Different scenarios attempting to describe the initial phases of the human dispersal from Asia into the New World have been proposed during the last two decades. However, some aspects concerning the population affinities among early and modern Asians and Native Americans remain controversial. Specifically, contradictory views based mainly on partial evidence such as skull morphology or molecular genetics have led to hypotheses such as the "Two Waves/Components" and "Single Wave" or "Out of Beringia" model, respectively. Alternatively, an integrative scenario considering both morphological and molecular variation has been proposed and named as the "Recurrent Gene Flow" hypothesis. This scenario considers a single origin for all the Native Americans, and local, within-continent evolution plus the persistence of contact among Circum-Arctic groups. Here we analyze 2D geometric morphometric data to evaluate the associations between observed craniometric distance matrix and different geographic design matrices reflecting distinct scenarios for the peopling of the New World using basic and partial Mantel tests. Additionally, we calculated the rate of morphological differentiation between Early and Late American samples under the different settlement scenarios and compared our findings to the predicted morphological differentiation under neutral conditions. Also, we incorporated in our analyses some variants of the classical Single Wave and Two Waves models as well as the Recurrent Gene Flow model. Our results suggest a better explanatory performance of the Recurrent Gene Flow model, and provide additional insights concerning affinities among Asian and Native American Circum-Arctic groups.

Different environmental and sex conditions induce phenotypic responses (behavioural, morphological and physiological) in many species. The crab Cyrtograpsus angulatus inhabits contrasting intertidal habitats, such as rocky shores and salt marshes, where they are exposed to a wide diversity of predators. However, their anti-predator responses differ substantially between these two habitats: while crabs in the salt marshes use or built burrows or they simply hide by burying in the sediment into the tidal channels, on rocky shores they find shelter below rocks, inside crevices or under seaweeds in tidal pools. Considering that refuges in salt marshes can be adjusted by the crabs according to their size and the morphology, while in rocky shores they have to fit in the available refuges, we expect that the body shape differs between individuals from each intertidal habitat. In order to test this hypothesis, we collected male and female crabs from a salt marsh and a rocky shore, separated by 3 km, in San José Gulf, Patagonia, and compared the carapace shapes using geometric morphometric methods. The results showed that carapace shape variation is explained by the interaction between sex and habitats. In both sexes, the mean carapace shape on the rocky shore is more slender and more lengthened than in the salt marsh individuals. Furthermore, the posterior margin of the female carapaces was wider than that of male carapaces, which were slender and more rounded posterolaterally, independent of the intertidal habitat.

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Diel vertical migration (DVM) of krill was studied throughout 36 h at a fixed station (46.05°S, 66.19°W; 98-m depth) located in the center of the San Jorge Gulf, Southern Patagonia area, during February 2014. Using an echosounder system, combined with an autonomous Video Plankton Recorder (Auto-VPR) and Jacknet samplings, we describe the migration pattern, the associated biomass and the macrozooplankton species involved. The net sampling and the Auto-VPR images allowed us to identify the krill species detected in the echosounder signals, which corresponded to Euphausia lucens, Euphausia vallentini and Nematoscelis megalops. The krill community followed a “normal pattern” of DVM, ascending at dusk (~18:30 h) and descending at dawn (~06:30 h), forming a dense layer near the bottom during the day. Krill vertical migration speed was estimated from the echogram data at ~ 1 cm s−1 (1 body length per s for 1-cm-long animal), and the integrated mean biomass was 57.8 g m−2. This study provides a description of temporal and spatial patterns of krill vertical distribution, which should be taken into account when studying the complexity of the SJG ecosystem dynamics and carbon flux.