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Karyotypes of seven species of North American wrens (Passeriformes: Troglodytidae).

Abstract. -- Karyotypes, new to cytology, are described for seven North American species of wrens (Troglodytidae): Campylorhynchus brunneicapillus (2n = 74), Salpinctes obsoletus (2N = 80), Catherpes mexicanus (2N = 80), Thryothorus ludovicianus (2n = 76), Thryomanes bewickii (2N = 76), Cistothorus platensis (2N = 76), and Cistothorus palustris (2N = 76). All species examined share the first three macrochromosomes.

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Compared to other vertebrate classes (e.g. mammals and reptiles), avian karyology is poorly known. Less than 10% of the world's species of birds have been karyotyped, of which very few have been passerines (Takagi & Sasak 1974; Tegelstrom & Ryttman 1981; Shields 1983; 1985; De Boer 1984). The family Troglodytidae includes some 45 species in 15 different genera (Morony et al. 1975; Sibley & Monroe 1990). Of these, only two species have been karyotyped. Udagawa (1956) described the chromosomes of the Nearctic species, Troglodytes troglodytes (2n = 86) and De Lucca & Chamma (1977) reported those of the neotropical wren, Thryothorus leucotis (2n = 78).

Nine species of wrens occur in North America north of Mexico (AOU 1983). This study provides the first description of the chromosomes of seven of these species: Cactus Wren (Campylorhynchus brunneicapillus), Rock Wren (Salpinctes obsoletus), Canyon Wren (Catherpes mexicanus), Carolina Wren (Thryothorus ludovicianus), Bewick's Wren (Thryomanes bewickii), Sedge Wren (Cistothorus platensis), and Marsh Wren (Cistothorus palustris). Nomenclature follows that of the AOU Check-list of North American Birds (1983). This study represents the only cytogenetic information reported for these species.

Materials and Methods

Cytological techniques followed those of Christidis (1985) and Hafner & Sandquist (1989). A chromosome was designated as a macrochromosome if either the centromere or separate arms could be differentiated. All other chromosomes were designated as microchromosomes. At least 10 metaphase cells of each species were examined in order to determine the diploid number. Both sexes were examined for each species. A total of 26 specimens were examined during the course of this study. Specimens were collected in accordance with scientific collecting permit numbers PRT-674149 (U.S. Fish and Wildlife Service) and SPR-0290-021 (Texas Parks and Wildlife Department) issued to Terry C. Maxwell. Voucher study skins of 24 salvageable specimens are deposited with the holdings of the Angelo State Natural History Collections (ASNHC) at Angelo State University.

Material examined. -- Thryomanes bewickii. -- 5.5 mi N, 4.5 mi W of San Angelo, Tom Green County, Texas, one male specimen (ASNHC 1058) and two female specimens (ASNHC 1054, 1056); 5 mi S of Christoval, Tom Green County, Texas, one male specimen (ASNHC 1057). Thryothorus ludovicianus. -- 5 mi S of Christoval, Tom Green County, Texas, two male specimens (ASNHC 1050, 1051) and one female specimen (ASNHC 1053); 4 mi S of Christoval, Tom Green County, Texas, one male specimen (ASNHC 1048). Campylorhynchus brunneicapillus. -- 10 mi S 4.5 mi W of San Angelo, Tom Green County, Texas, one male specimen (ASNHC 1073); 10 mi SW of San Angelo, Tom Green County, Texas, one male specimen (ASNHC 694); 6.3 mi N, 13.2 mi W of Mertzon, Irion County, Texas, one female specimen (ASNHC 1074). Salpinctes obsoletus. -- 10.5 mi S, 2.3 mi W of San Angelo, Tom Green County, Texas, three female specimens (ASNHC 1061, 1062, 1063). Catherpes mexicanus. -- 6.3 mi N, 13.2 mi W of Mertzon, Irion County, Texas, one female specimen (ASNHC 1063); 2 mi. S, 1 mi W of Leakey, Real County, Texas, one male specimen (ASNHC 1065) and one female specimen (ASNHC 1064). Cistothorus platensis. -- 11.8 mi N of Freeport, Brazoria County, Texas, two male specimens (ASNHC 1066, 1067) and three female specimens (ASNHC 1068, 1069 1070). Cistothorus palustris. -- 4 mi S of San Angelo, Tom Green County, Texas, one male specimen (ASNHC 1072) and one female specimen (ASNHC 1071).

