Sapling growth responses to warmer temperatures ‘cooled’ by browse pressure

Rising temperatures are predicted to cause temperate tree species to expand north into currently boreal dominated forests. Other factors, such as overabundant deer, may hinder temperate expansion. We examined how interactions among temperature, browse pressure, light availability, and initial size impact height and radial growth of naturally regenerated, competing temperate and boreal saplings across their overlapping range limits in central North America. In 9 of 10 growth model comparisons, the inclusion of mean summer temperature and browse damage as explanatory variables strongly improved model performance over the base model with only initial size and light availability as parameters. Potential growth reductions due to browse damage and temperature limitation were similar in magnitude (up to ~50%). Temperate sapling growth increased and boreal growth decreased with temperature across a regional summer temperature gradient (2.3 °C), causing a rank reversal in growth rates, and suggesting that temperature is a key driver of sapling performance and range boundaries. However, under high browse pressure positive temperate responses to temperature were eliminated, essentially pushing the crossover point in growth between temperate and boreal species further south. These results highlight the importance of interactions among global change agents and potential impediments for tree species to track a rapidly changing climate.     

Phosphorus nutrition and mycorrhiza effects on grass leaf growth. P status- and size-mediated effects on growth zone kinematics

This study tested whether leaf elongation rate (LER, mm h(-1)) and its components--average relative elemental growth rate (REGRavg, mm mm(-1) h(-1)) and leaf growth zone length (L(LGZ), mm)--are related to phosphorus (P) concentration in the growth zone (P(LGZ) mg P g(-1) tissue water) of Lolium perenne L. cv. Condesa and whether such relationships are modified by the arbuscular mycorrhizal fungus (AMF) Glomus hoi. Mycorrhizal and non-mycorrhizal plants were grown at a range of P supply rates and analysed at either the same plant age or the same tiller size (defined by the length of the sheath of the youngest fully expanded leaf). Both improved P supply (up to 95%) and AMF (up to 21%) strongly increased LER. In tillers of even-aged plants, this was due to increased REGRavg and L(LGZ). In even-sized tillers, it was exclusively due to increased REGRavg. REGRavg was strictly related to P(LGZ) (r2 = 0.95) and independent of tiller size. Conversely, L(LGZ) strictly depended on tiller size (r2 = 0.88) and not on P(LGZ). Hence, P status affected leaf growth directly only through effects on relative tissue expansion rates. Symbiosis with AMF did not modify these relationships. Thus, no evidence for P status-independent effects of AMF on LER was found.     

There is no heterotic effect upon developmental stability in the ventral side of the skull within the house mouse hybrid zone

Fluctuating asymmetry (FA) of a body is expected to be related to an organism's developmental instability. We studied patterns of FA in the ventral side of the skull along a transect across the central-European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and Mus musculus domesticus. We found that FA was not significantly different between introgression classes relative to differences between localities within those classes and that the within-class differences were much larger than differences between individual-signed asymmetries within localities. However, if year was added to the same analysis as another factor, FA was not significantly different among localities within the same introgression class. When individual asymmetries were plotted against individual hybrid indices, hybrids appeared more asymmetric than individuals from outside of the zone. Thus contrary to previous studies, we did not find lower FA indicating heterotic effect in hybrids for the traits studied. It is suggested that the impact of hybridization on FA in the ventral side of the mouse skull is negligible or overwhelmed by other factors.     

Temporally regulated expression of Cre recombinase in neural stem cells

The use of mouse gene targeting to study molecules important in neural development is oftentimes impaired by early embryonic lethality. In order to address later roles for such molecules, specifically in neural stem cells, we generated transgenic mice that express both the tetracycline-inducible molecule rtTA-M2 and GFP under the control of the neural precursor specific form of nestin. Developmental analysis of these mice demonstrates that GFP expression is exclusive to the neural tube. Adult expression of GFP is seen only in known areas of adult neurogenesis, namely, the subventricular zone and the dentate gyrus. When crossed with a second transgenic mouse (TetOp-Cre) that expresses the Cre recombinase under the control of the tetracycline responsive promotor, we demonstrate temporal induction of Cre in bigenic animals exposed to doxycycline. We further demonstrate the feasibility of this approach by using the ROSA-26 reporter mouse to mediate recombination in neural precursor cells.     

Small mammal diversity and dynamics within Nigeria,with emphasis on reservoirs of the lassa virus

Nigeria has a rich small mammal community, with several species implicated as carriers of zoonotic microbes such as the Lassa virus (LASV). We sought to elucidate the diversity and distribution of these animals (including known LASV reservoirs) geographically, habitat-wise and seasonally. Our DNA-assisted survey detected at least 19 small mammal species amongst 790 specimens. Diversity indices were similar between ecological zones and also between endemic and non-endemic areas for Lassa fever. Mastomys natalensis, the most renowned LASV host, was present in eight out of nine localities sampled. We also described the spatial occurrence of other known LASV hosts such as M. erythroleucus and Hylomyscus pamfi, including carriers of LASV-like arenaviruses such as Mus (Nannomys) spp. The most numerous rodents (Mastomys natalensis, M. erythroleucus, and Praomys daltoni) were captured mainly inside human dwellings. Reproductive activity occurred throughout the year, but led to population peaks for M. natalensis in the dry season and for M. erythroleucus and P. daltoni in the rainy season. Extensive geographic distribution of LASV rodent reservoirs, with population peaks in different seasons, shows that the risk of rodent-to-human transmission of LASV is greater than currently realized.     

