Sigmodon mascotensis

Abstract: The G- and C-banded karyotypes of Sigmodon ochrognathus (2n = 52) and S. fulviventer (2n = 28, 29, 30) are presented and compared to S. hispidus (2n = 52), which we regard as representative of the ancestral chromosomal type. Sigmodon ochrognathus differs from S. hispidus only by the addition of heterochromatic short arms on eight pairs of chromosomes. Sigmodon fulviventer possesses three unique chromosomes and lacks homologous counterparts for ten chromosomes found in S. hispidus . The available cytogenetic and immunological evidence suggests that S. fulviventer represents an evolutionary lineage well removed from all other North American species. We propose that S. hispidus, S. leucotis, S. alleni, S. ochrognathus, S. arizonae , and S. mascotensis comprise a species group and that S. fulviventer should be recognized as a separate monotypic species group.

Abstract: In tropical deciduous forest along the Pacific coast in Colima, Mexico, we conducted eight-night mark-recapture studies of Sigmodon mascotensis (January 2003–2005), evaluating habitat preferences and demography. Yearly we established five grids with 100 trapping stations (one ground and one elevated trap; 24,000 trap-nights), each evaluated for 14 environmental measures. We captured 96 S. mascotensis 274 times on 10 grids, most at ground level (85.6%), with densities of 0.84–25.31 individuals/ha. Adults predominated (88.2%), sex ratio (males:females) was 1:0.74, and males were heavier. Sigmodon mascotensis co-occurred with Oryzomys couesi and Baiomys musculus more often and Heteromys pictus less often than chance expectation. For 2004, univariate analyses indicated that stations frequented had more ground cover in woody plants, forbs and grasses; less in litter and bare ground; more vegetation low and less high; lower and more open canopy; and longer distance to nearest tree. Logistic regression indicated preference for open canopy, dense low vegetation, little litter and longer distance to nearest tree. Nonparametric multiplicative regression showed occurrence likelihood decreased as litter increased and increased with increasing slope, average hits at 1 m and average distance to nearest tree. The likelihood was high with no or low canopy, as well as high canopy.

Abstract: Abstract Sigmodon mascotensis Allen, 1897 is a cricetid commonly called the west Mexican cotton rat. From 1902 to 1969, it was designated a subspecies of S. hispidus after which, based on chromosomal and cranial characteristics, S. mascotensis was returned to species status. Dorsal pelage is brown and hispid, with ventral areas being whitish. This Mexican endemic rodent breeds throughout the year and inhabits tropical deciduous forest zones of western Mexico, mainly associated with grassy habitats. It is rare in tropical deciduous forest and abundant in grasslands and croplands. It prefers locations with higher percentages of ground cover in woody plants, forbs, and grasses, and lower in litter and bare ground. Preference is for more open and lower canopies. It is important prey for some carnivores, birds, and reptiles.