Great Patagonian Glaciation Research Articles

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.

Early and Middle Pleistocene glaciation of the southern Patagonian plain

Evidence of at least three Early to Middle Pleistocene glaciations is recorded in the stratigraphic exposures near the outer limit of glaciation in southern Patagonia. At Cabo Vírgenes, at the mouth of the Strait of Magellan, up to 70 m of till, gravel, sand, and stony silt were deposited in a grounding-line environment at the front of the Magellan lobe along a front several tens of kilometres wide. Accommodation space for the sediments was produced by glacio-isostatic depression resulting from the advance of the Magellan lobe to the Atlantic coast. At that time, the ‘moat’ in which the sediments accumulated may have been seaward of the modern Atlantic shoreline because the continental shelf is shallow and sea level was much lower than it is today. The sediments at Cabo Vírgenes are normally magnetized, carry no reversed overprints, and thus probably date to the Brunhes Chron (<0.774 Ma). Seacliff exposures south of the Strait of Magellan along the Atlantic coast of northern Tierra de Fuego expose two tills separated by glaciofluvial sediments. Although not dated, the tills record two advances of the Magellan lobe onto the Atlantic continental shelf. The location of the exposures relative to Cabo Vírgenes indicates that the upper of the two tills may correlate with the Cabo Vírgenes drift. The Tres de Enero highway cut, 90 km northwest of Cabo Vírgenes, exposes lodgement tills deposited during the Great Patagonian glaciation (GPG) – two stacked, normally magnetized tills overlie a reversely magnetized till. Truncated sand wedges separate each of the three tills, indicating that the tills record three separate Early to Middle Pleistocene glaciations. The younger of the two normally magnetized tills, and perhaps both, were deposited in the Brunhes Chron; the lowest, reversely magnetized till records extensive glaciation late during the Matuyama Chron (2.608–0.780 Ma). At Bella Vista in the Río Gallegos valley, a 0.89-Ma-old basalt flow caps a thick unit of normally magnetized glaciofluvial gravel, which was probably deposited during the Jaramillo Subchron (1.075–0.991 Ma), but certainly not later. Sediments at Tres de Enero and Bella Vista show that the GPG is not a single event as originally thought, but rather at least three glaciations, perhaps spanning several hundred thousand years.

Quaternary landscape evolution of patagonia at the Chilean Triple Junction: Climate and tectonic forcings

Glacial and fluvial landforms record the recent history of the Earth surface and have the potential to provide information about uplift and climate changes during Quaternary times. Patagonia hosts uniquely well-preserved moraine deposits, along with outwash and fluvial terraces. This offers the possibility of determining the timing of glacier advances since the Great Patagonian Glaciation (ca. 1.2 Ma) and allows us to investigate landscape response to climate and tectonic forcing.In this study, we present twenty-eight new in situ 10Be exposure ages for glacial deposits, outwash sediments, and fluvial terraces at the latitude of the Chile Triple Junction (∼46°30′S). We combine this database with a detailed mapping and a morphological analysis of the Deseado River terrace system. The glacial and outwash deposits document at least five major glacial advances in the Lago Buenos Aires valley before the deposition of the Moreno system during Marine Isotope Stage (MIS) 8. Key advances occurred during MIS 12 and MIS 16. Further ice expansions that resulted in Telken V and VI/VII outwash surfaces date to 780 ka and ca. 1.2 Ma respectively. Overall, our data show the difficulty of dating pre-LGM glacial deposits using surface exposure methods and reinforce the idea that outwash surfaces are better targets to determine the age of glacial sequences in the region.The Deseado River terrace system yields stratigraphically consistent ages that range from 1167 to 447 ka, which indicate that these terraces formed during Pleistocene times. Our analysis suggests that terraces T3, T7 and T8 may have been formed during cold stages, close to the glacial-interglacial transitions. We also calculated incision rates that reveal a strong initial pulse, from ca. 1200 to 900 ka, which was followed by significantly weaker river incision pulses.Finally, our geomorphological analysis confirms that the oldest fluvial terraces of the Deseado River system exhibit a NE-SW tilting through a broad area, next to the Atlantic Ocean. This was previously interpreted as the surface response to a long-wavelength dynamic uplift, a phenomenon that should be reassigned to the early Pleistocene.

