Molecular Phylogenetics and Evolution 48 (2008) 473–480 Contents lists available at ScienceDirect Molecular Phylogenetics and Evolution journal homepage: www.elsevier.com/locate/ympev The evolution of ecomorphological traits within the Abrothrichini (Rodentia: Sigmodontinae): A bayesian phylogenetics approach Enrique Rodríguez-Serrano a,*, R. Eduardo Palma a, Cristián E. Hernández b a Laboratorio de Biología Evolutiva, Departamento de Ecología, Facultad de Ciencias Biológicas, and Center for Advanced Studies in Ecology & Biodiversity, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago 6513677, Chile b Laboratorio de Diversidad Molecular y Filoinformática, Departamento de Zoología, Universidad de Concepción and Patagonian Ecosystems Research Center (CIEP), Casilla 160-C Concepción, Chile article info abstract Article history: The generally accepted hypothesis regarding the origin of fossorial mammals proposes adaptive conver- Received 4 September 2007 gence from open environments towards the use of subterranean environments. We evaluated this Revised 1 May 2008 hypothesis for South American mole-mice using conventional and Bayesian frameworks, with indepen- Accepted 8 May 2008 dent evidence. By using a molecular approach based on Cytochrome b and IRBP sequences, we evaluated Available online 14 May 2008 phylogenetic relationships, time of origin, the ancestral trait of fossoriality, and ancestral distributions of species belonging to the Andean Clade (Rodentia: Sigmodontinae). Our results indicate that the Andean Keywords: Clade is highly sustained; with one clade grouping all fossorial forms and another grouping all cursorial Andean Clade species. We hypothesized that fossoriality originated in the Miocene/Pliocene transition, in the Temper- Biogeography Fossorial ate Forests of southern South America. We conclude that the origin of fossorial ecomorphological traits Evolutionary ecology did not necessarily occur under a general model of open environments, the origin of these traits depends Molecular clock on the ecological-historical relationship of the taxon with the environment. Phylogenetic comparative method Ó 2008 Elsevier Inc. All rights reserved. Temperate forest 1. Introduction greatest diversity of species (n = 119) adapted to subterranean life (Nevo, 1979). The currently accepted hypothesis regarding the origin of fosso- Typical adaptations of fossorial rodents are the reduction of rial or semifossorial mammals proposes adaptive convergence eyes, ears, tail and fur (Prout, 1964; Reig et al., 1990; Yates and towards the use of subterranean environments (Nevo, 1979), due Moore, 1990). In addition there are also important modifications to the appearance of open environments (e.g., savannas, prairies, of the forelimbs, which allow for digging; these include modifica- steppes and deserts) during the Paleocene, and, particularly in tions in the bony process and in the size of the muscles of the ante- the Miocene (Webb, 1977). This is principally due to the phenom- rior extremities (Hildebrand, 1985, 1988). In addition, fossorial enon of desertification which occurred on the Earth during these rodents present physiological modifications of great adaptive epochs, as a consequence of the formation of mountains, extensive importance, such as a low basal metabolic rate (BMR), high ther- marine recessions and climatic changes (Webb, 1977). These open mal conductance and a wide range of thermoneutrality. These environments offered novel scenarios where the evolution of ter- modifications mainly promote water retention and the minimiza- restrial mammals gave rise to large cursorial and small fossorial tion of energy loss in the subterranean environment (McNab, taxa (Webb, 1977). According to Nevo (1979), the subterranean 1966, 1980). environment offered a more stable microclimate, food availability, The importance of open environments in generating fossoriality and, in particular, reduced predation risk as compared to open is supported for small mammals that inhabit the South American environments, resulting convergent evolution of unrelated mam- continent, with independent evidence emerging from two groups mals towards highly specialized fossorial trait. This process of fos- of Caviomorph rodents (Fernández et al., 2000; Galewski et al., sorialization has been observed in a few orders of mammals such 2005). However sigmodontine rodents present the greatest specific as those of Notoryctemorphia for Notoryctes; Eulipotyphla; Roden- diversity in South America, and are the second largest subfamily tia; and others sensu Nevo (1979), where Rodentia presents the within the mammals (Reig, 1986; Steppan et al., 2004). Recent studies on the phylogenetic relationships of sigmodontines (D’Elía, 2003; Smith and