Heteromys, IN, DESMARESTIANUS, 1817

Anderson, Robert P. & Timm, Robert M., 2006, A New Montane Species of Spiny Pocket Mouse (Rodentia: Heteromyidae: Heteromys) from Northwestern Costa Rica, American Museum Novitates 3509 (1), pp. 1-39 : 23-25

TAXONOMIC NOTES ON OTHER HETEROMYS IN COSTA RICA

HETEROMYS ORESTERUS : Our examinations indicate that Heteromys oresterus is known definitively from only three localities in the western portion of the Cordillera de Talamanca in central Costa Rica (fig. 10; appendix 2). In the original description, Harris (1932) named H. oresterus from El Copey de Dota, 6000 ft [1829 m] in the Provincia de San José [9 ° 399N, 83 ° 559W, McPherson, 1985]. In addition to the holotype, he made reference to eight other adult topotypes. The full series collected by Austin Smith in 1931 includes those nine adults plus one juvenal specimen (UMMZ 64026–64034, 66478) collected at elevations ranging from 6000 to 6500 ft [1829–1981 m]. In 1933, Smith obtained another specimen (UMMZ 67306) from a nearby locality on the Caribbean side of the continental divide in the Provincia de Cartago: El Muñeco, Río Navarro, 10 mi S of Cartago, 4300 ft [1311 m; 9 ° 489N, 83 ° 539W, McPherson, 1985]. A half century later, Duke S. Rogers and colleagues collected additional specimens in 1981 and 1982 from the Provincia de San Jose´: 2.2 km E (by road) La Trinidad de Dota, 2600 m [9 ° 409N, 83 ° 529W, IGCR, 1963; MVZ 164860–164864, 165786; Mascarello and Rogers, 1988; Rogers, 1989, 1990; Rogers and Rogers, 1992]. We have examined the specimens from these three localities and concur that they all represent H. oresterus (appendix 2; see also figs. 7, 10).

However, other specimens from the Provincia de San José reported in the literature as Heteromys oresterus do not represent that species, but rather individuals of the H. desmarestianus species complex (fig. 10; appendix 2). These include a series collected by Alfred L. Gardner in 1967 from Fila la Máquina, ca. 7.5 km E El Canaan, 8700 ft [2652 m; 9 ° 289N, 83 ° 349W; McPherson, 1985; LSUMZ 13132–13138] considered to be H. oresterus by McPherson (1985) and Rogers and Rogers (1992). Furthermore, we tentatively reidentify a single specimen collected by R.M.T. in 1986 from 4 km S, 2 km E Ojo de Agua, 2535 m [9 ° 359N, 83 ° 489W; Ashe and Timm, 1987a; FMNH 128459] reported as H. oresterus by Rogers and Rogers (1992). These specimens lack the narrow (and dorsally flared) rostrum of H. oresterus and have a wider interorbital constriction than that species (fig. 7).

The subgeneric placement of Heteromys oresterus remains controversial and unclear. Only two subgenera ( Heteromys and Xylomys ) have been proposed for the genus Heteromys . Xylomys was initially described by Merriam (1902) for the distinctive species H. nelsoni (which is the largest in the genus and shows extremely soft dorsal pelage). Goldman (1911) listed several additional cranial characters that appeared to distinguish Xylomys based on the material available at the time. Subsequently, Hall and Kelson (1959) and Hall (1981) considered H. oresterus a member of the subgenus Xylomys . However, more recent work has shown that the only morphological character that unites H. nelsoni and H. oresterus is their possession of soft dorsal pelage (Rogers, 1986; Rogers and Rogers, 1992; see Homan and Genoways [1978] for morphology of heteromyid hair). Unfortunately, spininess often varies clinally with elevation within a species of Heteromys — spinier in the lowlands and softer at higher elevations ( Anderson, 1999: 619, 2003b: 23, 26; Anderson and Jarrín-V., 2002: 12). Hence, we agree with Rogers (1986) and Rogers and Rogers (1992) in doubting the taxonomic utility of this character. No modern phylogenetic study of heteromyines has succeeded in determining the evolutionary relationships of the species of Heteromys , but morphological, karyological, and genetic data suggest that H. oresterus is probably more closely related to members of the H. desmarestianus species complex than to H. nelsoni (Rogers, 1986: 186–191, 1989, 1990; Mascarello and Rogers, 1988). We conclude that recognition of defensible subgenera in Heteromys awaits the results of future phylogenetic analyses.

