Body Fineness Ratio as a Predictor of Maximum Prolonged-Swimming Speed in Coral Reef Fishes

The ability to sustain high swimming speeds is believed to be an important factor affecting resource acquisition in fishes. While we have gained insights into how fin morphology and motion influences swimming performance in coral reef fishes, the role of other traits, such as body shape, remains poorly understood. We explore the ability of two mechanistic models of the causal relationship between body fineness ratio and endurance swimming-performance to predict maximum prolonged-swimming speed (U_max) among 84 fish species from the Great Barrier Reef, Australia. A drag model, based on semi-empirical data on the drag of rigid, submerged bodies of revolution, was applied to species that employ pectoral-fin propulsion with a rigid body at U _max. An alternative model, based on the results of computer simulations of optimal shape in self-propelled undulating bodies, was applied to the species that swim by body-caudal-fin propulsion at U_max. For pectoral-fin swimmers, U_max increased with fineness, and the rate of increase decreased with fineness, as predicted by the drag model. While the mechanistic and statistical models of the relationship between fineness and U_max were very similar, the mechanistic (and statistical) model explained only a small fraction of the variance in U_max. For body-caudal-fin swimmers, we found a non-linear relationship between fineness and U_max, which was largely negative over most of the range of fineness. This pattern fails to support either predictions from the computational models or standard functional interpretations of body shape variation in fishes. Our results suggest that the widespread hypothesis that a more optimal fineness increases endurance-swimming performance via reduced drag should be limited to fishes that swim with rigid bodies.     

The sterol-binding protein Kes1/Osh4p is a regulator of polarized exocytosis

Oxysterol-binding protein (OSBP)-related protein Kes1/ Osh4p is implicated in nonvesicular sterol transfer between membranes in Saccharomyces cerevisiae. However, we found that Osh4p associated with exocytic vesicles that move from the mother cell into the bud, where Osh4p facilitated vesicle docking by the exocyst tethering complex at sites of polarized growth on the plasma membrane. Osh4p formed complexes with the small GTPases Cdc42p, Rho1p and Sec4p, and the exocyst complex subunit Sec6p, which was also required for Osh4p association with vesicles. Although Osh4p directly affected polarized exocytosis, its role in sterol trafficking was less clear. Contrary to what is predicted for a sterol-transfer protein, inhibition of sterol binding by the Osh4p Y97F mutation did not cause its inactivation. Rather, OSH4(Y97F) is a gain-of-function mutation that causes dominant lethality. We propose that in response to sterol binding and release Osh4p promotes efficient exocytosis through the co-ordinate regulation of Sac1p, a phosphoinositide 4-phosphate (PI4P) phosphatase, and the exocyst complex. These results support a model in which Osh4p acts as a sterol-dependent regulator of polarized vesicle transport, as opposed to being a sterol-transfer protein.     

Latitudinal variation in diet and patterns of human interaction in the marine otter

The marine otter (Lontra felina) inhabits patches of rocky coastline from central Peru to southern Chile and is classified as Endangered by the IUCN. Given the limited information available about the species, we set out to assess marine otter diet with a view to detecting latitudinal differences, and to assess marine otter activity budgets and interspecific interactions (including anthropogenic) at Peruvian fishing villages and to compare results with similar Chilean studies. Nine study sites from central Chile to southern Peru were sampled for otter spraints to assess relative frequency of prey types and two fishing ports in southern Peru were monitored through focal and scan observations to assess activity patterns, interspecific interactions, habitat use patterns, and dive durations. Results indicate that toward the northern part of its range, crustaceans become less important and fish more important in the diet. Interactions were observed between marine otters and other species, including stray dogs and cats. The strong dependence of marine otters on the availability of safe rocky shelters, and the species’ apparent tolerance to living alongside humans raise conservation concerns about vulnerability to anthropogenic threats. These factors, if not correctly managed, could turn some of these rocky seashore patches into population sinks.     

