Carbon debt repayment or carbon sequestration parity? Lessons from a forest bioenergy case study in Ontario,Canada

Forest bioenergy can contribute to climate change mitigation by reducing greenhouse gas (GHG) emissions associated with energy production. We assessed changes in GHG emissions resulting from displacement of coal with wood pellets for the Atikokan Generating Station located in Northwestern Ontario, Canada. Two contrasting biomass sources were considered for continuous wood pellet production: harvest residue from current harvest operations (residue scenario) and fibre from expanded harvest of standing live trees (stemwood scenario). For the stemwood scenario, two metrics were used to assess the effects of displacing coal with forest biomass on GHG emissions: (i) time to carbon sequestration parity, defined as the time from the beginning of harvest to when the combined GHG benefit of displacing coal with biomass and the amount of carbon in regenerating forest equalled the amount of forest carbon without harvest for energy production; and (ii) time to carbon debt repayment, defined as the time from the beginning of harvest to when the combined GHG benefit of displacing coal with biomass and the amount of carbon in the regenerating forest equalled forest carbon at the time of harvest. Only time to carbon sequestration parity was used for the residue scenario. In the residue scenario, carbon sequestration parity was achieved within 1 year. In the stemwood scenario, times to carbon sequestration parity and carbon debt repayment were 91 and 112 years, respectively. Sensitivity analysis showed that estimates were robust when parameter values were varied. Modelling experiments showed that increasing growth rates for regenerating stands in the stemwood scenario could substantially reduce time to carbon sequestration parity. We discuss the use of the two metrics (time to carbon sequestration parity and time to carbon debt repayment) for assessing the effects of forest bioenergy projects on GHG emissions and make recommendations on terminology and methodologies for forest bioenergy studies.     

Comparative real-time kinetic analysis of human complement killing of Leishmania infantum promastigotes derived from axenic culture or from Phlebotomus perniciosus

Although Leishmania metacyclic promastigotes are generally considered resistant to human complement, studies of in vitro-cultured axenic stationary promastigotes using serum concentrations that approximate physiological plasma conditions indicate complement sensitivity. Natural Leishmania infection is caused by sand fly-inoculated promastigotes, whose complement resistance has not been analyzed systematically. We compared Leishmania susceptibility to human complement in L. infantum promastigotes derived from in vitro cultures and from sand flies. Phlebotomus perniciosus sand flies were fed with axenic promastigotes, L. infantum-infected U-937 cells, or spleen cells from L. infantum-infected hamsters. On selected days post-feeding, flies were dissected and promastigotes isolated; in addition, axenic promastigotes were obtained from culture at equivalent days of growth. In near-physiological serum concentration and temperature conditions, measurement of real-time kinetics of propidium iodide uptake showed that approximately 90% of axenic- and sand fly-derived promastigotes were rapidly killed by complement. We found no substantial differences between promastigotes from axenic culture, those isolated from flies on different post-feeding days, or those generated in flies fed with distinct inocula. The results indicate that Leishmania susceptibility to human complement is independent of promastigote developmental stage in the sand fly mid-gut and in axenic culture.     

Handling does not affect reproductive signals of male threespine stickleback

We examined the affect of handling on reproductive signal expression in male threespine stickleback, Gasterosteus aculeatus. Spectrophotometric techniques have become popular methods for measuring fish color, but the measurements require handling of the subjects in order to make measurements. Fish can undergo rapid physiological color change in response to stress. As such, handling fish may induce color changes and measured colour may not be representative of signal appearance under non-stressful conditions. We measured the reflectance characteristics of the opercular, ventro-lateral and dorso-lateral areas of 41 reproductive males from Hotel Lake, BC, Canada using spectroradiometry immediately upon capture and again at 2, 3, 4, 5, 10, 15, and 20 min post-capture. Repeated measures ANOVA revealed that post-capture handling did not affect opercular or ventro-lateral reflectance characteristics over the 20 min period. However, we did observe a change in dorso-lateral reflectance characteristics of parental males over the experiment. The results of our study show that handling does not influence reflective properties of two key components of stickleback reproductive signals during a time frame that is reasonable for taking field measurements of signal color.     

Microanatomy of the radius and lifestyle in amniotes (Vertebrata, Tetrapoda)

Radial cross-sections of 49 species of extant and two species of extinct amniotes of known lifestyle have been studied in order to assess the relationship between lifestyle (aquatic, amphibious or terrestrial) and bone microanatomy. Most compactness profile and body size parameters exhibit a phylogenetic signal; therefore, classical statistical tests should not be used. Permutational multiple linear regressions show an ecological signal in most compactness profile parameters and in the cross-section maximal diameter. A linear discriminant analysis is performed with these parameters to distinguish the various lifestyles. The discriminant function based on taxa of known lifestyle is used to infer the lifestyle of three extinct amniotes: the early nothosaur Pachypleurosaurus (amphibious), the therapsid Lystrosaurus (amphibious) and the synapsid Ophiacodon (aquatic). These predictions are congruent with classical palaeoecological interpretations. This model may be very useful when attempting to infer the ancestral lifestyle of amniotes and other early limbed vertebrates.     

