There Is No Evidence for a Temporal Link between Pathogen Arrival and Frog Extinctions in North-Eastern Australia

Pathogen spread can cause population declines and even species extinctions. Nonetheless, in the absence of tailored monitoring schemes, documenting pathogen spread can be difficult. In the case of worldwide amphibian declines the best present understanding is that the chytrid fungus Batrachochytrium dendrobatidis (Bd) has recently spread, causing amphibian declines and extinction in the process. However, good evidence demonstrating pathogen arrival followed by amphibian decline is rare, and analysis of putative evidence is often inadequate. Here we attempt to examine the relationship between Bd arrival and amphibian decline across north-eastern Australia, using sites where a wave-like pattern of amphibian decline was first noticed and at which intensive research has since been conducted. We develop an analytical framework that allows rigorous estimation of pathogen arrival date, which can then be used to test for a correlation between the time of pathogen arrival and amphibian decline across sites. Our results show that, with the current dataset, the earliest possible arrival date of Bd in north-eastern Australia is completely unresolved; Bd could have arrived immediately before sampling commenced or may have arrived thousands of years earlier, the present data simply cannot say. The currently available data are thus insufficient to assess the link between timing of pathogen arrival and population decline in this part of the world. This data insufficiency is surprising given that there have been decades of research on chytridiomycosis in Australia and that there is a general belief that the link between Bd arrival and population decline is well resolved in this region. The lack of data on Bd arrival currently acts as a major impediment to determining the role of environmental factors in driving the global amphibian declines, and should be a major focus of future research.     

NADPH oxidase 4 mediates upregulation of type 4 phosphodiesterases in human endothelial cells

The protective actions of prostacyclin (PGI(2) ) are mediated by cyclic AMP (cAMP) which is reduced by type 4 phosphodiesterases (PDE4) which hydrolyze cAMP. Superoxide (O2(-)) from NADPH oxidase (Nox) is associated with impaired PGI(2) bioactivity. The objective of this study, therefore, was to study the relationship between Nox and PDE4 expression in human umbilical vein endothelial cells (HUVECs). HUVECs were incubated with the thromboxane A(2) analog, U46619, 8-isoprostane F(2α) (8IP), or tumor necrosing factor alpha (TNFα) [±iloprost (a PGI(2) analog)] and the expression of PDE4A, B, C, and D and splice variants thereof assessed using Western blotting and qPCR and mRNA silencing of Nox4 and Nox5. Effects on cell replication and angiogenesis were also studied. U46619, 8IP, and TNFα increased the expression of Nox 4 and Nox 5 and all PDE4 isoforms as well as cell replication and tubule formation (index of angiogenesis), effects inhibited by mRNA silencing of Nox4 (but not Nox5) and iloprost and rolipram. These data demonstrate that upregulation of Nox4 leads to an upregulation of PDE4A, B, and D and increased hydrolysis of cAMP which in turn augments cell replication and angiogenesis. This mechanism may be central to vasculopathies associated with endothelial dysfunction since the PGI(2)-cAMP signaling axis plays a key role in mediating functions that include hemostasis and angiogenesis.     

CONVERGENT AND CORRELATED EVOLUTION OF MAJOR LIFE‐HISTORY TRAITS IN THE ANGIOSPERM GENUS LEUCADENDRON (PROTEACEAE)

Natural selection is expected to cause convergence of life histories among taxa as well as correlated evolution of different life‐history traits. Here, we quantify the extent of convergence of five key life‐history traits (adult fire survival, seed storage, degree of sexual dimorphism, pollination mode, and seed‐dispersal mode) and test hypotheses about their correlated evolution in the genus Leucadendron (Proteaceae) from the fire‐prone South African fynbos. We reconstructed a new molecular phylogeny of this highly diverse genus that involves more taxa and molecular markers than previously. This reconstruction identifies new clades that were not detected by previous molecular study and morphological classifications. Using this new phylogeny and robust methods that account for phylogenetic uncertainty, we show that the five life‐history traits studied were labile during the evolutionary history of the genus. This diversity allowed us to tackle major questions about the correlated evolution of life‐history strategies. We found that species with longer seed‐dispersal distances tended to evolve lower pollen‐dispersal distance, that insect‐pollinated species evolved decreased sexual dimorphism, and that species with a persistent soil seed‐bank evolved toward reduced fire‐survival ability of adults.     

