Integrative Taxonomy, Systematics and Distribution of the Genus Eligmodontia (Rodentia, Cricetidae, Sigmodontinae) in the Temperate Monte Desert of Argentina

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Original investigation Integrative taxonomy, systematics and distribution of the genus Eligmodontia (Rodentia, Cricetidae, Sigmodontinae) in the temperate Monte Desert of Argentina

By Cecilia Lanzone, R.A. Ojeda and M.H. Gallardo Grupo de Investigaciones de la Biodiversidad, Instituto Argentino de Investigaciones de las Zonas A´ridas, CONICET, Mendoza, Argentina and Instituto de Ecologı´a y Evolucio´n, Universidad Austral de Chile, Valdivia, Chile

Receipt of Ms. 22.6.2006 Acceptance of Ms. 24.9.2006

Abstract The systematics and distribution of South American sigmodontine rodents a matter of continuous revision and debate. The silky mice, genus Eligmodontia Cuvier, 1837, are among the most specialized murid rodents endemic to South America and its diversification for desert existence is associated with the uplift of the Andes and the early development of arid landscapes. Aiming to clarify the systematics of the species of silky mice occurring in the driest portion of the temperate Monte Desert in Argentina, qualitative and quantitative external and cranial characters, cytogenetics and molecular relationships, were studied. We characterized three karyotypes of Eligmodontia; two of which are described for the first time, and allocated them to previously named species. E. moreni Thomas, 1896 (2n=52 and FN=50), E. typus Cuvier, 1837 (2n=44 and FN=44) and E. marica Thomas, 1918. The later shows the same diploid number of E. typus, but its X— chromosome is not METACENTRIC but ACROCENTRIC . A discriminant analysis of external and cranial data separates E. moreni from E. typus and E. marica. Whereas these last ones show some degree of overlap. The morphological and chromosomal differentiation of Eligmodontia is sustained by DNA distances. Phylogenetic analyses show two major clades. One formed by E. moreni, E. puerulus and E. hirtipes, sharing a high FN and a northern distribution, and THE other formed by E. typus, E. marica and E. morgani with low FN and a central-southern distribution. Two centers of diversification are proposed to explain the evolution of Eligmodontia. r 2006 Deutsche Gesellschaft fu¨r Saügetierkunde. Published by Elsevier GmbH. All rights reserved.

Key words: Eligmodontia, sigmodontines, morphometry, karyotypes, phylogeny

Introduction The evolutionary history of South American America, with about 377 species (Musser and rodents is a topic of continuous revision and Carleton 2005), differentiated as a distinct debate (Hershkovitz 1962; Steppan 1995, lineage during middle to late Miocene (Reig 1998; Smith and Patton 1999; D’ Elı´a 2003; 1986; Salazar-Bravo et al. 2001; Steppan Musser and Carleton 2005). The sigmodon- et al. 2004). Their explosive radiation con- tines are the largest rodent fauna of South fronts researchers in deﬁning their species

1616-5047/$ - see front matter r 2006 Deutsche Gesellschaft fu¨r Sa¨ugetierkunde. Published by Elsevier GmbH. All rights reserved. doi:10.1016/j.mambio.2006.09.001 Mamm. biol. 72 (2007) 5 299–312 ARTICLE IN PRESS

