Genetic variation of Saxifraga paniculata Mill. (Saxifragaceae): molecular evidence for glacial relict endemism in central Europe

Saxifraga paniculata Mill. is an amphi-atlantic species that is widely distributed in the Alps but also occurs with disjunct populations in central Europe. These isolated populations are considered to be glacial relicts. In the study presented here, we analysed the genetic variation within and between populations of Saxifraga paniculata in central Europe to test whether the molecular data give evidence for the supposed relict endemism. We used RAPD analysis and the analysis of molecular variance (AMOVA) technique to investigate 30 populations of Saxifraga paniculata from different locations in central Europe and adjacent geographical areas. In the RAPD analysis, 319 fragments could be amplified of which 91.2% were polymorphic. The percentage of polymorphic bands within populations correlated significantly with population size, indicating a higher level of inbreeding in small populations. AMOVA revealed 43.60% of the variation within populations, only 15.45% between populations within locations, and 40.95% between locations. Genetic distance between locations (Φ_ST) correlated significantly with the geographical distance between locations, giving evidence for geographical isolation. In an UPGMA cluster analysis, based on RAPD data, the populations were grouped together according to their location. The results exhibit a strong genetic differentiation which is obviously due to genetic drift in the isolated populations. Our study therefore gives evidence for glacial relict endemism of Saxifraga paniculata in central Europe.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80, 11–21.     

Parmelina quercina (Parmeliaceae, Lecanorales) includes four phylogenetically supported morphospecies

Morphological and phylogenetic relationships of the worldwide Mediterranean lichen forming fungus, Parmelina quercina , have been studied. Specimens from western Europe, western North America and southern Australia were analysed using molecular data (nuITS rDNA, nuLSU rDNA and mtSSU rDNA) and selected morphological features (upper cortex maculae, scanning electron microscopy examination of the epicortex, ascospores and conidia shape and size, and amphithecial retrorse rhizines). The results conclusively reveal that: (1) there is not one single species but four separate species in the Mediterranean or sub Mediterranean areas of the world. Parmelina quercina and Parmelina carporrhizans (Euroasiatic species), Parmelina coleae sp. nov. (North America) and Parmelina elixia sp. nov. (Australia); (2) largely debated P. carporrhizans is not a synonym of P. quercina but supported as a valid species circumscribed to Macaronesic relict sites; (3) the geographical isolation of the Australian population is correlated with a large genetic distance; (4) morphological characters (ascospores and conidial variability and thallus epicortex) correlate with the phylogenetic hypothesis; (5) the new or revalidated species within Parmelina quercina are not cryptic species but morphologically recognizable taxa.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 455–467.     

Transient over-expression of barley BAX Inhibitor-1 weakens oxidative defence and MLA12-mediated resistance to Blumeria graminis f.sp. hordei

BAX Inhibitor-1 (BI-1) is a conserved cell death suppressor protein. In barley, BI-1 ( HvBI-1 ) expression is induced upon powdery mildew infection and when over-expressed in epidermal cells of barley, HvBI-1 induces susceptibility to the biotrophic fungal pathogen Blumeria graminis . We co-expressed mammalian pro-apoptotic BAX together with HvBI-1, and the mammalian BAX antagonist BCL-X_L in barley epidermal cells. BAX expression led to cessation of cytoplasmic streaming and collapse of the cytoplasm while co-expression of HvBI-1 and BCL-X_L partially or completely, respectively, rescued cells from BAX lethality. When B. graminis was attacking epidermal cells, a green fluorescent protein fusion of HvBI-1 accumulated at the site of attempted penetration and was also present around haustoria. Over-expression of HvBI-1 in epidermal cells weakened a cell-wall-associated local hydrogen peroxide burst in a resistant mlo -mutant genotype and supported haustoria accommodation in race-specifically resistant MLA12 -barley. HvBI-1 is a cell death regulator protein of barley with the potential to suppress host defence reactions.     

