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Home , Akodon, Akodontini, Bibimys, Bibimys chacoensis, Delomys, Irenomys

Mamm. biol. 68 (2003) 351±364 Mammalian Biology ã Urban & Fischer Verlag http://www.urbanfischer.de/journals/mammbiol Zeitschrift fuÈr SaÈ ugetierkunde

Original investigation Phylogenetic analysis of sigmodontine (), with special reference to the akodont Deltamys

By G. D'ELIÂA,E.M.GONZAÂLEZ, and U. F. J. PARDINÄ AS The University of Michigan Museum of , Ann Arbor, Michigan, USA, Laboratorio de EvolucioÂn, Facultad de Ciencias, Montevideo, Uruguay, Museo Nacional de Historia Natural, Montevideo, Uruguay and Centro Nacional Pa- tagoÂnico, Puerto Madryn, Chubut, Argentina

Receipt of Ms. 24. 06. 2002 Acceptance of Ms. 13. 01. 2003

Abstract

We present a comprehensive phylogenetic analysis based on cytochrome b gene sequences of sig- modontine rodents. Our particular interest is to estimate the phyletic position of Deltamys, a tax- on endemic to a small portion of the La Plata river basin in Argentina, , and Uruguay, and to assess its generic status. The three primary conclusions derived from our analyses are: (1) cotton (Sigmodon) are the of the remaining sigmodontines, (2) the tribe is monophyletic with moderate support, and (3) Deltamys falls outside of a containing all spe- cies of subgenera of yet examined, and thus we grant Deltamys status of full genus.

Key words: Akodon, Akodontini, Muroidea, , phylogeny

Introduction

The high diversity of muroid rodents to Thomas (1916, 1918) who recognised the belonging to the Sig- morphologic similarity among Akodon and modontinae has seriously challenged re- some other taxa ranked as genera by him searchers attempting to understand their (e. g., , Chroeomys, Deltamys, phylogenetic relationships and to classify Hypsimys, (= Bolomys), Thalp- them accordingly. Problems range from spe- omys, Thaptomys). Four decades later Vor- cies boundaries; to relationships among sig- ontzov (1959) coined the term Akodontini modontine taxa; to the limits and contents for this group. However, it was Reig (1984, of the subfamily, one of the most debated 1987) who made the most significant contri- topics in muroid systematics (see D'ElõÂa bution towards defining the group and un- 2000). derstanding its evolutionary history. Follow- Traditionally, sigmodontine genera have ing the removal of (Tate been delimited and grouped into tribes 1932) the contents of the akodontine group based on phenetic similarity. One of the lar- have been more or less stable. The major gest of these groups is the tribe Akodontini. discrepancy has revolved around Oxymyc- An akodontine concept can be traced back terus and similar genera (e. g., ,

1616-5047/03/68/06-351 $ 15.00/0. 352 G. D'ELIÂA et al.

Lenoxus, Blarinomys), which have been original description (Thomas 1917) has var- placed in a different but closely related ied from being considered a subgenus or tribe, Oxymycterini by some (Hopper and simply a synonym of Akodon (e. g., Eller- Musser 1964; Hershkovitz 1966); or in- man 1941; Cabrera 1961; Massoia 1964; cluded within the Akodontini by others Reig 1987; Musser and Carleton 1993) to (Reig 1980, 1987), a position followed in a full genus (e. g., Gyldenstolpe 1932; the most recent treatise of taxon- Massoia 1980; Bianchini and Delupi 1994; omy (McKenna and Bell 1997). GonzaÂlez and Massoia 1995). Although a major redefinition of generic A single , Deltamys kempi Thomas, contents of the tribe Akodontini has re- 1917 has been described, although two sub- cently been prompted by phylogenetic ana- species are currently recognised (GonzaÂlez lyses of molecular markers (Dickerman and Massoia 1995). Deltamys occupies wet 1991; Smith and Patton 1991, 1993, 1999; environments in a small area of the La Pla- D'ElõÂa et al. 2003) historically, much of ta river basin (Fig. 1). Its distribution ranges the debate on akodontine and from northern Buenos Aires and southern systematics has been centered on issues at Entre RõÂos provinces in Argentina (Mas- low taxonomic levels (see Reig 1987). This soia 1964, 1983), throughout Uruguay, and situation is especially true with regard to extends by the Atlantic litoral of the Brazi- the ranking of several taxa that morpholo- lian State of Rio Grande do Sul (GonzaÂlez gically closely resemble Akodon (e. g., Del- and Massoia 1995). The Argentinean popu- tamys, Hypsimys, Microxus, Thaptomys, lations correspond to the nominant subspe- ). In this study we focus on Del- cies, while the Uruguayan form is D. k. tamys, a poorly studied taxon that since its langguthi. Brazilian records have been ten-

