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Direction and timing of uplift propagation in the Peruvian Andes deduced frommolecular phylogenetics of highland biotaxa

Damien Picard a,1, Thierry Sempere b,⁎, Olivier Plantard a,2

a UMR INRA-ENSAR BiO3P, Domaine de la Motte, B.P. 35327, 35653 Le Rheu cedex, Franceb LMTG, Université de Toulouse, CNRS, IRD, OMP, 14 avenue Edouard Belin, 31400 Toulouse, France

A B S T R A C TA R T I C L E I N F O

Article history:Received 2 August 2007Received in revised form 8 April 2008Accepted 10 April 2008Available online 25 April 2008

Editor: H. Elderfield

Keywords:surface upliftCentral AndesPeruhighland biotaphylochronologyphylogeography

Physical paleoaltimetric methods are increasingly used to estimate the amount and timing of surface uplift inorogens. Because the rise of mountains creates new ecosystems and triggers evolutionary changes, biologicaldata may also be used to assess the development and timing of regional surface uplift. Here we apply thisidea to the Peruvian Andes through a molecular phylogeographic and phylochronologic analysis of Globoderapallida, a potato parasite nematode that requires cool temperatures and thus thrives above 2.0–2.5 km inthese tropical highlands. The Peruvian populations of this species exhibit a clear evolutionary pattern withdeeper, more ancient lineages occurring in Andean southern Peru and shallower, younger lineages occurringprogressively northwards. Genetically diverging G. pallida populations thus progressively colonized highlandareas as these were expanding northwards, demonstrating that altitude in the Peruvian Andes was acquiredlongitudinally from south to north, i.e. in the direction of decreasing orogenic volume. This phylogeographicstructure is recognized in other, independent highland biotaxa, and point to the Central Andean Orocline(CAO) as the region where high altitudes first emerged. Moreover, molecular clocks relative to Andean taxa,including the potato–tomato group, consistently estimate that altitudes high enough to induce bioticradiation were first acquired in the Early Miocene. After calibration by geological and biological tie-pointsand intervals, the phylogeny of G. pallida is used as a molecular clock, which estimates that the 2.0–2.5 kmthreshold elevation range was reached in the Early Miocene in southernmost Peru, in the Middle and LateMiocene in the Abancay segment (NW southern Peru), and from the latest Miocene in central and northernPeru. Although uncertainties attached to phylochronologic ages are significantly larger than those derivedfrom geochronological methods, these results are fairly consistent with coeval geological phenomena alongthe Peruvian Andes. They strongly suggest that orogenic volume initially developed in the CAO during mostof the Miocene until a breakthrough in the latest Miocene allowed the northward propagation of crustalthickening into central and northern Peru, possibly by ductile crustal flow from the CAO. Such a combinedphylogeographic and phylochronologic approach to regional uplift opens perspectives to estimate thedirection(s) and timing of acquisition of altitude over other Cenozoic orogens.

© 2008 Elsevier B.V. All rights reserved.

1. Introduction

1.1. Surface uplift envisioned from the phylogenetics of highland biotaxa

Estimation and timing of rock uplift and exhumation, as undergoneby a volume of rock to reach the Earth's surface, are routinelyaddressed by thermochronologic methods. The amount and timing ofsurface uplift, i.e. the increase in elevation undergone by the very

Earth's surface, can be assessed by a number of paleoaltimetricmethods based on physical markers (e.g., Kohn, 2007), but recon-structed paleoelevations are of local value and generally have largeuncertainties. Earth's surface, however, can be characterized moreregionally by biological markers, as biological taxa (biotaxa) oftenhave characteristic areal and altitudinal distributions and arecommonly obligate to specific physical environmental conditions, onwhich they can be expected to inform. Distribution of fossil biotaxa,for instance, was instrumental in Alfred Wegener's demonstrationthat continental breakups and displacements had occurred in the past(Wegener, 1915). Given the considerable progress achieved in the lastdecade in molecular phylogenetics, the time may be ripe to explorehow the wealth of molecular data derived from extant biota cancontribute to advance geological issues. Craw et al. (2008) recentlyused genetic differentiation among galaxiid fish populations to

Earth and Planetary Science Letters 271 (2008) 326–336

⁎ Corresponding author. Tel.: +33 561332640; fax: +33 561332560.E-mail addresses: damien.picard@univ-angers.fr (D. Picard),

sempere@lmtg.obs-mip.fr (T. Sempere), plantard@vet-nantes.fr (O. Plantard).1 Present address: Laboratoire “Paysages & Biodiversité”, Université d'Angers, 2

boulevard Lavoisier, 49045 Angers cedex 01, France.2 Present address: UMR 1300 INRA ENVN “BioEpAR”, Ecole Nationale Vétérinaire, B.P.

40706, 44307 Nantes cedex 03, France.

0012-821X/$ – see front matter © 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.epsl.2008.04.024

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estimate the age of Quaternary river drainage changes and relatedgeological events.

In this paper we use the key idea that emergence of mountainscreates new ecosystems and thus triggers a variety of adaptive bioticradiations. Phylogenetic data concerning mountain biotaxa shouldtherefore be relevant to characterize at least some aspects of orogenicuplift. Phylogeography (the analysis of phylogenetic trees in terms ofbiogeographic distributions) and phylochronology (the use of phylo-genetic trees as “molecular clocks”) can be employed to reconstructsynorogenic radiations and estimate their timing, respectively, andthus also to assess features and timing of emergence of highlandecosystems. Here we apply this idea to the case of the Central Andes,which result from crustal thickening (James, 1971) but whose uplifthistory is poorly known (Gregory-Wodzicki, 2000), and we show thatmolecular phylogenies of highland animal and plant taxa do provideindirect means to characterize and approximately date the acquisitionof altitude.

1.2. The Andes: a prime illustration of orogeny as a “species factory”

The Central and Southern Andes have been built by tectonic andmagmatic processes produced by oceanic subduction beneathwestern South America, in a non-collisional setting (e.g., Sempereet al., 2008). The ∼4000 km-long Central Andes form the largest andmost mountainous segment of the Andes (Fig. 1), which is itselfsegmented into the northern Central Andes (5°30'S–∼13°S), CentralAndean Orocline (CAO, ∼13°S–28°S), and southern Central Andes(28°S–37°S); the transition between the CAO and northern CentralAndes is formed by the Abancay deflection, a peculiar segment wherethe Andean structural strike exhibits a significant rotation (Roperchet al., 2006). The CAO covers an area of ∼1,300,000 km2 and itsorogenic volume is by far the largest of the entire Andes. Orogenicvolume intriguingly decreases along strike north and south of the CAO(Fig. 1). In Peru, the width of the emerged orogen is ∼500 km betweenLake Titicaca and Cusco, ∼360 km in south-central Peru, and ∼240 kmin northern Peru; correspondingly, mean maximum elevations alsodecrease northwards.

