Editorial

The history of South Atlantic palaeogeography begins with the supercontinent, Pangaea. The assembly of Pangaea began with the middle Palaeozoic collision of north-western Europe with North America on the west and the Siberian platform on the east to form the continent called Laurussia. Shortly thereafter (geologically), Gondwana collided with Laurussia. The final assembly of Pangaea occurred in the Early Triassic with the collision between North and South China that raised the Chinling Range (J. M. Parrish et al. 1986). No sooner had Pangaea come together than it began breaking up. Continental deposits associated with the initial rift valleys in eastern North America are Triassic in age. The Central Atlantic opened first between north-western Africa and south-eastern North America. Because South America and Africa were still one plate, the opening of the Central Atlantic caused relative motion between North and South America; the Gulf of Mexico and eventually the Caribbean formed in the intervening space. The opening of the South Atlantic began in the Early Cretaceous. The final plate separation in the circum-Atlantic region was between North America and north-western Europe. The central focus of this book is the history of connections between Africa and South America, and so the history of the South Atlantic forms the principal focus of this chapter. However, connections between North and South America and Africa and Europe (and thus North America) are also discussed.

Aim Several mechanisms contribute to the plant biodiversity of the Neotropics, with the highlands of South America serving as important hotspots of diversity. In particular, the Brazilian highlands exhibit high biodiversity due to complex diversification dynamics and a mixture of contributions from different biomes. In this study, we reconstruct the timing and potential triggers of diversification of Agalinis , hemiparasitic plants that inhabit open grassland habitats, to investigate their biogeographic history and migration patterns across the Americas. Location North, Central and South America. Taxon Agalinis . Methods We reconstructed dated phylogenies of Agalinis using a secondary calibration approach, sampling 73% of the known species, including multiple species from the Andes and Brazilian highlands. We inferred ancestral distributions to understand migration patterns between North and South America and within South America. Additionally, we investigated shifts in diversification rates within the genus and reconstructed ancestral pollination syndrome and life‐history strategy states. All analyses were performed across a distribution of trees to account for phylogenetic uncertainty. Results Agalinis likely originated in south‐eastern North America during the early Miocene and rapidly diversified, followed by movement into South America in the Late Miocene or Early Pliocene. We propose two possible routes for Agalinis movement into South America: either through the Andes or via the South American lowland grasslands (e.g., Chaco, Pampas, Cerrado, Caatinga, Llanos), using grassland corridors for dispersal within the continent. After its arrival in South American highlands, the clade underwent rapid diversification. State reconstructions indicated that the genus had a bee‐pollinated ancestor and that hummingbird pollination evolved only once, with many transitions back to bee pollination. In contrast, the perennial life strategy evolved multiple times within the genus, including at least once in the ancestor of all South American species and twice in the North American species. Main Conclusions Agalinis likely originated in North America and later migrated to South America, followed by rapid diversification (i.e., ‘dispersification’). Thus, Agalinis is a clade that refutes the tropical conservatism hypothesis and the out‐of‐the‐tropics model. Moreover, the dispersal to the Brazilian highlands was from nearby species pools and not from other highland habitats such as the Andes, followed by several in situ speciation events. These high diversification rates were partly associated with Quaternary climatic oscillations, and perennial and hummingbird‐pollinated species exhibited higher turnover rates.

Amphitropical species have disjunct distributions south and north of the equator. That is the case of Leptochloa crinita, a perennial grass found in dry and warm regions of South and North America, and recommended for rangeland restoration. We analyzed to what degree the distribution of the species in both subcontinents shaped its genetic differentiation and population variability. We collected seeds from 15 populations from South America and 7 from North America, and grew them in a common garden to evaluate adaptive variation. Three microsatellite markers and DNA sequences from one nuclear (ITS1-5.8S-ITS2) and one chloroplast region (rpl32-trnL) were used to analyze recent and historical gene flow, respectively. We used climatic niche models to infer past suitable habitats. We found significant genetic variability among populations within each subcontinent, but low genetic differences between populations from South vs. North America; these were detected only with microsatellites and not with DNA sequences. Results show that the species has diverged from a common gene pool in the recent past (~500-3300 generations ago [estimate: ~3000-20000 years]). Populations from South America had plants with more and taller inflorescences, more tillers and heavier seeds than the North American ones, which could represent adaptations to the less stressful environments that the species inhabits in South America. Climatic niche models indicate few potential habitats for the species in North America during the Last Glacial Maximum and Middle Holocene, in contrast to South America, where potential habitats seemed to be comparable or more extensive than at present. This and previous studies provide a view of the genetic resources of the species. Results suggest that —if necessary, and taking proper precautions— the admixture of L. crinita populations or the germplasm translocation between subcontinents are alternatives to consider in restoration practices.

