegeStation, Texas77843 USA
ABSTRACT.--Karyotypes
of six speciesof blackbirdswere prepared using in vivo techniques.Five speciesare karyotypicallysimilarand may be morecloselyrelatedthan traditional morphologicalcharacterssuggest.The EasternMeadowlark(Sturnellamagna),however, is very differentin karyotypeand may be moredistantlyrelatedto the otherspecies
than has been previouslythought. Karyotypicevidenceis consistentwith Beecher'shypothesisof a closerelationshipbetweenemberizinefinchesand blackbirds.Received
25 June
1981, accepted
18 December1981.
THE family Icteridae (Passeriformes)
is a di- mosomalvariationthat canrevealevolutionary
verse group of predominantly tropical New and phylogeneticrelationships.Among the
World songbirdsarrangedby variousinvesti- karyotypicallybest known vertebrategroups
gators into 89-101 species in 25-36 genera are the mammalian orders Chiroptera, Pri(Storer 1960, 1971; Blake 1968; Short 1968, 1969; mates, and Rodentia and the reptilian order
Clements 1978). Beecher (1951) believed that Testudines.These groups show diverse patthe radiation of the icteridswas an "explosive" terns of variation in the chromosomecompleevent, the family quickly filling all available ment (Capanna and Civitelli 1970, Gorman
niches. Later, Beecher (1953) described Icteri- 1973,Matthey 1973,Wilson et al. 1975,Bushet
dae as a terminal taxon, anatomicallyand be- al. 1977, Bickham and Baker 1979, Bickham
haviorallymore complexthan the group from 1981).The mammalianordersexhibit highly
which it arose.
variable karyotypes, while lower vertebrate
Early phylogeneticstudies of the icterids taxa usually are karyotypicallyconservative.
were confinedto plumagecolorationand gross Comparedto the karyologyof mammalsand
morphological charactersof the bill, skull, reptiles, avian karyology is relatively unexwing, and foot. In 1951, Beecherestablished plored,with lessthan3% of all species
karyothe mostrecentphylogenyof the group,based typed (Takagi and Sasaki 1974, Shields in
on jaw and skull musculatureand bill shape. press).Many avian taxa show little or no variHe hypothesizedthat the icteridsevolvedfrom ation in standardkaryotypes,yet someavian
the emberizinefinches,throughthe primitive genera (e.g. lunco) are composedof species
genus Molothrus,in three phyletic lines: the that share identical chromosomepolymorAgelaiine, Quiscaline, and Cassicine.Basedon phisms(Shields1973,1976).Shields(in press)
myologicaland foragingstudies,Raikow (1978) has reviewed the amount of variation in chrobelieved that Emberizinaeand Icteridaemay mosomesof birds, and studiescomparingthe
be sistergroups.
karyotypesof closelyrelated bird speciesare
Recently, comparative karyological studies rare. The availability of six speciesof icterids
have been used to discern patterns of chro- in our area provided an opportunity for comparative studies.
There are two basic strategiesfollowed in
karyotypicinvestigations.
The firstis to survey
related
forms
throughout
a
taxonin an attempt
• Presentaddress:
Departmentof EcologyandEvolutionaryBiology,The University of Arizona, Tuc- to determine patternsof karyotypevariation
amongsubgroups.The secondis to surveya
son, Arizona 85721 USA.
2 Presentaddress:Departmentof Biology,Texas large number of individualsfrom the rangeof
A&M University, CollegeStation,Texas77843USA.
a single speciesor speciesgroup to discern
514
The Auk 99: 514-518.July1982
JULY
1982]
Blackbird
Karyotypes
515
Fig.
1. Brown-headed
Cowbird
karyotype.
Acomplete
chromosome
set
from
amale;
inset
are
thesex
chromosomesfrom a female.
Chromosomes
werearranged
according
to
whatpatterns
of intraspecific
variation
and croscope.
size;terminology
for centromere
position
follows
polymorphism
arepresent
in natural
popula-Patton (1967).
tions.
