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ORIGINAL INVESTIGATION

A new record and an evaluation of the phylogenetic relationships

of Abrothrix olivaceus markhami (Rodentia: Sigmodontinae)

Enrique Rodrıguez-Serranoa,�, Cristian E. Hernandeza,b, R. Eduardo Palmaa

aLaboratorio de Biologıa Evolutiva, Departamento de Ecologıa, Facultad de Ciencias Biologicas and Center for Advanced Studies in

Ecology & Biodiversity, Pontificia Universidad Catolica de Chile, Casilla 114-D, Santiago 6513677, ChilebLaboratorio de Diversidad Molecular y Filoinformatica, Departamento de Zoologıa, Universidad de Concepcion and Patagonian

Ecosystems Research Center (CIEP), Casilla 160-C, Concepcion, Chile

Received 3 January 2007; accepted 2 October 2007

Abstract

Recent phylogenetic studies of the subfamily of cricetid rodents (Sigmodntinae) have validated the taxonomicclassification at the tribal level of the Andean Clade. It is possible that some endemic species from Patagonian SouthAmerica are part of this new tribe, but previous studies have not evaluated this hypothesis due to the difficulty ofobtaining samples. In this study, we evaluate the phylogenetic relationships of Akodon markhami (Pine, 1973), a speciesendemic to the Chilean Patagonia, using individuals recently captured at the type locality of this taxon. Our resultsindicate that this form of Akodon corresponds to a subspecies of Abrothrix olivaceus, and should be incorporated intothe Andean Clade as a geographic race of this widely distributed species on the South American continent. Based on amolecular clock calibration, we dated the origin of this geographic race during the last glacial cycles of the Quaternary,as the result of a vicariant process.r 2007 Deutsche Gesellschaft fur Saugetierkunde. Published by Elsevier GmbH. All rights reserved.

key words: Abrothrix olivaceus; Akodon markhami; Andean Clade; Biogeography; Chile

Introduction

During the last decade there has been a boom in thenumber of studies regarding the evolutionary history ofsigmodontine rodents (Rodentia: Cricetidae), princi-pally due to taxonomic problems with the numerousspecies in this subfamily, and their implications regard-ing the origin of South American rodents (Smith andPatton 1993, 1999; Engel et al. 1998; D’Elıa 2003).Many of these studies have validated the supragenericgroupings using phylogenetic analyses. Furthermore,some genera belonging to tribes with wide distributions

atter r 2007 Deutsche Gesellschaft fur Saugetierku

07.10.003

r.

rigs@bio.puc.cl (E. Rodrıguez-Serrano).

in South America have been regrouped into new taxa(Smith and Patton 1999). Such is the case for theAndean Clade, an informal tribal grouping whichincludes a group of genera traditionally assigned to theAkodontini tribe (Smith and Patton 1993; D’Elıa 2003).The genera that comprise this new tribe are: Abrothrix

Waterhouse 1837; Chelemys Thomas 1916; Geoxus

Thomas 1919; Notiomys Thomas 1890 and Pearsonomys

Patterson 1992. A notable characteristic of the AndeanClade is its restricted geographic distribution, whichcomprises the central-southern region of the Andesmountain range and adjacent low-lands (Reig 1987;Smith and Patton 1993). Together with their valuablesystematic discovery of the Andean Clade, Smith andPatton (1993, 1999) also provide evidence that other

nde. Published by Elsevier GmbH. All rights reserved.

Mamm. biol. 73 (2008) 309–317

ARTICLE IN PRESSE. Rodrıguez-Serrano et al. / Mamm. biol. 73 (2008) 309–317310

species inhabiting southern South America, such asAbrothrix sanborni and Akodon markhami, may alsobelong to the Andean Clade. Nevertheless, to date thesespecies have not been included in comparative analyses,due to the complexity of obtaining samples.

Of the two species mentioned above, the least studiedis Akodon markhami. This species is endemic to Chile,and was described in a brief article by Pine (1973), basedon two individuals captured in the locality of PuertoEden, Isla Wellington (491090S; 741270W) by B.J.Markham 1971. This locality corresponds to an islandnear the continent, situated in front of the southern icefields, in Magallanes Region, Chile (XII region; Fig. 1).The captured specimens were originally assigned asAbrothrix olivaceus brachiotis (Waterhouse 1837), byMarkham (1971). However, Pine (1973) noted distin-guishing morphological characters (i.e. total length, furcolor, curvature of the skull, shape of the rostrum),sustaining these specimens as Akodon markhami.