Although a large amount of work has been performed in theCentral Andes during the last decades, the chronology of the orogenyand related uplift is still debated (e.g., Sempere et al., 2008). Theexisting limited agreement between the many approaches used so farimplies that more data are needed to complement current knowledgeon the Andean uplift issue. Here we derive new independent datafrom Andean highland biotaxa, based on the idea that somegeographic and chronologic aspects of Andean surface uplift areembedded in their phylogeny. Indeed, orogeny imposed adaptivepressure on western South American biota, creating new ecosystemsand triggering a variety of speciations among plant and animal groups(e.g., Hughes and Eastwood, 2006), which resulted in the Andeanregion being one of the world's highest biodiversity centres. The risingAndes came to serve as a rain barrier: cloud forests developed alongtheir eastern side due to orographic concentration of the westward-moving Amazonian moisture, and environments became drier in thewest, with highland steppes extending above ∼2–3 km. Character-istically, the uplifted areas underwent a marked decrease in meanannual temperature (MAT). Relevant biomolecular data concerningAndean taxa adapted to these environments inform on synorogenicbiotic evolution and indeed should thus shed some light on the issueof Andean orogeny and surface uplift.

At tropical latitudes, i.e. between ∼20°N and ∼20°S, low-elevationMATs are assumed not to have changed significantly since theOligocene (e.g., Gregory-Wodzicki, 2002), and areas of lower MATsare highlands. Andean biotic radiations were commonly accompaniedby jumps in altitudinal range and related adaptation to coolerconditions (e.g., Willmott et al., 2001; Altshuler et al., 2004). Amongplants, one major adaptation to highland conditions is exemplified by

the wild potatoes (Solanum section Petota), with several CentralAndean species showing a pronounced tolerance to frost (Spooneret al., 1999; Hijmans and Spooner, 2001; Hijmans et al., 2003). Potatoparasites such as cyst-nematodes, which coevolved with the wildpotatoes, are also cold-adapted (Franco, 1977; Picard and Plantard,2006; see Section 4). In this paper we use the molecular phylogenyand phylogeography of highland potato cyst-nematodes, along withother published biological and geological data, to characterize aspectsof the Andean uplift in Peru. We observe that the uplift ages deducedfrom molecular clocks and those obtained by physical methods areconsistent and mutually help to clarify the geological and biologicalevolutions of the Peruvian Andes.

2. Materials and methods

We address the emergence of Andean highlands by selecting thepotatoes and their cyst-nematode parasites because they originated inresponse to uplift and because molecular data, including phylogenetictrees, are available. We therefore use and analyse mainly publishedbiological information concerning plants of the Solanum genus (thepotato and tomato groups, the eggplant) and cyst-nematode parasites(Heteroderidae: Punctoderinae, with special attention to the Globoderagenus), as well as other results concerning plant (Fuchsia; Siparuna;Oxalis tuberosa alliance) and animal (Metallura hummingbirds; selectedcaviomorph rodents) groups.

Fig. 1. Segmentation of the Andes Cordillera (modified after Sempere et al., 2002). Notethe decrease in orogenic volume northward and southward of the Central AndeanOrocline (CAO). Map from http://photojournal.jpl.nasa.gov/catalog/PIA03388.

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We estimate relevant divergence ages in phylogenetic dendro-grams concerning the Solanum and Globodera genera by usingappropriate chronological tie-points and making the commonassumption that evolutionary rates were constant during the corres-ponding time intervals. We use a simple calculation for the consideredSolanum species, but perform a more sophisticated analysis for the G.pallida data set, which results in two complementary molecular clocks(see Supplementary material). Divergence times between severalGlobodera species, and between clades within the G. pallida species,are estimated using the ITS1-5.8S-ITS2 (ribosomal DNA) and cyto-chrome b (mitochondrial DNA)molecular markers, in two steps due tothe nature of our data. Maximum-likelihood (ML) genetic distancesderived from ITS1-5.8S-ITS2 sequences are converted to time usinggeological time constraints and comparisons with the few publishedphylochronologic estimates (see Sections 4.4, 5.2 and 5.3, andSupplementary material). The selected time of divergence betweenG. pallida and its apparent sister species is then used to calibrate aML molecular clock based on the cytochrome b gene (see Supple-mentary material). Coevolution of the wild potatoes and their cyst-nematode parasites provides a test for checking the accuracy of thesephylochronologic results: these are compared for mutual consistencyand to other phylochronologic data, and are confronted with coevalgeological facts. Although large uncertainties are usually attached tophylochronologic dates (see Supplementary material), we observe afair agreement between our divergence time estimates and the moreprecise relevant geochronologic data, which we see as a confirmationof the validity of the approach introduced here.

3. Andean highland plants: the wild potatoes

3.1. Potatoes and tomatoes

The wild potatoes (Solanum section Petota) comprise N200 speciesirregularly distributed from the southwestern USA to southern SouthAmerica; most species are rare and have a restricted range; 75% of allspecies occur above 2.3 km and 91% above 1.75 km, with an averageelevation at about 2.77–2.89 km and amaximum altitude near 4.9 km;low-elevation occurrences in both hemispheres are from latitudesN20°, where MATs are cooler (Hijmans and Spooner, 2001). Speciesrichness is strongly correlated to highlands between latitudes 20°Nand 20°S, the highest numbers of species being found in Peru (93) andBolivia (39), and the highest number of species in a 50 km×50 km gridcell (22) occurring in southern Peru (Hijmans and Spooner, 2001). Thehighest species richness is observed along the eastern Andes between12°S and 26°S (southern Peru, central Bolivia, northwestern Argen-tina) and along all highlands between 12°S and 6°S (central Peru), andwild potatoes are thus thought to have originated in the Central Andes(Hijmans and Spooner, 2001; Spooner et al., 2005).

The wild tomatoes (Solanum section Lycopersicum) comprise 8species native to northwestern South America, and 1 endemic to theGalapagos Islands and most probably resulting from dispersal acrossseawater from the former region. Apart from the more widespread S.lycopersicum, the continental species grow along the western CentralAndes, from central Ecuador through Peru to northern Chile, and fromsea level up to ∼3.3 km (Peralta and Spooner, 2001). Wild tomatoesthus probably originated in the western lowlands of the CentralAndes, while wild potatoes originated in the Central Andeanhighlands.