Plant species disjunctions have attracted the interest of ecologists for decades. We investigated Trichloris crinita, a native C4 perennial grass with disjunct distribution between subtropical regions of North and South America, testing the hypothesis that the species has a similar realized climatic niche in both subcontinents. The climatic niche of T. crinita in North and South America was characterized and compared using presence records and five uncorrelated bioclimatic variables selected according to their ecological importance for the species. We used reciprocal modeling to make geographic projections of the realized niche within each subcontinent. Niche overlap between T. crinita distributions in North and South America was intermediate for the individual climatic variables and the multivariate space. In all cases the test of equivalence between climates inhabited by T. crinita indicated that the realized niche of the species differ significantly between subcontinents. Also, the similarity test showed that in the majority of cases the realized niche in both subcontinents was significantly different than that expected by chance. T. crinita occupied a greater diversity of environments in South than in North America, while in the latter its distribution was displaced to drier and warmer environments. The modeled geographic distribution using the actual occurrences of the species in North America did not accurately predict the distribution in South America, and vice versa. Together, these results led us to reject the hypothesis of similar niche of T. crinita in both subcontinents. This information may be useful to manage restoration efforts by presenting the suitable areas and climates for the species, and suggesting that translocation of individuals between subcontinents could only be recommended with caution because introduced genotypes can be potentially maladaptive, and could colonize sites actually not occupied by the species within each subcontinent.

Diversity of limno-terrestrial tardigrades of the Americas in relation to the Great American Biotic Interchange hypothesis (GABI)

Velocities and attenuation coefficient values of Rayleigh waves within the South American continent and Indian subcontinent have been determined in order to study velocity structure and Qβ structure, as well as their lateral variation, in those regions. Single-station and two-station data are combined to yield dispersion and attenuation data from periods of a few seconds to periods between 60 s and 100 s for each region. Both types of data are inverted using differential inversion schemes. This inversion process is found to sometimes allow the location of velocity discontinuities in the models directly from the dispersion data. Qβ models obtained from the inversion process are not constrained to have high values at large depths, a problem with earlier methods used to invert surface-wave attenuation data. The shear-velocity models for the Indian shield and eastern South America are similar to one another, and have somewhat slower velocities than those reported for shield regions of North America. The shear-velocity models for the Himalaya and Andes are similar to one another in crustal thickness but the velocities in the Andes are lower than those in the Himalayas in the uppermost mantle. A low-velocity zone can marginally be resolved in the upper mantle beneath the Himalaya, but not beneath the other regions in this study. Qβ models obtained for the stable regions of eastern North America and eastern South America exhibit similar Qβ values at mantle depths. The Indian shield, however, has much lower Qβ values, in both the crust and upper mantle, a result which may be related to the unusually high heat-flow observed for that stable region. Qβ for the tectonically active regions of western North America, western South America, and the Himalaya is considerably lower than Qβ for the stable regions throughout most of the crust and upper mantle. Minimum mantle values appear to be about 120 for stable regions and 40 or less for tectonically active regions. Thus, Qβ values in the upper mantle appear to vary regionally by a factor of 3 or more, whereas shear velocities in the same regions vary by no more than 13 per cent. The Qβ models obtained for the tectonically active regions adequately predict Q values reported from time domain measurements of Lg waves for those regions. The Q values for 1 Hz Lg waves predicted by those models of stable regions in eastern North and South America, and the Indian shield are, however, significantly smaller than the observed values for those regions. Our results, combined with reported values of Lg Q at 1 Hz, imply that Qβ in the crust is independent of frequency over the frequency range of this study in tectonically active regions, but varies with frequency in stable regions.

RAPD analysis of the relationship of North and South American subspecies of <i>Fragaria chiloensis</i>

Crop production variability in North and South America forced by life-cycles of the El Niño Southern Oscillation

During the Last Glacial Cycle (LGC), ice sheets covered large parts of Eurasia and North America which resulted in ~120 meters of sea level change. Ice sheet – climate interactions have considerable influence on temperature and precipitation patterns, and therefore need to be included when simulating this time period. Ideally, ice sheet – climate interactions are simulated by a high-resolution earth system model. While these models are capable of simulating climates at a certain point in time, such as the Pre-Industrial (PI) or the Last Glacial Maximum (LGM; 21,000 years ago), a full glacial cycle is currently unfeasible as it requires a too large amount of computation time. Nevertheless, ice-sheet models require forcing that captures the gradual change in climate over time to calculate the accumulation and melt of ice and its effect on ice sheet extent and volume changes. Here we simulate the LGC using an ice sheet model forced by LGM and PI climates. The gradual change in climate is modelled by transiently interpolating between pre-calculated results from a climate model for the LGM and the PI. To assess the influence of ice sheet – climate interactions, we use two different interpolation methods: The climate matrix method, which includes these interactions, and the glacial index method, which does not. To investigate the sensitivity of the results to the prescribed climate forcing, we use the output of several models that are part of the Paleoclimate Modelling Intercomparison Project Phase III (PMIP3). In these simulations, ice volume is prescribed and the climate is reconstructed. Here we test those models by using their climate to drive an ice sheet model over the LGC. We find that the differences caused by the climate forcing exceeds the differences caused by the interpolation method. Some GCMs produced unrealistic LGM volumes and only four resulted in reasonable ice sheets with LGM Northern Hemisphere sea level contribution ranging between 74 – 113 meters with respect to the present day. The glacial index and climate matrix methods result in similar ice volumes at LGM but yield a different ice evolution with different ice domes during the inception phase of the glacial cycle, and different sea-level rates during the deglaciation phase. The temperature-albedo feedback is the main cause of differences between the glacial index and climate matrix methods.