The zone currently inhabited by Akodon markhami

corresponds to islands in the Patagonian channels. Thiszone was especially affected by the glacier cycles of theQuaternary, and was almost totally covered by ice

Fig. 1. Sampled localities where specimens of Abrothrix

olivaceus markhami were collected in the Patagonian Channels

of southern Chile (Isla Wellington and Penınsula Exmouth).

(1) Corresponds to the type locality in Puerto Eden and (2) is

Caleta Level, a continental locality that allows us to expand

the range of A. o. markhami.

during the last glacial maximum (Hollin and Schilling1981; Clapperton 1994). For this reason, Smith andPatton (1993) proposed Akodon markhami, as a recentinvader to this insular region, which should, therefore,not be genetically different from ancestral populationson the continent. If this is so, this species would notconstitute a species of the genus Akodon, rather it wouldbe a subspecies of the continental species whichcurrently inhabits the area, such as the species in thegenus Abrothrix (A. olivaceus; A. longipilis). Here weevaluate this hypothesis, as well as provide a new recordof the species proposed by Pine (1973) as Akodon

markhami, from individuals captured at the type locality35 years after the original description of the species.Furthermore, we utilize a molecular phylogeneticapproach, based on the analysis of nucleotide sequencesof the mitochondrial gene, Cytochrome b and Hiper-variable Domain I, to evaluate the species status ofthis taxon, and to test the hypothesis regarding theorigin of Akodon markhami using a calibration of themolecular clock.

Material and methods

Samples and study area

Between January 27 and February 2, 2006, we collected and

measured eight specimens of Akodon markhami from two

localities in the Patagonian channels (one of which is the type

locality; Fig. 1, Table 2). The specimens were deposited in the

Coleccion de Flora y Fauna Profesor Patricio Sanchez Reyes

(SSUC), Departamento de Ecologıa, at the Pontificia Uni-

versidad Catolica de Chile, Santiago, Chile. Skins, skulls,

tissues, and data associated with each specimen were cross-

referenced directly to each voucher specimen and stored in the

above-mentioned University Collection. We followed the

guidelines of the American Society of Mammalogists during

the collection and handling of the animals used in this study

(Animal Care and Use Committee 1998). Three of the collected

individuals of A. markhami were used in the molecular

analyses. Cytochrome b nucleotide sequences from the other

species of the Andean Clade (Abrothrix olivaceus; A. andinus;

A. jelskii; A. longipilis; Chelemys macronyx; C. megalonyx;

Geoxus valdivianus; Notiomys edwarsii; Pearsonomys annectens),

and the Akodontini tribe (Akodon albiventer; A. torques), were

obtained from GenBank (Table 2).

DNA extraction and sequence analysis

DNA was extracted from frozen liver samples treated with

the WizardsGenomic DNA Purification Kit (PROMEGAs,

Madison, Wisconsin). We amplified the complete cytochrome

b gene of the mtDNA, via polymerase chain reaction (PCR).

Amplification was performed using the forward primer

L14724a (Anderson et al. 1981) and the reverse primer

H15767 (Edwards et al. 1991). Amplifications were carried

out following the thermal protocol outlined by Smith and

ARTICLE IN PRESSE. Rodrıguez-Serrano et al. / Mamm. biol. 73 (2008) 309–317 311

Patton (1993). Double-stranded PCR products were purified

with the Qiaquiks Purification kit (Qiagen Inc., Valencia,

California). Cycle sequencing (Murray, 1989) was performed

using the Big Dye Terminator kit (Perkin–Elmer, Norwalk,

Connecticut) in an ABI Prism 310 automated sequencer

(Applied Biosystems, Foster City, California). Sequence data

were aligned using the CLUSTAL X program (Thompson

et al. 1997) with the default values for all alignment parameters,

with posterior adjustments made by eye. These sequences are

available in GenBank according to the accession numbers

provided in Table 2.

