Arid Diagonal Research Articles

Towards a Monophyletic Infrageneric Circumscription of Adesmia DC. (Dalbergieae, Leguminosae): a Taxonomic Revision in Adesmia series Adesmia

The Adesmia clade comprises five genera, with Adesmia being the most diverse and speciose, and formerly containing 206 species and 37 varieties, distributed in two subgenera and 43 series. The genus inhabits almost exclusively the South American Arid Diagonal, which hosts some of the driest environments on Earth. Within Adesmia subgenus Adesmia, three series primarily inhabit the Pampa grasslands: series Muricatae, Bicolores, and Subnudae. These taxonomically complex series display overlapping morphological characters and geographical distribution ranges, and their monophyly has never been tested. We carried out a thorough systematic study of the three series, combining Maximum Likelihood and Bayesian analyses of 87 sequences of nrITS DNA of Adesmia. Beased on our phylogenetic results, we provide a taxonomic revision of the species in series Muricatae, Bicolores, and Subnudae. Series Subnudae and Bicolores are nested within series Muricatae, and synonymization of the first two under series Muricatae is here proposed. Three clades containing species with geographical and morphological coherence were unraveled inside Adesmia. Three varieties are elevated to species level, and another six were reduced to synonyms. Seven lectotypes and one neotype are proposed. We recognize 21 species in the new circumscription of Adesmia series Muricatae, and provide a species identification key, descriptions, illustrations, and maps, as well as comments on phenology, taxonomy, etymology, distribution, and habitat. We also present conservation assessments for the species of the series.

Phylogeography and ecological niche modelling of the South American cricetid rodent Graomys griseoflavus, with insights into its chromosomal evolution

Abstract The rodent Graomys griseoflavus has a wide geographical distribution in the Arid Diagonal of South America, showing variation in the diploid number (2n = 33–38) caused by three different Robertsonian (Rb) translocations. Two contrasting hypotheses have been proposed to explain the origin and evolution of this polymorphism: (i) unique and sequential events; or (ii) multiple and independent origins of Rb translocations. Here, we combined phylogeography and ecological niche modelling to elucidate the evolutionary history of G. griseoflavus and help to contrast these hypotheses. The results indicated a demographic increase that would have begun ~150 kya from the High Monte ecoregion. The spatial distributions of these populations were coincident with the areas of highest habitat suitability. The palaeoclimatic projections suggested the presence of two main glacial refugia coincident with the main genetic clusters. Graomys griseoflavus underwent two pulses of southward expansion at ~220 and ~210 kya. More recently (~20 kya), there was a secondary contact between the southern populations (Low Monte ecoregion) expanding northwards and the northern populations (High Monte ecoregion) expanding into marginal areas of the Chaco ecoregion. Combined with the cytogenetic evidence, our results support the multiple and independent origins of Rb translocations.

Calyceraceae: Unexpected diversification pattern in the Southern Andes

Calyceraceae comprises 46 species mostly endemic to the Andes and Patagonia in Southern South America, and it is the sister family of Asteraceae, one of the largest Angiosperm families. With a robust phylogeny and with an exceptionally good sampling fraction, we performed macroevolution and biogeographic analyses to understand paleodiversity dynamics through time and space, and its potential drivers. We address the impact of the Andean uplift, global temperature, life forms, and biogeography on Calyceraceae diversification through a time-calibrated phylogeny. Calyceraceae diversification was homogeneous through time and followed a low speciation rate for the last 24 Mya, with no lineage differing much in their diversification dynamics. In accordance with the homogeneous speciation rate, we found that neither the Andean uplift, nor the evolution of global average temperature, nor the different life forms have affected its diversification. The Southern Andes is the centre of origin of the family and major clades within it, and most dispersal events occurred from the Andes to Patagonia. Most Calyceraceae species seem to have originated, evolved, and dispersed within the Argentinean Arid Diagonal, indicating that niche conservatism could have played an important role in the evolution of Calyceraceae. Differences in macroevolution dynamics could explain the asymmetry of species richness in the two sister families Asteraceae-Calyceraceae.