At least10metaphaso
cellsof eachspecies
except
Thepurpose
of thispaperis to present
the I. graduacauda
were
examined
todetermine
thedip-
resultsof our karyotypic
studyof these'six 1oidnumber.Bothsexeswereexamined
for each
species
representing
fivegenera
ofIcteridae:
the species
except
I. graduacauda
(maleonly)andQ.
Brown-headedCowbird (Molothrusater), the quiscula
(female
only).
Sturnella
magna
(Brazos
Coun-
andI. graduacauda
(Webb
County,
Texas)
Great-tailedGrackle(Quigcalus
mexicanus),
the ty,Texas)
duringthebreeding
season;
allother
CommonGrackle (Q. quiscula),the Red- werecollected
were trappedfromwinteringpopulawingedBlackbird
(Agelaius
phoeniceus),
the individuals
tionsin BrazosCounty.Fifteenindividuals
of
Black-headed
Oriole(Icterus
graduacauda),
and aterwereexamined,
aswereat leasttwoeachof the
the EasternMeadowlark(Sturnellamagna).
otherspecies
except
I. graduacauda.
Thisrepresents
theonlycytogenetic
informa- Voucher
specimens
deposited
in theTexas
Cooptionreported
for mostof thesespecies,
al- erativeWildlifeCollection(TCWC)at TexasA&M
though
DNAamounts
werereported
forAge- University
are:NI. aterTCWC11029,
11030,
11031,
A. phoeniceus
TCWC11033,
11034;
Q.
laiusphoeniceus
and Sturnellamagnaby 11032,10926;
TCWC 11035,11036;Q. quisculaTCWC
Bachmannet al. (1972),and the karyotypeof mexicanus
andI. graduacauda
TCWC10910;
10specimens
the formerspecies
wasreportedby Makino 11028;
of M. ater,2 specimens
of S. magna,
1 of Q. mexiand Baldwin (1954).
canus,
2 of Q. quiscula,
and1 of A. phoeniceus
are
METHODS
uncatalogued.
Somatic
metaphase
chromosomes
wereprepared
RESULTS
from 27 icteridsusing in vivo bone marrow proce-
AT•R(2n = 78--80:Fig. 1), Qmsdures.Individualswere injectedintraperitoneallyMOLOTnRUS
with a 0.05%solutionof colchicine
at 0.3-0.4ml per
CALUS
t•EXlCAt•US
(2n = 76-78: Fig. 2A), Q.
100gbodyweight
andweresacrificed
afteraperiod QCnSCULA
(2n = 76: Fig. 2B),AGELAIUS
PnO•NI-
of 20-30min. Thefemurswereremovedandflushed C•US(2n = 80: Fig. 2C), ICTERUS
GRADIL4CAUDA
witha hypotonic
solution
of 0.075M KCIto obtain (2n = 76-78:Fig. 2D)
a suspension
of bonemarrow
cells,whichwasinThechromosomal
complements
of thesefive
cubated
in thehypotonic
solution
at37øC
for30min.
The cellswere then fixed(3 partsmethanolto 1 part
acetic
acid)for10minandresuspended
twoorthree
timesin freshfixativeto ensurefixation.Slideswere
species
aresimilar.
Thesixlargest
autosomal
pairs
(macrochromosomes)
aredistinguishable
bysizefromtheremaining
31-33pairs
(micro-
prepared
bydropping
three
orfourdrops
ofcellsus- chromosomes).
Thelargestpair of macrochropension
on cleaned
glass
slides
andigniting
the mosomes
is submetacentric,
thenextfourpairs
preparation.
Theslides
werethenstained
for5 min aresubtelocentric,
and
the
sixth
largestpair is
in a warm 10% Giemsasolution.Preparationswere
Microchromosomes
appearto be
observed
andphotographed
ona LeitzDialuxmi- acrocentric.
516
HOBART,
GUNN,
AND
BICKHAM
[Auk,
Vol.
09
zw
Fig.2. Partial
karyotypes
offiveicterids.
Onlythe10largest
autosomes
andsexchromosomes
areshown
forA.Great-tailed
Grackle,
female;
B.Common
Grackle,
female;
C.Red-winged
Blackbird,
female;
D.Black-
headedOriole,male;andE. Eastern
Meadowlark,
female.
acrocentricexceptfor two pairs of biarmed centric,and the fifth autosomeis acrocentric;
chromosomes.