Molecular phylogeny of the “salty” Liolaemus species (Reptilia: Squamata): anomalus group, endemic of the Argentina Monte Desert

In Argentina, the Monte ecoregion extends for more than 2,000 km from NW Argentina to borealPatagonia, and includes many salt-pans and barren flatlands colonized by the monophyleticLiolaemus anomalus group that includes seven species. Some of their external morphologicalcharacteristics and behaviors are very unusual for the genus, and this has led to a complextaxonomic history. The group is very poorly known except for a recent paper with descriptionsof three species and morphological-based phylogenetic hypotheses. Of the four recognizedspecies, two are threatened and one is vulnerable, and while the conservation status of thethree recently described species is unknown, they are suspected to also be under some degreeof threat. We reviewed all georeferenced localities known to produce a distribution map, andsequenced two mitochondrial and four nuclear genes, for representatives of all species. Weinferred a time-calibrated species tree showing that the evolutionary history of this clade occurredentirely during the Pleistocene, with most of the divergences very recent. The climaticand geomorphological changes driving this divergence started during the Great PatagonianGlaciation, initially separating the two northwestern-most distributed species (L. pipanaco +L. pseudoanomalus) from the rest. Given the very recent evolutionary history of the group andtheir unique and conserved morphology, incongruent topologies among datasets are expected; adetailed genome-wide dataset will be needed to fully assess and resolve their speciation history.

Connection, isolation and reconnection: Quaternary climatic oscillations and the Andes shaped the phylogeographical patterns of the Patagonian beeCentris cineraria(Apidae)

AbstractThe joint effect of the Andes as a geographical barrier and the Quaternary glaciations as promoters of genetic divergence remains virtually unexplored in southern South America. To help fill this knowledge gap, in this study we investigated the demographic history of Centris cineraria, a solitary bee mainly distributed in Patagonia. We used mitochondrial and nuclear markers and performed phylogeographical and dating analyses, adjusted spatio-temporal diffusion and species distribution models, and used Approximate Bayesian Computation to identify likely historical demographic scenarios. Our results revealed that during glacial periods the Andes represented a barrier due to the extent of the ice-sheets and the occurrence of unsuitable habitats, while interglacials allowed for gene flow across the Andes. Secondary contact between previously isolated lineages was evident across at least two low-altitude Andean areas, the northern one being a putative glacial refugium. Our findings also suggest that C. cineraria has persisted in situ in four periglacial refugia located along a north–south transect, congruent with the maximum extent of the ice sheet during the Greatest Patagonian Glaciation. As the first phylogeographical study of Patagonian insects, our work reveals that the interaction between Quaternary climatic oscillations and the Andes as a barrier was the main driver of the spatial and demographic history of C. cineraria.

Coalescent-based species delimitation in the sand lizards of the Liolaemus wiegmannii complex (Squamata: Liolaemidae)

Coalescent-based algorithms coupled with the access to genome-wide data have become powerful tools for assessing questions on recent or rapid diversification, as well as delineating species boundaries in the absence of reciprocal monophyly. In southern South America, the diversification of Liolaemus lizards during the Pleistocene is well documented and has been attributed to the climatic changes that characterized this recent period of time. Past climatic changes had harsh effects at extreme latitudes, including Patagonia, but habitat changes at intermediate latitudes of South America have also been recorded, including expansion of sand fields over northern Patagonia and Pampas). In this work, we apply a coalescent-based approach to study the diversification of the Liolaemus wiegmannii species complex, a morphologically conservative clade that inhabits sandy soils across northwest and south-central Argentina, and the south shores of Uruguay. Using four standard sequence markers (mitochondrial DNA and three nuclear loci) along with ddRADseq data we inferred species limits and a time-calibrated species tree for the L. wiegmannii complex in order to evaluate the influence of Quaternary sand expansion/retraction cycles on diversification. We also evaluated the evolutionary independence of the recently described L. gardeli and inferred its phylogenetic position relative to L. wiegmannii. We find strong evidence for six allopatric candidate species within L. wiegmannii, which diversified during the Pleistocene. The Great Patagonian Glaciation (∼1 million years before present) likely split the species complex into two main groups: one composed of lineages associated with sub-Andean sedimentary formations, and the other mostly related to sand fields in the Pampas and northern Patagonia. We hypothesize that early speciation within L. wiegmannii was influenced by the expansion of sand dunes throughout central Argentina and Pampas. Finally, L. gardeli is supported as a distinct lineage nested within the L. wiegmannii complex.