Potatoes and tomatoes belong to the same subgenus Potatoe andform indeed closely related sister groups (Olmstead and Palmer, 1997;Olmstead et al., 1999). Divergence of the potato clade was character-ized by the development of tuberization, a complementary reproduc-tive strategy that is likely to have accompanied adaptation of wildpotatoes to emerging harsher, cooler conditions. Thus phylochronolo-gic estimates of the divergence betweenpotatoes and tomatoes shouldprovide a time estimate of the early development of Andean uplift.

3.2. Estimating the potato–tomato divergence time

Although diversity in the family Solanaceae, at both generic andspecies levels, is presently concentrated in the Andean region, thefamily has a classic Gondwanan distribution (Symon, 1991), suggest-ing it emerged after breakup of Pangea but before long-distancedispersal of the Gondwanan continental blocks, i.e. at some timewithin the ∼185–100 Ma interval (dates after Veevers, 2004). Weunderline that biogeography and geological timing of continentalseparations place constraints on evolutionary history that apparentlyrequire older dates than currently considered for divergence of mainorders of phanerogams. The Gondwanan distribution of Solanaceaeindeed suggests that the ∼90 Ma age estimated for the divergence ofthe order Solanales, as illustrated by Davies et al. (2004), is only aminimum age. This is in agreement with consistent suggestions thatdiversification of angiosperms occurred much earlier than their first,Early Cretaceous, fossil record (e.g., McLoughlin, 2001; Morley, 2003;Bell et al., 2005).

Solanum, with over 1000 species, is one of the largest angiospermgenera, and is dominantly represented in South America (Olmsteadet al., 1999). Some species of Solanum however occur in the OldWorld.In particular, S. melongena (the eggplant), a native of Africa or Indiarelated to African species (Doganlar et al., 2002), belongs to themonophyletic subgenus Leptostemonum, that has wild representativesin Gondwanan continents (South America, Africa, India, Australia) andwhose African and Australian members derive from New Worldancestors (Fig. 2). The Old World Leptostemonum species form amonophyletic clade of African origin (Olmstead and Palmer, 1997) thatmust have diverged from South American Leptostemonum populationsat a time when plant interchanges were still possible between Africaand South America (Fig. 2). Considering the time of final separationbetween Africa and South America (∼100 Ma; Pitman et al., 1993;

Fig. 2. Maximum-parsimony tree of selected Solanaceae species based on cpDNArestriction site variation (modified after Olmstead and Palmer, 1997) displayingphylogenetic and phylogeographic relations used for estimation of the potato–tomatodivergence time (see Section 3.2; branch lengths are not proportional to time). OldWorld species form a clade nested in a largely South American clade, a topologyimplying that Solanaceae primarily originated in South America. The basal divergenceof the Old World clade is interpreted to have been triggered by the separation of Africaand South America (Australian species form a clade in turn nested in the African clade,implying a subsequent dispersal from Africa to Australia, possibly along southern Asia).Open diamond indicates node used for calibration, open circle divergence timeestimated in this paper (see Section 3.2 and Fig. 3).

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Veevers, 2004; Eagles, 2007), the fact that the Leptostemonumsubgenus diverged before this separation, and the ability of plants todisperse across seawater over moderate distances, we propose thatthis divergence occurred at 100±20 Ma, i.e. at some time within thebroad 120–80Ma interval. This time span is compatiblewith a ∼90Maor somewhat older age for the emergence of the order Solanales asdiscussed above.

Using this broad time range as a tie-interval, the age of the potato–tomato divergence can be estimated by comparing evolutionarychromosomal structural changes between S. tuberosum (the potato), S.lycopersicum (the tomato) and S. melongena (the eggplant). Thetomato and potato genomes differ by a total of 5 chromosomalrearrangements (5 inversions and 0 translocation; Tanksley et al.,1992) whereas the tomato and eggplant genomes differ by 28rearrangements (23 inversions and 5 translocations; Doganlar et al.,2002), and the potato and eggplant genomes by 24 rearrangements(19 inversions and 5 translocations; Doganlar et al., 2002).

Taking into account the numbers of chromosomal inversions only,the divergence age of the tomato and potato lineages is thus youngerthan that of the tomato and eggplant lineages approximately by afactor 5/23, and than that of the potato and eggplant lineagesapproximately by a factor 5/19. In this case, estimates for the potato–tomato divergence define respectively the 26.1–17.4 Ma and 31.6–21.1 Ma intervals (intervals A1 and A2, respectively).

Taking into account the total numbers of chromosomal rearrange-ments, the divergence age of the tomato and potato lineages isyounger than that of the tomato and eggplant lineages approximatelyby a factor 5/28, and than that of the potato and eggplant lineagesapproximately by a factor 5/24. In this case, estimates for the potato–tomato divergence are respectively the 21.4–14.3 Ma and 25.0–16.7 Ma intervals (intervals B1 and B2, respectively).

The age of the potato–tomato divergence can also be estimated byusing rough assessments of the total amount of nucleotide changes,which suggest that the tomato and eggplant are diverged 2.5 to 3.5times more than the tomato and potato (Doganlar et al., 2002). Thisleads to a rougher age interval estimate, namely the 44–20Ma interval(interval C).

Each of these intervals represents a probability time interval forthe potato–tomato divergence. Graphic “summing” of intervals A1, A2,B1, B2 and C defines the frequency at which possible divergence timesappear in the five calculations as a whole, and suggests that thisdivergence is most likely to have occurred at some time within the25.0–20.0 Ma interval (interval D; Fig. 3), with an apparent maximumprobability between 21.4 and 21.1 Ma (which we do not regard asparticularly reliable, although it matches other, independent results;see Section 5.2). We thus propose to consider interval D as areasonably secure estimate, i.e. that the potato–tomato divergenceoccurred at 22.5±2.5 Ma. Although the result of simple calculations,this estimate is in excellent agreement with the divergence intervalsof Andean potato–parasite nematodes that we independently obtain

using a more sophisticated phylochronologic analysis, and with other,independent phylochronologic results (see Section 5.2).

4. Andean highland plant parasites: the potato cyst-nematodes

4.1. The highland nematodes Globodera pallida and G. rostochiensis

Coevolution of hosts and parasites is a well-known phenomenon,and plant nematodes make no exception (Sturhan, 2002; Subbotinet al., 2004a). The cyst-nematode parasites of wild potatoes coevolvedwith their hosts and thus originated in the Andes (Franco, 1977; Stone,1985). The two known Andean species, Globodera pallida and G.rostochiensis (Heteroderidae: Punctoderinae), require cool to coldconditions because of their initial adaptation to highlands (Franco,1977; Picard and Plantard, 2006). Adaptation of both species to coolclimatic conditions is demonstrated by their unfortunately successfulintroduction by humans in low-elevation cool-temperate climatesworldwide (Franco, 1977).