Fig. 1. Map of a portion of the La Plata river basin where the sigmodontine genus Deltamys is distributed. Black circles indicate recorded populations of Deltamys taken from GONZAÂLES and PARDINÄ AS (2002). Sigmodontine rodents phylogenetics: Deltamys is a valid genus 353 tatively assigned to the latter form (GonzaÂ- long and end in a TAA or TAG stop codon. Other lez and Massoia 1995). sequences (e. g., , Chilomys, and Rhipid- The aim of this study was to assess the phy- omys) have an extra codon (i. e., 1 143 bp long) logenetic position of Deltamys within the and also end in a TAA or TAC stop codon. Other sigmodontine sequences did not end with a TAA sigmodontine radiation, and thus its taxo- or TAG stop codon. After the last codon, these nomic status. Our systematic philosophy is sequences have an extra T, which presumably gets that taxa above the species level should be polyadenylated to form a stop codon, as it was re- monophyletic. ported for the cytochrome b gene of (Bibb et al. 1981). Then, some sequences (e. g., those of Blarinomys, Lenoxus) were 1 141 bp long and Material and methods others (e. g., those of Abrothrix, , and Oecomys) were 1 144 bp long. From the align- We amplified and sequenced the cytochrome b ment it became clear that the position of the in- gene sequences reported in this study (Tab. 1) in sertions and/or deletions responsible for the dif- two fragments using primers located both intern- ference in gene length lies at the very end of the ally and in the flanking regions of the gene sequence, but it was impossible to unambiguously (MVZ 05 ± MVZ 16 and MVZ 103 ± MVZ 14, da determine its exact position (i. e., if it either corre- Silva and Patton 1993; Smith pers. com.). Nega- sponded to the codon number 379, 380 or 381). To tive controls were included in all experiments. avoid this problem, we based our analysis in the Dye-labelled PCR products were cleaned in Se- first 1 134 bases of the sequences. phadex columns and sequenced using an ABI Maximum parsimony (MP; Farris 1983) was the 377 automatic sequencer. In all cases both heavy optimisation criterion used to generate hypoth- and light DNA strands were sequenced and com- eses of phylogenetic relationships among sigmo- pared. dontine species. In all cases characters were trea- The phylogenetic analysis was based on complete ted as unordered and equally weighted. We cytochrome b sequences, therefore it not included employed two approaches to search for the most the partial sequences of the Deltamys specimens parsimonious tree(s). First, PAUP* 4.0b10 (Swof- UP 65 and MNHN 4150 (Tab. 1). These haplo- ford 2000) was used to perform 200 replicates of types, along with the others gathered from Delta- heuristic searches with random addition of se- mys specimens were employed in population level quences and tree bisection-reconnection branch comparisons. The phylogenetic dataset here ana- swapping. Second, two batches of Nixon's (1999) lysed was that of D'ElõÂa et al. (2003) with the fol- parsimony ratchet were performed in PAUP* lowing tree modifications. First, it was expanded using command files written with the help of the with 19 specimens belonging to 18 sigmodontine program PAUPRat (Sikes and Lewis 2001). The species (Tab. 1). Second, the specimen represent- difference between both ratchet batches was the ing Akodon montensis was changed to include number of perturbed characters, 15 and 25% re- one belonging to the type locality of the species. spectively. Each ratchet batch consisted of 20 ser- Third, one specimen of chacoensis was ies of 200 iterations. For each series a different excluded in to have only one specimen per command file was used. We carried out two mea- species. The exception to this pattern was Delta- sures of clade support. First, we performed 500 mys kempi, the target taxon, from which one spe- bootstrap (Felsenstein 1985) replications, each cimen of each subspecies was included. Then, the with three replicates of random sequence addi- dataset here analysed includes 134 taxa, of which tion. Second, we performed 500 parsimony jack- 111 belong to the sigmodontine ingroup and 23 knife (Siddall 1995) replications with three addi- to the outgroup (Fig. 2). Outgroup taxa, which in- tion sequence replicates each and a deletion of clude arvicoline, cricetine, neotomine, peromys- one third of the character data. In both bootstrap cine, and tylomyine species, were cho- and jackknife searches the branches with less than sen based on the results of an unpublished 50% of support were allowed to collapse. Molecu- comprehensive study of muroid phylogenetic re- lar synapomorphies were documented by examin- lationships carried out by D'ElõÂa and Weksler. ing PAUP* outputs and visualised using Mac- Sequence alignment was done using the program Clade 3.05 (Maddison and Maddison 1992). Clustal X (Thompson et al. 1997) under the de- Only those changes that held up irrespective of fault setting costs. Cytochrome b gene sequences the kind of character transformation used (i. e., of sigmodontine taxa vary in length (Smith and accelerated: ACCTRAN or delayed: DELTRAN) Patton 1999). Typical sequences, such as all of were taken into account. those reported in this study, were 1 140 base pairs 354 G. D'ELIÂA et al.

