Oryzomys nitidus (Thomas, 1884)

PATTON, JAMES L., DA SILVA, MARIA NAZARETH F. & MALCOLM, JAY R., 2000, Mammals Of The Rio Juruá And The Evolutionary And Ecological Diversification Of Amazonia, Bulletin of the American Museum of Natural History 2000 (244), pp. 1-306 : 160

Oryzomys nitidus (Thomas, 1884)

TYPE LOCALITY: Valley of Río Tulumayo, 10 km south of San Ramón, Amable María, 2000 ft, Departamento de Junín, Perú (as located by Gardner and Patton, 1976).

DESCRIPTION: See above, figures 95 and 96, and tables 38 and 40.

SELECTED MEASUREMENTS: See table 39.

DISTRIBUTION AND HABITAT: This species is widely distributed through the western margins of Amazonia, from Perú south through Bolivia, western and south­central Brazil, eastern Paraguay, and northeastern Argentina (Musser et al., 1998). As noted by these authors, O. nitidus is apparently absent from the ‘‘vast core of the Amazon Basin’’ (p. 187). In our survey of the Rio Jurua´, we obtained specimens of this species only in terra firme forest and at only one locality, Igarapé Porongaba (locality 1) in the Headwaters Region. The six specimens collected were all taken in Sherman traps set on the ground. At this locality, O. nitidus was sympatric with both O. perenensis and O. yunganus .

REPRODUCTION: We captured specimens only during the month of February. Three adult males had scrotal testes and enlarged vesicular glands (16 to 17 mm long) indicative of reproductive activity. Of the two adult females, one was pregnant with 5 embryos and the second was parous but neither pregnant nor lactating. A single nonreproductive young female (age class 1) was in sparse reddish juvenile pelage.

KARYOTYPE: 2n = 80, FN = 86. The chromosomal complements from two males ( MNFS 1147 and 1419) and two females ( MNFS 1223 and 1420) are identical to each other and the same as those reported by Gardner and Patton (1976) for samples from several localities in eastern Peru´. The autosomes consist of 35 pairs of acrocentrics, one distinctly large and the remainder graded from large to small, and four pairs of small metacentrics ; the sex chromosomes are a large subtelocentric X and a small acrocentric Y.

SPECIMENS EXAMINED (n = 6): (1) 3 m, 3 f — MNFS 1147, 1208, 1223, 1310, 1419– 1420.