300 C. Lanzone et al. limits, relationships and contents of the here, we propose to clarify these issues using major tribes (D’ Elıá 2000; Steppan et al. cytogenetic, morphological and molecular- 2004). Among sigmodontines, the represen- based phylogenetic approach. tatives of the Phyllotini tribe are small-sized rodents, and primarily distributed along the arid and semiarid landscapes of the Neotro- Material and methods pical southern cone. Among these, the genus Eligmodontia F. Cuvier, 1837, has a wide- Animals were collected at eight localities along the northern-central portion of the Monte desert spread distribution, ranging from the high biome. Localities, collected individuals, coordi- Andean plateau of southern Peru, western nates and provinces are as follows: Cafayate Bolivia and scrublands of Chile, to the Puna, (n=3) 261050/651580/1660 m, Salta Province; Cam- Monte and Patagonian aridlands biomes of po Arenal-Los Nacimientos (n=19), 27108050.3’’/ Argentina. It possesses several anatomical, 66140042.7’’/ 2139 m, Salar de Pipanaco (n=5), and physiological adaptations for xeric ex- 27149016.1’’/66114034.9’’/740 m, Catamarca Pro- istence (Mares 1977; Diaz and Ojeda 1999; vince; Ischigualasto Reserve (n=3), 30105019’’/ 0 Diaz 2001). 67156 0’’/1252 m, San Juan Province; Pampa de 0 0 The taxonomy, systematics and distribution las Salinas (n=1) 32113 /66136 /420 m, San Luis 1 0 of the genus Eligmodontia is confusing since Province; Telteca Reserve, (n=12), 32 23 35.5’’/ 68102046.8’’/520 m; 33 km NE of Costa de Araujo most species characterizations are based on (n=1) 321450/681250/520 m; Reserve of Nãcunãń, few external and cranial features of few (n=27), 34102041.1’’/97154033.9’’/565 m, Mendoza specimens. Cabrera (1961) recognizes two Province (Fig. 1). Voucher specimens and tissue species, E. puerulus and E. typus. In the first samples are housed at the mammal collection of the review of the genus, Hershkovitz (1962) Instituto Argentino de Zonas Aridas (IADIZA), synonymized all forms within E. typus with CONICET, Mendoza. two subspecies: E. t. typus and E. t. puerulus. Chromosomal preparations of 71 specimens were More recently, in their account of Neotropi- obtained using the standard hypotonic technique cal mammals, Redford and Eisenberg (1992) for bone-marrow (Ford and Hamerton 1956) with small modifications. Chromosomes were stained recognized only one species: E. typus, but with Giemsa (pH=6.8). Ten metaphases spreads suggest the existence of two others. Finally, were counted for each specimen. Fundamental Braun (1993) and Musser and Carleton Number of chromosome arms (FN) followed (2005) recognize six species (E. hirtipes, Patton (1967). E. marica, E. moreni, E. morgani, E. puerulus Five external (total length, tail length, hind foot and E. typus), and four species (E. typus, length, ear length and weight) and 21 standard E. moreni, E. morgani and E. puerulus), cranial features were measured using a caliper respectively, but no diagnostic features are rounded to the nearest 0.1 mm (Sikes et al. 1997; provided in either cases. Martin et al. 2001). Only animals with completely The integration of cytogenetic, morphologi- erupted dentition were used for the analyses. The cranial features used were: condylobasal length, cal and molecular studies has contributed to least interorbital breadth, zygomatic breadth, clarify the limits among Eligmodontia species greatest length of skull, basal length, breadth of in the southern part of their distributional braincase, length of maxillary toothrow, palatal range in Patagonia (Ortells et al. 1989; Kelt length, bullar length, bullar width, length of et al. 1991; Zambelli et al. 1992; Hillyard mandible toothrow, greatest length of mandible, et al. 1997; Sikes et al. 1997; Tiranti 1997). diastema length, palatal bridge, breadth of palate 1 3 Their results have shown a high karyotypic (in M and in M ), incisive breadth, incisive and molecular divergence, but rather little foramina, nasal breadth, nasal length, and rostrum morphological differentiation between: width. Univariate and multivariate discriminant analysis (MDA) were implemented using InfoStat E. typus and E. morgani (Hillyard et al. and Statistica programs. 1997; Sikes et al. 1997). For the molecular analyses, total DNA from liver Having in mind the confusing and contra- was extracted by the standard Phenol–Chloroform dictory taxonomy, systematic relationships, method (Sambrook et al. 1989). PCR amplification and delimitation of the geographic ranges of of a 687 pb of the cyt b gene was performed using Eligmodontia in the lowland Monte Desert primers MVZ 05 and MVZ 16 (Smith and Patton ARTICLE IN PRESS

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Fig. 1. Map of Central Argentina showing the populations of Eligmodontia analyzed. 1: Cafayate, 2: Campo Arenal, 3: Pipanaco, 4: Ischigualasto, 5: Pampa de las Salinas, 6: Telteca, 7: Costa de Araujo, 8: Nãcunãń and their type localities, a: Chumbicha, b: Chilecito, c: Buenos Aires.