Table 1. Specimens examined in this study (in addition to those of D'ELIÂA et al. 2003; see text fordetails and also Fig. 2) including catalog number, and locality (for the sequences presented here) and source of their se- quences. Voucher specimens for the individuals first reported in this study are or will be deposited in the follow- ing collections: Argentina, ColeccioÂn de MamõÂferos del Centro Nacional PatagoÂnico (UP); Brazil, Museu de Zoolo- gia da Universidade de SaÄo Paulo (CIT); USA, The University of Michigan Museum of Zoology (GD); and Uruguay, Museo Nacional de Historia Natural Montevideo (MNHN). Asterisks indicate sequences kindly provided by J. L. PAT- TON and M. F. SMITH (Museum of Vertebrate Zoology, University of California at Berkeley, USA); we have submitted these two sequences to GENBANK.

Species Catalog numberLocality Source

Deltamys kempi UP 42 Argentina, Buenos Aires, La Balandra AY195860 kempi (S 34°54'07'' W57°45'56) D. k. kempi UP 65 Argentina, Buenos Aires, La Balandra AY195861 (S 34°54'07'' W57°45'56) D. k. langutthi MNHN 4150 Uruguay, San JoseÂ, Ruta 1 sobre Arroyo Cufre AY195863 (S 34°21' W57°06') D. k. langutthi MNHN 4151 Uruguay, San JoseÂ, Ruta 1 sobre Arroyo Cufre AY195862 (S 34°21' W57°06') A. reigi MNHN 3682 Uruguay, Lavalleja, Paso AverõÂas AY195865 (S 33°36' W54°19'') A. montensis GD 513 Paraguay, Paraguari, SapucaÂi AY195864 (S 25°40' W56°56') A. paranaensis CIT 1131 Brazil, Rio Grande do Sul, Venancio Aires AY195866 (S 29°36' W52°12') Akodon affinis * AY196164 A. spegazzini * AY196165

A. sp. PARDINÄ AS et al. (2003) A. cursor AF184051 Calomys fecundus AF385592 C. hummelincki AF385598 C. laucha AF385593 C. muscullinus AF385603 C. sorellus AF385608 C. tener AF385596 Sigmodon alstoni AF293397 S. fulviventer AF293401 S. leucotis AF293401 S. peruanus AF293395 S. toltecus AF293402 Volemys kikuchii AF348082

