Host species composition influences infection severity among amphibians in the absence of spillover transmission

Wildlife epidemiological outcomes can depend strongly on the composition of an ecological community, particularly when multiple host species are affected by the same pathogen. However, the relationship between host species richness and disease risk can vary with community context and with the degree of spillover transmission that occurs among co‐occurring host species. We examined the degree to which host species composition influences infection by Batrachochytrium dendrobatidis (Bd), a widespread fungal pathogen associated with amphibian population declines around the world, and whether transmission occurs from one highly susceptible host species to other co‐occurring host species. By manipulating larval assemblages of three sympatric amphibian species in the laboratory, we characterized the relationship between host species richness and infection severity, whether infection mediates growth and survivorship differently across various combinations of host species, and whether Bd is transmitted from experimentally inoculated tadpoles to uninfected tadpoles. We found evidence of a dilution effect where Bd infection severity was dramatically reduced in the most susceptible of the three host species (Anaxyrus boreas). Infection also mediated survival and growth of all three host species such that the presence of multiple host species had both positive (e.g., infection reduction) and negative (e.g., mortality) effects on focal species. However, we found no evidence that Bd infection is transmitted by this species. While these results demonstrate that host species richness as well as species identity underpin infection dynamics in this system, dilution is not the product of reduced transmission via fewer infectious individuals of a susceptible host species. We discuss various mechanisms, including encounter reduction and antagonistic interactions such as competition and opportunistic cannibalism that may act in concert to mediate patterns of infection severity, growth, and mortality observed in multihost communities.There are many ways in which infection can be influenced by species diversity. Here we show experimentally that the interactions between species in a multi‐host amphibian community drive the severity of infection by the amphibian chytrid fungus. We find no evidence that infection is transmitted between two host species in our study, suggesting that spillover infection is not a cause of dilution effects in this system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111214/1/ece31385.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/111214/2/ece31385-sup-0001-FigureS1.pd

Sensitivity to nitrate and nitrite in pond-breeding amphibians from the Pacific northwest, USA

In static experiments, we studied the effects of nitrate and nitrite solutions on newly hatched larvae of five species of amphibians, namely Rana pretiosa, Rana aurora, Bufo boreas, Hyla regilla, and Ambystoma gracile. When nitrate or nitrite ions were added to the water, some larvae of some species reduced feeding activity, swam less vigorously, showed disequilibrium and paralysis, suffered abnormalities and edemas, and eventually died. The observed effects increased with both concentration and time, and there were significant differences in sensitivity among species. Ambrystoma gracile displayed the highest acute effect in water with nitrate and nitrite. The three ranid species had acute effects in water with nitrite. In chronic exposures, R. pretiosa was the most sensitive species to nitrates and nitrites. All species showed 15-d LC50s lower than 2 mg N-NO2 /L. For both N ions, B. boreas was the least sensitive amphibian. All species showed a high mortality at the U.S. Environmental Protection Agency- recommended limits of nitrite for warm-water fishes (5 mg N-NO2 /L) and a significant larval mortality at the recommended limits of nitrite concentration for drinking water (1 mg N-NO2 The recommended levels of nitrate for warm-water fishes (90 mg N- NO3 /L) were highly toxic for R. pretiosa and A. gracile larvaePeer reviewe

Projected climate-induced faunal change in the western hemisphere

Climate change is predicted to be one of the greatest drivers of ecological change in the coming century. Increases in temperature over the last century have clearly been linked to shifts in species distributions. Given the magnitude of projected future climatic changes, we can expect even larger range shifts in the coming century. These changes will, in turn, alter ecological communities and the functioning of ecosystems. Despite the seriousness of predicted climate change, the uncertainty in climate-change projections makes it difficult for conservation managers and planners to proactively respond to climate stresses. To address one aspect of this uncertainty, we identified predictions of faunal change for which a high level of consensus was exhibited by different climate models. Specifically, we assessed the potential effects of 30 coupled atmosphere–ocean general circulation model (AOGCM) future-climate simulations on the geographic ranges of 2954 species of birds, mammals, and amphibians in the Western Hemisphere. Eighty percent of the climate projections based on a relatively low greenhouse-gas emissions scenario result in the local loss of at least 10% of the vertebrate fauna over much of North and South America. The largest changes in fauna are predicted for the tundra, Central America, and the Andes Mountains where, assuming no dispersal constraints, specific areas are likely to experience over 90% turnover, so that faunal distributions in the future will bear little resemblance to those of today