An Analysis of Single Clutch Paternity in the Burrower Bug Sehirus cinctus Using Microsatellites

Recent studies of the burrower bug, Sehirus cinctus, have examined the genetic basis of parental care. An understanding of the burrower bug mating system, and the subsequent pattern of offspring relatedness that this system generates, is critical to further interpret genetic data. To this end, we developed three consistently amplifiable highly polymorphic microsatellite loci and used them to determine genotypic patterns at the level of both the population and the single clutch. We found that all clutches were sired by single males. Further, we find no evidence for inbreeding. We hypothesize that single paternity within a clutch may play an important role in reducing the potential for sibling rivalry, by increasing the relatedness among clutchmates.     

Endemic dengue associated with the co-circulation of multiple viral lineages and localized density-dependent transmission

Dengue is one of the most important infectious diseases of humans and has spread throughout much of the tropical and subtropical world. Despite this widespread dispersal, the determinants of dengue transmission in endemic populations are not well understood, although essential for virus control. To address this issue we performed a phylogeographic analysis of 751 complete genome sequences of dengue 1 virus (DENV-1) sampled from both rural (Dong Thap) and urban (Ho Chi Minh City) populations in southern Viet Nam during the period 2003-2008. We show that DENV-1 in Viet Nam exhibits strong spatial clustering, with likely importation from Cambodia on multiple occasions. Notably, multiple lineages of DENV-1 co-circulated in Ho Chi Minh City. That these lineages emerged at approximately the same time and dispersed over similar spatial regions suggests that they are of broadly equivalent fitness. We also observed an important relationship between the density of the human host population and the dispersion rate of dengue, such that DENV-1 tends to move from urban to rural populations, and that densely populated regions within Ho Chi Minh City act as major transmission foci. Despite these fluid dynamics, the dispersion rates of DENV-1 are relatively low, particularly in Ho Chi Minh City where the virus moves less than an average of 20 km/year. These low rates suggest a major role for mosquito-mediated dispersal, such that DENV-1 does not need to move great distances to infect a new host when there are abundant susceptibles, and imply that control measures should be directed toward the most densely populated urban environments.     

Marine biofilm bacteria evade eukaryotic predation by targeted chemical defense

Many plants and animals are defended from predation or herbivory by inhibitory secondary metabolites, which in the marine environment are very common among sessile organisms. Among bacteria, where there is the greatest metabolic potential, little is known about chemical defenses against bacterivorous consumers. An emerging hypothesis is that sessile bacterial communities organized as biofilms serve as bacterial refuge from predation. By testing growth and survival of two common bacterivorous nanoflagellates, we find evidence that chemically mediated resistance against protozoan predators is common among biofilm populations in a diverse set of marine bacteria. Using bioassay-guided chemical and genetic analysis, we identified one of the most effective antiprotozoal compounds as violacein, an alkaloid that we demonstrate is produced predominately within biofilm cells. Nanomolar concentrations of violacein inhibit protozoan feeding by inducing a conserved eukaryotic cell death program. Such biofilm-specific chemical defenses could contribute to the successful persistence of biofilm bacteria in various environments and provide the ecological and evolutionary context for a number of eukaryote-targeting bacterial metabolites.     

Exuviotrophic apostome ciliates from freshwater decapods in southern Alabama (USA) and a description of Hyalophysa clampi n. sp. (Ciliophora, Apostomatida)

Apostome ciliates from crayfish and freshwater shrimp in southern and central Alabama were surveyed in this study. Hyalophysa bradburyae was found on both crayfish and shrimp from 16 sites in eight drainages. A new species, Hyalophysa clampi n. sp., was found infesting crayfish at one site and simultaneously infesting crayfish with H. bradburyae at two sites. Characteristics of the trophont ciliature of H. clampi n. sp. separate it from other species in the genus. Particularly, the contractile vacuole pore is oriented posterior to the ventral kineties xyz, kineties 1 and 2 are undivided, an apparent second contractile vacuole pore is present between the ventral portions of kineties 1 and 2, the anterior ventral field is tightly arranged, and there is an apical field of kineties between kineties 4 through 6. This report expands the known range and diversity of the genus Hyalophysa in the state of Alabama.