Results and discussion with a marked deficit of guanine, especially in third positions. The mean base frequency The cytochrome b gene of Deltamys had a across all Deltamys haplotypes and across length of 1 140 base pairs. The haplotypes all base positions are A = 0.29873, showed a strong base compositional bias, C = 0.27932, T = 0.29537, and G = 0.12658. Sigmodontine rodents phylogenetics: Deltamys is a valid genus 355

Similar compositional biases have been good resolution with only four polytomies. found in other sigmodontine rodents (e. g., Three of those are in the outgroup part of Myers et al. 1995) and in in gen- the tree (Fig. 2 a). One major polytomy in- eral (Irwin et al. 1991). Three different cy- volves peromyscines, neotomines, and crice- tochrome b haplotypes were found among tines plus Scotinomys. A second polytomy the four sequenced specimens of Deltamys. appears within the cricetine subfamily, and Both individuals of D. k. langguthi shared a third involves different arvicoline the same haplotype. Haplotypes of the two lineages. Finally, the forth polytomy in- sequenced D. k. kempi specimens differed volves three lines within the sigmodontine in only one base pair. Interestingly, haplo- genus (Fig. 2 b). types from specimens belonging to the two The subfamily Sigmodontinae appears described subspecies differed in only one monophyletic, with four major . The or two positions. GonzaÂlez and Massoia most clade contains only the genus Sig- (1995) described D. k. langguthi based on modon (10 species included), the sole mem- differences in pelage colour and minor dif- ber of the tribe Sigmodontini. Several ferences in the relative size of the braincase authors (e. g., Hershkovitz 1972; Gardner and zygomatic arch. Clearly, morphological and Patton 1976; Reig 1980, 1984; Jacobs evolution is not necessarily coupled with and Lindsay 1984; Baskin 1986) have dis- evolution of mitochondrial genes and differ- cussed the identity of the basal sigmodontine ent degrees of differentiation in these two because it has direct implications for infer- systems are not surprising. However, the ring the biogeographic history of the group. low level of mitochondrial differentiation is This is a complex subject theme that falls be- remarkable and indicates that more com- yond the scope of this contribution, and we prehensive morphological and molecular refer to D'ElõÂa (2000). Although the basal analyses of variation are needed to further position of Sigmodon has low level of boot- assess the distinctiveness of the subspecies. strap and jackknife support, it is in agree- In this respect, the study of specimens from ment with the results of a more reduced Brazilian populations where several fixed phylogenetic analysis of four other mito- karyotypic rearrangements have been re- chondrial genes (Engel et al. 1998), as well ported (Castro et al. 1991) is much needed. as nuclear and mitochondrial DNA se- The dataset analysed phylogenetically had quences (D'ElõÂa 2002). It is worth noting 701 variable characters of which 582 were that no sequence phylogenetic analysis has parsimony informative. Both search meth- yet included representatives of the tribe ods (replicates of heuristic searches, and Ichthyomyini. The second sigmodontine two sets of iterative parsimony ratchet) em- clade to branch off is the thomasomyine tribe ployed in this study found the same four (sensu Smith and Patton 1999). The third shortest trees (length of 11 690 steps). De- main sigmodontine clade is very large and in- spite the large amount of homoplasy cludes phyllotines, oryzomyines and abro- (CI = 0.110, RI = 0.489) present in the data thricines and several unique sigmodontine set, the strict consensus tree (Fig. 2) result- lines (sensu Smith and Patton 1999). Rela- ing from the four shortest trees shows very tionships within this large group are weakly