Paleoenvironmental changes in the Brazilian Pampa based on carbon and oxygen stable isotope analysis of Pleistocene camelid tooth enamel

ABSTRACTHere we present paleoenvironmental and paleoclimatic reconstructions of the Brazilian Pampa based on stable isotopes (δ13C, δ18O) in tooth enamel of the Pleistocene camelidsLama guanicoeandHemiauchenia paradoxafrom the Chuy Creek fossil assemblage, including oneH. paradoxafrom a stratigraphic level within a loess unit deposited during the Last Glacial Maximum (26.5–19 ka b2k). The δ13C results show that both species fed mostly on C3 plants, although the mixed diets ofL. guanicoeincluded ~30% C4 or CAM plants.H.paradoxahad C3 diets with <10% C4 or CAM plants. Both species exhibit higher δ18O and aridity indexes compared to other mammals from the assemblage, consistent with ingestion of18O‐enriched water from plants growing in arid/semi‐arid conditions. A comparison with δ13C of camelids from Argentina indicates the camelids from Chuy Creek fed on vegetation similar to that of Dry Pampa, Monte and Patagonic xerophytic steppes. Aridification and expansion of dry steppes in southern Brazil suggest a climate‐driven northeastwards shift of the Arid Diagonal of South America that may have contributed to local extinction of the Pleistocene megafauna. These Lateglacial environmental changes are reflected in the characteristics of the plant and mammalian assemblages of the modern Brazilian Pampa.

Ancient climate changes and Andes uplift, rather than Last Glacial Maximum, affected distribution and genetic diversity patterns of the southernmost mycoheterotrophic plant Arachnitis uniflora Phil. (Corsiaceae)

Arachnitis uniflora (Corsiaceae) is a mycoheterotrophic plant native to South America that grows in tropical semi-humid forests of Peru and Bolivia, in the temperate Andean-Patagonian forests of Argentina and Chile, and in the moorlands of Malvinas/Falkland Islands. This widely distributed and disjunct species offers the opportunity to explore the dynamics of evolutionary processes using phylogeographic approaches, spatio-temporal and paleodistribution reconstructions; these tools allow us to test how ancient geological events and climate changes occurred in the Miocene-Pliocene and how the more recent Pleistocene events affected diversification, demography, and genetic diversity patterns over space and time. We sampled 28 sites, covering the whole geographic range of Arachnitis uniflora . We amplified and sequenced the internal transcribed spacer (ITS), 18S rRNA, and 26S rRNA nuclear regions in 141 individuals, and the plastid 16S rRNA gene in a subset of 90 individuals. In order to reconstruct the evolutionary history of the species, we performed phylogeographic, dating analyses, spatio-temporal diffusion models, and species paleo-distribution projections. Arachnitis uniflora has an ancient origin and diversified during the Late Miocene, splitting into two genetic groups named the Northern and Patagonian groups. Haplotype diversification of both groups dated about late Miocene and early Pliocene. We detected demographic expansion at the early Pleistocene, and most diversifications and colonizations occurred before the LGM. Paleo-distribution modelling predicted few changes of the species distribution from 800 Mya to the present, showing only a range expansion at the east during the LGM. Four areas of high genetic diversity were identified suggesting refugial areas where the species persisted. Orogeny and climate changes promoted by the Andes uplift during the Late Miocene produced the main ancient genetic divergence due to the formation of the Arid Diagonal. Most diversification, colonizations, and demographic processes occurred from early Pliocene to the beginning of the Pleistocene before the Great Patagonian Glaciation, revealing a low influence of the LGM glaciations on the species evolutionary history. • First study on the evolutionary history of a mycoheterotrophic plant species • Genetic divergence in correlation with the formation of the Arid Diagonal • Andes uplift rather than Pleistocene glaciations were responsible for main diversifications. • Hotspots areas are coincident with those recovered for its fungal symbiont.