Microchromosomes
arefigured thus,therearefourpairsof autosomalbiarmed
onlyforM. ater(Fig.1). Thelackof resolution macrochromosomes
ascomparedto five in the
due to smallsize and apparentsimilarity other species.The Z chromosomeis a mediumsizedmetacentric,
andtheW is probably
ac-
among specieslimits the usefulnessof micro-
chromosomes
for comparativestudies.We rocentric.There are 32 pairs of microchromohaveattemptedonly to enumeratethem.The somes.
Z chromosome,
whichisaboutthefourthlargest chromosomein size, is subtelocentricfor
all of these species.The W chromosomeis
probably an acrocentricmicrochromosomein
DISCUSSION
Beecher(1951)hypothesizedthat the icterids
all exceptM. ater,in whichit probablyis a evolved from the emberizine finches via the
He described
threephyletic
small metacentric chromosome.Makino and genusMolothrus.
lines
of
Icteridae
descending
from
Molothrus:
Baldwin(1954)reportedkaryotypes
for A.
the
Agelaiine,
containing
Agelaius,
Sturnella,
phoeniceus
andXanthocephalus
xanthocephalus
generanotreportedhere;
(theYellow-headed
Blackbird)
withmacrochro- Icterus,andseveral
mosomal complementsidentical to those re- the Quiscaline,containingthe subgenera
Quiscalus
(Q. quiscula)
and Cassidix
(Q. mexiportedin this study.
canus)
of thegenusQuiscalus
andseveral
genera not reportedhere;and the Cassicine,none
STURNELLA
MAGNA
(2n= 78:Fig.2E)
of which is reportedhere.Therefore,Molothrus
Thekaryotype
ofS.magna
differsfromthose mightbe expected
to possess
a primitive,or
described
fortheabovefivespecies
in several ancestral,icterid karyotype.
respects.The largestautosomalelementis subIn general,
thesixspecies
showlittlekaryotelocentric, the fourth autosome is subrectatypicvariation.The diploidnumbersrange
JvL¾1982]
Blackbird
Karyotypes
517
from 76 to 80 due to interspecificdifferencesin for a primitive biarmed W chromosome(the
the number of microchromosomes.
Five species only character in which M. ater differs from
appear to have identical macrochromosomal most other icterids). Certain biochemical studcomplements (Figs. 1 and 2A-D). Sturnella ies, however, indicate that Beecher was correct
magnadiffers from theseby centromereposi-
on this point also.
Smith and Zimmerman (1976) investigated
Molothrusater differsfrom all speciesstudied the biochemical geneticsof seven speciesof
by centromereposition of the W chromosome North American blackbirds representing the
(one of the larger microchromosomes).This Agelaiine and Quiscalinegroups. Of the Quistion in pairs 1, 4, 5, and the Z chromosome.
differencein W chromosome
morphologymay caline species,M. ater was the most similar to
be significant.The karyotypesof Emberizacit- the Agelaiine species,especiallyto Agelaius.
rinella(Hammar and Herlin 1975),E. fiaviven- This correlates well with Beecher's (1951)
tris (Hirschi et al. 1972),and E. bruniceps(Misra groupings, appearing to support the theory
and Srivastava 1978) are similar to the M. ater that Molothrusrepresentsthe primitive group
karyotype, differing in centromereposition in that could have given rise to both the Quisthree autosomal pairs. Emberiza citrinella caline and Agelaiine radiations. Another bioshares the metacentric condition of the W chrochemicalstudy (Prager et al. 1974) showed a
mosome
with
M. ater. Other
emberizine
closerelationshipbetweenMolothrusand Agespecies,however, are known to possessacro- laius,which could alsobe interpretedto supcentric W chromosomes,suchas Junco(Shields port Beecher's(1951)hypothesis.
1973)and Zonotrichia(Thorneycroft1976).
