Does elevated testosterone result in increased exposure and transmission of parasites?

Male-biased infection is a common phenomenon in vertebrate-parasite systems and male-biased transmission has been experimentally demonstrated. One mechanism that is hypothesized to create male-biased transmission is the immuno-suppressive effect of testosterone because it increases susceptibility to infection. Testosterone also influences host behaviour and, consequently, may increase exposure to parasites. To test how testosterone could increase exposure and transmission, we undertook a longitudinal mark-recapture study where we experimentally elevated testosterone levels in wild male rodents. Individuals in control populations reduced the average number of contacts over the treatment period, while populations with experimentally elevated testosterone levels maintained the number of contacts between hosts. As a result, the transmission potential was higher in testosterone treated populations compared to controls. Our results indicated that males with high-testosterone levels alter the population-level contacts, producing different social networks and increasing transmission potential compared to those where testosterone is at background levels.     

Mitonuclear Coevolution,but not Nuclear Compensation,Drives Evolution of OXPHOS Complexes in Bivalves

In Metazoa, four out of five complexes involved in oxidative phosphorylation (OXPHOS) are formed by subunits encoded by both the mitochondrial (mtDNA) and nuclear (nuDNA) genomes, leading to the expectation of mitonuclear coevolution. Previous studies have supported coadaptation of mitochondria-encoded (mtOXPHOS) and nuclear-encoded OXPHOS (nuOXPHOS) subunits, often specifically interpreted with regard to the “nuclear compensation hypothesis,” a specific form of mitonuclear coevolution where nuclear genes compensate for deleterious mitochondrial mutations due to less efficient mitochondrial selection. In this study, we analyzed patterns of sequence evolution of 79 OXPHOS subunits in 31 bivalve species, a taxon showing extraordinary mtDNA variability and including species with “doubly uniparental” mtDNA inheritance. Our data showed strong and clear signals of mitonuclear coevolution. NuOXPHOS subunits had concordant topologies with mtOXPHOS subunits, contrary to previous phylogenies based on nuclear genes lacking mt interactions. Evolutionary rates between mt and nuOXPHOS subunits were also highly correlated compared with non-OXPHO-interacting nuclear genes. Nuclear subunits of chimeric OXPHOS complexes (I, III, IV, and V) also had higher dN/dS ratios than Complex II, which is formed exclusively by nuDNA-encoded subunits. However, we did not find evidence of nuclear compensation: mitochondria-encoded subunits showed similar dN/dS ratios compared with nuclear-encoded subunits, contrary to most previously studied bilaterian animals. Moreover, no site-specific signals of compensatory positive selection were detected in nuOXPHOS genes. Our analyses extend the evidence for mitonuclear coevolution to a new taxonomic group, but we propose a reconsideration of the nuclear compensation hypothesis.     

Trumpeter Swan Abundance and Growth Rates in Yellowstone National Park

ABSTRACT Decreasing abundance of resident, nonmigratory trumpeter swans (Cygnus buccinator) in Yellowstone National Park (YNP), USA, raised concern that this population, which helped facilitate the restoration of the species across North America, may disappear. We quantified trends in abundance of resident and migratory trumpeter swans in YNP from 1967 to 2007 and investigated the potential mechanisms for declining population trends, including cessation of the supplemental feeding program and relocation programs outside of YNP, density dependence, and annual variations in environmental conditions. Estimated abundance of resident trumpeter swans in YNP ranged from 59 individuals in 1968 to 10 individuals in 2007. Using log-linear modeling, the best approximating model chosen from an a priori set of competing models estimated the annual growth rate (r) of resident swans from 1967 to 2007 was −0.036 (95% CI =−0.042 to −0.030, Akaike wt [w_i] = 0.44). A competing model provided evidence that decreases in abundance became more dramatic after supplemental feeding of grain outside of YNP was terminated in winter 1992–1993 (r̂_1967–1992 = −0.027, 95% CI = −0.039 to −0.015; r̂_1993–2007 = −0.053, 95% CI = −0.029 to −0.080; w_i = 0.42). There was little evidence of density-dependent effects on the resident population growth rates (βYNP_pop = 0.006, 95% CI = −0.017 to 0.007), but rates were lower following severe winters, wetter springs, and warmer summers. Our results indicate that the YNP population of trumpeter swans is decreasing and may act as a sink to surrounding populations. Thus, population levels of YNP trumpeter swans may depend on management outside the Park and we recommend the National Park Service collaborate with surrounding agencies in managing trumpeter swans throughout the Tri-state region where more productive habitats may exist.     

Thermodynamics and dynamics of the formation of spherical lipid vesicles

We propose a free energy expression accounting for the formation of spherical vesicles from planar lipid membranes and derive a Fokker–Planck equation for the probability distribution describing the dynamics of vesicle formation. We find that formation may occur as an activated process for small membranes and as a transport process for sufficiently large membranes. We give explicit expressions for the transition rates and the characteristic time of vesicle formation in terms of the relevant physical parameters.     