Novel Cell Preservation Technique to Extend Bovine In Vitro White Blood Cell Viability

Although cell-mediated immunity based diagnostics can be integral assays for early detection of various diseases of dairy cows, processing of blood samples for these tests is time-sensitive, often within 24 hours of collection, to maintain white blood cell viability. Therefore, to improve utility and practicality of such assays, the objective of this study was to assess the use of a novel white blood cell preservation technology in whole bovine blood. Blood samples from ten healthy cows were each divided into an unpreserved control sample and a test sample preserved with commercially-available cell transport medium. Samples were maintained at room temperature and stimulated with the mitogens pokeweed and concanavalinA, as well as with interleukin-12 p40. Stimulation was completed on days 1, 5, and 8 post-sampling. Viability of white blood cells was assessed through interferon gamma production determined with a commercial enzyme linked immunosorbent assay. In addition, mononuclear cell viability was assessed with propidium iodide flow cytometry. Greater interferon gamma production was observed on days 5 and 8 post-collection in preserved samples, with both pokeweed and concanavalinA stimulating positive interferon gamma production on day 5 post-collection. A greater proportion of the amount of interferon gamma produced on day 1 continued to be produced on days 5 and 8 post-collection with concanavalinA stimulation (with or without interleukin 12) as compared to pokeweed stimulation. Additionally, viable mononuclear cells were still present at eight days post-collection, with a higher mean proportion detected at days 5 and 8 in all stimulated preserved samples. This practical and simple method to extend in vitro white blood cell viability could benefit the efficient utilization of cell-based blood tests in ruminants.     

A REEVALUATION OF THE ORIGIN OF PENTADACTYLY

The hypothesis suggested by Coates that pentadactyly arose twice is based on the presumed affinities between Tulerpeton, embolomeres, and amniotes. Flaws were found in the coding of some characters that supported this clade and, once corrected, the matrix fails to support the proposed phylogeny. Furthermore, interpretation of the phylogeny of Coates is difficult because no amniotes and no lissamphibians were included in this analysis. A reappraisal of the affinities of Tulerpeton using a matrix composed of a greater range of taxa suggests that it is a stem-tetrapod, that pentadactyly arose only once, and that the first tetrapod was already pentadactyl.     

Incorporating phylogenetic uncertainty on phylogeny‐based palaeontological dating and the timing of turtle diversification

Methods improving the performance of molecular dating of divergence time of clades have improved dramatically in recent years. The calibration of molecular dating using the first appearance of a clade in the fossil record is a crucial step towards inferring the minimal diversification time of various groups and the choice of extinct taxa can strongly influence the molecular dates. Here, we evaluate the uncertainty on the phylogenetic position of extinct taxa through non‐parametric bootstrapping. The recognition of phylogenetic uncertainty resulted in the definition of the Bootstrap Uncertainty Range (BUR) for the age of first appearance of a given clade. The BUR is calculated as the interval of geological time in which the diversification of a given clade can be inferred to have occurred, based on the temporal information of the fossil record and the topologies of the bootstrap trees. Divergence times based on BUR analyses were calculated for three clades of turtles: Testudines, Pleurodira and Cryptodira. This resulted in extensive uncertainty ranges of topology‐dependent minimal divergence dates for these clades.     

Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru

Non-pathological densification (osteosclerosis) and swelling (pachyostosis) of bones are the main modifications affecting the skeleton of land vertebrates (tetrapods) that returned to water. However, a precise temporal calibration of the acquisition of such adaptations is still wanting. Here, we assess the timing of such acquisition using the aquatic sloth Thalassocnus, from the Neogene of the Pisco Formation, Peru. This genus is represented by five species occurring in successive vertebrate-bearing horizons of distinct ages. It yields the most detailed data about the gradual acquisition of aquatic adaptations among tetrapods, in displaying increasing osteosclerosis and pachyostosis through time. Such modifications, reflecting a shift in the habitat from terrestrial to aquatic, occurred over a short geological time span (ca 4 Myr). Otherwise, the bones of terrestrial pilosans (sloths and anteaters) are much more compact than the mean mammalian condition, which suggests that the osteosclerosis of Thalassocnus may represent an exaptation.