1993) following thermal profiles of 951C denatura- inspection. Uncorrected and Kimura two parameter tion (3 min), 501C annealing (1 min), and 721C (K2p) distances were calculated. Phylogenetic rela- extension (1 min) for 35 cycles. Negative controls tionships among Eligmodontia species were analysed were included in all experiments. The PCR using neighbour-joining (NJ), maximum parsimony products were purified with Wizard SV Gel and (MP) and maximum-likelihood (ML) in PAUP PCR clean UpSystem (Promega) and sequenced in 4.0B10 (Swofford 2002). Variable nucleotide posi- both directions. tions were equally weighted and treated as unordered Five individuals of different localities were sequenced characters. Data was subject to 1000 bootstrap (E. typus from Telteca; E. sp. with the karyotype 1 replications in the NJ and MP. MP analyses were from Campo Arenal; E. sp. with the karyotype 2 used with heuristic search with tree bisection from Campo Arenal and Telteca; E. puerulus reconnection (TBR) branch swapping and random Philippi 1896, from Abra Pampa, Jujuy) and four addition sequence. The distance used in NJ tree was Eligmodontia sequences from the GeneBank were K2p. ML parameter values were estimated in included to incorporate specimens of all recognized Modeltest 3.04 (Posada and Crandall 1998). The Eligmodontia species: E. typus (Accession Numbers: model selected by the AIC (minimum theoretical AF108692), E. morgani (NA: AF108691)andE. information criterion) was GTR+I+G (ln hirtipes (NA: AY341054; AF159289). Sequences of L=2718.5781) with the following parameters: per- related phyllotine Graomys griseoflavus (AN: centage of invariable sites =0.5369; gamma dis- AY275117), G. domorum (AN: AF159291)and tribution shape parameter =2.0428; assumed base Calomys laucha (AN: AY033190) obtained from frequencies A=0.3055, C=0.2740, G=0.1264, the GeneBank were used as outgroup species. T=0.2941; transition to transversion ratio Sequence alignment was carried out with Clustal X =9.4182, and the support for the nodes was (Thompson et al. 1997) and corroborated by eye evaluated for 100 replicates. ARTICLE IN PRESS

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Results E. typus: Externally, this species is larger than specimens with karyotype 1 and smaller than Karyotypes those with karyotype 2 (Tab. 1). The tail is Two major karyotypes differing in number longer than head and body and slightly and morphological features of chromosomes bicolored with a dark dorsal surface; not (2n=44 and 2n=52) were found. A third pencilled or with a tip of hairs less than 5 mm. karyotypic variant, coinciding with the The dorsum is brownish and darker than 2n=44-chromosome, but differing from it specimens with the karyotype 1 and the by the morphology of the X–chromosome venter has white or gray hairs at the base. was detected too. The coinciding 2n=44, The dorsum and the venter are delineated by NF=44 karyotype with that of E. typus a yellowish lateral line. Pelage around the (Ortells et al. 1989; Tiranti 1997) was found mouth is white; with a whitish patch behind in Costa de Araujo, Pampa de las Salinas, each eye. In the skull (Fig. 3a, b), the nasals Nãcunãn, and in one specimen from Telteca. are straight and the zygomatic arcs are This karyotype is characterized by a large- parallel and narrower than in those with the sized metacentric autosomal pair, whereas karyotype 2. In the anterior border of maxilla the rest of the elements are acrocentrics of the tubercule is absent or slightly developed decreasing size. The X–chromosome is a and rounded. The posterior margin of palate is straight. The maxillary foramina are large metacentric, and Y–chromosome is a 1 small submetacentric (Fig. 2a). located in the anterior half of M and larger A karyotype with 2n=44, NF=44, very than in specimens with the karyotype 2; similar to the one described for E. typus, foramen ovale present and rounded; para- but with an acrocentric X–chromosome pterygoid plate more expanded and flat than (karyotype 1) was found in all specimens in those with the karyotype 2. The petro- from Cafayate and the Salar, and in some tympanic fossa is elongated along the ante- from Campo Arenal (n=5). Although the rior edge of tympanic bullae; bullae moderately inflated with long bullar tubes. X–chromosome of this karyotype and that of 1 E. typus differ morphologically they have a M with anteromedian flexus slightly marked similar size (Fig. 2b). or absent; anterolingual style absent or A chromosome complement with 2n=52, slightly developed and mesostyle absent; no contact between labial (hypoflexus) and NF=50 (karyotype 2) was found in all 3 individuals from Ischigualasto and in some secondary lingual fold (metaflexus); M with- from Telteca (n=11), and Campo Arenal out enamel island; anteriormedian flexid (n=14). In this karyotype all autosomes are absent; posterolophid present. acrocentric and can be arranged by decreas- Eligmodontia with karyotype 1: Size small ing size. The X–chromosome is a large (Tab. 1); tail unicolored and pale, equal or acrocentric, and Y a small submetacentric sligthly larger than head and body, with no (Fig. 2c). Secondary constrictions were ob- penciled tip; hind feet smaller with hairy sole; served in pairs 3 and 7 in interstitial position dorsum light brown and greyish with white (Fig. 2c). hairs at the base; a light lateral coloration with a diffuse line; area around the mouth white; a whitish patch behind each eye. In the External and craniometrical analysis skull (Fig. 3c, d) the zygomatic arc is parallel Comparative morphology: A similar skull and narrower than in specimens with the morphology was found in specimens ascribed karyotype 2; anterior border of maxilla with to E. typus and to karyotype 1, while they are a developed and rounded tubercule; max- markedly different from specimens having the illary foramina located in the anterior half of karyotype 2. Diagnoses of major external and M1 larger than in specimens with the cranial characters of the three Eligmodontia karyotype 2; foramen ovale present and karyomorphs (E. typus, E. sp. with the rounded; parapterygoid plate more expanded karyotype 1 and with the karyotype 2) are as and flat than in those with the karyotype 2; follows: petrotympanic fossa elongated along the ARTICLE IN PRESS

