Spatial and temporal response of stream bacteria to sources of dissolved organic carbon in a blackwater stream system

1. We hypothesized that changes in bacterial colony growth would be correlated to shifts in riparian vegetation (via leachate quality) along a river continuum of a south-eastern, blackwater stream (U.S.A.). Spatially, we expected bacterial assemblages from downstream reaches to utilize more sources of leachate and at higher concentrations than bacteria collected from headwater reaches. Temporally, we predicted higher colony growth on leachate from autumn-shed (senescent) leaves compared with leachate from fresh, green leaves.
2. We examined spatial differences in assemblage growth by culturing bacteria sampled along the stream continuum on gradient plates using leachates from four common riparian species ( Taxodium distichum , Carya spp., Acer rubrum and Decumaria barbara ). Bacteria from the lowest site were able to use all sources provided and at all concentrations, whereas bacteria from upper reaches could not. Colony density was correlated to relative leachate concentration at all sites along the continuum.
3. Leachates from fresh and senescent A. rubrum leaves were used to determine temporal differences. Winter assemblages of bacteria could not grow on fresh leaf leachate at any concentration but grew well on autumn leaf leachate at higher concentrations. Differential response of bacterial assemblages indicated local adaptation to potential sources of dissolved organic matter.
4. Growth response of stream bacterial colonies appeared to be dependent on the timing and source of leachate as well as on sources of dissolved organic carbon from further upstream. Growth of bacterial assemblages exhibited 'generalist' characteristics in headwater reaches and 'specialist' characteristics at the mouth of our study stream drainage. Thus, our findings lend support to the argument that variable resource habitats favour a small, generalist assemblage, while environments with stable resource supplies allow for highly diverse assemblages dominated by specialists.     

Population differentiation in the marginal populations of the great tit (Paridae: Parus major)

The major subspecies group of the great tit, Parus major , has experienced demographic and spatial expansions during the last century in several sites at the edges of its distribution range. These expansions, although temporarily very even, have resulted in dissimilar patterns of molecular diversity. Populations locating at regions of contact to other subspecies groups (in Amur, Kirghizia–Kazakhstan, and Iran) show divergence from central population by nuclear and mitochondrial markers. In Amur, gene flow from minor group could be detected based on the existence of private minor alleles in the major population. In Kirghizia and Kazakhstan, the bokharensis and major groups share almost all the microsatellite alleles detected though frequencies differ. In Iran, three geographically close populations are distinct according to the mitochondrial sequences but also indications of present or recent admixture is detected. Populations, which have expanded to regions previously unoccupied by the species (northern UK and Finland), show divergence only by one of the markers. The variability in molecular differentiation may be due to dissimilar expansions, depending on whether the colonized regions have previously been occupied by another subspecies or not, on the amount of colonizing birds, and on the amount of past and present gene flow.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 201–210.     

Development and characterization of eight microsatellite markers in bullet tuna (Auxis rochei)

The bullet tuna (Auxis rochei) is a worldwide species of high commercial value in Spain. Nevertheless, little information is currently available about the genetic characteristics of wild A. rochei populations. In this survey, we have developed eight new microsatellites for the bullet tuna using an enriched genome library protocol. Primers were screened on a total of 78 individuals from three wild populations (Mediterranean, Atlantic, and Pacific), revealing seven to 27 alleles per locus with expected heterozygosities ranging from 0.63 to 0.97. These markers can be potentially useful tools for use in population genetic studies.     

The Crime of Manabozo

On the explanation here given of the nature of the trickster, as the projection in myth of the magical violator of taboo, the contradictory features he presents may be elucidated one by one. A secondary feature, hitherto ignored in the Algonkin trickster myth—namely, Manabozo's brother's death—is shown to conceal the ritual murder of a near-kinsman committed in order to obtain magical power for the benefit of the group.     

MINERAL COMPOSITION OF NUDIBRANCH SPICULES

Doridacean opisthobranchs have calcium carbonate spicules intheir mantle, foot, gills and rhinophores, which are generallyfusiform or spheroid in shape. There is surprising little knowledgeof their structure, and little information is available on theirmineral composition, generally considered to be calcite. Inorder to study their compositional variability and the possiblerole of environmental temperature in their calcification, thespicules of several doridaceans, collected at different latitudes,were analysed using a diffractometer (XRD) and a SEM microscopeequippedwith an EDS spectrometer. The study yielded the followingresults, concerning the minero-chemical composition of the spicules: 1) the fusiform spicules are mainly composed of calcite (CaCO₃)and brucite (Mg(OH)₂), with a small percentage of fluorite (CaF₂).The smaller spherules are almost pure calcite; 2) the mineral composition of fusiform spicules of species collectedat different latitudes showed inter-and intra-individual differences,but the Ca/Mg ratio does not seem to vary according to the environmentaltemperature. In fact, this ratio reflects the volume percentof calcite and brucite in a crystalline aggregate, and consequently,temperature has a poor influence on spicule composition. Onthe other hand, differences between foot and mantle, not onlywithin the same species but also in the same specimen, suggestthat the animal itself can influence the ratio ofcalcite andbrucite nucleation. In this case, the different pH in mantleand foot tissue could induce a different up-take and use ofcalcium and magnesium; 3) the presence of pure calcite spherules suggests that theycould be related to variations of the ion concentration in theskin caused by pH variations due to the dermal gland activityor, more simply, could be considered as a calcium reservoirand source for the production of the slender spicules. (Received 25 August 1994; accepted 28 December 1994)     

Cortical and Nuclear Events During Cell Division and Resting Cyst Formation in Colpoda inflata

Nuclear and cortical phenomena during dividing and resting cyst formation of Colpoda inflata are described. Cell division forms a cyst and produces two or four tomites. In each tomite, the right oral field results from the proliferation of the anterior extreme of a single kinety, and the left oral field results from the proliferation of four, five, or six somatic kineties. After macronuclear division, each macronuclear mass undergoes a chromatinic extrusion process. During resting cyst formation, the oral infraciliature of the vegetative cell is resorbed. The somatic kineties dispose in a radial way and some pairs of kinetosomes disappear. As in cell division, there is an extrusion process. From these results we conclude that the resting cysts of Colpoda inflata cannot be included in any group of the previous classifications for hypotrich resting cysts. Thus, we propose a new additional group to Walker and Maugel's classification called PKR (partial-kinetosome-resorbing) cysts.     