Echoes of the whispering land: interacting roles of vicariance and selection in shaping the evolutionary divergence of two Calceolaria (Calceolariaceae) species from Patagonia and Malvinas/Falkland Islands

A key to understanding the origin and identity of young species lays on the knowledge of the Quaternary climatic oscillations’ effect on gene flow and vicariance. Even though the effect of climatic fluctuations is relatively well understood for southern hemisphere plant species, little is known about their effect on the evolutionary histories of species from mainland and islands. Thus, we investigated whether Quaternary climate-driven fluctuations translated into lineage divergence and speciation, followed or not by climatic niche differentiation, in two allopatric plant species, Calceolaria uniflora and C. fothergillii from Patagonia and Malvinas/Falkland islands, respectively. We sampled the range of both species, and sequenced two chloroplastic (cpDNA; trnS–trnG and trnH–psbA), and one single copy “anonymous” non-coding nuclear region (nDNA). We performed phylogeographic and dating analyses, and adjusted spatio-temporal diffusion models. We complemented molecular evidence with climatic niche differentiation analyses and species paleo-distribution projections. A species coalescent reconstruction based on multi-locus data retrieved both species as monophyletic. Estimates from cpDNA indicated the species diverged during the Great Patagonian Glaciation. Chloroplast and nuclear DNA showed east–west distribution of the main genetic groups but with contrasting spatial genetic diversity. The spatio-temporal diffusion analyses showed that between 1–0.8 Mya and 570 Kya the lineage leading to C. fothergillii diverged from C. uniflora and arrived to the islands. Climatic niche projections hindcasted range expansions during glaciations, and contractions during the interglacial periods. Comparisons of climatic niches between the two study species indicated that temperature variables show evidence of niche conservatism while precipitation regimes supported niche divergence, even when considering the background environmental divergence. Our study indicates that glacial fluctuations affected the mainland/islands connections favouring speciation mediated not only by isolation, but also by climatic niche differentiation.

Low level of genetic divergence between Harpagifer fish species (Perciformes: Notothenioidei) suggests a Quaternary colonization of Patagonia from the Antarctic Peninsula

The evolution of the marine benthic fauna of Antarctica has been shaped by geological and climatic atmospheric factors such as the geographic isolation of the continent and the subsequent installation of the Antarctic Circumpolar Current (ACC). Despite this isolation process, strong biogeographic links still exist between marine fauna from the Antarctic Peninsula and southern South America. Recent studies in different taxa have shown, for example, that shallow benthic organisms with long larval stages maintained contact after the physical separation of the continents and divergence may be associated with the intensification of the ACC in the late Miocene—early Pliocene. In this context, here we performed phylogenetic reconstructions and estimated the level of molecular divergence between congeneric species of Harpagifer, a marine notothenioid from the Antarctic Peninsula (Harpagifer antarcticus) and Patagonia (H. bispinis) using the mitochondrial control region. Phylogenies were reconstructed using Maximum Parsimony and Bayesian Inference, while the divergence time of H. antarcticus and H. bispinis was estimated following a relaxed Bayesian approach and assuming a strict molecular clock hypothesis. According to our estimation, the divergence between H. bispinis and H. antarcticus is more recent than expected if it was associated with the intensification of the ACC during the mid to late Miocene. We propose that climatic and oceanographic changes during the coldest periods of the Quaternary (i.e., Great Patagonian Glaciation, 1–0.9 Ma) and the northward migration of the Antarctic Polar Front may have assisted the colonization of southern South America by Harpagifer, from the Antarctic Peninsula via the Scotia Arc Islands.