North and South America were the last continents to be explored and settled by modern humans at the end of the Pleistocene. Genetic data, derived from contemporary populations and ancient individuals, show that the first Americans originated from Asia and after several population splits moved south of the continental ice sheets that covered Canada sometime between ~17.5 and ~14.6 thousand years (ka) ago. Archaeological evidence shows that geographically dispersed populations lived successfully, using biface, blade, and osseous technologies, in multiple places in North and South America between ~15.5 and ~14 ka ago. Regional archaeological complexes emerged by at least ~13 ka ago in North America and ~12.9 ka ago in South America. Current genetic and archaeological data do not support an earlier (pre-17.5 ka ago) occupation of the Americas.

By altering or eliminating delicate ecological relationships, non-indigenous species are considered a major threat to biodiversity, as well as a driver of environmental change. Global climate change affects ecosystems and ecological communities, leading to changes in the phenology, geographic ranges, or population abundance of several species. Thus, predicting the impacts of global climate change on the current and future distribution of invasive species is an important subject in macroecological studies. The African clawed frog (Xenopus laevis), native to South Africa, possesses a strong invasion potential and populations have become established in numerous countries across four continents. The global invasion potential of X. laevis was assessed using correlative species distribution models (SDMs). SDMs were computed based on a comprehensive set of occurrence records covering South Africa, North America, South America and Europe and a set of nine environmental predictors. Models were built using both a maximum entropy model and an ensemble approach integrating eight algorithms. The future occurrence probabilities for X. laevis were subsequently computed using bioclimatic variables for 2070 following four different IPCC scenarios. Despite minor differences between the statistical approaches, both SDMs predict the future potential distribution of X. laevis, on a global scale, to decrease across all climate change scenarios. On a continental scale, both SDMs predict decreasing potential distributions in the species’ native range in South Africa, as well as in the invaded areas in North and South America, and in Australia where the species has not been introduced. In contrast, both SDMs predict the potential range size to expand in Europe. Our results suggest that all probability classes will be equally affected by climate change. New regional conditions may promote new invasions or the spread of established invasive populations, especially in France and Great Britain.

AimTrimerotropis pallidipennis represents a species complex of band‐winged grasshopper distributed over North and South America. Previous studies indicated a North American origin of the species and suggested that colonization of South America occurred during the Pleistocene after the closure of the Isthmus of Panama. Here we use a phylogeographical approach in order to test different biogeographical scenarios and determine how many distinct units exist within the species complex.LocationNorth and South America with specific emphasis on the Andes mountains of South America.MethodsWe sequenced two mitochondrial and two nuclear genes for multiple specimens belonging to each taxonomic unit. Using the concatenated dataset and a coalescent‐based approach we estimated the phylogeny of the complex. In order to distinguish the different biogeographical and species delimitation hypotheses we constrained our dataset to different taxon sets and ran Bayesian analyses in *beast. Posterior probabilities and DensiTree plots allowed us to determine the best hypotheses. We used a molecular clock approach to correlate geological events with observed phylogenetic splits.ResultsAll analyses indicate the existence of at least three distinct genetic lineages: Trimerotropis pallidipennis from North America, Trimerotropis ochraceipennis from Chile and an undescribed Trimerotropis species from Argentina. The split between North and South American forms took place about 1.3 Ma, long after the Isthmus of Panama had been completed. Biogeographical analyses suggest a first dispersal event from North to South America. Subsequent dispersion and vicariance probably led to the differentiation of the endemics now found in Chile and Argentina.Main conclusionsWe demonstrate the existence of three distinct genetic lineages in the Trimerotropis pallidipennis species complex. These lineages are also chromosomally differentiated as previous studies have indicated. Dispersion of T. pallidipennis from North to South America probably occurred during the early Pleistocene, when climatic conditions were more suitable. Subsequent diversification in South America was the result of range expansion and vicariance, possibly in response to later Pleistocene glaciations of the Andes.