Phylogenetic analyses

Phylogenetic analyses were initially performed using the

Maximum Likelihood (ML) criterion in PAUP* version

4.0b10 software (Swofford 2002). For this analysis, the

parameters of the best model were obtained using Modeltest

3.7 software (Posada and Crandall 1998). The Akaike

Information Criterion (AIC; Akaike 1974) indicated that the

optimal model was Transversional Model+Invariable Sites+

Gamma (TVM+I+G; �lnL ¼ 6143.9497, AIC ¼

12305.8994). The base frequencies of the selected model were:

freqA ¼ 0.3132, freqC ¼ 0.3334, freqG ¼ 0.0953, freqT ¼

0.2581; and the substitution rates were: [A�C] ¼ 1.6002,

[A�G] ¼ 22.4814, [A�T] ¼ 3.0752, [C�G] ¼ 0.7748, [C�T] ¼

22.4814, [G�T] ¼ 1.0000. The proportion of invariable sites

was I ¼ 0.5484 and the Gamma distribution shape parameter

was G ¼ 1.6557.

The best tree was obtained utilizing a heuristic search, and

the confidence values of the clades were evaluated by

performing 1000 non-parametric bootstrap replicates (Felsen-

stein 1985) with a heuristic search in each replicate. We rooted

the tree using Phyllotis xanthopygus and Wiedomys pyrrhorhi-

nus as outgroups, since these species constitute part of the

sister taxa (Phyllotini and Wiedomyini) of the Andean Clade

(D’Elıa 2003; Table 2). Following these initial analyses, we

conducted Maximum Parsimony analysis using only parsi-

mony informative characters. All of these characters were

analyzed as unordered and unweighted. The most parsimo-

nious tree was found through a heuristic search with the

Stepwise Addition algorithm setting at ‘‘random’’ with 10

random additions, and the Branch Swapping method of Tree

Bisection-Reconnection. Finally, we used the Neighbor-Join-

ing clustering algorithm to obtain a distance tree based on the

best-fit model TVM+I+G, found using the ML criterion.

Both the Maximum Parsimony and Neighbor-Joining topol-

ogies were supported through bootstrapping using 1000 non-

parametric bootstrap replicates (Felsenstein 1985), with a

heuristic search in each replicate.

Once the specific identity of the focal lineage was established

(see Results), we performed additional analysis of intraspecific

genealogical relationships. Based on a recent phylogeographic

study on Abrothrix olivaceus (Rodrıguez-Serrano et al. 2006),

we used the Hypervariable Domain I (HDI) of the mtDNA

Control Region, including the same individuals of

A. markhami used for Cyt b (subspecies: A. o. olivaceus;

A. o. pencanus; A. o. brachiotis and A. o. xanthorhinus; see

Table 2). The molecular protocols were based on Rodrıguez-

Serrano et al. (2006). A similar phylogenetic reconstruction was

performed for the second mtDNA matrix of HDI. The optimal

model was Tamura-Nei Model+Invariable Sites (TrN+I;

�lnL ¼ 885.7170, AIC ¼ 1781.4341). The base frequencies of

the selected model were: freqA ¼ 0.3209, freqC ¼ 0.2110,

freqG ¼ 0.0931, freqT ¼ 0.3751; and the substitution rates

were: [A�C] ¼ 1.0000, [A�G] ¼ 4.3652, [A�T] ¼ 1.0000,

[C�G] ¼ 1.0000, [C�T] ¼ 12.8216, [G�T] ¼ 1.0000. The pro-

portion of invariable sites was I ¼ 0.7671. This molecular

marker evolves twice as fast as Cytochrome b, and has been

shown to be informative at the intraspecific level (Rodrıguez-

Serrano et al. 2006).

