www.elsevier.de/mambio Short communication Genetic comparisons between Heteromys desmarestianus and the recently described H. nubicolens (Rodentia: Heteromyidae) in northwestern Costa Rica By R.P. Anderson and S.A. Jansa Department of Biology, City College of the City University of New York, New York, USA; Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History, New York, USA; and Department of Ecology, Evolution, and Behavior and Bell Museum of Natural History, University of Minnesota, St. Paul, USA Receipt of Ms. 9.11.2005 Acceptance of Ms. 2.4.2006 Key words: Heteromys, Costa Rica, cytochrome b, hybrid, spiny pocket mice The subfamily Heteromyinae (spiny pocket mice) represents a well-defined monophyletic group within the rodent family Heteromyidae (Hafner 1981; Hafner and Hafner 1983; Wahlert 1991). Two extant genera, Hetero- mys and Liomys, are recognized in the Heteromyinae. Species of Heteromys inhabit wet (typically evergreen) forests from south- ern Mexico to western Ecuador (Williams et al. 1993). Present taxonomy recognizes nine species of the genus, including H. nubicolens, a species recently described from northwestern Costa Rica (Patton 2005; An- derson and Timm 2006; see also Williams et al. 1993; Anderson and Jarrı´n-V. 2002; Anderson 2003). Anderson and Timm (2006) provided detailed morphological compari- sons between H. nubicolens and adjacent populations of H. desmarestianus (with which H. nubicolens was previously confused) and summarized available information regarding the natural history and biogeography of the new species (see also McCain 2004, 2006). Here, we undertake genetic comparisons between H. nubicolens and adjacent popula- tions of H. desmarestianus, also including available DNA sequences from other parts of the range of H. desmarestianus. Furthermore, we examine samples from two individuals from the contact zone between H. nubicolens and H. desmarestianus that are morphologi- cally intermediate and may represent hybrids between the two species. Two mountain ranges lie within northwestern Costa Rica, each oriented diagonally from southeast to northwest (Fig. 1; Castillo-M. 1984; Bergoeing 1998). To the west of the larger Cordillera Central de Costa Rica, a range of Tertiary volcanic peaks (o 2000 m) and ridges forms the Cordillera de Tilara´n, which is continuous at an elevation of ca. 1200 m. To the northwest of that range, the Cordillera de Guanacaste is comprised of a series of isolated Quaternary volcanoes, most of which reach 1500–2000 m. Low passes between most of the volcanoes of the Cordillera de Guanacaste connect the Car- ibbean and Pacific lowlands at elevations of 500–700 m. The two species of Heteromys present in northwestern Costa Rica show clear ecogeo- graphic patterns in their distributions (Fig. 1; Anderson and Timm 2006). In this region, H. desmarestianus occurs throughout the wet Caribbean lowlands, as well as at middle elevations on the Caribbean and Pacific ARTICLE IN PRESS 1616-5047/$ - see front matter r 2006 Published by Elsevier GmbH on behalf of Deutsche Gesellschaft fu ¨r Sa ¨ugetierkunde. doi:10.1016/j.mambio.2006.04.003 Mamm. biol. 72 (2007) 1 Á 54–61