489.

Coues’s Marsh Rice Rat

Oryzomys couesi

French: Oryzomys de Coues / German: Coues-Sumpfreisratte / Spanish: Rata arrocera de marisma de Coues

Other common names: Coues'’s Oryzomys, Coues'’s Rice Rat

Taxonomy. Hesperomys couesi Alston, 1877, Coban, Alta Verapaz, Guatemala.

Oryzomys couesi was once part of a highly polytypic and now demonstrably paraphyletic O. palustris; all Mexican, Central American, and Antillean rice rats are now regarded as geographically localized species (e.g. O. albiwenter, O. antillarum, O. nelsoni, and O. peninsulae) or part of a widely distributed but also polytypic O. couesu. Sympatry between O. couesi and O. texensis in southern Texas, USA, and adjacent Tamaulipas, Mexico, has cemented reciprocal status of these two species. Nevertheless, molecular phylogeographic analyses and, to a lesser extent, limited morphological comparisons indicate that O. couesi, as construed here, comprises at least four monophyletic clades each of which is posited to represent separate species-level taxa. Two of these are widely distributed; the senior synonyms of each are mexicanus named by J. A. Allen in 1897 (distributed along the west coast of Mexico south to El Salvador) and couesi named by E. R. Alston in 1877 (distributed around the Gulf of Mexico and Caribbean from southern Texas, USA, through Mexico and Middle America into northern South America). The other two clades, currently known only from single localities (one in northern Costa Rica and a second in central Panama), lack an available name and thus would require formal description should they be raised ultimately to species status. A thorough taxonomic revision that couples molecular phylogenetic structure with morphological diagnoses remains an urgent need to define taxon and geographical limits in this group ofrice rats. This species is certainly not monotypic, but which of the 22 formal names that are currently linked to this species should be recognized as valid subspecies requires appropriate study.

Distribution. Extreme S Texas, USA, and Mexico from CW Sonora in the W and Tamaulipas in the E, but excluding the NC plateau region, S through most of Middle America to EC Panama, and an isolated record from extreme NW Colombia.

Descriptive notes. Head-body 91-144 mm,tail 102-160 mm, hindfoot 26-34 mm (west coast); head—body 98-142 mm, tail 107-152 mm, ear 13-18 mm, hindfoot 27-33 mm; weight 43-82 g (east coast). Coues’s Marsh Rice Rat is medium-sized, with upperparts buffy brown to orange-brown, peppered with black; sides are bufty to orangish; and underparts are pale buffy to whitish. Fur is coarse and shaggy looking, somewhat glistening. Ears are relatively small, partially hidden by fur, and densely lined with orangish fur. Tail is long and clearly bicolored; hindfeet are long, with whitish dorsal surfaces; and ungual tufts are present but do not extend beyond claw tips. Morphological comparisons between west and east coast clade members have not been made. Chromosomal complement is 2n = 56, FNa = 56-58. X-chromosome is geographically variable: large submetacentric in Texas or either acrocentric or subtelocentric in Mexico and Honduras.

Habitat. Marshes and wetlands, including reed beds in deep water, mangrove swamps along coasts, and riparian vegetation adjacent to small bodies of standing water and along edges of streams in tropical deciduous and semideciduous forest, temperate deciduous forest, thorn forest, and pine-oak forest from sea level to eleations of ¢.2000 m. Coues’s Marsh Rice Rat is known to be a crop pest, particularly in rice fields and sugar cane plantations.

Food and Feeding. Diet of Coues’s Marsh Rice Rat includes green plant material, seeds, fruits, insects (ants, beetles, and caterpillars), crustaceans, and small fish.

Breeding. Coues’s Marsh Rice Rats are born year-round, especially in lowland areas that lack strong seasonality. Gestation lasts 21-28 days; litters have 2-7 young (average 3-4). Sexual maturity is reached at c.7 weeks old, and life span is short, less than 20 months.

Activity patterns. Coues’s Marsh Rice Rat is primarily nocturnal, with peak activity in late evening for adults. The species is terrestrial and semi-aquatic, but it can climb well and thus can be trapped in aboveground vegetation. If disturbed at night near water, an individual will usually dive in and swim away, often pausing to rest partially submerged at a safe distance.

Movements, Home range and Social organization. Nests are built aboveground in dense grasses, shrubby vegetation, or hollow logs. Local densities can vary considerably, apparently decreasing to zero for several years and then increasing to moderate to even high densities.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Coues’s Marsh Rice Rat faces no major conservation threats, although draining of wetlands likely has negative impacts on some populations.

Bibliography. Allen (1891b, 1897b, 1910), Allen & Chapman (1897a), Alston (1877), Alvarez et al. (1984), Benson & Gehlbach (1979), Bole (1937), Burt (1934b), Carleton & Arroyo-Cabrales (2009), Castro-Arellano & Lacher (2009), Elliot (1903a, 1904c), Goldman (1912a, 1915a), Hall (1960, 1981), Hall & Dalquest (1963), Hanson et al. (2010), Linzey et al. (2016), Lopez & Medellin (2014), Merriam (1901a, 1901c), Murie (1932), Reid (2009), Sanchez-Cordero & Valadez (1989), Schmidt & Engstrom (1994), Thomas (1893b, 1898a).