To assess the timing of the cladogenetic event which

originated Akodon markhami, we first evaluated the hypothesis

of a Generalized molecular clock using the likelihood ratio test

(LRT). This test evaluated whether our ML phylogenetic tree

based on cyt b reconstruction fits a generalized substitution

rate (Felsenstein 1981). In our LRT statistic, H0 represents the

likelihood score associated with the null hypothesis (clock-like

model), where the rate of evolution is homogeneous among all

branches in the phylogeny; H1 represents the likelihood score

associated with the alternative model (non-clock model). For

the LRT we used the w2 statistic with a significance level of

po0.05. Since our results did not support the generalized

molecular clock model (LR ¼ 46.7476, df ¼ 24, p ¼ 0.005), we

used a molecular clock with the Local Rate Deformation

Method (LRDM; Jobb 2005), in TREEFINDER software

version June 2007 (Jobb 2007). As the calibration point for the

molecular clock, we utilized the division of Akodon/Necromys,

which was dated at 3.5 MYBP (Pardinas et al. 2002). For the

Hypervariable Domain I tree the same likelihood test was

performed (LRT ¼ 29.43478, df ¼ 13, p ¼ 0.005). The point

of calibration was set by the recent phylogeographic analysis

of small mammals (Palma et al. 2005). We used the average

time of divergence between Abrothrix andinus and A. olivaceus

(1 MYA sensu Palma et al. 2005). The LRDM was performed

in TREEFINDER.

Results and discussion

Standard measurements and skull morphology

The standard measurements of the A. markhami

specimens captured during this expedition are presentedin Table 1. The values of these measurements are slightlygreater than those known for Abrothrix olivaceus

(Mann, 1978; Redford and Eisenberg, 1992). TheA. markhami skulls presented several distinctive characters,in particular an elongated rostrum and a laterallyinflated cranial cavity, as previously reported by Pine(1973), as well as a notorious interorbital widening ofthe nasal region (Fig. 2). Two of these characters are notas evident in A. olivaceus, since this species presents acranial cavity with rounded edges, as well as a taperednasal bone (Mann 1978). Nevertheless, the interorbitalwidening in A. olivaceus is very apparent, resemblingthat observed in A. markhami. Furthermore, thesubspecies A. o. brachiotis (inhabitant of the temperate

ARTICLE IN PRESS

Table 1. Standard measurement for the eight specimens of Abrothrix olivaceus markhami presented in mm

Voucher number Total length Tail length Hind foot length Ear length Weight (g)

SSUC-MaOO329/ER30* 172 72 26 18 30

SSUC-MaOO330/ER34* 157 70 24 14 20

SSUC-MaOO333/ER37 188 79 26 17 30

SSUC-MaOO334/ER38 195 81 27 16 40

SSUC-MaOO331/ER39 201 88 29 18 40

SSUC-MaOO335/ER40 198 84 27 16 42

SSUC-MaOO332/ER41 192 84 26 18 50

SSUC-MaOO336/ER43 210 94 27 20 50

Mean Value 189 82 26 17 38

Table 2. Museum catalogue numbers of the species included in the phylogenetic reconstruction

DNA

segment

Species or

subspecies

Voucher GenBank

access

number

Locality

Cyt b Abrothrix olivaceus

olivaceus

FMNH132309b AF027305 Chile; Coquimbo; Coquimbo

FMNH132348b AF027306 Chile; Valparaıso; Valparaıso

A. o. brachiotis FMNH131621 AF027307 Chile; Los Lagos; Bahıa Mansa

MVZ183257 AF027309 Chile; Valdivia; Fundo San Martın

FMNH131733 AF027311 Chile; Los Lagos; Puerto Octay

FMNH131468 AF297882 Chile; Aysen; Lago Riesco

A. o. xanthorhinus FMNH132591 AF297896 Chile; Aysen; Coyhaique

FMNH129877 AF297897 Chile; Aysen; Balmaceda

FMNH132593 AF297902 Chile; Aysen; Chile Chico

A. o. markhami. SSUC-MaOO329/ER30 EF118754 Chile; Magallanes; Isla Wellington; Puerto Eden

SSUC-MaOO335/ER40 EF118756 Chile; Magallanes; Isla Wellington; Caleta Malaca

SSUC-MaOO333/ER37 EF118755 Chile; Magallanes; Campos de Hielo Sur; Caleta

Level

Abrothrix andinus MVZ174065 AF108671 Peru; Arequipa; Sumbay

Cyt b Abrothrix jelskii MVZ173073 AY275114 Peru; Puno; Ollachea

Abrothrix longipilis MVZ154494 U03530 Argentina; Rıo Negro; Bariloche

Akodon albiventer NK96060 AY341042 Chile, Tarapaca; Suricayo

Akodon azarae GD 327 AY702964 Uruguay; San Jose; Kiyu

Akodon torques MVZ171720 M35700 Peru; Cusco; Paucartambo

Chelemys macronyx MVZ155800 U03533 Argentina; Rıo Negro; Bariloche

Chelemys

megalonyx

NK109253 DQ309559 Chile; Coquimbo; Parque Nacional Fray Jorge

Geoxus valdivianus MVZ154601 U03531 Argentina; Rıo Negro; Bariloche

Necromys temchuki UP22 AY273914 (cited in D’Elıa 2003)