c Fig. 2. Consensus tree of the 4 most parsimonious trees (length 11 690, CI = 0.110, RI = 0.489) obtained in the maximum parsimony analysis of 111 sigmodontine and 23 outgroup taxa. Numbers above branches indicate par- simony jackknife (right of the diagonal) and bootstrap (left to the diagonal) values of the nodes at their right. Only values above 50% are shown. For technical details of the analyses refer to the text. A) Details of the consen- sus tree corresponding to the outgroup taxa and the sigmodontine clade less the akodontine group. B) Part of the consensus tree corresponding to the akodontine clade. Branches leading to Deltamys species are drawn wider than those leading to the othertaxa. Node A = common ancestorof Akodon and Deltamys. Node B = common an- cestorof Akodon. Node C = common ancestorof the Deltamys clade. 356 G. D'ELIÂA et al. Sigmodontine rodents phylogenetics: Deltamys is a valid genus 357 358 G. D'ELIÂA et al. supported, and most lines collapse to a basal tioned the akodontine condition of Delta- polytomy in the bootstrap and jackknife ana- mys. However, it is important because so lyses. We note, as Smith and Patton (1993, far this is the only study based on shared 1999) did, that within the abrothricine clade derived similarity, in opposition to overall the genus Abrothrix appears as paraphyletic similarity, to have evaluated the phyloge- with respect to Chroeomys jelskii. However, netic relationships of this taxon. Deltamys this arrangement has low levels of support. appears as sister group of the Akodon clade Further studies are required to test the abro- (27 species included). This dichotomy has thricine topology that appears in the strict low level of support. It is worth noting that consensus tree. If this topology remains cladistic analysis based on nuclear and mi- stable, additional analyses will be needed to tochondrial DNA sequences of a more re- clarify if Chroeomys is in fact part of Abro- duced dataset also place Deltamys outside thrix, or if the generic name Abrothrix must the Akodon radiation (D'ElõÂa 2002). The be applied only to A. longipilis (type species topology obtained in the present study may of the genus) while A. andinus, A. olivaceus, be taxonomically interpreted either as re- A. xanthorrinus, and A. sp. are elevated to cognising Deltamys as a valid genus, or as their own genus or included in Chroeomys. expanding Akodon to include the Deltamys The fourth main sigmodontine clade corre- clade. The election of either taxonomic sce- sponds to the akodontine tribe (sensu Smith nario is a decision for each taxonomist. We and Patton 1999). consider that the first option, granting Del- A novel finding of our study with respect to tamys status of full genus, is the most appro- akodontine systematics is the placement of priate considering the level of morphologic, Akodon serrensis well outside the Akodon and karyotypic differences between the clade (Fig. 2 b). A. serrensis appears as sis- taxa. We do not intend to fully describe ter to the monotypic genus Thaptomys, and Deltamys here, and for those interested in this clade is sister to the genus Necromys that we refer them to the original descrip- (of which three species were included). tion by Thomas (1917) and the review of The sequence of A. serrensis was not gener- GonzaÂlez and PardinÄ as (2002). Here we ated by us and we did not have the chance simply point out some of the main features to study the specimen from which it came, that differentiate Deltamys from Akodon. although we do not have any reason to sus- Deltamys kempi is a small, dark coloured pect the specimen was misidentified. The , with conspicuously small eyes and phylogenetic position of Akodon serrensis dense velvety pelage. It is hardly distin- is surprising because to the best of our guished externally from middle-sized spe- knowledge nobody has cast doubt upon the cies of Akodon. However, the epidermal inclusion of A. serrensis within the genus scales of its tail are more conspicuous and Akodon. Moreover, A. serrensis has always the eyes notable smaller than in Akodon. been referred to the typical subgenus of The skull of Deltamys is narrower and ap- Akodon (Reig 1987; Musser and Carleton pears fragile. According to Thomas (1917) 1993). We will not make any taxonomic jud- this single feature allows easy discrimina- gement about this topology until further tion between both genera. In addition, the studies, including careful morphological interparietal of Deltamys is very reduced, comparisons and the sequencing of addi- much smaller than that of most Akodon. tional specimens, are carried out. However, The anterior border of the mesopterygoid a combined analysis of nuclear and mito- fossa is wider than in Akodon, and it does chondrial DNA sequences points in the