Chapter 3 Review of the Oryzomys couesi Complex (Rodentia: Cricetidae: Sigmodontinae) in Western Mexico MICHAEL D. CARLETON1 AND JOAQUIN ARROYO-CABRALES2 ABSTRACT The status and distribution of eight species-group taxa of the Oryzomys couesi group (Rodentia: Cricetidae: Sigmodontinae) described from western Mexico are evaluated based on morphological and morphometric comparisons. Four of these are recognized as valid species within the region: Oryzomys albiventer Merriam, 1901 (including molestus Elliot, 1903), from inland plateau of the Mesa de Ana´huac; O. couesi mexicanus J.A. Allen, 1897 (including bulleri J.A. Allen, 1897; lambi Burt, 1934; rufus Merriam, 1901), from Pacific coastal plain, contiguous lower mountain slopes, and interior valleys along the Rı´os Tepalcatepec–Balsas; O. nelsoni Merriam, 1898, from Isla Marı´a Madre; and O. peninsulae Thomas, 1897, from the southern tip of the Baja California Peninsula. Three other taxa named from uplands in interior Mexico— aztecus Merriam, 1901; crinitus Merriam; 1901; and regillus Goldman, 1915—are provisionally retained within O. couesi, but further study of their specific stature and relationships is required. The recommended taxonomic changes within western Mexico serve to discuss directions for future revisionary research that will refine the definition and distribution of O. couesi sensu stricto in Middle America. INTRODUCTION the nominotypical species and six geograph- ically isolated specific allies within Middle North and Middle American populations America (i.e., O. antillarum, O. cozulmelae, of the Oryzomys palustris group (sensu O. fulgens, O. gatunensis, O. nelsoni, and O. Merriam, 1901; Goldman, 1918) have been peninsulae). Goldman’s specific classification allocated to as many as 18 species (Merriam, was essentially maintained through the mid- 1901) or to as few as three (Hall, 1981). The dle 1900s (Miller and Kellogg, 1955; Hall and systematic contributions of Goldman (1918) Kelson, 1959). Subsequently, Hall (1960) and Hall (1960) have played historically influential roles in reversing the early view considered couesi to be synonymous with O. of specific diversity within the O. palustris palustris based on perceived intergradation of group. In his revision of the genus, Goldman populations along coastal Texas in certain (1918), perhaps emulating the revisionary cranial and chromatic traits. Although ar- model of Peromyscus as set forth by his gued within a very localized geographic colleague Osgood (1909), demoted many of context, Hall swept all of Goldman’s (1918) Merriam’s species to intergrading geographic subspecies of couesi, including those in races of the widely ranging, polytypic forms western Mexico and Central America, under O. couesi and O. palustris. Within the O. his expansive definition of O. palustris. His palustris group, Goldman designated two action set a broad-brushed precedent for sections, the O. palustris section, which assessing and taxonomically conveying mor- contained the single North American species, phological variation among populations and the O. couesi section, which contained of the Oryzomys palustris group. Soon 1 Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560- 0111 ([email protected]). 2 Laboratorio de Arqueozoologı´a ‘‘M. en C. Ticul A´lvarez Solo´rzano,’’ Subdireccio´n de Laboratorios y Apoyo Acade´mico, INAH, Moneda # 16, Col. Centro, 06060 Me´xico, D. F., Me´xico ([email protected]). 94 2009 CARLETON AND ARROYO-CABRALES: ORYZOMYS COUESI COMPLEX 95 afterward, other Middle American forms addition, we discuss possible systematic af- retained as species by Goldman (1918) or finities of other taxa named from uplands in Hall and Kelson (1959) were pro forma interior Mexico—O. c. regillus (Michoaca´n), brought into O. palustris as well (cozumelae O. c. aztecus (Morelos), and O. c. crinitus by Jones and Lawlor 1965; azuerensis and (Distrito Federal). gatunensis by Handley, 1966; fulgens, nelsoni, and peninsulae by Hershkovitz, 1971; antil- larum by Hall, 1981). MATERIALS AND METHODS Judged against today’s standards of sys- Specimens that form the basis of this tematic documentation, presentation of data report principally consist of skins with their and analysis to support these sweeping associated skulls and are contained in the taxonomic changes has been at best perfunc- following institutional and museum collec- tory, at worst nonexistent. Reexaminations tions (abbreviation in parentheses): American of the purported zone of intergradation Museum of Natural History, New York between couesi (aquaticus) and O. palustris (AMNH); Carnegie Museum of Natural (texensis) in Texas tellingly exposed the History, Pittsburgh (CM); Dickey Collection, fragile underpinnings of such an inclusive