Notiomys edwarsii MVZ163067 U03537 Argentina; Rıo Negro; Comallo

Phyllotis

xanthopygus

NK96033 AY341052 Chile; Tarapaca; Lago Chungara

Wiedomys

pyrrhorhinos

MVZ197567 AY275134 (cited in D’Elıa 2003)

HDI Abrothrix olivaceus

olivaceus

NK105535 AY840030 Chile; Coquimbo; Parque Nacional Fray Jorge

NK105537 AY840031 Chile; Coquimbo; Parque Nacional Fray Jorge

NK104631 AY840048 Chile; Santiago, San Carlos de Apoquindo

NK105424 AY840049 Chile; Santiago, San Carlos de Apoquindo

A. o. pencanus NK105964 AY840061 Chile; Bıo-Bıo; Tucapel

NK105967 AY840062 Chile; Bıo-Bıo; Tucapel

A. o. brachiotis NK104811 AY840065 Chile; Los Lagos; Panguipulli

NK106265 AY840066 Chile; Los Lagos; Valdivia

E. Rodrıguez-Serrano et al. / Mamm. biol. 73 (2008) 309–317312

ARTICLE IN PRESS

Table 2. (continued )

DNA

segment

Species or

subspecies

Voucher GenBank

access

number

Locality

NK95647 AY840077 Chile; Los Lagos; Chiloe

A. o. xanthorhinus NK104946 AY840079 Chile; Magallanes; Parque Nacional Torres del

Paine

NK104986 AY840081 Chile; Magallanes; Parque Nacional Torres del

Paine

A. o. markhami SSUC-MaOO329/ER30 EU155876 Chile; Magallanes; Isla Wellington; Puerto Eden

SSUC-MaOO335/ER40 EU155878 Chile; Magallanes; Isla Wellington; Caleta Malaca

SSUC-MaOO333/ER37 EU155877 Chile; Magallanes; Campos de Hielo Sur; Caleta

Level

Abrothrix andinus EPA04 AY840022 Chile; Tarapaca, Lago Chungara

We utilized the mitochondrial Cytochrome b (Cyt b) gene and the Hypervariable Domain I (HDI). All of the sequences were obtained from

Rodrıguez-Serrano et al. (2006) and from GenBank (http://www.ncbi.nlm.nih.gov/Genbank/index.html), with the exception of Abrothrix olivaceus

markhami, which was obtained from specimens processed in this study. FMNH ¼ Field Museum of Natural History, Chicago, USA.

MVZ ¼Museum of Vertebrate Zoology, University of California, Berkeley, USA. NK ¼ Kriovoucher Number, Museum of Southwestern Biology,

University of New Mexico, Albuquerque, USA. SSUC ¼ Coleccion de Flora y Fauna Profesor Patricio Sanchez Reyes, Departamento de Ecologıa,

Pontificia Universidad Catolica de Chile, Santiago, Chile. GD Field catalogue number of Guillermo D’Elıa. EP Field catalogue number of Eduardo

Palma.

E. Rodrıguez-Serrano et al. / Mamm. biol. 73 (2008) 309–317 313

forests north of 461S), presents the same characterstate for the rostrum as A. markhami (Mann 1978).Given that this morphological variation observed inA. markhami is very similar to observations for thegeographic races of A. olivaceus, A. markhami could be asubspecies of A. olivaceus – a widely distributed speciesthroughout Chile and Argentina.

