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Research
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My research focuses on the genetic and
behavioral dynamics of an avian hybrid zone, using the Tufted and Black-crested
Titmouse species complex of Oklahoma and Texas as a model system. Hybrid zones
such as this one, where two closely related species' ranges overlap, provide
insight into gene flow and speciation. Hybridization is interbreeding between
two populations that are distinguishable by "one or more heritable
characters" (Arnold 1997). Hybrid zones are postulated to arise most often
when two closely related species are separated and then contact secondarily in
a region in which they then interbreed. Most hybrid zones are narrow and long
(at the overlap of two populations' ranges), a shape resulting from a balance between
dispersal of parent organisms and selection against hybrids (Barton and Hewitt
1989), adaption of intermediate phenotypes to intermediate habitats (Moore
1977), or a combination of both factors (Arnold 1997).
Black-crested (Baeolophus atricristatus) and Tufted (B. bicolor) Titmouse are an excellent model system for hybrid zones
for several reasons. Titmice are common and easy to observe. They sing
frequently. They nest in nest boxes, allowing for estimations of fitness. Many
other birds in this family (Paridae) are well-studied (Otter 2007) and also
hybridize (R.L. Curry, et al. 2007), providing related species for comparison.
Black-crested and Tufted Titmice
hybridize in central Texas (TX), north-central TX, and southwestern Oklahoma
(OK) (Patten and Smith-Patten 2008). The exact extent of the contact zone is
poorly known outside of central Texas. The contact zone is often only described
for central Texas (Coldren 1992, Rising 1983), but as mentioned above also
occurs in north-central Texas (Dixon 1955) and southwestern Oklahoma (Patten
and Smith-Patten 2008). The unique aspect of the titmouse hybrid zone is a
difference in time since contact for the TX and OK zones. In southwestern OK
the contact is likely more recent (Rising 1983) than in TX (Dixon 1955; Dixon
1990) and is probably the result of shrub invasion (Callahan 2002; Patten and
Smith-Patten 2008).
I have only found one other example of
a well-studied hybrid zone containing different contact times: the Pied and
Collared Flycatchers (Saetre et al. 1999). The clinal mainland hybrid zone is
older than island hybrid zones (Saetre et al. 1999; Haavie et al. 2004).
However, mixed pairs are uncommon in both areas (Saetre et al. 1999), whereas
hybrids constitute the majority of titmice found within their hybrid zone
(personal observation). This suggests different dynamics maintain the titmouse
zone. Studying both the southwestern OK and north-central TX contact zones will
add to our knowledge of hybrid zone dynamics by comparing different stages of
secondary contact in a single species complex.
The
main objectives of the project are:
(1) Describe and compare variation in
phenotype, genotype, and songs between the younger southwestern OK contact zone
and the older north-central TX contact zone and within each parental species
adjacent to the hybrid zone;
(2) Determine why presumed differences in
song occur and to see if causes differ between the two contact zones;
(3) Determine how mate choice is affected
by song differences across hybrid zone; and
(4) Test which, if any, hybrid zone model
best describes the contact zones and determine if model fit differs between
zones.
(5) Natural history observations gathered
during all aspects of the study will be published to add to the sparse data on
Black-crested Titmouse.
Literature
Cited
Arnold,
M. L. 1997. Natural hybridization and evolution. Oxford University Press, New
York.
Barton, N. H., and G. M. Hewitt. 1989.
Adaptation, speciation and hybrid zones. Nature 341:497-503.
Callahan,
P. H. 2002. Progress from grassland to shrubland: woodly enchroachment in North
American grasslands. Pp. 92. University of Oklahoma, Norman.
Coldren,
C. L. 1992. A comparison of the songs of the Tufted and Black-crested Titmice
in Texas. Texas A&M University, College Station.
Curry,
R. L., L. M. Rossano, and M. W. Reudink. 2007. Behavioral aspects of chickadee
hybridization. Pp. 95-110 in K. A. Otter, ed. Ecology and behavior of
chickadees and titmice: an integrated approach. Oxford University Press,
Oxford.
Dixon,
K. L. 1955. An ecological analysis of the inter-breeding of crested titmice in
Texas. University of California Publications in Zoology 54:125-206.
Dixon,
K. L. 1990. Constancy of margins of the hybrid zone in titmice of the Parus
bicolor complex in coastal Texas. Auk 107:184-188.
Haavie,
J., T. Borge, S. Bures, L. Z. Garamszegi, H. M. Lampe, J. Moreno, A. Qvarnstrom,
J. Torok, and G.-P. Saetre. 2004. Flycatcher song in allopatry and
sympatry--convergence, divergence and reinforcement. Journal of Evolutionary
Biology 17:227-237.
Moore,
W. S. 1977. An evaluation of narrow hybrid zones in vertebrates. The Quarterly
Review of Biology 52:263-277.
Otter,
K. A., ed. 2007. Ecology and behavior of chickadees and titmice: an integrated
approach. Oxford University Press, Oxford.
Patten,
M. A., and B. D. Smith-Patten. 2008. Black-crested Titmouse (Baeolophus atricristatus) in A. Poole,
ed. The Birds of North America Online. Cornell Lab of Ornithology, Ithaca.
Rising,
J. D. 1983. The Great Plains hybrid zones. Current Ornithology 1:131-157.
Saetre,
G.-P., K. Kral, S. Bures, and R. A. Ims. 1999. Dynamics of a clinal hybrid zone
and a comparison with island hybrid zones of flycatchers (Ficedula hypoleuca and F.
albicollis). Journal of Zoology 247:53-64.
Contact
information:
Department of Zoology
University of Oklahoma
730 Van Vleet Oval
Room 314
Norman, OK 73019
This
page last updated 21 August 2010.