Glacial, fluvial and volcanic landscape evolution in the Laguna Potrok Aike maar area, Southern Patagonia, Argentina

We describe the Pleistocene evolution of the landscape in the Laguna Potrok Aike area in southern Patagonia, Argentina, based on a geomorphological survey. Basaltic eruptions generated tablelands and scoria cones between the Late Miocene and Middle Pleistocene, and phreatomagmatic eruptions produced maars during Middle and Late Pleistocene time. The first glaciations during the Early Pleistocene generated a gently undulating to flat landscape that was affected by cryogenic processes; they are documented but not dated. Outwash surfaces indicate that the Greatest Patagonian Glaciation was multi-phased. The eruption that produced Potrok Aike maar truncated terrace levels dating to a Middle Pleistocene glaciation. The abundance of maars dating to this time may be linked to large amounts of water associated with meltwater streams and permafrost. The landscape in the Potrok Aike area has changed little since the Middle Pleistocene and only minor modifications of landforms have occurred due to cryogenesis, moderate fluvial incision, mass wasting and eolian activity.

Divergence between passerine populations from the Malvinas - Falkland Islands and their continental counterparts: a comparative phylogeographical study

Bursts of speciation have followed colonization of remote oceanic islands by diverse taxa, a process evidenced by island endemics around the world. The present study explores whether the Malvinas – Falkland Islands (MFI), a relatively understudied archipelago off the South Atlantic coast of Patagonia, harbour endemic genetic lineages of passerine birds. Nine passerine species nest regularly in the MFI (Cinclodes antarcticus, Muscisaxicola maclovianus, Troglodytes cobbi, Cistothorus platensis, Turdus falcklandii, Anthus correndera, Melanodera melanodera, Sturnella loyca, and Carduelis barbata). Mitochondrial DNA (cytochrome c oxidase I sequences) are used to quantify and compare divergence between insular and continental populations, finding genetic patterns to vary across these nine species. Most MFI passerines do not show significant genetic differentiation from continental populations, whereas C. platensis, M. melanodera, and T. falcklandii are modestly diverged. Finally, T. cobbi differes markedly from its closest continental relative Troglodytes aedon, a result that is confirmed using nuclear and vocal data. The study also identifies broadly divergent lineages within continental populations of C. platensis and T. aedon. Taken together, these results suggest that the land bird populations of the MFI were established at different times. Troglodytes cobbi is the oldest MFI land bird, splitting from continental T. aedon during the Great Patagonian Glaciation of the Pleistocene. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••–••.

Late Cenozoic glaciations in Patagonia and Tierra del Fuego: an updated review

The Patagonian glaciations developed from the latest Miocene (c. 6 Ma) in multiple events of varied duration and intensity. Most of the present glacial landscape is the result of the glacial modelling during the Pleistocene, since the Great Patagonian Glaciation (GPG; c. 1 Ma). The Patagonian Andes were covered by a continuous mountain ice sheet, from 37°S to Cape Horn (56°S), in at least five major glaciations over more than 15 cold events over the last million years. Before GPG, the glaciers were restricted to isolated ice caps along the mountain ranges. The present drainage network was developed after the Last Glacial Maximum [LGM; c. 25 calibrated kiloyears before present (cal. ka BP)], particularly those cases with drainage reversal, when the glaciers began to melt as a result of global climatic changes. The environmental impact of glaciations extended not only all over Patagonia, but to the Pampas as well.

Neosclerocalyptus spp. (Cingulata: Glyptodontidae: Hoplophorini): cranial morphology and palaeoenvironments along the changing Quaternary

We propose that the particular high latitudinal distribution of Neosclerocalyptus (Glyptodontidae) and the cyclic nature of the Pleistocene glacial–interglacial events were factors that probably stimulated morphological evolution of its fronto-nasal sinuses, a feature unique among glyptodonts. The distributions of the species, and the majority of its records, are associated with sediments related to arid and semiarid environments. Four species are recognized during the last million years in southern South America. The first record of Neosclerocalyptus (N. pseudornatus) coincides with the “Great Patagonian Glaciation” and shows the lowest grade of pneumatization on its skull. Neosclerocalyptus paskoensis (the most derived species), limited to Oxygen Isotopic Stage 2, shows the greatest development of fronto-nasal pneumatization. The restricted geographic range of Neosclerocalyptus, the possible absence of geographic barriers during the Pleistocene, and the absence of cases of sympatry, allow us to speculate the existence of a single continuous lineage of successive species, showing an anagenetic process.

