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Aberrant pelage coloration in Sigmodon from Texas.

Aberrant pelage coloration is not a commonly reported phenomenon in the hispid cotton rat, Sigmodon hispidus. Accounts in the literature on white S. hispidus in the wild are restricted to albino specimens. Gardner (1948) reported two albino juvenile males from Brooks County, Georgia, and Sherman (1951) reported an albino taken near Tampa, Florida. Dowler and Engstrom (1979) reported an adult female albino from Russell County, Kansas. Sherman (1951) also reported an unusually dark animal that was captured near Tampa.

In contrast, there are no published records of albinism among captive-reared S. hispidus. All reports of white S. hispidus from captive populations have been of nonalbino animals, generally with some tan in the pelage. Danforth and Schwentker (1949) reported on two white or predominantly white S. hispidus resulting from spontaneous mutations. Tan mutants also have been described from among captive animals (McWhirter et al., 1974).

On 16 April 1987, a predominantly white, subadult S. hispidus (Fig. 1) was captured in an old pile of boards located 6.5 km. S, 4.05 km. E College Station Post Office (about 20 meters SE off Graham Rd, 640 meters from intersection with FM 2154), 30[degrees]33'28"N, 96[degrees]16'40"E, 97 m., Brazos County. The specimen was deposited (no. 48863) in the Texas Cooperative Wildlife Collections (TCWC) of Texas A & M University. External measurements (mm) are: total length, 120; length of tail, 49; length of hind foot, 18; length of pinna, 12; weight 12 grams; testes, 3 X 5. We observed at least five other subadult animals of the same species in the board pile, and captured one. All were of the standard grizzled brown pelage type common in the College Station area.

Examination of S. hispidus in the TCWC revealed one additional specimen (TCWC 48864) with aberrant coloration (Fig. 1). This specimen, an adult female obtained on 10 November 1984 from 3.5 mi. W College Station, 350 ft., Brazos County, does not show white color to the extent as in the subadult specimen reported here (Fig. 1).


Our report of a nonalbino white S. hispidus is all the more unusual when one considers the scarcity of males among the reported color mutants of this species. Those described by Danforth and Schwentker (1949) both were females; sexes of the offspring were not stated. Based on presence of the mutation in two females, Danforth and Schwentker (1949) postulated that it was not sex-linked. From the resemblance of our specimen to specimens illustrated in Danforth and Schwentker, we suspect that the same type of mutation may be involved.

Among specimens of Sigmodon ochrognathus in the TCWC, one (TCWC 6197; Fig. 1) shows less extensive expression of a phenotype similar to that of our specimen of S. hispidus. This specimen is a female (with four fetuses) that was captured on 26 July 1956 at Grapevine Spring, Chisos Quad., 3000 ft., Brewster County. Measurements (mm) are as follows: total length, 250; tail length, 114; length of hind foot, 31; length of pinna 14; weight 88.5 grams. Findley and Jones (1960) reported various shades in different populations of S. ochrognathus, but all individuals were uniformly colored.

Average litter sizes in S. hispidus have been reported to range from 4.75 in Louisiana to 5.9 from Oklahoma (Svihla, 1929; Meyer and Meyer, 1944; Goertz, 1965; Kirkpatrick, 1965). The average litter size reported for white mutant specimens is 5.25 (N = 8, range one to eight--Danforth and Schwentker, 1949), which falls well within the reported range for the species. Dowler and Engstrom (1979) reported that although their albino specimen had an unusually larger litter, this phenomenon probably was correlated with latitude rather than any other factor. Average litter size in S. ochrognathus has been reported as 3.6 (range three to five--Baccus, 1971). The specimen of S. ochrognathus in the TCWC falls within this range, suggesting no negative correlation between litter size and pelage color.

The unusual coloration of the subadult S. hispidus did not appear to be associated with any chromosomal abnormality, as its karyotype was normal in all respects. The rarity of nonalbino white S. hispidus in the wild warrants further investigation to clarify the phenomenon, in particular given that both aberrantly colored Sigmodon hispidus were collected in the same vicinity.

We thank I. F. Greenbaum for a thorough review of a previous version of this manuscript.


Baccus, J. 1971. The influence of a return of native grasslands upon the ecology and distribution of small rodents in Big Bend National Park. Unpublished Ph.D. dissertation, North Texas State Univ., Denton, 114 pp.

Danforth, C. H., and V. Schwentker. 1949. Snowball: a repeated mutation in the cotton rat. J. Hered., 40:252-256.

Dowler, R. C., and M. D. Engstrom. 1979. Albinism and large litter size in a cotton rat (Sigmodon hispidus) from Kansas. Trans. Kansas Acad. Sci., 81:375-376.

Findley, J. S., and C. J. Jones. 1960. Geographic variation in the yellow nosed cotton rat. J. Mamm., 41:462-469.

Gardner, M. C. 1948. Albino cotton rats. J. Mamm., 29:185.

Goertz, J. W. 1965. Reproductive variation in cotton rats. Amer. Midland Nat., 74:329-340.

Kirkpatrick, R. D. 1965. Litter size and fetus numbers in the cotton rat. J. Mamm., 46:514.

McWhirter, D. W., P. L. Dalby, and J. H. Asher, Jr. 1974. A new mutant in the yellow-bellied cotton rat. J. Hered., 65:316-319.

Meyer, B. J., and R. K. Meyer. 1944. Growth and reproduction of the cotton rat, Sigmodon hispidus hispidus, under laboratory conditions. J. Mamm., 25:107-129.

Sherman, H. B. 1951. Abberant color phases of the cotton rat, Sigmodon. J. Mamm., 32:217.

Svihla, A. 1929. Life history notes on Sigmodon hispidus hispidus. J. Mamm., 10:352-359.


Department of Wildlife and Fisheries Sciences, Texas A & M University, College Station, Texas 77843-2258
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Title Annotation:GENERAL NOTES
Author:Ruedas, Luis A.; Noel, Joni
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:Nov 1, 1991
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