not surpass the posterior margin of the M3. same direction (D'ElõÂa 2002). The upper incisors project forward, and Finally, with respect to Deltamys, the phylo- their angle with the molar surface is be- genetic analysis shows that this taxon is in tween 80±83°. The lower first molar has a fact an akodontine . This result may very reduced procingulum. Conspicuous be considered trivial since nobody has ques- differences between Deltamys and Akodon Sigmodontine rodents phylogenetics: Deltamys is a valid genus 359 are also evident in the gross morphology of strongly supported (100% of bootstrap and their karyotypes; the karyotype of Deltamys jackknife support) group of akodon-like sig- lacks the small pair of metacentric chromo- modontine rodents widely distributed in somes characteristic of the genus Akodon . However, most of the (Sbalqueiro et al. 1984). branching pattern within this clade is weakly In addition, the present study reveals sev- supported as indicated by the collapsing of eral synapomorphies of the cytochrome b most groups in both bootstrap and jackknife gene that diagnose the clade composed by analyses. Similarly, the majority of the other 27 species of Akodon on one hand and the suprageneric groups of sigmodontine have Deltamys clade on the other (Tab. 2). Eight low values of bootstrap and jackknife sup- character state transformations occurred port, although the latter are in general slightly along the line leading from the common an- higher than the former. For instance, with the cestor of Akodon and Deltamys (node A in exception of the abrothricine clade, all main Fig. 2 b) to the common ancestor of Ako- suprageneric groups within the sigmodontine don species (node B in Fig. 2 b). However, clade collapsed in the bootstrap analysis. these synapomorphies are obscured by the Meanwhile, a moderate support (62%) for fact that in at least one case for each syna- both the basal position of Sigmodon and for pomorphy a reversal to the primitive char- the akodontine tribe was obtained in the jack- acter state has occurred within the Akodon knife analysis. Smith and Patton (1999) ear- clade. 74 nucleotide characters have chan- lier documented this general pattern where ged state along the line leading from node most sigmodontine suprageneric groups lack A to the common ancestor of the Deltamys support when analyses are based on cyto- forms (node C in Fig. 2 b). 18 of these de- chrome b gene sequences. It is unclear at the rived character states have not evolved in- moment if the lack of resolution of supra- dependently in any of the 27 Akodon spe- generic groups of sigmodontines results from cies in consideration. The other 56 derived the limited resolving power of the cytochrome character states of Deltamys also arose in- b gene at that taxonomic level and/or to an dependently at least in one internal line of explosive radiation of the group following the Akodon clade (see Tab. 2 for details). their entry into South America. This fact is not unexpected given the high Clearly, phylogenetic analyses of other amount of homoplasy (CI = 0.110) for the sources of evidence are needed to further cytochrome b gene. In summary, according evaluate the hypothesis about the generic to the present study there are 83 molecular validity of Deltamys, as well as those other synapomorphies that diagnose Deltamys hypotheses prompted by phylogenetic ana- and Akodon. Of these shared derived char- lyses of cytochrome b gene sequences (e. g., acter states, 18 allow unambiguously deter- Smith and Patton 1999; D'ElõÂa et al. mination of Deltamys from Akodon. It must 2003). Of those possible sources of evi- be noted that the sequencing of more speci- dence, the study of more slowly evolving mens could potentially decrease these num- DNA sequences not linked to the mito- bers. When DNA sequences are translated chondrial genome (i. e., nuclear sequences; to amino acids, the changes along the line see D'ElõÂa 2002), as well as broad morpho- leading to the Deltamys clade include nine logical analyses not limited to craniodental synapomorphies (Tab. 3). Of these, five in- features, are needed. Another approach dependently also arose in at least one line that should be pursued to test our results is within the Akodon clade. Therefore, there to expand the taxonomic coverage of the are four amino acid synapomorphies that study to include representatives of addi- allow unambiguous diagnosis of Deltamys tional akodontine taxa believed to be clo- with respect to Akodon. sely related to Akodon, such as Thalpomys The clade Akodon-Deltamys is sister to the and Podoxymys. The inclusion of these taxa clade ((Thaptomys-ªAkodonº serrensis) may also help to stabilise parts of the sig- Necromys), which together constitute a modontine tree. 360 G. D'ELIÂA et al.