Phylogenetic analyses

All three phylogenetic reconstruction algorithms usedin this study provided congruent topologies for theresulting cytochrome b trees (Fig. 3). The ML value ofthe tree was �ln 6138.62370. The single most parsimo-nious phylogenetic tree had 952 steps, with ConsistencyIndex ¼ 0.6917. The only topology, obtained under thereconstruction criteria used here, shows two stronglysustained clades, which form exclusive groups betweenthe species recognized as fossorial rodents (i.e. Chel-

emys; Geoxus; Notiomys; Pearsonomys) and all theforms of the genus Abrothrix. Within the Abrothrix

clade one can observe that the species Abrothrix

olivaceus originates at NODE 1 (Fig. 3). The specimensof Akodon markhami form part of the clade composed ofthe diverse subspecies of A. olivaceus, and is the sistergroup of the meridional forms (A. o. brachiotis andA. o. xanthorhinus). Similar results have been obtained forthe mtDNA control region, positioning A. markhami as asubspecies of Abrothrix olivaceus and as a sister taxon ofAbrothrix olivaceus brachiotis (Fig. 4). Furthermore, allof the species of Akodon considered in this study arephylogenetically distant from the Andean Clade, where

Akodon markhami was originally included. Given theresults from the phylogenetic analyses, we propose thatAkodon markhami constitutes a subspecies of Abrothrix

olivaceus, for which we propose the name Abrothrix

olivaceus markhami. In the last species account Musserand Carleton (2005), considered Akodon markhami as afull species of Abrothrix naming it as Abrothrix

markhami. However this classification is just an exten-sion of Smith and Patton (1993, 1999) studies onAkodontini, since these authors did not recognize thegenus Akodon for the Patagonia and southcentral Chilebut Abrothrix. Furthermore, the classification includedin Musser and Carleton’s (2005) species account was notevaluated in a phylogenetic context. Therefore, in lightof our results, Akodon markhami and Abrothrix mar-

khami are synonyms of Abrothrix olivaceus markhami

(description below).Within the clade including all of the meridional forms

of A. olivaceus, A. o. brachiotis has traditionally beenrecognized as a subspecies (Osgood, 1943; Mann, 1978),while A. o. xanthorhinus was recently included as asubspecific form by Pearson and Smith (1999) and Smithet al. (2001). Smith et al. (2001) proposed that the mostaustral forms of A. olivaceus originated from a dispersalprocess over an environmental gradient, from thetemperate forest of Chile to the Argentine Patagonia,during the last glacial retreat. Nevertheless, given thatSmith et al. (2001) did not include a molecular clockcalibration or another way of dating the biogeographicscenario, it was not possible to evaluate the time periodin which the dispersal event occurred, or to relateevolutionary time with some of the last glacial retreatsof the Quaternary (at least six events, Clapperton, 1994).

ARTICLE IN PRESS

Fig. 2. Skull of Abrothrix olivaceus markhami (SSUC-Ma-

OO330) from Puerto Eden, Isla Wellington: (A) dorsal view;

(B) lateral view; (C) ventral view; (D) lateral view of right

lower jaw. The scale-bar represents 5mm.

90 62 98

0.1 Substitution/site

A-o-br-BahiaMansa

A-o-br-SanMartin

A-o-br-PuertoOctay

A-o-xa-Coyhaique

A-o-xa-ChileChico

A-o-xa-Balmaceda

A-o-br-LagoRiesco

A-o-markhami-ER30

A-o-markhami-ER37

A-o-markhami-ER40

A-o-ol-Coquimbo

A-o-ol-Valparaiso

Abrothrix andinus

Abrothrix longipilis

Abrothrix jelskii

Geoxus valdivianus

Pearsonomys annectens

Chelemys macronyx

Chelemys megalonyx

Notiomys edwardsii

Akodon albiventer

Akodon-torques

Akodon azarae

Necromys temchuki

Phyllotis chilensis

Wiedomys pyrrhorhinos

ML/MP/NJ Tree

A. o. brachiotis and

A. o. xanthorhinus

Abrothrix olivaceus

markhami

A. o. olivaceus

60 69 73

68 77 61

NODE 193

100 100

-62 64

70 80 85

62 53 70

99 99

100 96 81 90 -

62 98

Fig. 3. Phylogenetic position of Abrothrix olivaceus markhami

in a reconstruction under the Maximum Likelihood criterion.

(The Maximum Parsimony and Neighbor-Joining algorithms

show the same topology.) The three values near the branches

correspond to the Bootstrap percentage for ML, MP and N-J,

respectively, all of which support the topology.