Response of shallow lakes in the arid-semiarid Pampas of Argentina to Late Holocene hydroclimatic change

This study presents a paleolimnological and paleoclimatological reconstruction based on diatoms and phytoliths of four Pampean shallow lakes (from south to north, La Salada, Sauce Grande, Los Chilenos, and Puan) strategically located along a climatic gradient from arid (south) to semiarid conditions (north). This research aims to identify the main drivers and mechanisms of long-term ecological change, and the main climatic mechanisms behind the regional hydroclimatic variability. It was found that these lakes were initially temporary, with clear waters, and eventually, became permanent with turbid waters. We propose that this change is due to an increase in precipitation in the last ca 1000 years, which resulted in higher lake levels and an increase in surface area, leading to an increased fetch and subsequent resuspension of sediment. This climatic amelioration occurred after ∼910 cal yr BP, first in what is today the arid Pampean region, then in the semiarid region, and finally in the modern humid region at ∼ -9 cal yr BP (1959 CE). Variations in lake's water level were the main driver of ecological change, followed by salinity (in Puan and La Salada) and nutrient load (in Los Chilenos and Sauce Grande). In general, those lakes on the southwest, located closer to the limit of moisture influence originating in the Pacific and Atlantic oceans (Arid Diagonal) were more sensitive to hydroclimatic changes than those located in the central Pampean region.

Historia biogeográfica de las briófitas de Chile

Some biogeographical features of bryophytes associated with subtropical-temperate ecosystems in Chile are examined, including diversity, concentration of species richness, endemism, biogeographical composition and disjunctions. The historical-biogeographical interpretation of these characteristics considers the major evolutionary changes of the group in three different temporal scenarios, according to geological, paleobotanical and molecular evidences. First, simple- and complex-thalloids liverworts represented in Chile are examined, belonging to the Classes Haplomitriopsida and Marchantiopsida- Marchantiidae, archaic lineages linked to the pre-Cenozoic colonization of the Pangea mega-continent. Examples of simple-thalloids liverworts of Class Jungermanniopsida-Pelliidae, hornworts of the Class Anthocerotopsida and mosses of the Classes Bryopsida and Polytrichopsida illustrate the paleo-austral distribution patterns of bryophytes from the temperate region of Chile, related to the Gondwana breakup and expansion of Angiosperms during the Cretaceous/Paleogene. A second scenario, considers the final uplift of the Andes and the development of the Arid Diagonal of South America during the Neogene, processes that have played a major role in the biogeographical structure of the Chilean and South American floras. In this context, leafy liverworts associated with the relict forests of the Chilean semi- arid coast stand out, particularly epiphyllous liverworts of the two most diverse families of the Class Jungermanniopsida-Jungermanniidae, Lejeuneaceae and Plagiochilaceae, adapted to microclimates favored by coastal fogs. The last scenario discusses the significant role of the Pleistocene glacial cycles in the expansion of the sub-Antarctic temperate-cold element throughout central-southern Chile, and its effects on the concentration of bryophyte richness associated with Chile’s temperate-rain ecosystems.

Volcanism rather than climatic oscillations explains the shared phylogeographic patterns among ecologically distinct plant species in the southernmost areas of the South American Arid Diagonal

Shared genetic patterns within a community of ecologically distinct species may reflect the role of past geoclimatic events imprinting species evolutionary history. Although Pleistocene glaciations are the most important processes evoked as drivers of these shared patterns, in some regions Quaternary volcanic activity should also be considered as a potential process shaping genetic diversity distribution. Additionally, phenotypic attributes related to dispersal and persistence may affect the time and manner in which species respond to geoclimatic changes. We performed a comparative phylogeographical study within a plant community of the South American Arid Diagonal to assess whether genetic patterns are better explained by climatic changes or volcanisms, taking into account the possible influence of life form and dispersal syndromes of the focal species. Chloroplast intergenic spacers were sequenced for five plant species. Genealogy, divergence time estimates, demographic and range expansion analyses were performed. Approximate Bayesian computation was used to test plausible shared phylogeographic scenarios. Climatically stable areas during the last glacial period were inferred with distribution modeling. Results showed that most species were split into northern and southern lineages separated by a phylogeographic break at around 37.5 °S, with the northern populations being genetically less diverse, inhabiting both climatically stable and unstable areas, but being severely affected by intense Plio-Pleistocene magmatic activity; the southern populations, less influenced by volcanism, appeared to be genetically more diverse and occupied climatically stable areas through time. Most recent range expansions and effective population size increases occurred after most of the volcanic episodes, before and during the Last Glacial Maximum. All species shared the same geographic origin of the detected spatial expansion. Overall, our results suggest a preponderant effect of Quaternary volcanism rather than climatic oscillations on the evolutionary history of this xerophytic community. Additionally, we found evidence that autecological traits would have modulated the community historical responses.

