Phylogeography of the Patagonian otter Lontra provocax: adaptive divergence to marine habitat or signature of southern glacial refugia?

<p>Abstract</p> <p>Background</p> <p>A number of studies have described the extension of ice cover in western Patagonia during the Last Glacial Maximum, providing evidence of a complete cover of terrestrial habitat from 41°S to 56°S and two main refugia, one in south-eastern Tierra del Fuego and the other north of the Chiloé Island. However, recent evidence of high genetic diversity in Patagonian river species suggests the existence of aquatic refugia in this region. Here, we further test this hypothesis based on phylogeographic inferences from a semi-aquatic species that is a top predator of river and marine fauna, the huillín or Southern river otter (<it>Lontra provocax</it>).</p> <p>Results</p> <p>We examined mtDNA sequences of the control region, ND5 and Cytochrome-b (2151 bp in total) in 75 samples of <it>L. provocax </it>from 21 locations in river and marine habitats. Phylogenetic analysis illustrates two main divergent clades for <it>L. provocax </it>in continental freshwater habitat. A highly diverse clade was represented by haplotypes from the marine habitat of the Southern Fjords and Channels (SFC) region (43°38' to 53°08'S), whereas only one of these haplotypes was paraphyletic and associated with northern river haplotypes.</p> <p>Conclusions</p> <p>Our data support the hypothesis of the persistence of <it>L. provocax </it>in western Patagonia, south of the ice sheet limit, during last glacial maximum (41°S latitude). This limit also corresponds to a strong environmental change, which might have spurred <it>L. provocax </it>differentiation between the two environments.</p

The Structure of the Mammalian Predator Guild in the Santa Cruz Formation (Late Early Miocene)

The Santa Cruz Formation (late early Miocene, Santacrucian age) registers 11 species of mammalian predators (Metatheria, Sparassodonta). Together with large carnivorous flightless birds, they comprised the terrestrial predator guild. The Santacrucian sparassodonts were diverse in body size, had different locomotory habits, and were primarily hypercarnivores. The objective of this work is to analyze the guild structure of the sparassodonts of the Santa Cruz Formation, using the variables of body mass, diet, and locomotion as proxies. Furthermore, we analyze the interaction with other predators and potential prey. The univariated test V of Poole and Rathcke and the multivariated test of Clark-Evans were used to construct the models. In the multivariate test, we made a Principal Component Analysis to resume and standardize the variables. With body mass and locomotion we obtained an evenly spaced pattern of segregation for the sparassodont species, being non-significant and significant, respectively. The pattern was aggregated and significant only with diet. The analysis of all variables together resulted in an evenly spaced and significant pattern, which is consistent with character displacements (segregation of species throughout the morphospace) that would help to diminish interspecific competition during the Santacrucian age and would allow selection of prey species of different sizes and substrate specializations. When the body size pattern of predator birds and sparassodonts were plotted together, the pattern is evenly spaced and nonsignificant. Other factors, including locomotion, would differentiate these species and their ecological niches.Fil: Ercoli, Marcos Darío. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Prevosti, Francisco Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

A baseline paleoecological study for the Santa Cruz Formation (late–early Miocene) at the Atlantic coast of Patagonia, Argentina

Coastal exposures of the Santa Cruz Formation (late-early Miocene, southern Patagonia, Argentina) between the Coyle and Gallegos rivers have been a fertile ground for recovery of Miocene vertebrates for more than 100 years. The formation contains an exceptionally rich mammal fauna, which documents a vertebrate assemblage very different from any living community, even at the ordinal level. Intensive fieldwork performed since 2003 (nearly 1200 specimens have been collected, including marsupials, xenarthrans, notoungulates, litopterns astrapotheres, rodents, and primates) document this assertion. The goal of this study is to attempt to reconstruct the trophic structure of the Santacrucian mammalian community with precise stratigraphic control. Particularly, we evaluate the depauperate carnivoran paleoguild and identify new working hypotheses about this community. A database has been built from about 390 specimens from two localities: Campo Barranca (CB) and Puesto Estancia La Costa (PLC). All species have been classified as herbivore or carnivore, their body masses estimated, and the following parameters estimated: population density, on-crop biomass, metabolic rates, and the primary and secondary productivity. According to our results, this model predicts an imbalance in both CB and PLC faunas which can be seen by comparing the secondary productivity of the ecosystem and the energetic requirements of the carnivores in it. While in CB, the difference between carnivores and herbivores is six-fold, in PLC this difference is smaller, the secondary productivity is still around three times that of the carnivore to herbivore ratio seen today. If both localities are combined, the difference rises to around four-fold in favour of secondary productivity. Finally, several working hypotheses about the Santacrucian mammalian community and the main lineages of herbivores and carnivores are offered. © 2010 Elsevier B.V. All rights reserved