E. Rodrıguez-Serrano et al. / Mamm. biol. 73 (2008) 309–317314

Our molecular clock calibration allowed us to date theseparation of A. o. markhami from A. o. brachiotis atabout 0.24 MYBP (for the cytochrome b gene), and 0.20MYBP (for the HDI gene; Fig. 4). Therefore, the time

period of origin of A. o. markhami is before the lastglaciation (Clapperton 1994). In this temporal frame-work, the explanation for the origin of this taxon is notsupported by a recent postglacial dispersal event, as wasoriginally proposed by Smith et al. (2001). As analternative, we propose that the origin of A. o. markhami

occurred as a vicariant process, a hypothesis which issupported by two lines of evidence. First, the topologyof the reconstructed phylogeny indicates A. o. markhami

as a monophyletic clade, represented by specimens thatonly inhabit west of the southern ice fields (Fig. 1).Furthermore, one of the captured specimens inhabitedthe continental region next to the southern ice fields(ER37; 4910301200S; 7412105500W). In other words, theforms inhabiting areas to the west of this greatgeographical barrier constitute a unique lineage, isolatedfrom the lineages of A. olivaceus which inhabit theeastern part of the southern ice fields. Secondly, IslaWellington, the type locality for this taxon, was the onlyarea in the Patagonia channels that provided a glacialrefuge during the Quaternary in the last glacialmaximum (Ashworth et al. 1991). Although our resultspartially coincide with the proposal by Smith andPatton (1993, 1999), in that A. o. markhami is not adifferent species from the continental forms, our study

ARTICLE IN PRESSE. Rodrıguez-Serrano et al. / Mamm. biol. 73 (2008) 309–317 315

suggests that this geographic race is not a postglacialinvader of Isla Wellington as was previously proposed(Smith and Patton 1999). These findings allow us toextend the distribution of this Patagonian sigmodontineto the continental area east of Isla Wellington, near theSouthern Ice Fields.

Finally, we consider that it is important to utilizemolecular approximations to resolve this type ofsystematic confusion. This is especially useful in com-plex geographical scenarios, such as those produced byglacial dynamics, where the high amounts of intraspe-cific variability are probably produced by local processesof adaptation, and not necessarily by diversificationprocesses. In particular, A. olivaceus has three subspe-cies south of 411S, and some possibly not yet evaluatedforms from the Magellanic islands, which also form partof this species, such as Akodon hershkovitzi (Pattersonet al. 1984). This hypothesis could be tested usingphylogeographic approaches (Avise 2000) based onmolecular markers. Using these approaches, researcherswill be able to evaluate and understand the mode andtime of origin of this and other still controversialgenealogical lineages of the austral sigmodontines.

Abrothrix olivaceus markhami, new subspeciesSynonymy:Akodon olivaceus brachiotis Markham, 1971Akodon markhami Pine, 1973Abrothrix markhami Musser and Carleton, 2005Holotype – Adult male described by Pine (1973), skin

and skull under collection number USNM501221

0.40.60.8 0.40.60.8

Fig. 4. The molecular clock calibrated with the separation betw

Deformation Method. The cladogenetic event which originated the g

at about 0.20 million years ago. This tree is based on the Hypervar

(National Museum of Natural History, Washington,DC, USA), collected on April 2, 1971 by B. J. Markhamfrom Puerto Eden, Isla Wellington, Magallanes, Chile.

Distribution – Currently know from the Isla Well-ington (491090S; 741270W) and the continental area tothe west of the Southern Ice Fields (4910301200S;7412105500W) in Chile. The dominant flora of these areasis evergreen forest composed by Nothofagus dombeyi,N. betuloides, Drimys winteri and Lomatia ferru-

ginea. Arbustive stratum is composed by Tepualia

stipularis and Blechnum magellanicum. This subspeciesis syntopic with another sigmodontine Oligoryzomys

longicaudatus.Diagnosis – Size slightly greater than Abrothrix

olivaceus brachiotis (Table 1); pelage long, smooth anddense; dorsum varying from gray-brown to brown;lateral region with a distinctive pale brown to yellowantero–posterior band, that projects to the sides of nose;venter gray with hairs blackish at bases. Tail tricolor,dorsum dark, lateral pale brown and venter gray; manusand foots dominant pale brown.

