Artículos

 

The karyotype of Peromyscus grandis (Rodentia: Cricetidae)

 

Cariotipo de Peromyscus grandis (Rodentia: Criceidae)

 

Nicté Ordóñez-Garza^1*, Vicki J. Swier³, John D. Hanson⁴, Cibele G. Sotero-Caio¹, and Robert D. Bradley^{1, 2}

 

¹ Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409. E-mail: nicte.ordonez-garza@ttu.edu (NO-G), cibele.caio@ttu.edu (CGS-C), robert.bradley@ttu.edu (RDB). ^*Corresponding author.

² Natural Science Research Laboratory, Museum of Texas Tech University, Lubbock, TX 79409. E-mail: robert.bradley@ttu.edu (RDB).

³ Biomedical Sciences Department, Creighton University, Omaha, NE 68178. E-mail: vicki_swier@hotmail.com (VJS).

⁴ Research Testing Laboratory 104 Garfield Dr. Building #340, Lubbock, TX 79416. E-mail: j.delton.hanson@researchandtesting.com (JDH).

 

Sometido: 23 de abril de 2013.
Revisado: 12 de septiembre de 2013.
Aceptado: 23 de octubre de 2013.

 

Abstract

Peromyscus grandis is a rodent whose distribution is restricted to the mountain ranges of central Guatemala. This note represents the first report of karyotypic data for this species. The karyotype (fundamental number = 58) closely resembles karyotypes of other species of Peromyscus.

Keywords: chromosomes, Cricetidae, endemic, karyogram, Peromyscus mexicanus group.

 

Resumen

Peromyscus grandis es un roedor cuya distribución está restricta a las montañas del centro de Guatemala. Esta nota es el primer reporte de datos cariotípicos para esta especie. El cariotipo (número fundamental = 58) resulta muy parecido al de otras especies de Peromyscus.

Palabras clave: cariograma, Cricetidae, cromosomas, endémico, grupo Peromyscus mexicanus.

 

Introduction

Many species of rodents are endemic to the highlands of Mesoamerica (i.e. species of Habromys, Microtus, Reithrodontomys, and Peromyscus- Hooper 1952; Conroy et al. 2001; Carleton et al. 2002; Dawson 2005). Although this region is considered one of the biodiversity hotspots for conservation priorities (Myers et al. 2000), basic biological information for many Mesoamerican rodents remains unknown. The P. mexicanus group is among the most speciose and ecologically diverse species group within the genus Peromyscus (Carleton 1989), and to date species limits and phylogenetic relationships among taxa within the group are not well resolved (Rogers and Engstrom 1992; Bradley et al. 2007; Ordóñez-Garza et al. 2010). Although most species within this group have been shown to exhibit extreme karyotypic conservation with few taxa varying in their (sex) chromosome composition (Smith et al. 1986; Peppers et al. 1999). Peromyscus grandis is the only species within the P. mexicanus group for which chromosomal data are unavailable. Herein, the karyotype of P. grandis is described and compared with karyotypes of other closely related species of Peromyscus.

 

Material and Methods

Sampling. Individuals of P. grandis were lived-trapped from natural populations in Reserva Chelemhá, Alta Verapaz, Guatemala, 2,090 m, coordinates 15.3859 N and -90.0062 W. Voucher specimens and tissues samples were deposited in the National Museum of Natural History, Smithsonian Institution and the Natural Science Research Laboratory, Museum of Texas Tech University and are listed in Appendix I.

Chromosome data. Karyotypes were prepared under field conditions at Reserva Chelemhá, following the standard bone marrow technique of Lee and Elder (1980) as modified by Baker et al. (2003). At least five metacentric spreads were examined and photographed per individual and the diploid (2n) and fundamental numbers of autosomal arms (FN) were determined for each individual. Karyograms were initially constructed by arranging bi-armed chromosomes based on size (largest to smallest); inferences of homology were then made using the chromosomal morphology depicted in the Committee for Standardization of Chromosomes of Peromyscus (1977) and Greenbaum et al. (1994) and were compared to karyotypes and FNs previously reported for the P. mexicanus species group (Hsu and Arrighi 1986; Smith et al. 1986; Bradley and Ensink 1987; Peppers et al. 1999).