Atmospheric dust dynamics in southern South America: A 14-year modern dust record in the loessic Pampean region

Mineral aerosols profoundly impact global climate. Modeling of the dust cycle is the main tool used to gauge this effect. However, the scarcity of in situ modern dust flux measurements is the main reason why validation of existing models is hampered. We present the first long-term (14-year) record of dust flux in the Pampas, southern South America, home to the largest loess deposit in the Southern Hemisphere. Measured 14-year mean deposition (40 g m−2 year−1) and horizontal (362 g m−2 year−1) fluxes imply that current models underestimate the power of the central Pampas as a dust sink. Based on cross-spectral analysis, both wet and, to a lesser extent, dry deposition are found to play significant roles in atmospheric dust extraction. Dust is sourced regionally from the South American Arid Diagonal and from the shores of Mar Chiquita lake (~260 km), which we find to be the main contributor of dust particles >30 µm. Cross-spectral and satellite image analyses show that surface wind speed and precipitation at the Puna-Altiplano Plateau are controlling factors for horizontal dust flux in the Pampas. El Niño Southern Oscillation probably plays a role in controlling interannual horizontal dust flux periodicities. Finally, preliminary comparisons between modern vertical dust fluxes and loess accumulation rates point to the Pampas as a more powerful dust sink during the last deglaciation and Antarctic Cold Reversal (18–12.5 ka).

Old divergence and restricted gene flow between torrent duck (Merganetta armata) subspecies in the Central and Southern Andes.

AimTo investigate the structure and rate of gene flow among populations of habitat‐specialized species to understand the ecological and evolutionary processes underpinning their population dynamics and historical demography, including speciation and extinction.LocationPeruvian and Argentine Andes.TaxonTwo subspecies of torrent duck (Merganetta armata).MethodsWe sampled 156 individuals in Peru (M. a. leucogenis; Chillón River, n = 57 and Pachachaca River, n = 49) and Argentina (M. a. armata; Arroyo Grande River, n = 33 and Malargüe River, n = 17), and sequenced the mitochondrial DNA (mtDNA) control region to conduct coarse and fine‐scale demographic analyses of population structure. Additionally, to test for differences between subspecies, and across genetic markers with distinct inheritance patterns, a subset of individuals (Peru, n = 10 and Argentina, n = 9) was subjected to partial genome resequencing, obtaining 4,027 autosomal and 189 Z‐linked double‐digest restriction‐associated DNA sequences.ResultsHaplotype and nucleotide diversities were higher in Peru than Argentina across all markers. Peruvian and Argentine subspecies showed concordant species‐level differences (ΦST mtDNA = 0.82; ΦST autosomal = 0.30; ΦST Z chromosome = 0.45), including no shared mtDNA haplotypes. Demographic parameters estimated for mtDNA using IM and IMa2 analyses, and for autosomal markers using ∂a∂i (isolation‐with‐migration model), supported an old divergence (mtDNA = 600,000 years before present (ybp), 95% HPD range = 1.2 Mya to 200,000 ybp; and autosomal ∂a∂i = 782,490 ybp), between the two subspecies, characteristic of deeply diverged lineages. The populations were well‐differentiated in Argentina but moderately differentiated in Peru, with low unidirectional gene flow in each country.Main conclusionsWe suggest that the South American Arid Diagonal was preexisting and remains a current phylogeographic barrier between the ranges of the two torrent duck subspecies, and the adult territoriality and breeding site fidelity to the rivers define their population structure.