Table 2. Molecularsynapomorphies of Deltamys (1±74) and Akodon (75±81) as revealed by maximum parsimony analysis of cytochrome b gene sequences. 74 fixed derived character states were found in Deltamys. Of these, 18 derived character states, which are indicated by asterisks, have not evolved independently in any species of Ako- don. The remaining 56 derived states have also secondarily appeared in at least one species of Akodon. Numbers between parentheses indicate, respectively at both sides of the bar, the number of Akodon species in which the character state under consideration is present and the number of times it evolved within theAkodon clade. Seven synapomorphies were recovered for the Akodon clade. The numberof species of Akodon that secondarily reverse to the primitive character state as well as the number of times this event has taken place are indicated between parentheses at both sides of the bar respectively.

Character State Nucleotide position/ Akodon and Deltamys com- Akodon species Akodon species Codon position Deltamys com- mon ancestor common an- mon ancestor and subspecies cestor

1 15/3 A orG T A orG A/G/T (1/1) 2 20/2 A C* A A 3 66/3 A C* A A 4 124/1 A G A A/G (10/1) 5 129/3 C T C T/C (4/4) 6 156/3 C T C C/T (4/4) 7 178/1 A G A A/G (1/1) 8 189/3 C T* C C 9 198/3 C T A C/A/T (1/1) 10 210/3 C T C C/T (3/3) 11 222/3 C T C C/T (4/4) 12 240/3 C T C C/T (1/1) 13 261/3 C T C C/T (5/3) 14 288/3 C T C C/T (5/3) 15 291/3 C T C C/T (10/3±6) 16 327/3 C T C C/T (3/3) 17 345/3 C T C C/T (5/4) 18 358/1 T C T T/C (5/2±3) 19 360/3 C G* C C/T 20 363/3 C orT A C orT C/T/A (1/1) 21 366/3 A T* A A 22 384/3 C T C C/T (13/3±4) 23 396/3 A T A A/G/T (1/1) 24 405/3 A G A A/G (2/2) 25 417/3 C A* C C/T 26 426/3 G C* G A/G/T 27 447/3 C T C C/T (3/2) 28 459/3 C T C C/T (4/4) 29 462/3 C T* C C/A 30 474/3 C T* C C 31 498/3 T G T A/G/T/C (2/2) 32 501/3 A orC G C A/T/C/G (1/1) 33 510/3 T C T T/C (9/4) 34 573/3 C T C C/T (3/2) 35 574/1 T C T T/C (3/3) 36 592/2 C T C C/T (8/5) 37 598/2 C T* C C 38 600/3 T A* T T/C 39 630/3 C T C C/T (1/1) 40 645/3 C A* C C/T Sigmodontine rodents phylogenetics: Deltamys is a valid genus 361

Table 2. (continued)

Nucleotide Character State position/ Codon position Akodon and Deltamys com- Akodon species Akodon species Deltamys com- mon ancestor common an- mon ancestor and subspecies cestor

41 669/3 C T* C C 42 672/3 C T C C/T (2/2) 43 684/3 T C T T/C (5/4) 44 712/1 G A G G/A (1/1) 45 723/3 T C T T/C (1/1) 46 750/3 C A C C/T/A (5/2) 47 759/3 A T* A A/C 48 765/3 T C T T/C (3/3) 49 768/3 T C T T/C (8/6) 50 786/3 C A C A/T/C (1/1) 51 789/3 C T C C/T (1/1) 52 801/3 C T* C C 53 813/3 A G A A/G (5/3±4) 54 828/3 T C T T/C (1/1) 55 831/3 C T C A/C/T (3/2) 56 834/3 C T C C/T (10/4±8) 57 843/3 T A T T/C/A (3/1) 58 846/3 A G* A A 59 858/3 C T C C/T (1/1) 60 879/3 C T C C/T (1/1) 61 883/1 A G A A/C/G (9/3) 62 897/3 A T C C/T (2/1) 63 907/1 G A G G/A (7/5) 64 921/3 A G A A/G (5/3±4) 65 945/3 A G A G/A (1/1) 66 1014/3 T C T T/C (4/3) 67 1020/3 C T C G/C/T (8/8) 68 1035/3 C T C C/T (9/7) 69 1053/3 A G A A/G (2/2) 70 1080/3 C A ? C/T/A (1/1) 71 1087/1 A G* A A/C 72 1093/1 C orT A* C orT T/C 73 1095/3 A T A C/G/T/A (6/2) 74 1113/3 T C T T/C (12/6)

75 114/3 C C T T/C (7/2) 76 252/3 C C T T/C (9/4) 77 558/3 A A T C/T/A (1/1) 78 615/3 T T C C/T (7/3) 79 631/1 C C T T/C (7/5) 80 837/3 T T C C/T (6/4) 81 874/1 C C T T/C (7/5±6) 362 G. D'ELIÂA et al.