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Fig. 2. Bone marrow standard Giemsa staining karyotype of (A) Eligmodontia typus from Costa de Araujo; (B) karyotype 1 from the salt basin of Pipanaco; (C) karyotype 2 from Telteca and Campo Arenal. anterior edge of tympanic bullae; bullae out enamel island; anteriormedian flexid moderately inflated with long bullar tubes. absent; posterolophid present. M1 with anteromedian flexus slightly marked Eligmodontia with the karyotype 2: Size or absent; anterolingual style absent or larger than the others. Tail longer than head slightly developed and mesostyle absent; no and body, markedly bicolored and moder- contact between labial (hypoflexus) and ately haired, with dark dorsal surface and a secondary lingual fold (metaflexus); M3 with- pencilled tip of hairs longer than 5 mm. Large ARTICLE IN PRESS

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Table 1. Descriptive statistics (mean7SD and range) for external and cranial variables (in mm) and signiﬁcant levels for Kruskal–Wallis test.

E. typus Karyotype 1 Karyotype 2 (N=26) (N=14) (N=28) VARIABLE Mean7SD Mean7SD Mean7SD P

Total length 178.70724.80 170.0078.00 185.71710.34 0,0002 (83.00–222.00) (159.00–183.00) (168.00–202.00) Tail length 94.67713.68 90.3677.38 106.3978.14 o0,0001 (72.00–110.00) (80.00–104.00) (93.00–120.00) Hind-foot length 22.0171.78 21.8771.53 24.1870.90 o0,0001 (16.00–25.00) (19.00–24.00) (22.10–26.00) Ear length 17.8372.10 17.0771.07 19.4371.27 o0,0001 (11.00–23.00) (15.00–19.00) (16.00–21.50) Weight 17.6573.65 18.3673.87 17.6373.31 0,8646 (12.50–26.86) (13.50–26.00) (12.50–24.50) Condylobasal length 21.0970.68 20.9970.61 21.9570.86 0,0004 (19.90–22.70) (20.00–22.40) (20.3–23.4) Least interorbital breadth 3.7970.17 3.8970.16 4.2270.16 o0,0001 (3.50–4.30) (3.60–4.10) (3.90–4.60) Zygomatic breadth 12.1770.39 12.1870.32 12.7470.56 0,0003 (11.20–12.90) (11.80–12.90) (11.60–13.90) Greatest length of skull 23.8570.94 23.9070.77 24.9470.84 0,0001 (21.00–25.70) (22.50–25.30) (23.30–26.40) Basal length 19.9172.07 19.1770.60 19.9970.81 0,0067 (17.30–29.50) (18–20.4) (18.20–21.30) Breadth of braincase 11.2370.26 11.3370.27 11.7370.29 o0,0001 (10.60–11.70) (10.9–11.9) (11.20–12.20) Length maxillary tooth row 3.7870.14 3.6170.14 3.9770.16 o0,0001 (3.50–4.00) (3.40–3.80) (3.70–4.30) Palatal length 11.8170.50 11.8170.38 12.2570.51 0,0059 (11.10–13.20) (11.00–12.40) (11.20–13.00) Bullar width 4.7770.14 4.7370.15 5.4070.16 o0,0001 (4.50–5.00) (4.50–5.00) (5.10–5.60) Bullar length 6.2170.31 5.4370.21 6.2770.20 o0,0001 (5.50–6.70) (5.10–5.80) (5.90–6.60) Length mandible tooth row 3.7270.13 3.5670.13 3.8970.15 o0,0001 (3.40–4.00) (3.20–3.80) (3.60–4.30) Greatest length mandible 11.8470.46 11.7070.47 12.3370.65 0,0027 (11.10–12.90) (11.00–12.60) (11.20–13.20) Diastema length 5.5570.26 5.5870.29 5.5370.35 0,8387 (5.10–6.30) (5.20–6.20) (4.90–6.10) Palatal bridge 4.9870.28 4.6970.39 5.2770.28 o0,0001 (4.40–5.80) (4.20–5.60) (4.60–6.00) Length palate in M1 3.0370.15 2.9170.15 2.9470.17 0,0220 (2.60–3.30) (2.70–3.20) (2.60–3.30) Length palate in M3 2.7270.15 2.6070.15 2.6770.18 0,0620 (2.40–3.00) (2.20–2.90) (2.40–3.10) Incisive width 1.4170.12 1.5670.10 1.5870.10 o0,0001 (1.20–1.60) (1.30–1.70) (1.40–1.80) Incisive foramina 5.0070.25 4.8370.28 4.9470.39 0,0843 (4.40–5.40) (4.40–5.30) (4.20–5.70) Nasal width 2.1270.13 2.2570.18 2.2170.14 0,0148 (1.80–2.40) (1.90–2.60) (1.90–2.50) Nasal length 9.1070.65 9.1170.47 8.9970.45 0,8159 (7.70–10.30) (8.30–10.00) (8.00–9.60) 7 Rostral width 3.7870.14 3.7670.18 3.91 0.19 0,0121 (3.60–4.20) (3.40–4.00) (3.60–4.30) ARTICLE IN PRESS