Shallow ground temperature measurements on the highest volcano on Earth, Mt. Ojos del Salado, Arid Andes, Chile

AbstractMt. Ojos del Salado (6893 m a.s.l.) lies within the Andean Arid Diagonal, on the Chilean–Argentinean border. Due to the extremely arid climate, surface ice is not widespread on Mt. Ojos del Salado and at similar high‐altitude massifs in the region, although ice‐bearing permafrost might be present. However, the thermal regime of the ground is relatively unknown in the region, especially outside of rock glaciers at high elevations north of 30°S. To study ground thermal regimes, in‐situ shallow ground temperature and snow coverage from satellite imagery have been surveyed for four years (2012–2016) at six sites between the elevations of 4200–6893 m a.s.l. on Mt. Ojos del Salado (27°07′S, 68°32′W). According to the ground temperature and snow coverage data at the six monitoring sites, the presence of permafrost is unlikely below 4550 m a.s.l. but likely above 5250 m a.s.l. on Mt. Ojos del Salado. In addition, the active layer becomes extremely thin around 6750 m a.s.l.

Across the Arid Diagonal: deglaciation of the western Andean Cordillera in southwest Bolivia and northern Chile

Here we review published cosmogenic records of glaciation and deglaciation from the western cordillera of the arid subtropical Andes of northern Chile and southwest Bolivia. Specifically, we examine seven published studies describing exposure ages from moraines and glaciated bedrock spanning the glaciological Arid Diagonal, the region of the dry Andes where there is no clear evidence for glaciation over at least the last global glaciation. We also present new cosmogenic 36Cl exposure ages from two previously undated sets of moraines in the deglaciated region near 22ºS. Taken together, these records indicate that the most extensive regional glaciation occurred ca. 35-45 ka, followed by slow, punctuated retreat through the global last glacial maximum, and rapid retreat after ~15-17 ka. In the vicinity of the large Altiplanic lakes that existed during the late glacial stage, the 15-17 ka moraines overrode the earlier moraines, whereas elsewhere regionally, on both sides of the Arid Diagonal, late glacial wet periods are represented only by less-prominent moraines in more retracted positions.

Travelling to the south: Phylogeographic spatial diffusion model in Monttea aphylla (Plantaginaceae), an endemic plant of the Monte Desert.

Effects of Pleistocene climatic oscillations on plant phylogeographic patterns are relatively well studied in forest, savanna and grassland biomes, but such impacts remain less explored on desert regions of the world, especially in South America. Here, we performed a phylogeographical study of Monttea aphylla, an endemic species of the Monte Desert, to understand the evolutionary history of vegetation communities inhabiting the South American Arid Diagonal. We obtained sequences of three chloroplast (trnS–trnfM, trnH–psbA and trnQ–rps16) and one nuclear (ITS) intergenic spacers from 272 individuals of 34 localities throughout the range of the species. Population genetic and Bayesian coalescent analyses were performed to infer genealogical relationships among haplotypes, population genetic structure, and demographic history of the study species. Timing of demographic events was inferred using Bayesian Skyline Plot and the spatio-temporal patterns of lineage diversification was reconstructed using Bayesian relaxed diffusion models. Palaeo-distribution models (PDM) were performed through three different timescales to validate phylogeographical patterns. Twenty-five and 22 haplotypes were identified in the cpDNA and nDNA data, respectively. that clustered into two main genealogical lineages following a latitudinal pattern, the northern and the southern Monte (south of 35° S). The northern Monte showed two lineages of high genetic structure, and more relative stable demography than the southern Monte that retrieved three groups with little phylogenetic structure and a strong signal of demographic expansion that would have started during the Last Interglacial period (ca. 120 Ka). The PDM and diffusion models analyses agreed in the southeast direction of the range expansion. Differential effect of climatic oscillations across the Monte phytogeographic province was observed in Monttea aphylla lineages. In northern Monte, greater genetic structure and more relative stable demography resulted from a more stable climate than in the southern Monte. Pleistocene glaciations drastically decreased the species area in the southern Monte, which expanded in a southeastern direction to the new available areas during the interglacial periods.