Results and Discussion

The diploid number of chromosomes of wren species examined during this study ranges from 74 in Campylorhynchus to 80 in both Salpinctes and Catherpes and is similar to diploid numbers reported in most birds. Shields (1980) reported that 70% of all birds karyotyped have diploid numbers between 76 and 84. Although no intraspecific polymorphisms were detected in karyotypes examined during this study, larger sample sizes with wider geographic representation would be required to accurately assess intraspecific variation.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Campylorhynchus brunneicapillus (Cactus Wren) exhibits a diploid number of 74 (Fig. 1). The eight largest pairs of macrochromosomes (including the sex chromosomes) are distinguishable by size from the remaining 29 pairs of smaller microchromosomes. The two largest pairs of macrochromosomes are submetacentric, the third largest pair is subtelocentric, the next two pairs are submetacentric and the sixth and seventh pair are telocentric. The eighth pair of macrochromosomes are the sex chromosomes. In this species, the W chromosome is telocentric, whereas the Z chromosomes are subtelocentric.

[FIGURE 3 OMITTED]

Cistothorus palustris (Marsh Wren) (Fig. 2) and C. platensis (Sedge Wren) (Fig. 3) appear to have identical karyotypes, each with a diploid number of 76. They have eight pairs of macrochromosomes (including the sex chromosomes) and 30 pairs of microchromosomes. In both species, the largest pair is submetacentric, the next four pairs are subtelocentric, and the two smallest pairs are telocentric. The W chromosome appears to be telocentric, whereas the Z chromosome is subtelocentric.

Thryomanes bewickii (Bewick's Wren) (Fig. 4) and Thryothorus ludovicianus (Carolina Wren) (Fig. 5) also appear to exhibit identical karyotypes with a 2n of 76. They have nine pairs of macrochromosomes (including the sex chromosomes) and 29 pairs of microchromosomes. All other species in this study exhibited eight pairs of macrochromosomes. The largest pair for both species are submetacentric, the next two pairs are subtelocentric, the fourth pair is submetacentric and the four smallest pairs are telocentric. Again, the W chromosome is telocentric, whereas the Z chromosomes are subtelocentric. The diploid number of 76 observed in this study for T. ludovicianus differs from that reported for the only other karyotyped species within the genus. De Lucca & Chamma (1977) reported a 2n of 78 for T. leucotis.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

Salpinctes obsoletus (Rock Wren) (Fig. 6) and Catherpes mexicanus (Canyon Wren) (Fig. 7) have very similar karyotypes, both with a diploid number of 80. Both have eight pairs of macrochromosomes (including the sex chromosomes) and 32 pairs of microchromosomes. In both species, the largest pair is submetacentric, the next four pairs are subtelocentric, and the two smallest pairs are telocentric. The Z chromosome appears to be a large telocentric. The only difference in the karyotypes appears to be the W chromosome. In the Rock Wren, the W chromosome is metacentric, whereas that of the Canyon Wren appears to be telocentric. Some authors have considered these two species to be congeneric (Mayr & Short 1970; Morony et al. 1975).

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

All genera of wrens that have been karyotyped share the first three largest pairs of macrochromosomes, with one exception; the second pair in Campylorhynchus is submetacentric instead of subtelocentric as in all the others. The tendency for the largest three or four pairs of chromosomes to be identical among different groups of birds is fairly common (Stock et al. 1974; Ryttman et al. 1979; Ryttman & Tegelstrom 1981). Cistothorus, Catherpes, and Salpinctes all share pairs four and five whereas Thryothorus, Thryomanes, and Campylorhynchus share pair four. With regard to pair five, Campylorhynchus is submetacentric, whereas Thryothorus and Thryomanes are both telocentric. All species share pairs six and seven. Only Thryothorus and Thryomanes have the eighth pair of macrochromosomes. Thryomanes, Thryothorus, Cistothorus, and Campylorhynchus all appear to share the Z and W chromosomes. Catherpes, and Salpinctes share the same Z chromosome but appear to have different W chromosomes.