Infection Potential of Hairy Nightshade (Solanum sarrachoides) by Phytophthora infestans and Late Blight Implications of the Alternate Host

Infection of hairy nightshade ( Solanum sarrachoides Sendt.) by Phytophthora infestans has been reported. However, the epidemiological significance of hairy nightshade to potato late blight is not well known. Disease development and infection rates of P. infestans were quantified on hairy nightshade relative to tomato (cv. Brandywine) and potato (cv. Shepody) hosts to evaluate infection potential at 14, 18, 22 and 26°C and 72, 82, 87, and 92% relative humidity (RH). The susceptibility of hairy nightshade to inoculum levels, weed ontogeny, and sporangia production potential were also investigated. Late blight development varied among hairy nightshade, tomato and potato hosts. Pathogen infection rates ranged from 0.0325 to 0.4674 gompits/day (unit for quantifying infection rates), and were significantly (P < 0.05) greater on potato and tomato than on hairy nightshade. Late blight severity was variably affected by RH. Disease levels on hairy nightshade varied with inoculum load; and ranged from 9 to 26% and 26 to 37% at low (5 × 10³) and high (25 × 10³) sporangia concentrations, respectively. Late blight was recorded irrespective of hairy nightshade ontogeny, and was significantly greater on 8–10 than 4–6-week-old plants. These results indicate that pathogen, environmental and host factors affect late blight development on hairy nightshade.     

Physiological and morphological response to water deficit in seedlings of five provenances of Pinus canariensis: potential to detect variation in drought-tolerance

To assess the potential of short-term screenings for drought resistance at the seedling stage to detect ecotypic variation and predict field performance, we studied the responses to water deficit of seedlings of Pinus canariensis from five geographic origins under controlled conditions and compared these responses with the performance of provenances in a multi-site field trial. Leaf water potential, the osmotic component, leaf chlorophyll fluorescence and growth and biomass partitioning were measured as seedlings were subjected for 11 days to two levels of osmotic potential generated by polyethylene glycol (PEG 6000), −1 MPa (slowly imposed water deficit; S) and −1.5 MPa (fast imposed water deficit; F), and a control treatment (no PEG added to the nutrient solution; C). Leaf water potential declined to final mean values of −1.2, −2.7 and −4.7 MPa in the C, S and F treatments, respectively. The ratio of variable to maximum chlorophyll fluorescence declined to final mean values of 0.77, 0.66 and 0.40 in the C, S and F treatments, respectively, with no differences amongst provenances. All provenances showed an active osmotic adjustment (OA) in response to water deficit which varied depending on the drying rate. A slow imposition of water deficit favoured solute accumulation. Pooling all treatments, the index of OA ranged from 0.28 to 0.40, but rose considerably when only C and S treatments were considered (0.56 to 0.70). There was a positive and significant correlation between the overall index of OA (all treatments pooled) and the drought period in the site of origin, suggesting ecotypic variation in OA as a result of drought duration. Seedlings allocated more dry matter to roots than shoots when subjected to moderate and slowly imposed water deficit; only one provenance showed no increase in the root to shoot ratio at the end of the treatment period compared with control seedlings. Responses to controlled water deficits were only qualitatively related to performance (survival and growth) of provenances in several field sites, indicating the involvement of complex mechanisms to cope with drought under natural conditions. However, the provenance with the highest overall index of OA outgrew and outsurvived the other provenances in the most arid site, and the only provenance not modifying the root to shoot ratio in response to water deficit survived the least in all field sites. Acclimation of root to shoot ratio and net solute accumulation to water deficit could hence favour drought-tolerance beyond the seedling stage and be used as preliminary predictors of field performance.     

Inter-sexual differences in Antarctic fur seal pup growth rates: evidence of environmental regulation?

We investigated the variation of Antarctic fur seal (Arctocephalus gazella) pup growth rates in response to sex, breeding season and duration of both maternal foraging trip and attendance bouts. Data were collected during five consecutive rearing seasons at Cape Shirreff, the most important breeding colony in the South Shetland Islands, Antarctica. Our results showed significant interannual and sexual variations in pup growth rates. Male pups grew significantly faster than female pups during 2000, 2001, 2002 and 2004 seasons, whilst during 2003 no difference was found. The interannual variation in pup growth rates was correlated with the interannual fluctuation in maternal foraging trip and attendance bouts. There was a significant effect of pup sex and maternal foraging trip duration on pup growth rates, which varied between years having foraging trip duration a major effect during 2003, when females spent more time at sea and interestingly on that year there were no sexual differences in pup growth rates. The effect of attendance bout on pup growth rates was not significant. Diet analysis showed that Antarctic krill (Euphausia superba) was the most frequent prey item during the study period. Analysis of krill size distribution showed a significant difference in krill length, during 2003, when A. gazella preyed upon the smallest sizes of krill. In this study, sex was the most important factor on pup growth rates, but when prey availability seemed more limited, there are longer foraging trips and shorter attendance bouts the sex factor became less significant.     

Stability studies of hydrazide and hydroxylamine-based glycoconjugates in aqueous solution

Glycoconjugates can be readily formed by the condensation of a free-reducing terminus and a strong α-effect nucleophile, such as a hydrazide or a hydroxylamine. Further characterization of a series of glycoconjugates formed from xylose, glucose and N-acetylglucosamine, and either p-toluenesulfonyl hydrazide or an N-methylhydroxylamine, was carried out to gain insight into the optimal conditions for the formation of these useful conjugates, and their stability. Their apparent association constants (9-74 M⁻¹) at pH 4.5; as well, as rate constants for hydrolysis, at pH 4.0, 5.0 and 6.0 (37 °C), were determined. The half-lives of the conjugates varied between 3 h and 300 days. All the compounds were increasingly stable as the pH approached neutrality. Conjugate hydrolysis rates mirrored those found for O-glycoside hydrolysis where conjugates formed from electron-rich monosaccharides hydrolyzed more rapidly.