Distribution of ostracods in west-central Argentina related to host-water chemistry and climate: implications for paleolimnology

Ecological and biogeographical studies of Neotropical non-marine ostracods are rare, although such information is needed to develop reliable paleoecological and paleoclimatic reconstructions for the region. An extensive, yet little explored South American area of paleoclimatic interest, is the arid-semiarid ecotone (Arid Diagonal) that separates arid Patagonia from subtropical/tropical northern South America, and lies at the intersection of the Pacific and Atlantic atmospheric circulation systems. This study focused on the Laguna Llancanelo basin, Argentina, a Ramsar site located within the Arid Diagonal, and was designed to build a modern dataset using ostracods (diversity, spatial distribution, seasonality, habitat preferences) and water chemistry. Cluster and multivariate analysis of the data indicated that salinity is the most significant variable segregating two ostracod groups. Limnocythere aff. staplini is the only species that develops abundant populations in the saline ephemeral Laguna Llancanelo during almost all seasons, and is accompanied by scarce Cypridopsis vidua in summer. The latter species is abundant in freshwater lotic sites, where Ilyocypris ramirezi, Herpetocypris helenae, and Cyprididae indet. are also found in large numbers. Darwinula stevensoni, Penthesilenula incae, Heterocypris incongruens, Chlamydotheca arcuata, Chlamydotheca sp., Herpetocypris helenae, and Potamocypris smaragdina prefer freshwater lentic conditions (springs), with C. arcuata and Chlamydotheca sp. found only in the Carapacho warm spring, which has a year-round constant temperature of ~20 °C. Seasonal sampling was necessary because some taxa display a highly seasonal distribution. Species that were recorded have either subtropical or Patagonian affinities, although a few taxa are endemic or common to both regions. These data can serve as modern analogues for reconstructing the late Quaternary history of the area, and to investigate the extent and position of the arid/semiarid ecotone (Arid Diagonal) during past glacial/interglacial cycles.

Upper Quaternary evolution of the dune field of the Bolsón de Fiambalá, Catamarca: Sand dispersal at the Andes piedmonts

The South American Arid Diagonal extends in Argentina from Puna to Patagonia regions. Several dune fields are scattered between the Andes and Pampas ranges, covering plains and plateaus. One of the northernmost dune fields is occupying the tectonic valley known as Bolsón de Fiambalá (27°S; 67°W) White transverse dunes extend from west to east, climbing to the Fiambalá Range. Some outcrops from the surrounding area allow to understand the evolution of this dune field. At the Chaschuil valley, a profile composed of 4 m of stratified sands and gravels were sampled at Las Lozas site. Epiphytes and benthic diatom assemblages suggest a shallow lake located at 3700 m altitude. Many of these brackish/freshwater aerophilous taxa tolerate desiccation periods and salt concentration. The assemblages were dominated by Nitzschia frustulum, Nitzschia linearis, Achnanthes thermalis var. rumrichorum, Epithemia adnata, Pinnularia viridis y Nitzschia capitellata. Limestones from this outcrop were dated on 32,000 ± 520 and 29,380 ± 410 14C years BP (Garleff et al., 1993), suggesting the Marine Isotopic Stage 3. The Holocene Interglacial is recorded either at the Chaschuil and Abaucán rivers valleys. Lake deposits at 3000 m altitude gave ages between 6175 ± 70 and 2990 ± 70 14C years BP (Garleff et al., 1993). The sand of this dune field at the northern part of the Bolsón de Fiambalá was supplied by the fanglomerates located to the west, at Medanitos. There is also a significant supply of pumicite, derived from the Cerro Blanco volcanic dome. An aridity increase have been previously recorded from archaeological data and confirmed by the discharge records of the Abaucán River during the 1919–1957 interval. Although these sand dunes with a high content in volcanic glass clearly derived from the Andes, other sand dunes of central Argentina derived from the deactivation of the Desaguadero-Curacó system.

