Diversification dynamics in Caribbean rain frogs (Eleutherodactylus) are uncoupled from the anuran community and consistent with adaptive radiation

Adaptive radiation is proposed to play a key role in generating differences in species richness among lineages and geographical regions. Due to the importance of ecological divergence in adaptive radiation, species richness is predicted to be influenced by equilibrium diversity dynamics, although the concept continues to generate much debate. An additional important question is whether radiating clades have intrinsic biological characteristics that make them particularly prone to diversify. We tackle these questions by analysing (i) the temporal patterns of diversification of Caribbean Eleutherodactylus frogs, and (ii) assembly of the complete native anuran community of the Caribbean archipelago (197 species), testing for the presence of equilibrium dynamics and whether diversification patterns of Eleutherodactylus differ from those of the rest of the Caribbean anurans. Diversification rates follow the predicted pattern of rapid diversification early in the radiation which gradually decreases towards the present. Eleutherodactylus diversification is significantly faster than that of the Caribbean anuran community, and although equilibrium dynamics influence richness of all Caribbean anurans, Eleutherodactylus shows higher carrying capacity. Our results indicate that ecological opportunity per se is not sufficient for adaptive radiation and that diverse lineages present intrinsic characteristics that enable them to make the most of available opportunity.

Stability of patch-turnover relationships under equilibrium and nonequilibrium metapopulation dynamics driven by biogeography

Two controversial tenets of metapopulation biology are whether patch quality and the surrounding matrix are more important to turnover (colonisation and extinction) than biogeography (patch area and isolation) and whether factors governing turnover during equilibrium also dominate nonequilibrium dynamics. We tested both tenets using 18 years of surveys for two secretive wetland birds, black and Virginia rails, during (1) a period of equilibrium with stable occupancy and (2) after drought and arrival of West Nile Virus (WNV), which resulted in WNV infections in rails, increased extinction and decreased colonisation probabilities modified by WNV, nonequilibrium dynamics for both species and occupancy decline for black rails. Area (primarily) and isolation (secondarily) drove turnover during both stable and unstable metapopulation dynamics, greatly exceeding the effects of patch quality and matrix conditions. Moreover, slopes between turnover and patch characteristics changed little between equilibrium and nonequilibrium, confirming the overriding influences of biogeographic factors on turnover.

Dynamic force spectroscopy of synthetic oligorotaxane foldamers

Wholly synthetic molecules involving both mechanical bonds and a folded secondary structure are one of the most promising architectures for the design of functional molecular machines with unprecedented properties. Here, we report dynamic single-molecule force spectroscopy experiments that explore the energetic details of donor-acceptor oligorotaxane foldamers, a class of molecular switches. The mechanical breaking of the donor-acceptor interactions responsible for the folded structure shows a high constant rupture force over a broad range of loading rates, covering three orders of magnitude. In comparison with dynamic force spectroscopy performed during the past 20 y on various (bio)molecules, the near-equilibrium regime of oligorotaxanes persists at much higher loading rates, at which biomolecules have reached their kinetic regime, illustrating the very fast dynamics and remarkable rebinding capabilities of the intramolecular donor-acceptor interactions. We focused on one single interaction at a time and probed the stochastic rupture and rebinding paths. Using the Crooks fluctuation theorem, we measured the mechanical work produced during the breaking and rebinding to determine a free-energy difference, ΔG, of 6 kcal·mol^-1 between the two local conformations around a single bond.