However, G. pallida is better adapted to cold MATs than is G.rostochiensis, and the wild potato species most resistant to G. pallidaare also the most resistant to frost, suggesting that speciation of G.rostochiensis occurred in a warmer area of the paleo-Andes, and thatspeciation of G. pallida occurred in a colder environment (Franco,1977). Although they are both found around Lake Titicaca, the twospecies display almost distinct distributions as G. rostochiensis is onlyknown south of Lake Titicaca whereas G. pallida is mostly knownnorth of it (it is noteworthy that this same area was identified bySpooner et al. (2005) as the locus of a major cladistic split for wildpotatoes of the Solanum brevicaule complex). In Peru, G. pallida occursmostly between 2.0–2.5 and 4.0–4.3 km elevation, with the heaviestinfestations between 2.9 and 3.8 km (Franco, 1977; Picard andPlantard, 2006). Although it is apparently adapted to somewhatwarmer MATs, G. rostochiensis also requires cool conditions but itsaltitudinal range is not securely known.

G. pallida and nematodes ascribed to G. “mexicana” form amonophyletic clade, whereas G. rostochiensis and G. tabacum formits sister monophyletic clade (Fig. 4; Subbotin et al., 2000, 2001,2004b; Picard et al., 2007). G. “mexicana” is in fact a poorly knownspecies whose individuals analysed here were sampled in Mexico,where it parasites wild members of Solanaceae (Thiéry et al., 1997);however this taxon is likely to have dispersed from South America toCentral America along with members of Solanaceae following thePliocene establishment of the Panamanian land bridge. Unfortunately,too little is known about G. “mexicana” to compare its MAT range withits sister taxon G. pallida. In contrast, because development andreproduction of G. tabacum (subsp. solanacearum) is optimum at 27±3 °C (Adams et al., 1982), it is clear that speciation of its sister taxon G.rostochiensiswas necessarily accompanied by a significant decrease inoptimum MAT, hence corroborating that after divergence this potatocyst-nematode coevolved with its hosts while these adapted to

Fig. 3. Frequency of time intervals retrieved in 5 calculations (detailed in Section 3.2) concerning the potato–tomato divergence.

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emerging cooler, highland conditions. Hence dating the divergence ofG. rostochiensis and G. tabacum, and the speciation of G. pallida, shouldprovide two estimates of the time at which the Andes reachedelevations sufficient to produce divergence of cold-adapted biota.

Furthermore, in contrast with G. tabacum and G. “mexicana”,which parasite a wider range of Solanaceae (including, for the latter,the genus Nicotiana, i.e. the tobaccoes), G. rostochiensis, as G. pallida,preferentially parasites potatoes. This indicates that G. rostochiensis isspecialized when compared to G. tabacum, from which it diverged.The same may be true for G. pallida in relation with G. “mexicana”, butlack of data concerning the latter hampers a secure conclusion.

4.2. Phylogeography of Globodera pallida

The existence of biogeographically structured lineages of G. pallidaseparated by high genetic distances (Fig. 5) indicates that a long andsignificant evolutionary history of reproductive isolation developedwithin this species along the Andean backbone (most likely incoevolution with wild potatoes). Such high levels of sequencedivergence point to N1 Myr evolutionary times, in contrast with theb0.001 Ma age of potato domestication (Picard et al., 2007). Each G.pallida lineage must therefore have independently infected cultivatedpotatoes in its respective area during the last millennia.

G. pallida dendrograms, as those based on the (mitochondrial)cytochrome b marker (cytb) and on 8 microsatellite loci (Fig. 5),exhibit a clear south-to-north phylogeographic pattern, with thebasalmost, i.e. deepest, clade grouping the southernmost populations(Lake Titicaca area) and the crownmost, i.e. shallowest, clade groupingpopulations of northern Peru. Characteristically, the shallower is aclade in the dendrogram, the more northern are its representatives.

The same south-to-north pattern is also observed for allelicrichness using (nuclear) microsatellite markers (Picard et al., 2007).The allelic richness is nearly twice in the south than in the north. Thesame pattern is also observed for the genetic divergence between the

cytb haplotypes of each clade. Total pairwise sequence divergencesamong G. pallida, including G. “mexicana” (as outgroup), range from 0to 15%. The variation in percentage divergences between pairwiseindividuals is much larger for the southern clade (0–11%) anddecreases dramatically northwards (southern central Peru: 0–5%;northern central Peru: 0–1%; northern Peru: 0–0.5%). G. pallidapopulations in Peru are thus also characterized by a clear south-to-north decrease in both allelic richness and pairwise sequencedivergence, in complete agreement with the phylogeographic struc-ture illustrated in Fig. 5, and with the interpretation below.

4.3. South-to-north colonization of the Peruvian Andes by Globoderapallida

Globodera pallida and most of its potato hosts thrive above 2.0–2.5 km in the Andes (Franco, 1977; Hijmans and Spooner, 2001; Picardand Plantard, 2006). Because radiations induced by uplift aregenerally associated with abrupt jumps in altitudinal range (e.g.,Willmott et al., 2001; Altshuler et al., 2004), we consider hereafter the2.0–2.5 km elevation range as the threshold altitude for colonizationsof Andean areas by G. pallida, making this species a paleoaltitudinalmarker.

The phylogeographic structure displayed by G. pallida dendro-grams (Fig. 5) belongs to a well-known type and implies colonizationof progressively emerging favourable areas (e.g., Mendelson and Shaw,2005). This marked south-to-north pattern indicates that dispersionof G. pallida populations in Peru developed northwards from anancestral stock in the southernmost Peruvian highlands. Thischaracteristic south-to-north colonization implies that availability ofnew areas for the host–parasite pair developed northwards. As newareas available for colonization needed to have been uplifted abovethe threshold altitude, viz. 2.0–2.5 km, this clearly points to anorthward propagation of Andean surface uplift in Peru.

4.4. Dating the divergence of highland cyst-nematodes

Although nematode biogeography is hampered by incompleteknowledge of the distribution of known species and by incompleteidentification of taxa parasiting non-cultivated plants (Ferris, 1979),available data allow towork out a coarse phylogeography of the genusGlobodera. First, no Globodera species is known to be native to anyGondwanan continent except South America. Second, molecularphylogenies (Subbotin et al., 2001, 2004b) show that the genus Glo-bodera forms a monophyletic clade nested in the Punctoderinae clade,whose members are mostly established on Laurasian continentalmasses (Fig. 4). This Globodera clade in turn comprises a Eurasian sub-clade (with species such as G. achilleae and G. artemisiae, parasitingAsteraceae; Ferris, 1979) and an essentially South American subclade(grouping species parasiting Solanaceae) (Fig. 4). This variety of hostsconfirms that related cyst-nematode groups may parasite distantlyrelated or unrelated plant taxa (Sturhan, 2002; Subbotin et al., 2004a),suggesting that speciation among cyst-nematodes may also haveoccurred by opportunistic parasiting of new host groups.