Systematics of Eligmodontia in the Monte Desert 305 hind feet with hairs. The coloration is samples. This analysis accurately assigned brownish in the dorsum and the venter is 98.6% of individuals to the corrected species white to the base of the hairs. Dorsum and in a post hoc comparison. The remaining venter are delineated by a yellowish lateral error (1.4%) is explained by a specimen line. The area around the mouth is white and misclassified as E. typus. In a step-wise has a whitish patch behind each eye. Inter- discriminant function analysis, the variables orbital region of the skull is slightly divergent which most contributed to the discrimination posteriorly and with edges angled for ap- were: least interorbital breadth, greatest proximately half its length; nasals straight up length of skull, length of maxillary tooth to the middle of their length and then row, bullar length, bullar width, breadth of expanded to their anterior margin; zygomatic palate in M1, incisive foramina and nasal arcs parallel or slightly convergent anteriorly, length. narrow and slender; deep zygomatic notch with ovate internal border; anterior border of maxilla with a developed and rounded Molecular data tubercule; posterior margin of palate Low sequence divergence in individuals hav- rounded; small maxillary foramina located ing the same karyotype, but large interkar- in the anterior half of M1; a tear shaped yotypic differences, was found. Distance foramen ovale present; pterygoid plate ex- between the 52 chromosome karyotype from panded; petrotympanic fossa narrow; bullae Telteca and Campo Arenal was 1.5% and the inflated with bullar tubes short (Fig. 3e, f). distance between E. typus (2n=44) from M1 with anteromedian flexus marked to Telteca and Rio Negro was 1%. E. typus slightly marked; anterolingual and mesostyle differed between 8.6% and 9.3% from those present; labial fold (hypoflexus) in contact with 2n=52 (uncorrected), and 9.3% and with secondary lingual fold (metaflexus); M3 10% (K2p), whereas specimens with the with enamel island; with anteriormedian karyotypes 1 and 2 were 9.6% and 11% flexid variable; condyloid process narrower (uncorrected and K2p, respectively). On the than the angular process. The presence of a contrary, the divergence between E. typus wide petrotympanic fissure (middle lacerate 2n=44 and the specimen with the karyotype foramen) and a protuberant stapedial spine 1(2n=44) was 2.4% (uncorrected) and 2.5% of auditory bulla in specimens with the (K2p). karyotype 1 and E. typus contrast with the Analyses using NJ, MP and ML retrieved a reduction of both structures in specimens monophyletic genus Eligmodontia. Specimens with the karyotype 2 (Fig. 3b, d, f). with identical karyotype are consistently Kruskal–Wallis test was not significant for grouped together (Fig. 5). All phylogenetic differences between males and females (uni- trees resulted in a similar topology, although variate analyses) in E. typus and in specimens complementaries non-resolved polytomies with the karyotype 1. Males and females with are recovered in the last two methods, which the karyotype 2 are differentiated in their involved E. hirtipes and E. morgani, respec- total length and tail length; no significant tively. Two major clades are found in the NJ differences were detected in other external or tree (Fig. 5a). One composed of species cranial variables. The three karyotypic forms mostly distributed in the north, with the showed significant differences in external and ((E. puerulus+specimens with 2n=52)+ cranial variables (Tab. 1), however, there is a E. hirtipes) relationship consistent with a great degree of overlap in measurements high support. Another clade that includes the among the three groups. MDA of external central-southern species ((E. typus+speci- and cranial measurements, showed a clear mens with karyotype 1)+E. morgani)is separation of specimens with karyotype 2 and recovered with a low support (Fig. 5a). some degree of overlap in E. typus and The data set of the MP analyses has 234 specimens with the karyotype 1 (Fig. 4). variable characters of which 163 are infor- Because of differences in sample size, prior mative. Only one most parsimonious tree probabilities were set equal to sizes of resulted from this analysis (length=405, ARTICLE IN PRESS