Table 3. Amino acid synapomorphies of Deltamys. The translation of the DNA sequences into amino acid se- quences revealed nine fixed derived character states in the Deltamys clade with respect to the Akodon clade. How- ever, five of those character states have also independently appeared at least one time within theAkodon clade. Numbers between parentheses indicate, respectively, the number of Akodon species in which the character state underconsideration is present and the numberof times it has evolved within the Akodon clade. The remaining four Deltamys aminoacid synapomorphies, which are indicated by asterisks, have not evolved independently in any species of Akodon. Aminoacid abreviations are as follow: Asn = Asparagine, Ala = Alanine, Ileu = Isoleucine, Leu = Leucine, Met = Methionine, Phe = Phenylalanine, Thr= Threonine, Val = Valine.

Codon Character state number Akodon and Deltamys Deltamys common an- Akodon species com- Akodon species common ancestor cestorand subspecies mon ancestor

1 7 Asn Thr* Asn Asn 2 42 Met Val Met Met/Ileu/Val (10/1) 3 60 ThrAla ThrThr/Ala(1/1) 4 120 Phe Leu Phe Phe/Leu (5/2±3) 5 238 Ala Thr* Ala Ala/Val/Ileu 6 295 Ileu Val Ileu Ileu/Leu/Val (9/3) 7 303 Ala ThrAla Ala/Ileu/Thr(6/5) 8 363 Ileu Val* Ileu Ileu/Leu/Thr 9 365 Leu Ileu* Leu Leu

Finally, we point out the significance of the Acknowledgements present work for conservation biology. There is general agreement that the design We are grateful to Yatito Yonenaga-Yassuda of conservation strategies should also take who provided tissue samples. Jim Patton and Peg into account evolutionary diversity (Moritz Smith provided unpublished sigmodontine se- quences. Phil Myers, Jim Patton, Marcelo 1994; Dimmick et al. 1999). The finding that Weskler, and 2 anonymous reviewers made valu- Deltamys represents an important branch able comments on an earlier version of this study. within the sigmodontine radiation (i. e., is Dario Podesta helped us during fieldwork. Fi- not nested into the radiation of Akodon) nancial support was granted by The American So- implies that conservation efforts must be di- ciety of Mammalogists, the Museum of Zoology rected to preserve populations of this main and Rachkam Graduate School from the Univer- sigmodontine evolutionary line for which sity of Michigan (GD), Vida Silvestre (EMG), only one species, with two subspecies, has Fundacion Antorchas and CONICET (UFJP). been so far described.

Zusammenfassung

Phylogenetische Analyse sigmodontiner Nager (Muroidea), mit besonderer BeruÈcksichtigung der akodonten Gattung Deltamys Die Autoren stellen eine umfassende phylogenetische Analyse der sigmodontinen Nagetiere mit Hil- fe von Cytochrom b Gen-Sequenzen vor. Von besonderem Interesse ist dabei die phyletische Stel- lung und derfragliche generische Status von Deltamys, einem Taxon, das endemisch in einem klei- nen Gebiet des La Plata Fluûdeltas in Argentinien, Brasilien und Uruguay vorkommt. Die Studie lieferte drei wesentliche Ergebnisse: (1) Baumwollratten (Sigmodon) bilden die basale Gruppe der Unterfamilie Sigmodontinae, (2) das Tribus Akondontini ist monophyletisch, und (3) Deltamys faÈllt auûerhalb einer Gruppe, die alle untersuchten Arten von Akodon umfaût, und sollte daherGat- tungsrang erhalten. Sigmodontine rodents phylogenetics: Deltamys is a valid genus 363

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