Soil nematodes being plate-tectonic markers (Ferris et al., 1976),the fact that Globodera is unknown from Africa strongly suggests thatthis genus appeared in South America after this continent separatedfrom Africa (∼100 Ma; Pitman et al., 1993; Veevers, 2004; Eagles,2007). Dichotomy of this genus into a South American clade and aLaurasian clade (Fig. 4) indicates that the current distribution ofGlobodera involved a connection between South America andLaurasia. The most parsimonious explanation of the availablephylogenetic and biogeographic relationships would be that thePunctoderinae clade originated in Laurasia (as proposed by Ferris,1979) and that a population ancestor to the South American Globo-dera species dispersed from North America to South America during aperiod when both continents were connected, and after South

Fig. 4. Maximum-parsimony tree of selected Punctoderinae species based on ITSsequence data (modified after Subbotin et al., 2004a,b) displaying phylogenetic andphylogeographic relations used for calibration of Globodera clocks (see Section 4;branch lengths are not proportional to time). South American Globodera species form aclade nested in a Laurasian clade, a topology implying that Punctoderinae and theGlobodera genus primarily originated in Laurasia. The basal divergence of the SouthAmerican Globodera clade is interpreted as a consequence of dispersal of a Globoderapopulation from North to South America when a connection existed between thesecontinents. Open diamond indicates node used for calibration, open circles divergencetimes estimated in this paper (see Sections 4.4 and 5.3, and Table 1).

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America had completely separated from Africa (∼100 Ma). Diver-gence of the two Globodera subclades must be explained by a b100Madispersal enabled by the establishment of a temporary connectionbetween North and South America. This is quite compatible with thepaleontologic and geologic record, which richly documents thatsubstantial biotic interchanges occurred between North and SouthAmerica during the ∼80–60 Ma interval (Gayet et al., 1992; Marshalland Sempere, 1993; Marshall et al., 1997). This connectionwas brokenin the Paleocene, resulting in the isolationof SouthAmerica fromNorthAmerica (until the Pliocene emergence of the Panama isthmus).

We thus propose that the divergence of the South American andLaurasian Globodera sub-clades occurred between 80 and 60 Ma, andwe use this age interval to calibrate a molecular clock for the former(see Supplementary information). Applying this calibration interval toour ITS1-5.8S-ITS2 data set (Table 1), we find that G. rostochiensisdiverged from G. tabacum most probably at some time in the 24.7–18.5 Ma interval (latest Oligocene–Early Miocene), and that G. pallidadiverged from G. “mexicana” most probably in the 20.6–15.4 Mainterval (Early Miocene). Within G. pallida, basal divergence of clades1 and 2 of the cytb dendrogram (Fig. 5) respectively occurred at sometime in the 17.8–13.4 Ma (Middle Miocene) and 11.8–8.8 Ma (LateMiocene) intervals.

This ITS molecular clock can be tested by estimating the age of theCactodera– (Punctodera+Globodera) divergence, which is close to the

Heteroderinae–Punctoderinae divergence (Fig. 4). Because the Punc-toderinae originated in Laurasia, they are expected to have divergedafter separation of Laurasia and Gondwana, i.e. after ∼185 Ma(Veevers, 2004): our ITS estimate for the Cactodera– (Punctodera+Globodera) divergence, i.e. the 173–130Ma interval (Table 1), is indeedyounger than this date.

5. Discussion: propagation and timing of Andean uplift

5.1. Phylogeographic evidence for south-to-north propagation of Andeanuplift in Peru

As evidenced in Section 4.2 above, the south-to-north phylogeneticstructure displayed by G. pallida populations in Peru implies that newareasweremade available for colonization, and thus uplifted above the2.0–2.5 km altitude, from south to north. This directly points to anorthward propagation of Andean surface uplift in Peru, originating inthe southernmost highlands of the country (Lake Titicaca area). Thecurrent lack of samples from adjacent Bolivia precludes furtherregional conclusions, but the fact that the Lake Titicaca area isapparently a biotic/phylogenetic boundary (G. pallida–G. rostochiensisbiogeographic boundary; first-order divergence in the Solanumbrevicaule complex [Spooner et al., 2005]) suggests it may haverepresented an environmental threshold at some time in the past.

Fig. 5. Topographic image of the Central Andes with two phylogenetic trees of Globo-dera pallida based respectively on a maximum-likelihood analysis of the cytochrome bpartial gene, and on a neighbour-joining analysis of 8 microsatellite loci (redrawn afterPicard et al., 2007). Fine red lines link sampling sites (red circles) to the correspondingterminal branches of the tree; thick blue dashed lines demarcate the principalphylogenetic divergences and their geographic steps. Each tree exhibits a structurecharacterised by older (deeper) lineages established in the south and younger(shallower) lineages successively arranged toward the north.

Table 1Estimated divergence dates using nuclear ribosomal (ITS1-5.8S-ITS2) andmitochondrial (cytochrome b) sequences

Calibration Divergence Estimated divergence date(Ma) and 95% C.I.

A: Divergence ages estimated by RHINO (see Supplementarymaterial), with 95% confidenceintervals (C.I.), using 852 bp of nuclear ribosomal (ITS1-5.8S-ITS2) sequences of 24 taxa, aHKY-Gmolecular-nodemodel, and 80 Ma and 60 Ma dates bounding the time intervalduring which the American and Eurasian Globodera clades diverged (see Section 4.4and Fig. 7)

American G. clade–Laurasian G. clade=80 Ma

Cactodera–Globodera 173 (144–213)

G. rostochiensis–G. tabacum

24.7 (16.7–35.1)

G. pallida–G. “mexicana”

20.6 (12.4–31.7)

G. pallida Clade 1–Clade 2+3+4

17.8 (11.2–27)

G. pallida Clade 2–Clade 3+4

11.8 (5.2–21.2)

American G. clade–Laurasian G. clade=60 Ma

Cactodera–Globodera 130 (108–160)

G. rostochiensis–G. tabacum

18.5 (12.5–26.4)

G. pallida–G. “mexicana”

15.4 (9.3–23.8)

G. pallida Clade 1–Clade 2+3+4

13.4 (8.4–20.3)

G. pallida Clade 2–Clade 3+4

8.8 (3.9–15.9)

B: Divergence ages estimated by RHINO (see Supplementary material), with 95%confidence intervals (C.I.), using 872 bp of mitochondrial (cytochrome b) sequences of33 taxa, a HKY-Gmolecular-nodemodel, and 21 Ma and 15 Ma dates bounding the timeinterval during which Globodera pallida and G. “mexicana” diverged (see Section 5.3 andFig. 7)