Soluble nitrogen and phosphorus excretion of exotic freshwater mussels (Dreissena spp.): potential impacts for nutrient remineralisation in western Lake Erie

1. Recent increases in phytoplankton biomass and the recurrence of cyanobacterial blooms in western Lake Erie, concomitant with a shift from a community dominated by zebra mussels (Dreissena polymorpha) to one dominated by quagga mussels (D. bugensis), led us to test for differences in ammonia‐nitrogen and phosphate‐phosphorus excretion rates of these two species of invasive molluscs. 2. We found significant differences in excretion rate both between size classes within a taxon and between taxa, with zebra mussels generally having greater nutrient excretion rates than quagga mussels. Combining measured excretion rates with measurements of mussel soft‐tissue dry weight and shell length, we developed nutrient excretion equations allowing estimation of nutrient excretion by dreissenids. 3. Comparing dreissenid ammonia and phosphate excretion with that of the crustacean zooplankton, we demonstrated that the mussels add to nitrogen and phosphorus remineralisation, shortening nitrogen and phosphorus turnover times, and, importantly, modify the nitrogen and phosphorus cycles in Lake Erie. The increased nutrient flux from dreissenids may facilitate phytoplankton growth and cyanobacterial blooms in well‐mixed and/or shallow areas of western Lake Erie.     

Microsatellite DNA markers for the study of Atlantic salmon (Salmo salar) kinship,population structure,and mixed‐fishery analyses

Eleven microsatellite DNA loci were identified and characterized for Atlantic salmon (Salmo salar) collected from the Penobscot River, Maine, USA and the River Nith, Scotland, UK. The markers revealed high levels of genetic diversity (seven to 48 alleles per locus), heterozygosity (to 100%), and allelic heterogeneity (all comparisons). Considerable differentiation was observed as the genetic distance (chord) between the two collections was 0.680 and the pairwise F_ST, 0.12, was highly significant. These findings are consistent with patterns of continental‐level differentiation observed previously using an alternate suite of microsatellite loci. Locus‐by‐locus analyses of molecular variance suggested that most markers were suitable for delineating kinships and population genetic structure.     

Long-term survival despite low genetic diversity in the critically endangered Madagascar fish-eagle

The critically endangered Madagascar fish-eagle ( Haliaeetus vociferoides ) is considered to be one of the rarest birds of prey globally and at significant risk of extinction. In the most recent census, only 222 adult individuals were recorded with an estimated total breeding population of no more than 100–120 pairs. Here, levels of Madagascar fish-eagle population genetic diversity based on 47 microsatellite loci were compared with its sister species, the African fish-eagle ( Haliaeetus vocifer ), and 16 of these loci were also characterized in the white-tailed eagle ( Haliaeetus albicilla ) and the bald eagle ( Haliaeetus leucocephalus ). Overall, extremely low genetic diversity was observed in the Madagascar fish-eagle compared to other surveyed Haliaeetus species. Determining whether this low diversity is the result of a recent bottleneck or a more historic event has important implications for their conservation. Using a Bayesian coalescent-based method, we show that Madagascar fish-eagles have maintained a small effective population size for hundreds to thousands of years and that its low level of neutral genetic diversity is not the result of a recent bottleneck. Therefore, efforts made to prevent Madagascar fish-eagle extinction should place high priority on maintenance of habitat requirements and reducing direct and indirect human persecution. Given the current rate of deforestation in Madagascar, we further recommend that the population be expanded to occupy a larger geographical distribution. This will help the population persist when exposed to stochastic factors (e.g. climate and disease) that may threaten a species consisting of only 200 adult individuals while inhabiting a rapidly changing landscape.     

Enhanced litter input rather than changes in litter chemistry drive soil carbon and nitrogen cycles under elevated CO2: a microcosm study