Measurements – External measurements for theholotype are total length, 184mm; length of tail,77mm; length of hind foot, 25mm; and ear from notch,15mm; weight 30 g. Means for external measurementsfor two topotypes (ER30; ER34) are total length,165mm; length of tail, 71mm; length of hind foot,25mm; and ear from notch, 16mm; weight 25 g. Meansfor external measurements of six individuals from CaletaMalaca and Caleta Level are total length, 197mm;

AomarkhamiER40

AomarkhamiER30

AomarkhamiER37

Aobrachiotis3

Aobrachiotis2

Aobrachiotis1

Aopencanus2

Aopencanus1

Aoxanthorhinus2

Aoxanthorhinus1

Aoolivaceus4

Aoolivaceus3

Aoolivaceus2

Aoolivaceus1

Aandinus

0.00.2Million Years

AomarkhamiER40

AomarkhamiER30

AomarkhamiER37

Aobrachiotis3

Aobrachiotis2

Aobrachiotis1

Aopencanus2

Aopencanus1

Aoxanthorhinus2

Aoxanthorhinus1

Aoolivaceus4

Aoolivaceus3

Aoolivaceus2

Aoolivaceus1

Aandinus

0.00.2Million Years

een Abrothrix andinus/A. olivaceus, using the Local Rated

eographic form of Abrothrix olivaceus markhami was estimated

iable Domain I of the mtDNA control region.

ARTICLE IN PRESSE. Rodrıguez-Serrano et al. / Mamm. biol. 73 (2008) 309–317316

length of tail, 85mm; length of hind foot, 27mm; andear from notch, 18mm; weight 42 g.

Etymology – Pine (1973) described Akodon markhami

honoring the extensive contributions of Brent J. Mark-ham to the knowledge of Magellan vertebrates. Forthese reasons, we think that this denomination must stayin this taxon, determining the geographic race ofAbrothrix olivaceus that inhabit the Isla Wellingtonand the adjacent continental region of Chile.

Acknowledgements

This paper was greatly improved by comments fromPaula E. Neill, Teresa M. Tapia, Margarita Marchantand two anonymous reviewers. The community ofPuerto Eden, especially Don Jose Navero, Sra. Nelda,Manuel Navero, Carabineros de Chile and CONAFRegion de Magallanes y Antartica Chilena, providedessential logistical support on Isla Wellington. We aregrateful for financial support from FONDECYT Grants#3050092 and 1070331, the Center for EcosystemResearch in Patagonia (CIEP) through the DIUC-Patagonia Grant #205.113.0651sp to C. E. Hernandez,and FONDAP-FONDECYT Grant #1501-0001 (Pro-gram 2) to R. E. Palma through the Center forAdvanced Studies in Ecology & Biodiversity (CASEB),and the NIH Hantavirus Ecology-Chile grant. We alsothank Nicolas Howard of NAVIMAG Ferries forproviding a significant portion of transportation coststo Isla Wellington. We are grateful to the IDEA WILDFOUNDATION for technological support. E. Rodrı-guez-Serrano was supported by a DIPUC DoctoralFellowship.

Zusammenfassung

Ein neuer Fund und eine Neubewertung der phyloge-

netischen Einstufung von Abrothrix olivaceus markhami(Rodentia: Sigmodontinae)

Neue phylogenetische Studien an der Subfamilie voncricetiden Nagetieren (Sigmodontinae) erlauben eineValidierung der taxonomischen Klassifikation auf Tri-busebene, die u.a. in einer neuen Gruppe resultiert: demAndinen Kladus. Es ist moglich, dass einige endemischeArten aus dem sudlichsten Teil Sudamerikas diesemKladus zuzurechnen sind, wobei fruhere Studien dieseHypothese aufgrund der Schwierigkeit, Probenmaterialzu erhalten, nicht bewertet haben. In dieser Studiebewerten wir die phylogenetischen Beziehungen vonAkodon markhami (Pine, 1973), einer im chilenischenPatagonien endemischen Art, basierend auf kurzlich anihrer Typuslokalitat gefangenen Individuen dieser Art.Unsere Ergebnisse zeigen, dass diese Form von Akodon

einer Unterart von Abrothrix olivaceus entspricht undals eine geographische Rasse dieser auf dem sudameri-kanischen Kontinent weit verbreiteten Art dem AndinenKladus zugeordnet werden sollte. Auf der Basis einermolekularen Uhr-Kalibrierung wird der Ursprungdieser geographischen Rasse auf die jungsten Glazial-zyklen im Quartar als das Ergebnis eines Vikarianz-Prozesses datiert.

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