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Fig. 3. Ventral cranial views of species of Eligmodontia and detail of auditory bulla. (A, B) E. typus; (C, D) karyotype 1; (E, F) karyotype 2. ptf=petrotympanic fossa, wid=wide interbullar distance, nid=narrow interbullar distance, sts=stapedial spine, bt=bullar tube.

CI=0.7, RI=0.7). The close relationship specimens with the karyotype 2 are again between E. typus and that with the karyotype recovered as sister taxa, but specimens of 1 is supported by high bootstrap value, while E. hirtipes form a basal polytomy (Fig. 5b). E. morgani is joined externally to this clade The results of the ML analysis (Fig. 5c) with a lower support (63%). E. puerulus and corroborate the close relationship of ARTICLE IN PRESS

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Fig. 4. Plot of canonical discriminant analysis using all cranial and external characters in the three Eligmodontia karyotypes.

E. puerulus and specimens with karyotype 2; orno et al. 2001; Lanzone et al. unpubl. data). while E. hirtipes appears sister to this group, The intraspecific variation in these cytotypes like in the NJ tree, but with a lower support. is due to Robertsonian translocations (Ortells The clade formed by specimens with 2n=44 et al. 1989; Zambelli et al. 1992; Lanzone are again recovered, but E. morgani is joined et al. unpubl. data) which is the most at the base of the Eligmodontia tree as a non- frequent chromosomal rearrangement in ro- resolved polytomy. dents (Patton and Sherwood 1983). We suggest that the karyotype with 2n=52 Discussion (NF=50), from Mendoza, San Juan and Catamarca, should correspond to E. moreni Despite the rather little morphological differ- Thomas, 1896 since its type locality is entiation between sigmodontines, cytogenetic Chilecito, La Rioja, Argentina (Thomas studies have been important in clarifying the 1896), approximately 100 km from our sam- species limits (Pearson and Patton 1976; pling site in Ischigualasto. The telocentric Fagundes et al. 2000; Spotorno et al. 2001). karyotype of E. moreni is reported here for In Eligmodontia, four basic karyotypes have the first time and corresponds to the highest been described and can be assigned to the diploid and fundamental numbers recorded following species: E. typus,2n=43–44, in Eligmodontia. The high molecular and NF=44 (Ortells et al. 1989; Zambelli et al. morphological distinctiveness of these speci- 1992; Tiranti 1997); E. morgani, mens as reported for other well differentiated 2n=32–33–34, NF=32 (Ortells et al. 1989; sigmodontines (Hillyard et al. 1997; Steppan Kelt et al. 1991; Zambelli et al. 1992; Tiranti 1995, 1998; Smith and Patton 1993, 1999; 1997); E. hirtipes,2n=50, NF=48 (Pearson D’ Elıá 2003), confirms its full status as a and Patton 1976; Ortells et al. 1989; Kelt et species. al. 1991; Spotorno et al. 1994) and The karyotypes with 2n=44, NF=44 from E. puerulus with 2n=32–34, NF=48 (Spot- Telteca, Costa de Araujo and Nãcunãń ARTICLE IN PRESS

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Fig. 5. Results of phylogenetic analyses for Eligmodontia species based in cytochrome-b sequences. (A): Neighbour-joining tree; (B): Maximum parsimony; (C): Maximum-likelihood tree. Bootstrap support values for nodes are shown above each leading branch, respectively. ARTICLE IN PRESS

