Aim: The species of the genus Chionodraco (Notothenioidei) are the most abundant icefish on the continental shelf of the Weddell Sea. While previous studies indicated that only Chionodraco hamatus and Chionodraco myersi inhabit the Weddell Sea, the third Chionodraco species, Chionodraco rastrospinosus, was recently sampled in the area. As C. rastrospinosus is supposed to be found only at the Antarctic Peninsula and Scotia Arc, this study aimed at confirming the species classification of C. rastrospinosus by molecular methods and identifying its putative source population. Given the documented evidence of introgression among the three species, we tested whether the newly found C. rastrospinosus shared any genetic variability with the other Chionodraco species. To explain the pattern of distribution of the Chionodraco species, we aimed at estimating the hydrodynamic connectivity between the Antarctic Peninsula and the Weddell Sea. Location: Antarctic Peninsula, southern Scotia Arc and the south-eastern Weddell Sea. Methods: We genotyped 19 microsatellites and sequenced the mitochondrial D-loop for 560 Chionodraco individuals. We simulated the dispersal of more than 3 million drifters (Lagrangian model). Results: The molecular analyses support the presence of C. rastrospinosus in the Weddell Sea and its homogeneity with C. rastrospinosus from the Antarctic Peninsula. Bayesian clustering identifies three putative hybrids among C. rastrospinosus and the other congenerics. Lagrangian simulations do not support connectivity driven by the oceanographic features of the Antarctic Peninsula and Weddell Sea via passive larval dispersal only. Main conclusions: This study documents, for the first time, the presence of C. rastrospinosus in the Weddell Sea unveiling more biodiversity than previously known in this region. The sympatry of the three Chionodraco species explains the occurrence of occasional, ongoing events of hybridization in the genus. Alternative possible
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Aim Locally abundant species are usually widespread, and this pattern has been related to properties of the niches and traits of species. However, such explanations fail to account for the potential of traits to determine species niches and often overlook statistical artefacts. Here, we examine how trait distinctiveness determines the abilities of species to exploit either common habitats (niche position) or a range of habitats (niche breadth) and how niche position and breadth, in turn, affect abundance and occupancy. We also examine how statistical artefacts moderate these relationships. Location Sixteen sites in the Neotropics. Time period 1993–2014. Major taxa studied Aquatic invertebrates from tank bromeliads. Methods We measured the environmental niche position and breadth of each species and calculated its trait distinctiveness as the average trait difference from all other species at each site. Then, we used a combination of structural equation models and a meta-analytical approach to test trait–niche relationships and a null model to control for statistical artefacts. Results The trait distinctiveness of each species was unrelated to its niche properties, abundance and occupancy. In contrast, niche position was the main predictor of abundance and occupancy; species that used the most common environmental conditions found across bromeliads were locally abundant and widespread. Contributions of niche breadth to such patterns were attributable to statistical artefacts, indicating that effects of niche breadth might have been overestimated in previous studies. Main conclusions Our study reveals the generality of niche position in explaining one of the most common ecological patterns. The robustness of this result is underscored by the geographical extent of our study and our control of statistical artefacts. We call for a similar examination across other systems, which is an essential task to understand the drivers of commonness across the tree of life.
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