Antimicrobial and antibiofilm activity of pleurocidin against cariogenic microorganisms

Dental caries is a common oral bacterial infectious disease of global concern. Prevention and treatment of caries requires control of the dental plaque formed by pathogens such as Streptococcus mutans and Streptococcus sobrinus. Pleurocidin, produced by Pleuronectes americanus, is an antimicrobial peptide that exerts broad-spectrum activity against pathogenic bacteria and fungi. Moreover, pleurocidin shows less hemolysis and is less toxic than other natural peptides. In the present study, we investigated whether pleurocidin is an effective antibiotic peptide against common cariogenic microorganisms and performed a preliminary study of the antimicrobial mechanism. We assayed minimal inhibitory concentration (MIC), minimal bactericide concentration (MBC) and bactericidal kinetics and performed a spot-on-lawn assay. The BioFlux system was used to generate bacterial biofilms under controllable flow. Fluorescence microscopy and confocal laser scanning microscopy (CLSM) were used to analyze and observe biofilms. Scanning electron microscopy was used to observe the bacterial membrane. MIC and MBC results showed that pleurocidin had different antimicrobial activities against the tested oral strains. Although components of saliva could affect antimicrobial activity, pleurocidin dissolved in saliva still showed antimicrobial effects against oral microorganisms. Furthermore, pleurocidin showed a favorable killing effect against BioFlux flow biofilms in vitro. Our findings suggest that pleurocidin has the potential to kill dental biofilms and prevent dental caries.     

乌江河岸带维管植物区系的初步研究

对乌江河岸带维管植物区系的研究结果表明,河岸带共有维管植物69科187属302种,其中蕨类植物9科10属16种,裸子植物1科1属1种,被子植物59科176属285种。生活型以草本为主,其次是灌木。科、属、种的分布区类型多样,在科级水平上有7个类型和4个变型,在属级水平上有13个类型和10个变型,在种级水平上有15个类型和13个变型。地理联系较为广泛,与北温带植物区系联系最为紧密,其次是泛热带植物区系和东亚植物区系。科、属的优势现象较为明显。该河岸带植物区系呈亚热带性质,与热带植物区系有较高的亲缘关系。     

Glinal variation in morphology among eastern populations of the waterstrider, Aquarius remigis Say (Hemiptera: Gerridae)

We examined morphological variation among populations of the stream-dwelling waterstrider, Aquarius remigis. A previous analysis of allozyme variation along a transect from southern Quebec to southern North Carolina revealed two distinct 'types' of A. remigis, north and south of a transition zone in southern New York and northern Pennsylvania. To assess the concordance of morphological and allozyme differentiation, adults were sampled from 15 populations along the original transect, as well as 11 additional populations in New York, Connecticut and New Jersey. Eight measurements of leg and body size were taken of preserved individuals. Univariate and multivariate analyses (multiple regression, PCA, discriminant analysis) reveal significant differentiation between northern and southern populations with a transition zone between latitudes 39^oand 42^onorth. Strong clines within each region and a clear transition between regions support previous suggestions that there are two distinct 'types' of this species in eastern North America. The transition zone, in morphology coincides with that revealed by the allozyme variation, but extends further south. The covariance of allozyme frequency and morphometric traits suggests that differentiation has occurred through vicariance and secondary contact, and that in this system, cladistic and adaptive differentiation are coupled.     

Nitrogen dynamics in the hyporheic zone of a forested stream during a small storm, Hokkaido, Japan

Water and dissolved nitrogen flows through the hyporheic zone of a 3rd-order mountain stream in Hokkaido, northern Japan were measured during a small storm in August 1997. A network of wells was established to measure water table elevations and to collect water samples to analyze dissolved nitrogen concentrations. Hydraulic conductivity and the depth to bedrock were surveyed. We parameterized the groundwater flow model, MODFLOW, to quantify subsurface flows of both stream water and soil water through the hyporheic zone. MODFLOW simulations suggest that soil water inflow from the adjacent hill slope increased by 1.7-fold during a small storm. Dissolved organic nitrogen (DON) and ammonium (NH ₄ ⁺ ) in soil water from the hill slope were the dominant nitrogen inputs to the riparian zone. DON was consumed via mineralization to NH ₄ ⁺ in the hyporheic zone. NH ₄ ⁺ was the dominant nitrogen species in the subsurface, and showed a net release during both base and storm flow. Nitrate appeared to be lost to denitrification or immobilized by microorganisms and/or vegetation in the riparian zone. Our results indicated that the riparian and hyporheic system was a net source of NH ₄ ⁺ to the stream.