Systematics of Eligmodontia in the Monte Desert 309 correspond to E. typus Cuvier, 1837 (Ortells FN shared among these three northwestern et al. 1989; Zambelli et al. 1992; Hillyard taxa supports their close phylogenetic rela- et al. 1997; Sikes et al. 1997; Tiranti 1997). tionship. This distinctive species is the only one in the Several studies have dealt with sigmodontine genus that has a biarmed X-chromosome relationships at the generic level (Smith and morphology, suggesting that it is a derived Patton 1993, 1999; D’ Elıá 2003; Steppan character. et al. 2004, and references therein), but The 2n=44, NF=44 karyotype with an analyses on intrageneric relationships are ancestral X-chromosome is reported here rather scarce (Steppan 1998). We propose a for the first time. We suggest that this phylogenetic tree for the silky mice Eligmo- karyotype should be assigned to E. marica dontia, with two major clades (lineages) Thomas, 1918, since its type locality in representing the ‘‘northern’’ and ‘‘central- Chumbicha (Catamarca province), is 80 km southern’’ species. Major clades in our tree from our collecting locality (Pipanaco). are in agreement with previous analysis Nevertheless, the morphological overlap and (Spotorno et al. 2001), but differ with the limited molecular distinctiveness of E. typus proposition made by Braun (1993) who and E. marica, which are in the upper limit of considers E. marica as a highly differentiated, genetic distance observed for intraspecific early offshoot in the phylogeny of the group. variation in Eligmodontia from Patagonia Our results indicate the opposite, and suggest (Hillyard et al. 1997), render doubt about its a recent origin as supported by our data sets specific status. However, the karyotypic (i.e. low morphological, karyotypical and differentiation between E. typus and molecular divergence). Moreover, the rela- E. marica might result in sterility of female tionship between E. moreni and E. morgani, hybrids (King 1993). In fact, the hetero- as well as between E. hirtipes and E. puerulus morphic pairing of X-chromosomes in fe- as proposed by Braun (1983) is not supported males is likely to produce duplications and either by molecular or karyotypic data. deficiencies in the absence of preventing Mapping karyotypes data onto the phylo- mechanisms to chiasma formation (King geny of Eligmodontia indicates convergence 1993). to low diploid numbers in both clades, with The close relationship among specimens with Robertsonian fusion as the major force 2n=44 karyotypes is confirmed by chromo- directing the karyotypic evolution (Gardner somal, morphological and molecular ana- and Patton 1976; Pearson and Patton 1976) lyses. The molecular data show that a sister in the northern clade. Nevertheless, no such species to this group is the Patagonian silky correlation exists in the southern one, where mouse E. morgani. Although, their relation- karyotypes cannot be derived by invoking ships have a low support, they are recovered Robertsonian rearrangement only. Even in the NJ and MP analyses. These three taxa though relevant banding patterns are not share also a low FN and a central southern known yet, the difference between these distribution, which sustain their close rela- karyotypes strongly suggest a complex array tionship compared to other Eligmodontia of chromosomal rearrangements, involving species. pericentric inversions and or tandem fusions In the other group, molecular data indicate (Ortells et al. 1989) in the southern species. that E. moreni is more related to E. puerulus, Convergent evolution to reduced diploid and that relationship is recovered in all trees number in different intrageneric lines was ob- with high bootstrap. However, this last served in other related phyllotines (Steppan species has a highly derived karyotype (Spot- 1998; Salazar-Bravo et al. 2001). orno et al. 2001; Lanzone et al. unpubl. data). The Miocene–Pliocene uplift of the Andes, On the other hand, the Andean species, followed by the Quaternary climatic events, E. hirtipes is karyotypically more similar to provided a topographically diverse scenario E. moreni, which appears to have an extra for the evolution of desert adapted rodents in pair of acrocentric autosomes (Spotorno et the high Puna desert and Andean rocky al. 1994; Lanzone and Ojeda 2005). The high foothills (Mares 1975; Reig 1986). The ARTICLE IN PRESS