University of California, Los Angeles definition of O. palustris (Benson and Gehl- (UCLA); Museum of Natural History, Uni- bach, 1979; Schmidt and Engstrom, 1994). versity of Kansas, Lawrence (KU); Field As a result of these regional studies, O. couesi Museum of Natural History, Chicago (Alston) was resurrected as a species distinct (FMNH); National Museum of Natural from North American O. palustris (Harlan), History, Smithsonian Institution, Washing- but most other Middle American taxa have ton, D.C. (USNM, formerly the U.S. Na- remained as synonyms of a broadly ranging O. couesi (e.g., Honacki et al., 1982; Corbet tional Museum); the Natural History Muse- and Hill, 1991; Musser and Carleton, 1993, um, London (BMNH, formerly the British 2005), an arrangement based on classificatory Museum of Natural History), and the Uni- inertia rather than on actual documentation versity of Michigan Museum of Zoology, of consanguinity. Ann Arbor (UMMZ). Type specimens and Herein, we review morphological and original series of most taxa described for morphometric evidence for intergradation populations of Oryzomys in western Mexico among forms of the Oryzomys couesi complex were examined firsthand, namely those of whose distribution lies in western Mexico. albiventer Merriam, 1901; aztecus Merriam, The region encloses striking topographic and 1901; bulleri Allen, 1897; crinitus Merriam, biotic diversity and accordingly has proven to 1901; mexicanus Allen, 1897; nelsoni Mer- be strategic for unraveling specific diversity in riam, 1898; peninsulae Thomas, 1897; regillus other taxonomically problematic rodent gen- Goldman, 1915; and rufus Merriam, 1901. era, such as Peromyscus (Carleton, 1977; Original topotypes of lambi Burt, 1934, were Carleton et al., 1982; Bradley et al., 1989, consulted, but we did not personally examine 1996) and Sigmodon (Zimmerman, 1970; the holotype; William T. Stanley examined Carleton et al., 1999; Peppers et al., 2002). and measured the FMNH type of molestus Eight type specimens of species-group epi- Elliot, 1903, for us. thets currently allocated to Goldman’s (1918) Approximately 600 specimens were exam- O. couesi section originate from this area (see ined (see registration numbers and full fig. 1). In particular, we address the status locality information under Taxonomic Sum- and relationships of taxonomically recog- mary) and measured, of which 284 adults nized populations of Oryzomys that occur at were grouped into 11 geographically cohesive the southernmost tip of Baja California (O. samples for univariate and multivariate couesi peninsulae), on the Tres Marı´as Islands analyses. According to current taxonomic (O. nelsoni), along coastal lowlands in Sonora understanding, these operational taxonomic (O. c. lambi) and from Sinaloa through units (OTUs), their abbreviations as em- Oaxaca (O. c. mexicanus), and on the inland ployed in figures, specific localities, and plateau region of Jalisco (O. c. albiventer). In sample sizes are recognized as follows: p-x- ; / 96 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 331 \. famb/ (^^ / \ ID \"b ^{ \ \ x^v (^ MEXICO /^^ \ 1 ^ \KX ^ \ yL^_ &. J ^ \ m ^^-^/ \ ( \^^ r \' % k& \-/ w { iJ \ 1 \ v \ ?^p*n/n#wf## r fh ^" *> I rufwa /^ ' L/ 7 /^ \ * \ y"^ <L nelsoni ® \ ^H > 3000 m o mexicanus] -v •1 2000-3000 m @e r %> 1000-2000 m I I < 1000 m Fig. 1. Type localities of 11 taxa of the Oryzomys couesi species group described from western and central Mexico and discussed in the present study. Taxa and localities include: albiventer Merriam (1901) from Ameca, Jalisco; aztecus Merriam (1901) from Yautepec, Morelos; bulleri Allen (1897) from Valle de Banderas, Nayarit; crinitus Merriam (1901) from Tlalpan, Distrito Federal; lambi Burt (1934) from San Jose´ de Guaymas, Sonora; mexicanus Allen (1897) from Tonila, Jalisco; molestus Elliot (1903) from Ocotla´n, Jalisco; nelsoni Merriam (1898) from Isla Marı´a Madre, Nayarit; peninsulae Thomas (1897) from Santa Anita, Baja California; regillus Goldman (1915) from Los Reyes, Michoaca´n; rufus Merriam (1901) from Santiago, Nayarit. Topography of Mexican sierras is indicated by 1000 m elevational bands. Oryzomys couesi albiventer: (J3) Jalisco, Oryzomys couesi peninsulae: (BC) Baja Ameca, N 5 12. California Sur, San Jose´ del Cabo, N 5 14. Oryzomys couesi mexicanus: (C1) Colima, Oryzomys nelsoni: (TM) Nayarit, Tres vicinity of Santiago, N 5 33; (C2) Colima, 5 Marı´as Islands, Isla Marı´a Madre, N 5 4. mi NW Manzanillo, N 5 20; (J1) Jalisco, Four external dimensions were transcribed localities to the N and E of Barra de from skin tags to the nearest whole millimeter Navidad, N 5 60; (J2) Jalisco, Cuitzamala, (mm): total length (TOTL); tail length (TL); N 5 20; (N1) Nayarit, 1 mi S Cuautla,