Territorial Management, Environmental Degradation and Resilience in Rural Areas of the Argentinian Temperate Arid Diagonal

Rural areas located in the South of Buenos Aires province represent a clear example of an extra marginal Pampean area with evidence of environmental degradation. The area is located in the Argentinean Temperate Arid Diagonal and presents a semi-arid to arid climate with high variability, mostly regarding precipitation regimes. Throughout the twentieth century and up to the present, these lands were incorporated into the new logics of globalized agricultural production leading to the deforestation of the native forest and the development of unsustainable agriculture with methods and techniques which are highly aggressive towards the environment. In addition to these practices, the absence of public policies aiming at territorial planning even enforced the environmental degradation of the area. Degradation in these areas involves three aspects of the same reality: Firstly, the natural aspect, which refers to changes in soil characteristics causing desertification and loss of biodiversity. Then, the economical aspect with an increasing indebtedness of the farmers and consequently rural impoverishment. Finally, the social aspect that manifests itself in the degradation associated with land abandonment, rural exodus and the loss of cultural values and traditions. The goal of this article is to develop a concept, based upon three models, constituting the framework for a stepwise development towards sustainability and resilience: (1) a conceptual model explaining different land management processes in which shaped these rural areas, (2) a process model covering the relationship between (land use/management) processes and environmental degradation and (3) a future model, proposing alternatives for rural land management, related to the concept of rural resilience.

Zooming out from archaeological discontinuities: The meaning of mid-Holocene temporal troughs in South American deserts

Building on previous research at smaller scales, in this paper we assemble paleoecological data and archaeological time-series for deserts located in three latitudinal bands along the South American Arid Diagonal (16°–41°S, ∼1,236,000km2 of area). Diverse proxies suggest the existence of arid and extremely arid conditions in large parts of these deserts. Working with a database composed of 914 archaeological dates falling between the first human presence in each region and 3000years BP, which produce a minimum number of 578 occupational events, we identify a series of patterns at a macro-regional scale: a robust increase in the temporal signal at the beginning of the mid-Holocene (8000–7600years BP) followed by two troughs (7600–7200, 6800–6400years BP) during this period. The spatial scope of the data presented provides an opportunity for disentangling processes of spatial re-localization from actual changes in population size. We present a demographic hypothesis at a macro-regional scale, which suggests the existence of mid-Holocene population bottleneck(s). This hypothesis would account not only for the mid-Holocene troughs, but also for the posterior record of an intense and relatively rapid population growth (release) observed in many regions of the arid diagonal. These mid-Holocene events provide the context for independent trajectories of economic intensification based on different sets of resources -marine foods, camelids, and also probably wetland resources-, some of which lead to domestication processes. These cases occur in association with a tendency towards reduced residential mobility in regions that may have acted as refugia during arid periods of the mid-Holocene.The analysis produces testable expectations for future research at different scales and for different research domains, including human DNA and morphometric evidence. We consider that these issues have a fecund comparative potential, since the analysis of the socio-demographic meaning of archaeological discontinuities in different continents shares a similar conceptual structure.

Spatiotemporal diversification of a low‐vagility Neotropical vertebrate clade (short‐tailed opossums, Didelphidae: Monodelphis)

AbstractAimTo infer historical‐biogeographical patterns and processes in South America based on estimated divergence times and ancestral distributions for a diverse clade of small marsupials (Monodelphis).LocationSouth America.MethodsWe estimated a time‐scaled phylogeny using sequence data from four nuclear genes and one mitochondrial gene for most currently recognized species, which we also scored for biome occupancy. We used maximum‐likelihood methods that explicitly model historical‐biogeographical processes to estimate ancestral distributions.ResultsThe earliest cladogenetic events in the genus occurred in the late Miocene, with subsequent diversification from the early Pliocene to the late Pleistocene. Model selection suggests an important role for founder‐event speciation, a process seldom accounted for in previous biogeographical analyses of continental clades. Two equivalently optimal models that incorporate this process each reconstruct the most recent common ancestor of Monodelphis as occurring in both Amazonia and the Atlantic Forest, from which the Andes, the Arid Diagonal (Caatinga, Cerrado, Chaco) and other neighbouring biomes were colonized during the Pliocene and Pleistocene.Main ConclusionsThe diversification of Monodelphis was not restricted to a narrow time interval, suggesting that speciation cannot be attributed to a single leading factor such as tectonism or Pleistocene climatic fluctuations. In particular, speciation within the Atlantic Forest biome appears to have occurred in the Neogene, whereas most Amazonian speciation events are substantially younger. Amazonia and/or the Atlantic Forest hosted most diversification events within Monodelphis and were the historical sources of lineages that subsequently colonized other areas. Founder‐event speciation, a concept traditionally associated with long‐distance dispersal among islands, must sustain other interpretations in historical‐biogeographical analyses of non‐vagile organisms in continental contexts. Possible mechanisms for founder‐event speciation in Monodelphis include historically transient connections between currently disjunct biomes and rapid reproductive isolation of populations colonizing adjacent but ecologically disparate biomes.