It seemsthat morphologic,karyotypic, and
data are consistent
with the
We found no intraspecificpolymorphismin biochemical
the karyotypesof thesespecies,althoughthe groupings of Beecher,with some reservation
limited samplesizesleave room for doubt. We concerningS. magnabased on the karyotypic
have studied 15 specimensof M. ater from a data. Overall, the chromosomal variation noted
Texas wintering population that has been could be attributed to pericentric inversions,
shown to be made up of birds that breed as have been observed in the genus Junco
throughoutthe MississippiRiver drainageand (Shields 1973) and Zonotrichia albicollis (Thorbeyond(Coonand Arnold 1977),sowe may be neycroft 1976), or to additions or deletions of
justifiedin believingthat karyotypicpolymor-
heterochromatin.
phisms do not exist in this species.
The interspecificdifferencesin microchromosomenumbersare difficult to interpret, particularly in view of the difficulties of optical
resolution of these very small chromosomes.
mologies and the rearrangementsleading to
variation is not possible without studying
differentiallystainedchromosomes.
Thesedata
seem to support Shields' (in press) contention
permit the microchromosomesto be seen well
this is stated with reservation
The
demonstration
of ho-
that chromosomal
changesdo not play a major
Only the very best of karyotypepreparations role in the speciationprocessof birds. Again,
due to the dif-
enough to be accuratelycounted.Use of mi- ferencesnoted for S. magna.
crochromosome
numbersand morphologiesin
ACKNOWLEDGMENTS
cytosystematic
studiesawaitsfurther improvement of resolutionby advancesin cytogenetic This study was supportedby NSF grantsDEBtechnique.
7713467 and DEB-7921519 to J. W. Bickham. We wish
The close resemblance
of emberizine
and ic~
to thank K. Arnold, A. Bivings,J. Bostick,R. Dowler,
terid karyotypesis indicative of a relatively M. Engstrom, N. Garza, J. Sites, O. Ward, G.
closephylogeneticrelationship.Likewise, the Shields, and M. Witmet for providing assistance
identical
macrochromosomal
sets of the icter-
ids reported, exceptS. magna,indicate a close
phylogeneticrelationship.It appearsthat the
chromosomal
data
are consistent
with
Bee-
cher'shypothesisthat icteridsevolvedfrom the
during the study and/orreviewing earlier draftsof
the manuscript.
BACHMANN,K., B. A. H.•WRXNGTON,
& J.P. CR_•XG.
1972. Genome size in birds. Chromosoma (Berlin) 37: 405-416.
emberizinefinches.The primitive natureof M.
ater is not well establishedon karyological B•ECH•R,W. J. 1951. Adaptationsfor food-getting
in the American blackbirds. Auk 68: 411-440.
grounds,becauseno strongcasecan be made
518
--.
HOBART,
GUNN,ANDBICKHAM
1953. A phylogenyof the Oscines.Auk 70:
270-333.
BICKHAM,J. W. 1981. Two-hundred-million-yearold-chromosomes:
deceleration
of the rate of
karyotypic evolution in turtles. Science 212:
1291-1293.
--,
[Auk, Vol. 99
Mzsl•, M., & M.D. L. SRIVASTAVA.1978. Karyotypes of seven Passeres.Cytologia 43: 485-495.
PATTON,J. L. 1967. Chromosome studies of certain
pocketmice, genusPerognathus
(Rodentia:Heteromyidae). J. Mammal. 48: 27-37.
PRAGER,E.M.,
g. H. BRUSH,R. g. NOLAN, M. NA-
& R. J. BAKER.1979. Canalization model of
chromosomal evolution. Bull. Carnegie Mus.
lcANISHI, & A. C. WILSON. 1974. Slow evolution
Nat. Hist.
micro-complementfixation analysis. J. Mol.
13: 70-84.
BLAKE,E. R. 1968. Family Icteridae, American oriolesand blackbirds. Pp. 138-202 in Check-listof
birds of the world, vol. 14 (R. A. Paynter,Ed.).
Cambridge,Massachusetts,
Mus. Comp. Zool.
BUSH, G. L., S. M. CASE,A. C. WILSON, • J. L. PAT-
of transfertin and albumin in birds accordingto
Evol. 3: 243-262.