Elevated CO₂ has been shown to stimulate plant productivity and change litter chemistry. These changes in substrate availability may then alter soil microbial processes and possibly lead to feedback effects on N availability. However, the strength of this feedback, and even its direction, remains unknown. Further, uncertainty remains whether sustained increases in net primary productivity will lead to increased long‐term C storage in soil. To examine how changes in litter chemistry and productivity under elevated CO₂ influence microbial activity and soil C formation, we conducted a 230‐day microcosm incubation with five levels of litter addition rate that represented 0, 0.5, 1.0, 1.4 and 1.8 × litterfall rates observed in the field for aspen stand growing under control treatments at the Aspen FACE experiment in Rhinelander, WI, USA. Litter and soil samples were collected from the corresponding field control and elevated CO₂ treatment after trees were exposed to elevated CO₂ (560 ppm) for 7 years. We found that small decreases in litter [N] under elevated CO₂ had minor effects on microbial biomass carbon, microbial biomass nitrogen and dissolved inorganic nitrogen. Increasing litter addition rates resulted in linear increase in total C and new C (C from added litter) that accumulated in whole soil as well as in the high density soil fraction (HDF), despite higher cumulative C loss by respiration. Total N retained in whole soil and in HDF also increased with litter addition rate as did accumulation of new C per unit of accumulated N. Based on our microcosm comparisons and regression models, we expected that enhanced C inputs rather than changes in litter chemistry would be the dominant factor controlling soil C levels and turnover at the current level of litter production rate (230 g C m⁻² yr⁻¹ under ambient CO₂). However, our analysis also suggests that the effects of changes in biochemistry caused by elevated CO₂ could become significant at a higher level of litter production rate, with a trend of decreasing total C in HDF, new C in whole soil, as well as total N in whole soil and HDF.     

Postlogging Succession and Habitat Usage of Shrubland Birds

ABSTRACT In the first decades after logging, the vegetation structure of harvested areas changes rapidly due to succession. For shrubland birds, many of which specialize on regeneration of specific ages, the changing vegetation structure makes determining how much habitat is available for individual species difficult. We conducted a meta-analysis to determine how populations of shrubland birds in the eastern United States and Canada respond to succession in the first 20 years after timber harvest. Based on those results, we used the area under the abundance-time regression curves to estimate the proportion of regenerating forest actually used by each bird species. Of the 28 species for which we had sufficient data, 14 showed significant changes in abundance over time. For 6 species, abundance was highest immediately after logging and decreased thereafter. Abundances of 7 other species were initially low, peaked roughly 10 years after harvest, and declined thereafter. Based on these results, shrubland birds would be expected to occupy a mean of just 53% (SD = 17%) of regenerating forests up to 20 years old. Thus, current estimates of habitat availability for shrubland birds may be too high by a factor of 2. Our findings also suggest that managed openings should be maintained on longer rotations than are currently used, providing habitat for birds that prefer older regeneration.     

Response of carbon fluxes to drought in a coastal plain loblolly pine forest

Full accounting of ecosystem carbon (C) pools and fluxes in coastal plain ecosystems remains less studied compared with upland systems, even though the C stocks in these systems may be up to an order of magnitude higher, making them a potentially important component in regional C cycle. Here, we report C pools and CO₂ exchange rates during three hydrologically contrasting years (i.e. 2005–2007) in a coastal plain loblolly pine plantation in North Carolina, USA. The daily temperatures were similar among the study years and to the long‐term (1971–2000) average, whereas the amount and timing of precipitation differed significantly. Precipitation was the largest in 2005 (147 mm above normal), intermediate in 2006 (48 mm below) and lowest in 2007 (486 mm below normal). The forest was a strong C sink during all years, sequestering 361 ± 67 (2005), 835 ± 55 (2006) and 724 ± 55 (2007) g C m^?2 yr^?1 according to eddy covariance measurements of net ecosystem CO₂ exchange (NEE). The interannual differences in NEE were traced to drought‐induced declines in canopy and whole tree hydraulic conductances, which declined with growing precipitation deficit and decreasing soil volumetric water content (VWC). In contrast, the interannual differences were small in gross ecosystem productivity (GEP) and ecosystem respiration (ER), both seemingly insensitive to drought. However, the drought sensitivity of GEP was masked by higher leaf area index and higher photosynthetically active radiation during the dry year. Normalizing GEP by these factors enhanced interannual differences, but there were no signs of suppressed GEP at low VWC during any given year. Although ER was very consistent across the 3 years, and not suppressed by low VWC, the total respiratory cost as a fraction of net primary production increased with annual precipitation and the contribution of heterotrophic respiration (R_h) was significantly higher during the wettest year, exceeding new litter inputs by 58%. Although the difference was smaller during the other 2 years (R_h : litterfall ratio was 1.05 in 2006 and 1.10 in 2007), the soils lost about 109 g C m^?2 yr^?1, outlining their potential vulnerability to decomposition, and pointing to potential management considerations to protect existing soil C stocks.