Combined premedical-medical programmes: programme structure and student outcomes at four universities

Many American universities now support combined premedical-medical programmes which shorten and integrate the education of doctors. This paper reviews combined baccalaureate-MD programmes at four institutions: Boston University, the City College of New York, The University of Michigan-Ann Arbor, and the University of Missouri-Kansas City. In comparison to most US medical schools, the combined programmes have admitted and educated larger portions of women students. In addition, some have had large proportions of graduates choosing primary-care careers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75128/1/j.1365-2923.1986.tb01053.x.pd

Effects of the pathogenic water mold Saprolegnia ferax on survival of amphibian larvae

Infectious diseases are a significant threat to worldwide biodiversity. Amphibian declines, a significant part of current biodiversity losses, are in many cases associated with infectious disease. Water molds are one group of pathogens affecting amphibians on a worldwide basis. Although water molds have been studied extensively for their effects on host embryos, little information is available about how they affect post-embryonic amphibians. We tested the effects of one species of water mold, Saprolegnia ferax, in a comparative study of larvae of 4 amphibian species: Pseudacris regilla (Pacific treefrog), Rana cascadae (Cascades frog), Ambystoma macrodactylum (long-toed salamander), and R. aurora (red-legged frog). S. ferax can kill amphibians at the embryonic and juvenile life history stages, depending on the amphibian species. In the present study, a 1 wk exposure to S. ferax killed P. regilla larvae and a 2 wk exposure killed R. aurora larvae. Larvae of the other host species were unaffected after 1 wk of exposure to S. ferax. Our results suggest that S. ferax can kill amphibian larvae and further suggest that evaluation of how pathogens affect amphibians at the population level requires investigation at various life stages

Evidence for a Proton–Protein Symport Mechanism in the Anthrax Toxin Channel

The toxin produced by Bacillus anthracis, the causative agent of anthrax, is composed of three proteins: a translocase heptameric channel, (PA63)7, formed from protective antigen (PA), which allows the other two proteins, lethal and edema factors (LF and EF), to translocate across a host cell's endosomal membrane, disrupting cellular homeostasis. It has been shown that (PA63)7 incorporated into planar phospholipid bilayer membranes forms a channel capable of transporting LF and EF. Protein translocation through the channel is driven by a proton electrochemical potential gradient on a time scale of seconds. A paradoxical aspect of this is that although LFN (the N-terminal 263 residues of LF), on which most of our experiments were performed, has a net negative charge, it is driven through the channel by a cis-positive voltage. We have explained this by claiming that the (PA63)7 channel strongly disfavors the entry of negatively charged residues on proteins to be translocated, and hence the aspartates and glutamates on LFN enter protonated (i.e., neutralized). Therefore, the translocated species is positively charged. Upon exiting the channel, the protons that were picked up from the cis solution are released into the trans solution, thereby making this a proton–protein symporter. Here, we provide further evidence of such a mechanism by showing that if only one SO3−, which is essentially not titratable, is introduced at most positions in LFN, through the reaction of an introduced cysteine residue at those positions with 2-sulfonato-ethyl-methanethiosulfonate, voltage-driven LFN translocation is drastically inhibited. We also find that a site that disfavors the entry of negatively charged residues into the (PA63)7 channel resides at or near its Φ-clamp, the ring of seven phenylalanines near the channel's entrance

Effects of Ultraviolet Radiation on Amphibians: Field Experiments

Numerous reports suggest that populations of amphibians from a wide variety of locations are experiencing population declines and/or range reductions. In some cases, unusually high egg mortality has been reported. Field experiments have been used with increasing frequency to investigate ultraviolet radiation as one of the potential factors contributing to these declines. Results from field experiments illustrate that hatching success of eggs is hampered by ultraviolet radiation in a number of species, while other species appear to be unaffected. Continued mortality in early life-history stages may ultimately contribute to a population decline. Although UV-B radiation may not contribute to the population declines of all species, it may play a role in the population decline of some species, especially those that lay eggs in open shallow water subjected to solar radiation and in those that have a poor ability to repair UV-induced DNA damage.Peer reviewe