G. pallida–G. “mexicana”=21 Ma

G. pallida Clade 1–Clade 2+3+4

12.5 (9.8–15.6)

G. pallida Clade 2–Clade 3+4

11.1 (8.6–13.9)

G. pallida Clade 3–Clade 4

6.3 (4.7–8.4)

G. pallida–G. “mexicana”=15 Ma

G. pallida Clade 1–Clade 2+3+4

8.9 (7.0–11.1)

G. pallida Clade 2–Clade 3+4

7.9 (6.1–10.0)

G. pallida Clade 3–Clade 4

4.5 (3.4–5.9)

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The wild potatoes (Solanum section Petota) being the natural hostsof G. pallida, a similar south-to-north evolutionary pattern is obviouslyexpected. However, the situation for the host is much less clear thanfor the parasite because current taxonomic classifications of wildpotatoes are being seriously challenged by molecular studies (e.g.,Castillo and Spooner, 1997; Spooner et al., 2005). Some facts mayhowever be mentioned. On the basis of cpDNA restriction data(Castillo and Spooner, 1997), wild potatoes of the series Conicibaccatado exhibit a south-to-north phylogenetic pattern from the CentralAndes toMexico, with all Peruvian and Bolivian taxa forming themostbasal and deepest branches. Furthermore, all 20 species from Peru andBolivia analysed in Castillo and Spooner's (1997) study are diploids(with only 3 exceptions: 1 tetraploid from the Peru–Bolivia borderarea, 1 tetraploid from central Peru, and 1 hexaploid from northernPeru) whereas all 11 species from Ecuador toMexico are tetraploids orhexaploids (Castillo and Spooner, 1997): because among plantspolyploids derive from diploids, the Peruvian and Bolivian Conicibac-cata species again appear as basal, and data concerning polyploidy inthis series are compatible with the idea that diversification occurredfrom Bolivia northwards.

The members of the Oxalis tuberosa alliance, which includes theAndean tuber crop known as oca, occur along the Andes fromnorthwest Argentina to Venezuela. On the basis of the phylogeo-graphic structure of O. tuberosa and outgroups, Emshwiller (2002)concluded that the ancestor of the O. tuberosa alliance emerged in theAndes of southern Peru and northwestern Bolivia, i.e. in the northernregion of the CAO, and radiated southwards and, more markedly,northwards along the Andean backbone. Emshwiller's (2002) conclu-sions regarding O. tuberosa in Peru coincide with our conclusionsabout Globodera pallida.

Species of Metallura hummingbirds thriving above the 2.8 kmaltitude (elevation ranges from Fjeldså and Krabbe, 1990) apparentlyexhibit the same phylogeographic pattern: the section of García-Moreno et al.'s (1999) phylogenetic tree referring to these species hasa basal clade established in western Bolivia and southern Peru (again,the northern region of the CAO), and two shallower cladesrespectively in central Peru and, in part, northernmost Peru toColombia. The species Metallura tyrianthina, whose range includeslower elevations (≥1.7 km) along the eastern slopes of the Andes fromcentral Bolivia to western Venezuela, is sister to all other Metallura(García-Moreno et al., 1999). It is thus likely that the divergencebetween the lower-elevation M. tyrianthina clade and the higher-elevation Metallura clade was induced by Andean uplift in thenorthern CAO region.

Furthermore, a cladistic analysis of the external morphology of theAndean highland lizard genus Proctoporus also concluded thatdiversification within this genus occurred from south to north alongthe Andes, from Bolivia to Venezuela, with the deepest phylogeneticbranches established in Bolivia and southern Peru (Doan, 2003).

It is noteworthy that these south-to-north phylogenetic patternsare clearly consistent although they concern unrelated Andeanhighland biota. Applied to Peru, they strongly support that altitudewas initially acquired in the CAO and later progressively from south tonorth, i.e. that Andean uplift initially developed in the CAO region andpropagated northwards from there.

5.2. Mutual consistency of independent molecular clocks relative to onsetof Andean uplift

No molecular clock can be built, at this time, based on the Oxalistuberosa alliance or the Metallura hummingbirds. However, the timeintervals estimated above for the respective divergences of thehighland taxa Solanum sect. Petota (the potatoes; 25–20 Ma, intervalD), Globodera rostochiensis (24.7–18.5 Ma, ITS ages), and G. pallida(20.6–15.4 Ma, ITS ages) span the latest Oligocene and Early Miocene,agreeing fairly and supporting the idea that the wild potatoes and

their Globodera parasites coevolved and adapted to highland condi-tions at about the same time.

It is noteworthy that our results are also in close agreement withother, independent, published phylochronologic estimates related tothe Andean uplift issue. A phylogenetic tree of the plant genus Fuchsia(Myrtales: Onagraceae) approximately calibrated by fossil pollenimplied that a major Andean radiation started at ∼22 Ma, and thatFuchsia sect. pachyrrhiza, from the western Andean slopes of Peru, andFuchsia sect. fuchsia, from the eastern slopes, diverged at ∼18.3 Ma(Berry et al., 2004). This study also recognized a major interconti-nental diversification of Fuchsia at ∼31 Ma, an age that is close to theEocene–Oligocene boundary (34 Ma), which was a time of consider-able change in global climate and thus in plant composition anddiversity, in particular in South America (Jaramillo et al., 2006). Wetherefore propose a minor recalibration of Berry et al.'s (2004) tree byidentifying this major intercontinental radiation of Fuchsia as aconsequence of the 34-Ma global climatic upheaval and related bioticreorganization (Fig. 6). This results in revised ages of ∼24 Ma for theinitiation of the major Andean radiation of Fuchsia, and of ∼20 Ma forthe ecological separation of the western and eastern slopes of AndeanPeru, to which we apply a 5-Myr uncertainty window (Fig. 7).Furthermore, Andean cloud forest species in the plant genus Siparuna(Laurales: Siparunaceae) underwent an accelerated radiation between∼22 and ∼17 Ma (Renner, 2004), suggesting that new ecosystemswere created by Andean uplift at that time along the eastern slopes ofthe Cordillera. In addition, lowland and highland rodents formingsister clades (Dinomys and Chinchilla, respectively) are estimated tohave diverged between 21 and 17 Ma (Huchon and Douzery, 2001) orat 19.1±2.7 Ma (Opazo, 2005).

These 7 estimates share the 21.8–21.5Ma interval as an intersection(Fig. 7) and the mean of their mean values is 20.7±2.1 Ma (1 SD). Thisleads to identify the 22.8–18.6 Ma interval (i.e., the early and middleEarly Miocene) as an acceptable phylochronologic estimate for theonset of many biotic radiations induced by Andean surface uplift.