RAIlCOW,R. J. 1978. Appendicular myology and relationships of the New World nine-primaried
oscines (Aves: Passeriformes).Bull. Carnegie
Mus.
Nat.
Hist.
7: 143.
TON. 1977. Rapid speciationand chromosomal SHIELVS,G. F. 1973. Chromosomalpolymorphism
evolution
in mammals.
Proc. Natl. Acad. Sci.
common to severalspeciesof Junco(Aves). Can.
USA 74: 3942-3946.
J. Genet. Cytol. 15: 461471.
CAPANNA, E.t & M. V. CIVITELLI. 1970. Chromoß 1976. Meiotic evidence for pericentric inversomal mechanismsin the evolution of chiropsion polymorphismin Junco(Aves). Can. J. Geterankaryotype.Chromosomal
tablesof chiropnet. Cytol. 18: 747-751.
tera. Caryologia23: 79-111.
ß In press. Comparativeavian cytogenetics:a
review. Condor.
CLEMENTS,J. F. 1978. Birds of the world: a checklist. New York, The Two Continents Publ.
SHORT,L. L. 1968. Sympatryof Red-breastedMeaGroup.
dowlarks in Argentina and the taxonomy of
meadowlarks (Aves: Leistes,Pezites, and SturCooN, D. W., & K. A. ARNOLD. 1977. Origins of
nella). Amer. Mus. Novit. 2349.
Brown-headed Cowbird populations wintering
in central Texas. North Amer. Bird Bander 2: 7ß 1969. A new speciesof blackbird (Agelaius)
11.
from Peru. Occ. Pap. Mus. Zool. Louisiana State
Univ. 36: 14.
GORMAN,G. C. 1973. The chromosomesof the Reptilia, a cytotaxonomicinterpretation. Pp. 349- SMITH, J. K., & E.G. ZIMMERMAN. 1976. Biochemical
424 in Cytotaxonomyand vertebrateevolution
geneticsand evolutionof North American black(A. B. Chiarelli and E. Capanna, Eds.). New
birds, family Icteridae. Comp. Blochem.PhysYork, Academic Press.
HAMMAR,B., & M. HERLIN.1975.Karyotypesof four
bird speciesof the order Passeriformes.Hereditas 80: 177-184.
HIRSCHI, M., E. HAUSCHTECK-JUNGEN,
& V. ZlSWlL-
ER. 1972. Karyotypen yon zwei vogelarten,
Euodicecontans(Estrildidae)und Emberizafiaviventris (Pyrrhuloxiidae, Emberizinae). Cytologia 37: 525-529.
MAlcINO, S., & P. H. BALVWIN. 1954. The chromo-
somes of the American blackbirds, Agelaius
iol. 53B: 317-324.
STORER,
R. W. 1960. The classificationof birds. Pp.
57-93 in Biology and comparativephysiologyof
birds, vol. 1 (A. J. Marshall, Ed.). New York,
Academic
Press.
1971. Classificationof birds. Pp. 1-18 in
Avian biology, vol. 1 (D. S. Farner and J. R.
King, Eds.). New York, Academic Press.
TAKAGI, N., 8t M. SASAKI.1974. A phylogenetic
study of bird karyotypes.Chromosoma(Berlin)
46: 91-120.
H. B. 1976. A cytogeneticstudy of
phoeniceusand Xanthocephalus
xanthocephalus THORNEYCROFT,
(Family Icteridae). Cytologia 19: 217-224.
MATTHEY, R. 1973. The chromosome formulae of
eutherian mammalsßPp. 531-616 in Cytotaxonomy and vertebrate evolution (A. B. Chiarelli
and E. Capanna, Eds.). New York, Academic
Press.
the White~throatedSparrowZonotrichiaalbicollis
(Gmelin). Evolution 29: 611-621.
WILSON, A. C., G. L. BUSH, S. M. CASE, & M. C.
KINe. 1975. Social structuring of mammalian
populationsand rate of chromosomalevolutionß
Proc. Natl.
Acad. Sci. USA 72: 5061-5065.