Mammalia 72 (2008): 35–43  2008 by Walter de Gruyter • Berlin • New York. DOI 10.1515/MAMM.2008.009 Article in press - uncorrected proof 2007/9 Hair structure of small rodents from central Argentina: A tool for species identification Regino Cavia 1,2, *, Analı ´a Andrade 2 , Martı´n E. Zamero 1 , Marı´a S. Ferna ´ ndez 1,2 , Emiliano Muschetto 1,2 , Gerardo R. Cueto 1 and Olga V. Sua ´ rez 1,2 1 Departamento de Ecologı´a, Gene ´ tica y Evolucio ´ n, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina, e-mail: rcavia@ege.fcen.uba.ar 2 Concejo Nacional de Investigaciones Cientı´ficas y Tecnolo ´ gicas, Argentina *Corresponding author Abstract Mammal hairs differ among species and may therefore be used for diagnoses at the species level. We charac- terized dorsal guard hairs of most small rodent species that may be found in central Buenos Aires province (Argentina), according to their geographic distribution: Cavia aperea, Rattus rattus, R. norvegicus, Mus muscu- lus, Holochilus brasiliensis, Scapteromys aquaticus, Oxy- mycterus rufus, Oligoryzomys flavescens, Akodon azarae, Deltamys kempi, Calomys laucha and C. musculinus. We provide discriminant functions and a dichotomic key to identify hairs at the species level based on hair length and width and scale morphology observed in specific sections of dorsal guard hairs. Discriminant functions require fewer measurements and are faster than the use of the key. Keywords: hair cuticle; hair medulla; hair structure; identification key; rodents. Introduction The aim of this paper is to characterize the dorsal guard hairs of most small rodents from the central Buenos Aires province as a tool for species identification. Mammal hair structure presents characters that differ among species and may therefore be used for diagnoses at species level (Day 1966, Gurini 1985). Hair morphology is especially useful to identifying predator pellets, pelt remains found in burrows (Day 1966) and monitoring fau- na by means of hair tube surveys (Dickman 1986, Gurnell et al. 2001, 2004, Sanecki and Green 2005). A previous study conducted in Argentina found no differences in the pattern of cuticle scales among some rodent species from Buenos Aires province (Piantanida and Petriella 1976). However, a more recent study developed an iden- tification key for 11 species of rodents and 1 marsupial from Buenos Aires province, using both cuticle patterns and medulla types of guard hairs (Busch 1986). Chehe ´- bar and Martı´n (1989) proposed a hair key for the iden- tification of Patagonian mammals. Gurini (1985) developed a key to identify mammal species from the Delta of the Parana ´ River in Buenos Aires province based on the general shape of guard hairs, cuticle patterns and types of medulla, and the presence of grooves. None of the previous studies included all the species which are likely to be found in the area covered by this study. Gurini (1985) did not include Calomys species; Busch (1986) did not include Rattus spp., Scapteromys aquaticus Thomas 1920 and Deltamys kempi Thomas 1917. Day (1966) and Ferna ´ ndez and Rossi (1998) consid- ered two hair types: guard and fine hairs, while Gurini (1985) also recognized a third type: the intermediate hairs. Moreover, there are a variety of specialized hairs that occur only in some groups. Guard hairs are longer, thicker and less flexible than fine hairs. Fine hairs often present constrictions and these are absent in guard hairs. Guard hairs frequently show grooves on their dorsal face, ventral face or both. Intermediate hairs are similar to guard hairs in their distal portion, whereas the proximal section is more similar to fine hairs (Gurini 1985). Mammal hair has four structural components: (1) the cuticle (epidermicula) or outside cover, with scales; (2) the cortex or inner sheath, with strongly keratinized cells disposed lengthwise; (3) the medulla or central region with groups of keratinized cells or their skeletons, with intercellular spaces that may be filled with air; and (4) pigment granules located in the cortex and medulla (Meyer et al. 2002). These hair components show differ- ences among species and may be used for species iden- tification; however, only the morphology of guard hairs varies consistently among species (Dearbon 1939, Day 1966, Gurini 1985, Ferna ´ ndez and Rossi 1998, Meyer et al. 2002). Materials and methods The study includes most small rodent species that may be found in central Buenos Aires province (Galliari et al. 1991, Figure 1): the caviid Cavia aperea Erxleben 1777; the introduced murines (Family Muridae, Subfamily Muri- nae) Rattus rattus (Linnaeus 1758), Rattus norvegicus (Berkenhout 1769) and Mus musculus Linnaeus 1758; and the native sigmodontines (Family Cricetidae, Sub- family Sigmodontinae) Holochilus brasiliensis (Desmarest 1819), S. aquaticus Thomas1920, Oxymycterus rufus (Fischer 1814), Oligoryzomys flavescens (Waterhouse 1837), Akodon azarae (Fischer 1829), D. kempi Thomas 1917, Calomys laucha (Fischer 1814) and Calomys mus- culinus (Thomas 1913). C. laucha and C. musculinus were considered at genus level, because there were not enough specimens identified at species level in the con- sulted collections. Brought to you by | Penn State - The Pennsylvania State University Authenticated | 128.118.88.48 Download Date | 5/31/13 12:37 AM