5.3. Timing of Andean uplift in Peru by a cytb molecular clock

ITS phylochronology based on Globodera is remarkably consistentwith other andmutually independent results: themean ITS age for the

Fig. 6. Ultrametric maximum-likelihood tree of Fuchsia based on combined ITS, trnL–trnF, and rpl16 data sets, with branch lengths approximately proportional to time(modified after Berry et al., 2004; see Section 5.2).

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uplift-induced divergence of G. rostochiensis, 21.6 Ma, falls in thenarrow intersection of the 5 non-Globodera estimates (Fig. 7), and theoldest ITS age for the uplift-induced divergence ofG. pallida, 20.6Ma, isvery close to theirmean (21.0±2.1Ma,1 SD).We therefore select 21Maas the basal divergence age ofG. pallida for calibration of amore precisemolecular clock based on cytochrome b sequences (see supplementaryinformation, Table 1 and Fig. 7). This cytb clock complements the ITSclock for central and northern Peru (Table 1; Figs. 7 and 8). Inconjunction, the two Globodera clocks allow to estimate the timing ofsouth-to-north propagation of surface uplift in Peru, indicating thatthe 2.0–2.5 km threshold elevation range was reached in the EarlyMiocene in southernmost Peru, in the Middle and Late Miocene in theAbancay segment, and starting in the latest Miocene in central andnorthern Peru (Fig. 8).

5.4. Consistency of phylogeographic and phylochronologic results withgeological data

Although more phylogeographic results are needed in order tofully confirm the preliminary synthesis exposed in this paper, theCentral Andean Orocline (CAO), by far the segment of largest orogenicvolume in the entire Andes (Fig. 1), appears as the region of origin of avariety of unrelated highland biotaxa and therefore as the Andeanregion where high altitudes were first acquired. This suggests thatAndean crustal thickening, which produced surface uplift, initiallydeveloped in the CAO, and that the larger orogenic volume thereresults from a longer cumulative crustal building. It is consistent thataltitudes high enough to create new ecosystems and trigger radiationsof highland taxa were initially acquired in the region currentlycharacterized by the largest Andean orogenic volume.

In Peru, colonization of Andean regions by highland biotaxadeveloped from the CAO northwards, indicating that high altitudeswere acquired in that direction. This is matched by the markeddecrease in orogenic volume observed in the same direction (Figs. 1, 5and 8), implying again a correlation between the age of high altitudeacquisition and the current orogenic volume. This is compatible withthe idea that the crust of Andean segments north and south of the CAOwas progressively thickened by ductile crustal flow from the CAO(Husson and Sempere, 2003; Yang et al., 2003).

Using the assumed threshold altitude range specified above, ourage estimates indicate that the Andes of southern Peru were above

2.0–2.5 km at ∼23–19 Ma. This result fairly agrees with Sébrier et al.'s(1988) independent conclusion, based on geomorphic observations,that the same region was at least 2.0 km-high at ∼20–17 Ma. It alsosuggests that the regional deformation initiated at ∼26 Ma in theEastern Cordillera of western Bolivia (Sempere et al., 1990) and theincrease in exhumation rates reported at ∼25±5 Ma in the same area(Kennan, 2000) were produced by a major, highland-forming orogeny.It also agrees with Dunai et al.'s (2005) finding from cosmogenic 21Nemeasurements that soft geomorphic surfaces in northern Chile havebeen barely affected by erosion since 25 Ma, implying thatpredominantly hyperarid conditions have prevailed west of the CAOsince the latest Oligocene, and thus that high mountains in the CAOwere already acting as an efficient rain barrier at that time.

Our results apparently disagree with MATs and altitude estimatesdrawn from the analysis of fossil leaf morphology, according to whichelevation of a locality in the western Bolivian Altiplano, close tosouthern Peru and now 3.94 km above sea level, was comprised at10.7 Ma between 0 and 2.4 km (Gregory-Wodzicki, 2000) or 0.5 and1.8 km (Gregory-Wodzicki, 2002). Kowalski (2002) however showedthat, at least in Bolivia and East Asia, the current leaf morphologymethod systematically underestimates altitudes when these are high(as it overestimates MATs, by as much as 15 °C) because applyingequations generated from forests in North America to unrelated forestsis inaccurate. Low Late Miocene paleoaltitudes estimated by fossil leafmorphology in Andean Bolivia are thus likely to be underestimations.Our results suggest that there is indeed a bias attached to the leafmorphology method, and that in any case the upper end of paleo-elevation intervals estimated by this method should be preferred.

On the basis of measurements of δ18O and of 13C–18O binding ratesin paleosol carbonate nodules, respectively, Garzione et al. (2006) andGhosh et al. (2006) published paleoaltitude estimates for the Corquebasin, in the central Altiplano of Bolivia. The estimates concerning≥10.3 Ma-old deposits were discussed by Hartley et al. (2007; reply byGarzione et al., 2007) and Sempere et al. (2006; reply by Eiler et al.,2006), respectively, because they apparently disagreed with theregional geological record. The questioned estimates, however, werelater corrected by Garzione et al. (2007) and Quade et al. (2007),respectively: depending on the method used, the Altiplano wouldhave been before 10.3 Ma between 0.4 and 2.2 km elevation (Garzioneet al., 2007) or, more precisely, between 0.4 and 0.8 km (Quade et al.,2007). Our results again suggest that the upper end of these

Fig. 7. Synopsis of time estimates for phylogenetic divergences and radiations related to Andean uplift in Peru and adjacent regions. ITS and cytb ages and confidence intervals wereestimated by RHINO (see Supplementary material). ITS ages: red or pink respectively correspond to 80 Ma or 60 Ma as the calibration age used for the divergence of the SouthAmerican Globodera lineage (Section 4.4); cytb ages: dark or light blue respectively correspond to the 21 Ma (preferred) or 15 Ma calibration age used for the basal divergence ofGlobodera pallida (Section 5.3). Other ages and uncertainty intervals (open bars) were obtained by simple calculation and from the literature (see Sections 3.2 and 5.2).

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paleoaltitude intervals might be preferable. However, the fault-bounded Corque Basin was apparently a pull-apart basin, the surfaceof which may have been at significantly lower altitudes thansurrounding highlands (Sempere et al., 2006).