Migratory aquatic birds play an important role in the maintenance and spread of avian influenza viruses (AIV). Many species of aquatic migratory birds tend to use similar migration routes, also known as flyways, which serve as important circuits for the dissemination of AIV. In recent years there has been extensive surveillance of the virus in aquatic birds in the Northern Hemisphere; however in contrast only a few studies have been attempted to detect AIV in wild birds in South America. There are major flyways connecting South America to Central and North America, whereas avian migration routes between South America and the remaining continents are uncommon. As a result, it has been hypothesized that South American AIV strains would be most closely related to the strains from North America than to those from other regions in the world. We characterized the full genome of three AIV subtype H11N9 isolates obtained from ruddy turnstones (Arenaria interpres) on the Amazon coast of Brazil. For all gene segments, all three strains consistently clustered together within evolutionary lineages of AIV that had been previously described from aquatic birds in North America. In particular, the H11N9 isolates were remarkably closely related to AIV strains from shorebirds sampled at the Delaware Bay region, on the Northeastern coast of the USA, more than 5000 km away from where the isolates were retrieved. Additionally, there was also evidence of genetic similarity to AIV strains from ducks and teals from interior USA and Canada. These findings corroborate that migratory flyways of aquatic birds play an important role in determining the genetic structure of AIV in the Western hemisphere, with a strong epidemiological connectivity between North and South America.

The winners and losers of El Niño

The first steps in the history of South American mammals took place ca. 130 Ma., when the South American plate, still connected to the Antarctic Peninsula, began to drift away from the African-Indian plate. Most of the Mesozoic history of South American mammals is still unknown, and we only have a few enigmatic taxa (i.e., a Jurassic Australosphenida and an Early Cretaceous Prototribosphenida) that pose more evolutionary and biogeographic questions than answers. The best-known Mesozoic, South American land-mammal fossils are from Late Cretaceous Patagonian beds. These fossils represent the last survivors of non- and pre-tribosphenic Pangaean lineages, all of them with varying endemic features: some with few advanced features (e.g., ?Eutriconodonta and “Symmetrodonta”), some very diversified as endemic groups (e.g., ?Docodonta Reigitheriidae), and others representing vicariant types of well known Laurasian Mesozoic lineages (e.g., Gondwanatheria as vicariant of Multituberculata). These endemic mammals lived as relicts (although advanced) of pangeic lineages when a primordial South American continent was still connected to the Antarctic Peninsula and, at the northern extreme, near the North American Plate. By the beginning of the Late Cretaceous, the volcanic and diastrophic processes that finally led to the differentiation of the Caribbean region and Central America built up transient geographic connections that permitted the initiation of an overland inter-American exchange that included, for example, dinosaurian titanosaurs from South America and hadrosaurs from North America. The immigration of other vertebrates followed the same route, for example, polydolopimorphian marsupials. These marsupials were assumed to have differentiated in South America prior to new discoveries from the North American Late Cretaceous. The complete extinction of endemic South American Mesozoic mammals by the Late Cretaceous-Early Paleocene, and the subsequent and in part coetaneous immigration of North American therians, respectively, represent two major moments in the history of South American mammals: a Gondwanan Episode and a South American Episode. The Gondwanan Episode was characterized by non- and pre-tribosphenic mammal lineages that descended from the Pangeic South American stage (but already with a pronounced Gondwanan accent, and wholly extinguished during the Late Cretaceous-Early Paleocene span). The South American Episode, in turn, was characterized only by therian mammals, mostly emigrated from the North American continent and already with a South American accent obtained through isolation. The southernmost extreme of South America (Patagonia) remained connected to the present Antarctic Peninsula at least up until about 30 Ma., and both provided the substratum where the primordial cladogenesis of “South American” mammals occurred. The resulting cladogenesis of South American therian mammals followed Gould's motto: early experimentation, later standardization. That is to say, early cladogenesis engendered a great variety of taxa with scarce morphological differentiation. After this early cladogenesis (Late Eocene-Early Oligocene), the variety of taxa became reduced, but each lineage became clearly recognizable distinctive by a constant morphologic pattern. At the same time, those mammals that underwent the “early experimentation” were part of communities dominated by archaic lineages (e.g., brachydont types among the native “ungulates”), whereas the subsequent communities were dominated by mammals of markedly “modern” stamp (e.g., protohypsodont types among the native “ungulates”). The Gondwanan and South American Episodes were separated by a critical latest Cretaceous-earliest Paleocene hiatus, it is as unknown as it is important in which South American land-mammal communities must have experienced extinction of the Gondwanan mammals and the arrival and radiation of the North American marsupials and placentals (with the probable exception of the xenarthrans, whose biogeographic origin is still unclear).