Multiple periglacial refugia in the Patagonian steppe and post‐glacial colonization of the Andes: the phylogeography of Calceolaria polyrhiza

AbstractAim We perform a phylogeographical study of an endemic Patagonian herbaceous plant to assess whether geographical patterns of genetic variation correspond to in situ Pleistocene survival or to glacial retreat and post‐glacial expansion. We also seek to determine the locations of potential glacial refugia and post‐glacial colonization routes.Location Southern Andes and Patagonian steppe.Methods We used Calceolaria polyrhiza, a widely distributed Patagonian herbaceous plant that occurs mainly in the understorey of Nothofagus rain forests and in the arid Patagonian steppe, as our model system. The chloroplast intergenic spacer trnH–psbA was sequenced for 590 individuals from 68 populations. Sequence data were analysed using phylogenetic (maximum parsimony, maximum likelihood and Bayesian inference) and population genetic (spatial analyses of molecular variance, mismatch distributions and neutrality tests) methods. Nested clade phylogeographic analyses, and divergence time estimates using a calibrated molecular clock, were also conducted.Results A total of 27 haplotypes identified in the present study clustered into four primary genealogical lineages, revealing three significant latitudinal phylogeographical breaks. The two high Andean lineages probably split first, during the late Miocene, and the Patagonian lineage split around 4 Ma, coincident with the establishment of the Patagonian steppe. Within each haplogroup, major diversification occurred in the Pleistocene. The Patagonian groups show a pattern consistent with a rapid post‐glacial expansion and colonization of the Andean flanks, achieved independently by four lineages. The highest haplotype diversity was found along a longitudinal transect that is remarkably congruent with the limit of the ice‐sheet extension during the Greatest Patagonian Glaciation. A north‐east expansion is evident, which is probably associated with the ‘Arid Diagonal’ fluctuations.Main conclusions Glacial climate fluctuations had a substantial impact on the diversification, distribution and demography of the study species. A scenario of multiple periglacial Pleistocene refugia and subsequent multiple recolonization routes, from eastern Patagonia to the Andean flanks, may explain the phylogeographical patterns observed. However, current genetic structure also preserves the imprints of older events that probably occurred in the Miocene and Pliocene, providing evidence that multiple processes, operating at different spatial and temporal scales, have moulded biodiversity in Patagonia.

Glaciations in Patagonia and Tierra del Fuego during the Ensenadan Stage/Age (Early Pleistocene–earliest Middle Pleistocene)

While the Ensenadan Stage/Age (ca. 2.1 to 0.5 Ma) was characterized by certain mammal associations in the Pampean plains, the Andean ranges of Patagonia and Tierra del Fuego, their piedmont areas and, in some cases, the adjacent lowlands were undergoing a well-defined alternating sequence of glacial and interglacial stages driven by the regional climate of Southernmost South America and Antarctica. This paper reviews the available geographical, geological and chronological evidence of glaciation during the Ensenadan stage/age, with perhaps more than 15 distinct glacial events, including the Great Patagonian Glaciation (GPG) and other cold episodes that took place before and after it. Finally, a tentative correlation of Patagonian glacial episodes and the Pampean biostratigraphic stages, based on radiometric dating and paleomagnetic studies, is herein presented.

Can glacial erosion limit the extent of glaciation?

In southern South America, the maximum areal extent of ice during the Quaternary Period, the Greatest Patagonian Glaciation (GPG, [Mercer, J.H., 1983. Cenozoic glaciation in the southern hemisphere. Annual Reviews of Earth and Planetary Science 11, 99–132.]), occurred at 1.1 Ma and subsequent glaciations were overall less extensive. The GPG preceded global minimum temperatures and maximal volume of ice, which occurred in the last ~ 800 kyr, as recorded in the marine δ 18O record. Significant modification of the drainage morphology of the southern Andes from a non-glaciated to glaciated landscape occurred throughout the Quaternary Period. We infer a non-climatic relationship between glacial modification of the mountains and the decreasing extent of ice and we discuss processes of landscape development that could have caused the trend. Specifically, these include modification of valleys, such as development from a V- to a U-shape, and lowering of mass-accumulation areas. Such changes would strongly affect glacial dynamics, the mass balance profile and mass-flux during succeeding glaciations, especially for low-gradient outlet glaciers occupying low areas. Other areas around Earth (at least where ice has been warm-based) also may exhibit a non-random trend of decreasing extent of ice with time, ultimately because of glacial erosion in the Quaternary Period.