Our results estimate that the Abancay segment was uplifted above2.0–2.5 km in the Middle and early Late Miocene (Fig. 8). Apatitefission-track ages also indicate that this segment underwent exhuma-tion in the Middle and Late Miocene (van Heiningen et al., 2004).Respective lengths of segments in Fig. 8 suggest that propagation ofuplift remained somewhat stalled in the Abancay segment during theMiddle and early Late Miocene, and that a breakthrough occurred inthe latest Miocene, allowing uplift to rapidly propagate into centraland northern Peru. The Abancay segment coincides with a markedoffset in the shape of the Cordillera (Figs. 1, 5 and 8), which may berelated to this longitudinal orogenic breakthrough. Because theAbancay segment forms the northern termination of the CAO(Roperch et al., 2006), this strongly suggests that crustal thickening,and thus the very Central Andean orogeny, developed only in the CAOduring (the Late Oligocene and) most of the Miocene, i.e. that prior to∼9 Ma most of the Central Andean orogenic volume was restricted tothe CAO. A confirmation of this interpretation may be viewed in theclose geographic association of the Abancay segment with theFitzcarrald megafan (Fig. 8): this poorly dated giant alluvial fan islikely to have developed at the outlet of a large mountain fluvialsystem that longitudinally drained the NW termination of the CAOwhen only minor uplift had affected this area and adjacent centralPeru. In this perspective, the current isolation of the Altiplano basin is

likely to have resulted from Late Miocene enhanced uplift in theAbancay segment and adjacent central Peru. We suggest that theexpansion of a large lake system ~10.3Ma ago in the northern BolivianAltiplano (Garzione et al., 2006) was caused by the damming, duringthis uplift episode, of the longitudinal mountain fluvial systemhypothesized to have fed the Fitzcarrald megafan until then.

Because vertical-axis tectonic rotations evidenced by paleomagnet-ism reflect mountain building (Rousse et al., 2003), timing of rotationsprovide indirect information about uplift. It is therefore noteworthy thatthe Ayacucho area of southern central Peru, at the northern end of theAbancay segment, underwent 11±5° of counterclockwise rotationbetween 9 and 7 Ma (Rousse et al., 2002). Our cytb molecular clockbased onG. pallida suggests that theAyacucho regionwas uplifted above2.0–2.5 km in the Late to latest Miocene, i.e. at about the same time.

Our results also estimate that central Peru was uplifted above 2.0–2.5 km starting in the latestMiocene. Uplift was particularly significantin the Cordillera Blanca area (Fig. 8). Apatite fission-track analysesindicate that the mean exhumation rate of the Cordillera Blancabatholith has been high, ∼1 km/Myr, since ∼8 Ma (Montario, 2001). Amajor phase of canyon incision was produced between 8 and 5 Ma bycoeval uplift (Montario et al., 2005), while the area underwent 15±7°of counterclockwise rotation (Rousse et al., 2003). Regional fission-track andU+Th/He ages consistently indicate that uplift was especiallyvigorous between 6 and 2 Ma (Garver et al., 2003; Perry and Garver,2004; Garver et al., 2005). In central Peru, our phylochronologicresults are thus in good agreement with the known exhumationhistory.

Fig. 8. The phylogenetic tree of Globodera pallida shown in Fig. 5 is used as a molecular clock (ages from Table 1 and Fig. 7) to estimate the timing of propagation of Andean uplift fromsouthern to northern Peru.

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6. Conclusions

Combined phylogeographic analyses and phylochronologic resultsconsistently indicate that in Peru altitudes in excess of 2.0–2.5 kmwere initially acquired in the Central Andean Orocline region and inthe Early Miocene. Uplift produced a profound modification of surfaceconditions which triggered a variety of radiations of cold-adaptedhighland biota, among which are the wild potatoes and their cyst-nematode parasites used in this paper. In Peru, uplift progressivelypropagated northwards along the Andean backbone, rising new areasabove altitude thresholds and thus making them available forcolonization by highland, southern biota. Accordingly, these biotaxadisplay phylogenetic patterns that reflect a marked south-to-northphylogeographic structure, which is compatible with the idea ofcrustal thickening by ductile crustal flow from the Central AndeanOrocline (Husson and Sempere, 2003; Yang et al., 2003).

Because they yield ages consistent with other biological andgeological chronologic data, our Globodera pallida phylochronologictools appear to provide reasonable estimates for the timing of upliftpropagation. In particular, they indicate that the 2.0–2.5 km elevationthreshold range has been slowly reached during the Middle and earlyLate Miocene in the Abancay segment (northwesternmost CAO), andsince the latest Miocene in central and northern Peru. The picture thatemerges from these results is that high altitudes and crustalthickening remained essentially restricted to the Central AndeanOrocline during most of the Miocene, and that an orogenic break-through occurred in the Late Miocene, allowing uplift and thus crustalthickening to rapidly propagate into central and northern Peru. Thissuggests that crustal thickening in the Central Andes developed in twosteps (Sempere et al., 2008), one starting in the Late Oligocene and/orearliest Miocene, and the second in the Late Miocene, in agreementwith recent thermochronologic and paleoaltimetric results fromsouthern Peru and Bolivia (e.g., Ghosh et al., 2006; Garzione et al.,2006; Gillis et al., 2006; Schildgen et al., 2007; Quade et al., 2007;Thouret et al., 2007).

The consistent agreement of our phylogeographic and phylochro-nologic results with the available geological data validates ourapproach and demonstrates that molecular phylogenetic data areindeed able to shed valuable lights on geological issues, at least inspecific instances. It is evident that a signature of geological events isembedded in the topology of most molecular phylogenies becauseEarth's plate-tectonic and climatic evolution has participated sig-nificantly in the shaping of extant biotaxa. Analyses of phylogenetictrees in terms of biogeographic distributions evidence phylogeo-graphic patterns which provide valuable insights as to where specificbiotaxa and related environmental conditions originated. When usedas molecular clocks, phylogenetic data provide phylochronologicestimates of the approximate time at which these specific environ-mental conditions have emerged. However, because these estimatesare individually imprecise, a necessary caveat is that several inde-pendent biotaxa should always be used in order to average the resultsand improve their precision, reliability, and significance. We expect inparticular that combined phylogeographic and phylochronologicapproaches to uplift issues should open perspectives to estimate theregional direction(s) and timing of acquisition of altitude over otherCenozoic orogens.

Acknowledgments

This work was funded by the Région Bretagne and the (French)Ministère des Affaires Étrangères. We thank the Servicio Nacionalde Sanidad Agraria (SENASA, Peru), the Instituto Nacional de Inves-tigación Agraria (INIA, Peru), and particularly M. Scurrah, E. Carbo-nell-Torres and S. Chumbiauca for their help in sampling potatocyst-nematodes in Peru. Thanks also to Carmala N. Garzione fordrawing our attention to the updated paleoelevation estimates that

were published during the 2nd half of 2007, and for providinguseful orientations to conciliate paleoaltimetric results based onstable isotopes with the Central Andean geological record and ourresults.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.epsl.2008.04.024.

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