Testing the hypothesis of an impoverished predator guild in the Early Miocene ecosystems of Patagonia: An analysis of meat availability and competition intensity among carnivores

© 2020 Elsevier B.V. The lower Miocene Santa Cruz Formation (dated to ~18–16 Ma) of Southern Patagonia, Argentina, preserves rich vertebrate faunas, which are representative of communities that existed prior to the Great American Biotic Interchange (GABI). Some previous researchers have hypothesized that these pre-GABI faunas had a low richness of mammalian carnivores (an impoverished predator guild), while others argue for a predator/prey ratio similar to those of recent communities. In this paper, we analyze faunas from the lower part of the Santa Cruz Formation (FL 1–7) using a methodology that allows us to quantify (i) the meat resources that were available to the secondary consumers of the palaeocommunity; and (ii) the competition intensity for these resources. In our modeling, we considered different scenarios related to meat consumption, including the possibility that several taxa had a scavenging behavior, and also differences in mortality rates between young and adult prey. Our results provide estimates of the nutritional requirements from the predator/scavenger guild under maximum and minimum quantities of meat offered by the prey community, which indicate the presence of a well-balanced palaeocommunity. Moreover, the competition indices point to a relatively high level of competition for prey of small-to-medium size, although competition for resources from large mammal prey was rather low. This suggests that the predator/scavenger guild was not impoverished, although there were insufficient carnivore species to fully consume the megaherbivore biomass

New toxodontid (Notoungulata) from the Early Miocene of Mendoza, Argentina

We describe a new toxodontid species, Nesodon taweretus sp. nov., from the Aisol Formation in Mendoza Province, central-west Argentina. Nesodon is a frequently found Toxodontidae, member of the Notoungulata, an extinct endemic group of Cenozoic South American mammals that are ecologically similar to current hoofed ungulates. The holotype of N. taweretus sp. nov. is a skull, and we tentatively assign some mandibular fragments and postcranial bones. N. taweretus sp. nov. differs from the other Nesodon species in several cranial and dental features, and close comparisons were made with the Patagonian Nesodon imbricatus, common in the Santa Cruz Formation (Santacrucian Age, Early Miocene). The material is of a similar size to N. imbricatus, with a body mass estimation of about 550 kg. The phylogenetic analysis groups N. taweretus sp. nov. with other species of Nesodon. The absolute age of the Aisol Formation has been established at ca 19.480 ± 0.025 Ma (Burdigalian; Early Miocene) by means of U–Pb zircon dating. The vertebrate association is encompassed by the Santacrucian Age. Latitudinal separation between Mendoza and Patagonia in the south would have favored taxonomic differences, as reflected in the species of Nesodon. = Wir beschreiben eine neue Art der Toxodontiden, Nesodon taweretus sp. nov., aus der Aisol-Formation in der Provinz Mendoza, im Zentralwesten von Argentinien. Nesodon ist ein häufig vorkommendes Taxon der Toxodontidae, die zu den Notoungulaten, einer ausgestorbenen Gruppe von endemischen Säugetieren des Känozoikums in Südamerika, gehören und den rezenten gehuften Ungulata ökologisch ähnlich waren. Der Holotyp von N. taweretus sp. nov. ist ein Schädel, dem wir vorläufig einige Unterkieferfragmente und postkraniale Knochen zuweisen. N. taweretus sp. nov. unterscheidet sich von den anderen Nesodon-Arten in mehreren Merkmalen des Schädels und der Bezahnung. Enge Vergleiche wurden mit dem aus Patagonien stammenden und in der Santa-Cruz-Formation (Santacruzium, frühes Miozän) verbreiteten Nesodon imbricatus gemacht. Das Material ist von ähnlicher Grösse wie N. imbricatus, Schätzungen der Körpermasse ist etwa 550 kg. Die phylogenetische Analyse gruppiert N. taweretus sp. nov. mit anderen Arten von Nesodon. Das absolute Alter der Aisol-Formation wurde mittels der U–Pb Zirkondatierung auf etwa 19.480 ± 0.025 Ma (Burdigalium, Unteres Miozäns) gesetzt. Die Wirbeltiervergesellschaftung in das Santacruzium eingeschlossen worden. Latitudinale Trennung zwischen Mendoza und Patagonien im Süden hätte taxonomischen Unterschiede begünstigt, wie das anhand der Arten von Nesodon widergegeben ist