The Eph/ephrinB signal balance determines the pattern of T-cell maturation in the thymus

In order to carry out an in-depth study of the roles of EphB receptors in T-cell development and to determine the specific relevance of forward and reverse signals in the process, we established severe combined immunodeficient (SCID) mice chimeras with wild-type (WT) or EphB-deficient bone marrow cells. The obtained results demonstrate that EphB2 contributes more significantly than EphB3 in the control of CD4(-)CD8(-) (DN)-CD4(+)CD8(+) (DP) progression, and that reverse signals generated in SCID mice receiving EphB2LacZ precursors, which express the EphB2 extracellular domain, partially rescue the blockade of DN cell maturation observed in EphB2-null chimeras. In addition, increased apoptotic DP thymocytes occurring in EphB2 and/or EphB3 SCID chimeras also contribute to the reduced proportions of DP cells. However, EphB2LacZ chimeras do not show any changes in the proportions of apoptotic DP cells, thus suggesting that there is a role for ephrinB reverse signaling in thymocyte survival. The maturation of DP to CD4(+)CD8(-) or CD4(-)CD8(+) seems to need EphB2 forward signaling and EphB3; a fact that was confirmed in reaggregates formed with either EphB2- or EphB3-deficient DP thymocytes and WT thymic epithelial cells (TECs). The DP thymocyte-TEC conjugate formation was also affected by the absence of EphB receptors. Finally, EphB-deficient SCID chimeras show profoundly altered thymic epithelial organization that confirms a significant role for EphB2 and EphB3 receptors in the thymocyte-TEC crosstalk.     

The evolution of island gigantism and body size variation in tortoises and turtles

Extant chelonians (turtles and tortoises) span almost four orders of magnitude of body size, including the startling examples of gigantism seen in the tortoises of the Galapagos and Seychelles islands. However, the evolutionary determinants of size diversity in chelonians are poorly understood. We present a comparative analysis of body size evolution in turtles and tortoises within a phylogenetic framework. Our results reveal a pronounced relationship between habitat and optimal body size in chelonians. We found strong evidence for separate, larger optimal body sizes for sea turtles and island tortoises, the latter showing support for the rule of island gigantism in non-mammalian amniotes. Optimal sizes for freshwater and mainland terrestrial turtles are similar and smaller, although the range of body size variation in these forms is qualitatively greater. The greater number of potential niches in freshwater and terrestrial environments may mean that body size relationships are more complicated in these habitats.     

Cebus phylogenetic relationships: a preliminary reassessment of the diversity of the untufted capuchin monkeys

The untufted, or gracile, capuchin monkeys are currently classified in four species, Cebus albifrons, C. capucinus, C. olivaceus, and C. kaapori, with all but C. kaapori having numerous described subspecies. The taxonomy is controversial and their geographic distributions are poorly known. Cebus albifrons is unusual in its disjunct distribution, with a western and central Amazonian range, a separate range in the northern Andes in Colombia, and isolated populations in Trinidad and west of the Andes in Ecuador and northern Peru. Here we examine previous morphological and molecular hypotheses of the taxonomy and phylogeny of Cebus. We construct a time-calibrated phylogeny based upon mitochondrial DNA sequences from 50 Cebus samples from across their range. Our data indicate that untufted capuchins underwent a radiation at about 2 Ma, and quickly diversified in both the Andes and the Amazon. We provide a provisional reassessment for the taxonomy of untufted capuchins in the Amazon, the Llanos, the Andes, Trinidad, and Central America, splitting currently paraphyletic taxa into several species, including: at least two Amazonian species (C. yuracus and C. unicolor); a species from the Guiana Shield (most likely the same as Humboldt's C. albifrons); two northern Andean species, C. versicolor, C. cesarae; C. brunneus (with trinitatis a junior synonym) on the Venezuelan coast, and C. adustus in the region of Lake Maracaibo; C. capucinus in northwestern Ecuador and Colombia, and Panama; C. imitator in Central America; C. olivaceus and C. castaneus occupying a large part of the Guiana Shield; and C. kaapori in the eastern Amazon, south of the Rio Amazonas. More intensive and extensive geographic sampling is needed, including that for some subspecies not represented here. Taxa from the southwestern Amazon (yuracus, cuscinus, and unicolor) and the phylogenetic position of Humboldt's Simia albifrons from the Orinoco remain particularly poorly defined.