HETEROMYS DESMARESTIANUS SPECIES COMPLEX: Even after recognizing Heteromys nubicolens as a distinct species, H. desmarestianus remains a confusing complex of morphologically similar species that range from Mexico to Colombia and vary widely in karyology and protein allozymes. Except for H. gaumeri (2n 5 56) and H. nelsoni (2n 5 42), all Heteromys with known karyotypes have a diploid number of 2n 5 60 ( Engstrom et al., 1987; Rogers, 1989); however, the species with a diploid number of 2n 5 60 vary widely in fundamental number (FN). At least nine karyotypic forms exist within the H. desmarestianus species complex (including H. goldmani and a sample of ‘‘ Heteromys sp. ’’ from near Ciudad Nielly in southwestern Costa Rica; Mascarello and Rogers, 1988; Rogers, 1989; see also Genoways, 1973: 298; Burton et al., 1987; Engstrom et al., 1987). Four standard karyotypes are known from populations of Heteromys in Costa Rica (fig. 10; appendices 1, 2). The cytotype F of Rogers (1989) has a FN 5 86 and was found for individuals from the Provincia de Puntarenas: Monteverde, John Campbell’s woods (appendix 1) that represent the species now known as H. nubicolens . Cytotype F also was encountered in populations of the H. desmarestianus species complex from the Provincia de Guanacaste: 4.1– 5 km NE (by road) Tilarán, 650 m (appendix 1) in northwestern Costa Rica and from the Provincia de Limón: 4.6 km W (by road) Limón, 25 m [9 ° 599N, 83 ° 049W, IGN, 1978] in southeastern Costa Rica (Rogers, 1989). The second variant, cytotype G of Rogers (1989), corresponds to samples of the H. desmarestianus species complex from the Provincia de Cartago: Río Reventazón, 5.6 km SE (by road) Turrialba, 450 m [9 ° 539N, 83 ° 399W, IGN, 1981] in southeastern Costa Rica, and it displays a FN 5 80. Individuals of the H. desmarestianus species complex ( Heteromys sp. of Rogers, 1989) from the Provincia de Puntarenas: 1.1 km SE (by road) Ciudad Nielly, 25 m [8 ° 399N, 82 ° 579W, IGN, 1980] in southwestern Costa Rica constitute the third moiety and show a FN 5 90 (Rogers, 1989). By comparison, the karyotype of H. oresterus from the Provincia de San Jose´: 2.2 km E (by road) La Trinidad de Dota, 2600 m (see above) in central Costa Rica has a FN 5 78 (Rogers, 1989). In addition to these differences in fundamental number, individuals of the H. desmarestianus species complex from near Ciudad Nielly and from near Tilarán (see above) also differed strongly in karyological banding patterns ( Mascarello and Rogers, 1988; Rogers, 1989). While karyological data alone cannot be used to elucidate species boundaries accurately (note similarity in standard karyotype between H. nubicolens and some populations of the H. desmarestianus species complex), these data reflect substantial cytogenetic discontinuities within the H. desmarestianus species complex.

Members of the Heteromys desmarestianus species complex also show extensive variation in protein allozymes (Rogers, 1990; based on many of the same individuals as the karyological studies cited above; fig. 10; appendices 1, 2). Two samples from southwestern Costa Rica referred to as Heteromys sp. showed a strong divergence in allozymes from other samples of the H. desmarestianus species complex: Provincia de Puntarenas: 1.1 km SE (by road) Ciudad Nielly, 25 m (see above; locality 16 of Rogers, 1990); Provincia de San Jose´: 16.3 km SE (by road) San Isidro, 525 m [9 ° 159N, 83 ° 389W, IGN, 1970; locality 17 of Rogers, 1990]. These two samples were most similar to a sample of two individuals from eastern Panama in the Provincia del Darién: ca. 6 km NW Cana, E. slope Cerro Pirre, 1400 m [7 ° 519N, 77 ° 449W, Fairchild and Handley, 1966; locality 26 of Rogers, 1990; there considered H. australis ]. These specimens from Panama represent a member of the H. desmarestianus species complex and were considered H. d. crassirostris by Anderson (1999). A single specimen from a slightly lower elevation (Provincia del Darién: ca. 6 km NW Cana, E. slope Cerro Pirre, 1200 m; locality 27 of Rogers, 1990; there considered H. anomalus ) represents true H. australis ( Anderson, 1999) . Several species-level taxa described based on material from Costa Rica and Panama currently are considered synonyms of H. desmarestianus ( Goodwin, 1946; Williams et al., 1993). Detailed specimenbased revisionary studies of alpha-level taxonomy are necessary to determine the true species limits in the H. desmarestianus species complex in central and eastern Costa Rica (and throughout Panama), clarify the synonymy of named forms, and determine the nomenclatural status of the species found near Ciudad Nielly and San Isidro.