Patton, 1993, 1999) have established a new suprageneric group, known as the ‘‘Andean Clade” (also * Corresponding author. Fax: +56 02 354 2621. ‘‘Abrotrichini”), which includes 5 genera of rodents traditionally E-mail address: [email protected] (E. Rodríguez-Serrano). ascribed to the tribe Akodontini (Reig, 1987). These are: Abrothrix 1055-7903/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.ympev.2008.05.012 474 E. Rodríguez-Serrano et al. / Molecular Phylogenetics and Evolution 48 (2008) 473–480 Waterhouse 1837; Chelemys Thomas 1916; Geoxus Thomas 1919; Bank (Appendix A). We completed the sequence database with Notiomys Thomas 1890 and Pearsonomys Patterson, 1992. The An- samples of the ninth species (Chelemys megalonyx: Chile; Coquim- dean clade possesses three particularities which make it unique bo; Parque Nacional Fray Jorge Voucher NK109253, Colección de within the Sigmodontinae: i) a restricted geographic distribution, Flora y Fauna Profesor Patricio Sánchez Reyes, Departamento de with populations found only in the central—southern regions of Ecología, Pontificia Universidad Católica de Chile, Santiago, Chile), the Andes Mountain chain and adjacent lowlands (Reig, 1987; following the procedure outlined in the American Society of Smith and Patton, 1993); (ii) 4 of the 5 genera have adaptations Mammalogists Guidelines for the collection and handling of ani- for subterranean life, and are considered fossorial: Chelemys, Geo- mals (Animal Care and Use Committee, 1998). For C. megalonyx xus, Notiomys and possibly Pearsonomys (Mann, 1978; Pearson, we obtained genomic DNA using the ‘‘WizardÒ Genomic DNA Puri- 1984; Reig, 1986; Redford and Eisenberg, 1992); and (iii) of the fication Kit” (PROMEGAÒ, Madison, Wisconsin). The Cytochrome b 380 species in the subfamily, only 7 are fossorial, 5 of which belong was amplified following the protocol by Smith and Patton (1993), to the Andean Clade. whereas for the IRBP gene we followed the protocol by Jansa and Given that these fossorial genera are distributed almost exclu- Voss (2000). Cycle sequencing was performed using the Big Dye sively in the Valdivian rainforest and Patagonia (Pearson, 1984; Terminator kit (Perkin-Elmer, Norwalk, Connecticut) and an ABI Redford and Eisenberg, 1992; but see Ojeda et al., 2005), Smith Prism 310 automated sequencer (Applied Biosystems, Foster City, and Patton (1993) proposed that they derived from a Central An- California). dean radiation of sigmodontines, together with the tribes Akodon- tini and Phyllotini. Nevertheless, considering the hypothesis 2.2. Conventional phylogenetic analyses and molecular clock regarding the origin of the ecomorphological fossorial traits in calibration Rodentia, one would expect that these taxa originated in one of the novel open environments which appeared in South America The nucelotide sequences were aligned using the Clustal X pro- (e.g., Patagonia, Cerrado and Caatinga, Intermediate Desert: see gram (Thompson et al., 1997) with alignment parameters set at the Cabrera and Willink, 1973) or in equivalent types of environments default values. The phylogenetic analyses were performed under during the Miocene/Pliocene transition. This transition corre- the criterion of Maximum Likelihood (ML) using PAUP* version sponds to the beginning of the radiation of Sigmodontinae, and la- 4.0b10 software (Swofford, 2002). The parameters of the best mod- ter biogeographic events have been suggested to have confined the el utilized for the ML analysis were obtained using Modeltest 3.7 Andean Clade to southern South America (Steppan et al., 2004). To software (Posada and Crandall, 1998). The Akaike Information Cri- test this hypothesis we used complementary approaches: molecu- terion (AIC; Akaike, 1974) indicated that the optimal model was lar phylogenetics and the phylogenetic comparative method (Har- General Time Reversion + Invariable Sites + Gamma model vey and Pagel, 1991; Pagel, 1997). Using this multiple approach we (GTR + I + C; Rodríguez et al., 1990; ÀlnL = 7891.0093, evaluated the time, mode and the conditions of the ecogeographic AIC = 15802.0186). The proportion of invariable sites (I) was region in which the fossorial traits of the species belonging to the 0.6002 and the Gamma distribution shape parameter (C) was ‘‘Andean Clade” originated. 0.9030. The best tree was obtained using an exhaustive search, and the confidence values of the clades were evaluated by performing 1000 2. Materials and methods bootstrap replicates with an exhaustive search in each replicate. We rooted the tree using the following outgroups: Wiedomys pyr- 2.1. Specimens and DNA sequences rhorhinos (Wiedomyini), Phyllotis xanthopygus (Phyllotini), Akodon azarae and Necromys temchuki (Akodontini) (Appendix A) since