This study represents the only cytogenetic information reported for these species of wrens. Further karyological investigation, with chromosomal banding, should provide clarification of divisions within this phylogenetically challenging assemblage.

Acknowledgments

We acknowledge the field and laboratory assistance of the following individuals: A. Boyd, D. Roeder, D. Marsh and S. Parrish. Thanks to the Boulware family for use of the Head-of-the-River Ranch and for their scholarship which partially funded this research. We also thank the staff of the U.S. Fish and Wildlife Service, San Bernard National Wildlife Refuge for their assistance in collecting Sedge Wrens.

Literature Cited

American Ornithologists' Union. 1983. Check-list of North American Birds, 6th Edition. Allen Press, Inc., Lawrence, Kansas, xxix + 877 pp.

Christidis, L. 1985. A rapid procedure for obtaining chromosome preparations in birds. Auk, 102:892-893.

De Boer, L. E. M. 1984. New developments in vertebrate cytotaxonomy VIII. A current list of references on avian karyology. Genetica, 65:3-37.

De Lucca, E. J. & L. Chamma. 1977. Estudo do complemento cromosomico de 11 especies de aves das Ordens Columbiformes, Passeriformes e Tinamiformes. Rev. Bras. de Pesquisas Med. e Biol., 10:97-105.

Hafner, J. C. & D. R. Sandquist. 1989. Post mortem field preparation of bird and mammal chromosomes: an evaluation involving the pocket gopher, Thomomys bottae. Southw. Nat., 34(3):330-337.

Mayr, E. & L. L. Short. 1970. Species Taxa of North American Birds. Publ. No. 9, Nuttall Ornith. Club., Cambridge, Mass.

Morony, J. J., Q. J. Bock & J. Farrand. 1975. Reference list of the birds of the world. American Museum of Natural History, New York.

Ryttman, H., H. Tegelstrom & H. Jansson. 1979. G- and C-banding in four related Larus species (Aves). Hereditas, 91:143-148.

Ryttman, H. & H. Tegelstrom. 1981. G-banded karyotypes of three Galliformes species, Domestic Fowl (Gallus domesticus), Quail (Coturnix coturnix japonica), and Turkey (Meleagris gallopavo). Hereditas, 94:165-170.

Shields, G. F. 1980. Avian cytogenetics: New methodology and comparative results. Proc. XVIII Intern. Ornith. Cong., 1978:1226-1231.

Shields, G. F. 1983. Bird chromosomes. Pp. 189-209, in Current Ornithology Vol. 1 (Richard F. Johnston, ed.), New York, Plenum Press.

Shields, G. F. 1985. Organization of the avian genome. Pp. 271-290, in Perspectives in Ornithology (A. H. Brush and G. A. Clark, Jr., ed.), Cambridge University, New York.

Stock, A. D., F. E. Arrighi & K. Stefos. 1974. Chromosome homology in birds; banding patterns of the chromosomes of domestic chicken, ring-necked dove, and domestic pigeon. Cytogenet. Cell Genet., 13:410-418.

Sibley, C. G. & B. L. Monroe, Jr. 1990. Distribution and taxonomy of birds of the world. Yale Univ. Press, New Haven, Conn. xxiv + 1111 pp.

Takagi, N. & M. Sasaki. 1974. A phylogenetic study of bird karyotypes. Chromosoma, 46:91-120.

Tegelstrom, H. & H. Ryttman. 1981. Chromosomes in birds (Aves): evolutionary implications of macro- and microchromosome numbers and lengths. Hereditas, 94:225-233.

Udagawa, T. 1956. Karyogram studies in birds VIII. The chromosomes of some species of the Turdidae and Troglodytidae. Jap. Jour. of Zool. 12:105-111.

*Shamone M. Minzenmayer, Terry C. Maxwell and Robert C. Dowler

Department of Biology, Angelo State University, San Angelo, Texas 76909

*Present address: Department of Wildlife and Fisheries Sciences, Texas A & M University, College Station, Texas 77843
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Author:Minzenmayer, Shamone M.; Maxwell, Terry C.; Dowler, Robert C.
Publication:The Texas Journal of Science
Geographic Code:100NA
Date:Nov 1, 1995
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