310 C. Lanzone et al. evolution of phyllotines based on chromoso- species of Eligmodontia took place. In mal changes suggests that high diploid this region we recorded two areas of numbers, as found in species of the Andean sympatry between E. moreni and E. marica plateau is the ancestral karyotype (Pearson (Campo Arenal) and E. typus and E. moreni and Patton 1976; Spotorno et al. 2001). (Telteca Reserve). Other contact zones in Accordingly, phylogenetically derived spe- Eligmodontia have been reported for the cies, with low diploid numbers and mostly Patagonian populations of E. typus and E. biarmed karyotypes should be distributed morgani (Zambelli et al. 1992; Hillyard et al. in the lowlands. Nevertheless, we found 1997; Sikes et al. 1997). Whether the mechan- high and low diploid numbers in both, the isms of coexistence of these sympatric popu- Andean plateau and lowlands, complicating lations are mediated through habitat the classical scheme of chromosomal evolu- selection or food partitioning deserves tion in the phyllotine rodents (Bonvicino further studies and is beyond the scope of et al. 2003 and literature cited there; Olds this research. et al. 1987). Regarding the origin of Eligmodontia, Reig (1986) proposed a differentiation of the genus Acknowlegements from an ancestral, Andean stock of Calomys, to the desert lowlands about 11.6 myr (Sala- Our thanks to Steve Lougheed for his zar-Bravo et al. 2001). Our results expand assistance with the molecular analyses and Reig’s (1986) proposition since they suggest to Agustina Ojeda for her critical comments that arid lowlands acted as a second diversi- and suggestions to the first draft of our ms; to fication center. A similar proposition of more Soledad Albanese, Daniela Rodriguez, Mari- than one divergent lines in the basal radiation ana Dacar and Silvia Brengio for her of genera was suggested for other species of cooperation in the field and in the laboratory; sigmodontines (Salazar-Bravo et al. 2001; Marisa Rosi for help with cranial photo- Steppan 1998). graphs, and to Nelly Horak for her assistance Biogeographically, the north-central portion with the English version. The map of of the Monte biome is a rain shadow desert localities was produced by Daniel Duenãs surrounded by Andean and preAndean at the CRICYT. This study was partially mountain ranges. These arid landscapes funded by CONICET PIP 2884 and Agencia compose the scenario where the speciation Secyt 11768 to RAO in Argentina, and FNC and adaptation processes of the lowland 1010727 to MHG in Chile.

Zusammenfassung Integrative Taxonomie, Systematik und Verbreitung der Gattung Eligmodontia (Rodentia, Cricetidae, Sigmodontinae) in der gema¨Xigten Monte-Wu¨ste in Argentinien

Systematik und Verbreitung der sigmodontinen Nager Su¨damerikas sind Gegenstand sta¨ndiger Revisionen und Kontroversen. Die Hochland-Wu¨stenma¨use der Gattung Eligmodontia Cuvier, 1837 geho¨ren zu den am meisten spezialisierten Muriden unter den endemischen Nagern Su¨damerikas. Ihre vielfa¨ltige Anpassung an das Wu¨stenleben ist mit der Anhebung der Anden und der fru¨hen Bildung arider Landschaften korreliert. Um die Systematik der Arten von Hochland-Wu¨stenma¨usen, die den trockensten Teil der Monte-Wu¨ste Argentiniens besiedeln, zu kla¨ren, wurden qualitative und quantitative Ko¨rper- und Scha¨delmaXe, Chromosomen und genetische Beziehungen untersucht. Wir fanden drei verschiedene Karyotypen von Eligmodontia, zwei davon erstmals hier beschrieben, und beziehen sie auf bereits beschriebene Taxa: E. moreni Thomas, 1896 (2n=52 und FN=50), E. typus Cuvier, 1837 (2n=44 und FN=44) und E. marica Thomas, 1918. Die letzte Form hat dieselbe 2n wie E. typus, aber ihr X-Chromosom ist metazentrisch statt akrozentrisch. In einer Diskriminanzanalyse externer und kranialer Daten wird E. moreni von E. typus und E. marica getrennt, wa¨hrend die letzten ARTICLE IN PRESS

Systematics of Eligmodontia in the Monte Desert 311 beiden Arten U¨ berlappungen zeigen. Die morphologische und zytologische Differenzierung von Eligmodontia wird durch DNA Distanzen unterstu¨tzt. Phylogenetische Analysen zeigen zwei groXe Gruppen. Eine wird von E. moreni, E. puerulus und E. hirtipes gebildet, die eine hohe FN-Zahl und eine no¨rdliche Verbreitung aufweisen. Die andere Gruppe umfasst E. typus, E. marica und E. morgani mit niedriger FN-Zahl und einer zentralen bis su¨dlichen Verbreitung. Zwei Artbildungszentren werden vorgeschlagen, um die Evolution von Eligmodontia zu erkla¨ren. r 2006 Deutsche Gesellschaft fu¨r Sa¨ugetierkunde. Published by Elsevier GmbH. All rights reserved.

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