Cueva Huenul 1 Archaeological Site, Northwestern Patagonia, Argentina: Initial Colonization and Mid-Holocene Demographic Retraction

In this paper 1 present an intensively dated chrono-stratigraphic sequence for the Cueva Huenul 1 archaeological site, Neuquen Province, Argentina. Located in the inland deserts of northwestern Patagonia, Cueva Huenul 1 offers a remarkable temporal record of events for a largely unstudied desert region. I connect this local record with available data on a macroregional scale to reassess (1) the timing of the first human colonization of the area and its implications for explaining the extinction of megafauna (ca. 14,000-10,000 cal B.P.) and (2) the decrease in human occupation recorded in several South American deserts during parts of the mid-Holocene (ca. 8000-6000 cal B .P.). The data presented here show a gap of about 1,500 calendar years between the extinction of megafauna and the appearance of humans. A review of evidence from the northern Patagonia and southern Cuyo regions is consistent with this record, favoring ecological causes for regional extinction ofmegafaunal taxa. Integration of this record with those indicating the earliest human presence in South America (e.g., Monte Verde, Chile) is consistent with a process of human radiation to the inland Patagonian deserts from nodes of initial occupation. The chrono-stratigraphic sequence from Cueva Huenul 1 also contributes to an assessment of a trough in human occupation along the South American Arid Diagonal around 8000-6000 cal B.P. Evidence for a decrease in occupational intensity during this period is found in the highland and lowland deserts in Mendoza and San Juan, the Puna region in northwestern Argentina, the Atacama Desert in Chile, and possibly the Pampean region. Previous researchers have suggested that persistent arid conditions would have produced increasing landscape fragmentation, particularly affecting desert areas. A more specific understanding of the demographic processes underlying this archaeological signal is needed. In this paper I suggest that this trough reflects not only spatial and social rearrangements, but also a macro-regional demographic retraction. This could have caused a population bottleneck with lasting biological and cultural implications.

Geographic and Potential Distribution of a Poorly Known South American Bat,Histiotus macrotus(Chiroptera: Vespertilionidae)

The vespertilionid bat Histiotus macrotus occurs in western Argentina, central regions of Chile and south of Argentina and Chile, and it may be also present in Bolivia and southern Peru. In this work, we analyzed the geographic and potential distribution of a poorly known species of South American bat. As a tool, environmental niche modeling has been used to study the distributional patterns of species and more recently, taxonomic boundaries of cryptic species. We used MaxEnt v 3.3.e, Worldclim database and a vegetation map, covering the entire area of species' occurrence. We registered 64 localities from Argentina (43), Chile (10), Peru (8) and Bolivia (5). We divided recording localities in different datasets according to several taxonomic schemes, and analyzed potential distribution models separately (i.e., all known records; Argentina-Chile; Peru) in five different models. Models including all known localities showed a disjoint distribution, with two basic core areas of high predictive values, one in NW Argentina and another in southern Chile and SW Argentina separated by the South American Arid Diagonal. A third area appeared in Atacama and Sechura deserts in the models that included Peruvian and Bolivian localities. Model including only Peruvian localities showed the opposite pattern, with high predictive values only in arid environments from southern Peru. We interpreted that localities correctly assigned to H. macrotus belong to a taxonomic complex distributed in two contrasting areas, each one inhabited by a different taxon: 1) Bolivia and NW Argentina and 2) S and central Chile and SW Argentina. Given the systematic uncertainty of Histiotus, these two forms might be sister species or may not share an immediate common ancestor within the genus. Further, we consider that the specimens from localities referred to H. macrotus from southern Peru should be revised. These alternatives await a comprehensive molecular phylogenetic analysis of Histiotus.