The genomic binding sites of Polycomb group (PcG) complexes have been found to cluster, forming Polycomb "bodies" or foci in mammalian or fly nuclei. These associations are thought to be driven by interactions between PcG complexes and result in enhanced repression. Here, we show that a Polycomb response element (PRE) with strong PcG binding and repressive activity cannot mediate trans interactions. In the case of the two best-studied interacting PcG targets in Drosophila, the Mcp and the Fab-7 regulatory elements, we find that these associations are not dependent on or caused by the Polycomb response elements they contain. Using functional assays and physical colocalization by in vivo fluorescence imaging or chromosome conformation capture (3C) methods, we show that the interactions between remote copies of Mcp or Fab-7 elements are dependent on the insulator activities present in these elements and not on their PREs. We conclude that insulator binding proteins rather than PcG complexes are likely to be the major determinants of the long-range higher-order organization of PcG targets in the nucleus.

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Distribution history of the widespread Neotropical genus Hypostomus was studied to shed light on the processes that shaped species diversity. We inferred a calibrated phylogeny, ancestral habitat preference, ancestral areas distribution, and the history of dispersal and vicariance events of this genus. The phylogenetic and distribution analyses indicate that Hypostomus species inhabiting La Plata Basin do not form a monophyletic clade, suggesting that several unrelated ancestral species colonized this basin in the Miocene. Dispersal to other rivers of La Plata Basin started about 8 Mya, followed by habitat shifts and an increased rate of cladogenesis. Amazonian Hypostomus species colonized La Plata Basin several times in the Middle Miocene, probably via the Upper Paraná and the Paraguay rivers that acted as dispersal corridors. During the Miocene, La Plata Basin experienced marine incursions, and geomorphological and climatic changes that reconfigured its drainage pattern, driving dispersal and diversification of Hypostomus. The Miocene marine incursion was a strong barrier and its retraction triggered Hypostomus dispersal, increased speciation rate and ecological diversification. The timing of hydrogeological changes in La Plata Basin coincides well with Hypostomus cladogenetic events, indicating that the history of this basin has acted on the diversification of its biota.

Distribution history of the widespread Neotropical genus Hypostomus to shed light on the processes that shaped species diversity. We inferred a calibrated phylogeny; ancestral habitat preference, ancestral areas distribution, and the history of dispersal and vicariance events of this genus. The phylogenetic and distributional analyses indicate that Hypostomus species inhabiting La Plata Basin do not form a monophyletic clade, suggesting that several unrelated ancestral species colonized this basin in the Miocene (~17 Mya). Dispersal to other rivers of La Plata Basin started about 8 Mya, followed by habitat shifts and an increased rate of cladogenesis. Amazonian Hypostomus species colonized La Plata Basin several times in the Middle Miocene, probably via the Upper Paraná and the Paraguay rivers that acted as biogeographic corridors. During the Miocene, La Plata Basin experienced marine incursions; and geomorphological and climatic changes that reconfigured its drainage pattern, driving the dispersal and diversification of Hypostomus. The Miocene marine incursion was a strong barrier and its retraction triggered Hypostomus dispersal, increased speciation rate and ecological diversification. The timing of hydrogeological changes in La Plata Basin coincides well with Hypostomus cladogenetic events, indicating that the history of this basin has acted on the diversification of its biota.

Aim Understanding the mechanisms that drive phenotypic divergence along climatic gradients is a long‐standing goal of biogeography. To fulfil this objective, we tested if neutral and/or adaptive effects drive phenotypic diversification. We quantified the effects of neutral evolution and natural selection on morphological variability of a well‐suited mammalian species, the fox, Lycalopex culpaeus. Location South America. Methods We analysed variations in skull shape, jaw shape and skull size in L. culpaeus. The processes underlying our models were: local adaptation, and short‐ or long‐term neutral evolution. We inferred genetic population structure using mitochondrial and nuclear markers, we quantified morphological differences among populations by performing geometric morphometric analyses, and we inferred an ecological niche model for calculating environmental resistance between populations. Results We identified six genetically differentiated populations of the Andean fox, which correspond well to the described subspecies. We showed that skull shape variation is explained by population structure. Skull size showed a clear Bergmannian pattern with larger animals in higher latitudes (in absolute values). Skull size divergence is driven by the combined effects of environmental factors and population structure. Intriguingly, none of the models explains the variation observed in jaw shape. Main Conclusion Population phenotypic variation in the Andean fox L. culpaeus is driven by deterministic and neutral processes. The methodological framework presented here opens up new opportunities to study phenotypic evolution; it allowed us to demonstrate that the processes explaining trait variation can differ among traits and to show empirically for the first time that a trait can diverge among populations due to simultaneous adaptation and neutral evolution.