 

Results

Karyotypic data. Karyotypes were obtained from two individuals of P. grandis from Reserva Chelemhá, Alta Verapaz, Guatemala and 16 individuals of P. mexicanus from five localities in Honduras (see Appendix I). Comparison to the standard karyotype for Peromyscus (Committee for Standardization of Chromosomes of Peromyscus 1977; Greenbaum et al. 1994) using chromosomal size as a reference, revealed that P. grandis possessed six pairs of biarmed chromosomes (presumably pairs 1, 2, 3, 9, 22, and 23), a large sub-telocentric X, and a small acrocentric Y. The remaining autosomes are acrocentric (see Fig. 1a).

 

Discussion

Although the chromosomal data depicted herein are based on standard karyotypes (non-differentially stained), many inferences can be made relative to the G-banded datasets depicted in Greenbaum et al. (1994) and those pertaining to the P. mexicanus species groups (see below). The karyotype of P. grandis (2n = 48, FN = 58) resembled that described for other members of the P. mexicanus species group (Robbins and Baker 1981; Rogers et al. 1984; Stangl and Baker 1984; Smith et al. 1986; Peppers et al. 1999) examined to date, with two exceptions. First, Bradley and Ensink (1987) reported a FN = 56 karyotype for individuals of P. m. saxatilis from El Hatillo, Honduras. The karyotype of P. m. saxatilis appears to be missing chromosomal material above the centromere in the 3^rd largest pair of chromosomes, leading Bradley and Ensink (1987) to conclude that it was acrocentric. P. grandis possesses a minute, but visible, amount of chromosomal material above the centromere on the 3^rd largest pair of chromosomes. To further examine this apparent discrepancy, we examined the karyotypes of 17 individuals of P. m. saxatilis collected from five localities in Honduras (Appendix I). All possessed a FN = 58 similar to that proposed for P. grandis. It is not known whether the FN = 56 form reported in Bradley and Ensink (1987) was a result of over contracted chromosomal material in P. m. saxatilis, population variation restricted to El Hatillo, Honduras, or if it represented a unique taxonomic character.

The second difference observed in the karyotype of P. grandis, relative to its sister taxon, P. guatemalensis (Ordóñez-Garza et al. 2010) and other members of the P. mexicanus species group involves minor differences in the morphology of the X and Y chromosomes. In P. grandis, the X chromosome, presumably is large and subtelocentric; whereas the Y chromosome is exceptionally small, acrocentric, and resembles that of P. guatemalensis, P. mexicanus, P. stirtoni, and P. zarhynchus (Rogers et al. 1984; Smith et al. 1986; Peppers et al. 1999). In general, the karyotype of P. grandis agrees with the conclusions of Smith et al. (1986) that karyotypic conservatism is consistent throughout the P. mexicanus species group as envisioned by Musser and Carleton (2005).

 

Acknowledgments

We thank R. J. Baker for advice with field karyotyping techniques. Field and collecting equipment were provided by the USGS Patuxent Wildlife Research Center at National Museum of Natural History, Smithsonian Institution (N. Woodman), Museo de Historia Natural de la Universidad de San Carlos de Guatemala, and Natural Science Research Laboratory at Museum of Texas Tech University. We thank Consejo Nacional de Areas Protegidas (CONAP) and the people of the Reserva Chelemhá for granting collecting permits. Partial funding was provided by UTMB (C. F. Fulhorst), NSRL (by J. Sowell), Walter and Judy Bulmer, Ralph P. and Mary Eckerlin, Sharon Parsons, and John O. Matson.

 

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Notas:

Editor asociado: Jesús Maldonado

Diseño gráfico editorial: Gerardo Hernández