Synergistic effects of climate change and local stressors: CO2 and nutrient-driven change in subtidal rocky habitats

Climate-driven change represents the cumulative effect of global through local-scale conditions, and understanding their manifestation at local scales can empower local management. Change in the dominance of habitats is often the product of local nutrient pollution that occurs at relatively local scales (i.e. catchment scale), a critical scale of management at which global impacts will manifest. We tested whether forecasted global-scale change [elevated carbon dioxide (CO₂) and subsequent ocean acidification] and local stressors (elevated nutrients) can combine to accelerate the expansion of filamentous turfs at the expense of calcifying algae (kelp understorey). Our results not only support this model of future change, but also highlight the synergistic effects of future CO₂ and nutrient concentrations on the abundance of turfs. These results suggest that global and local stressors need to be assessed in meaningful combinations so that the anticipated effects of climate change do not create the false impression that, however complex, climate change will produce smaller effects than reality. These findings empower local managers because they show that policies of reducing local stressors (e.g. nutrient pollution) can reduce the effects of global stressors not under their governance (e.g. ocean acidification). The connection between research and government policy provides an example whereby knowledge (and decision making) across local through global scales provides solutions to some of the most vexing challenges for attaining social goals of sustainability, biological conservation and economic development.     

Growth, carbon-isotope discrimination, and drought-associated mortality across a Pinus ponderosa elevational transect

Drought‐ and insect‐associated tree mortality at low‐elevation ecotones is a widespread phenomenon but the underlying mechanisms are uncertain. Enhanced growth sensitivity to climate is widely observed among trees that die, indicating that a predisposing physiological mechanism(s) underlies tree mortality. We tested three, linked hypotheses regarding mortality using a ponderosa pine (Pinus ponderosa) elevation transect that experienced low‐elevation mortality following prolonged drought. The hypotheses were: (1) mortality was associated with greater growth sensitivity to climate, (2) mortality was associated with greater sensitivity of gas exchange to climate, and (3) growth and gas exchange were correlated. Support for all three hypotheses would indicate that mortality results at least in part from gas exchange constraints. We assessed growth using basal area increment normalized by tree basal area [basal area increment (BAI)/basal area (BA)] to account for differences in tree size. Whole‐crown gas exchange was indexed via estimates of the CO₂ partial pressure difference between leaf and atmosphere (p_a?p_c) derived from tree ring carbon isotope ratios (δ¹³C), corrected for temporal trends in atmospheric CO₂ and δ¹³C and elevation trends in pressure. Trees that survived the drought exhibited strong correlations among and between BAI, BAI/BA, p_a?p_c, and climate. In contrast, trees that died exhibited greater growth sensitivity to climate than trees that survived, no sensitivity of p_a?p_c to climate, and a steep relationship between p_a?p_c and BAI/BA. The p_a?p_c results are consistent with predictions from a theoretical hydraulic model, suggesting trees that died had a limited buffer between mean water availability during their lifespan and water availability during drought – i.e., chronic water stress. It appears that chronic water stress predisposed low‐elevation trees to mortality during drought via constrained gas exchange. Continued intensification of drought in mid‐latitude regions may drive increased mortality and ecotone shifts in temperate forests and woodlands.     

Phyllanthus section Choretropsis (Euphorbiaceae) in Brazil

Section Choretropsis genus Phyllanthus (Euphorbiaceae) is formed by plants whose branches are modified into phylloclades. Despite the suitable characteristics of phylloclades within the Phyllanthus genus, the systematics of these species are poorly understood. Morphological data are presented here to allow future revision of this taxonomic group. The section is represented by nine species distributed in South America, eight of them endemic to Brazil. Our taxonomic studies distinguish the species and propose the synonymization of nine varieties of P. klotzschianus and two varieties of P. flagelliformis based on vegetative and reproductive characters. The diversity of branching and the morphology of phylloclades are discussed.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 131–164.     

The mushroom habitat as an ecological arena for global exchange of Wolbachia

Wolbachia infect a variety of arthropod and nematode hosts, but in arthropods, host phylogenetic relationships are usually poor predictors of strain similarity. This suggests that new infections are often established by horizontal transmission. To gain insight into the factors affecting the probability of horizontal transmission among host species, we ask how host phylogeny, geographical distribution and ecology affect patterns of Wolbachia strain similarity. We used multilocus sequence typing (MLST) to characterize Wolbachia strain similarity among dipteran hosts associated with fleshy mushrooms. Wolbachia Supergroup A was more common than Supergroup B in Diptera, and also more common in mycophagous than non‐mycophagous Diptera. Within Supergroup A, host family within Diptera had no effect on strain similarity, and there was no tendency for Wolbachia strains from sympatric host species to be more similar to one another than to strains from hosts in different biogeographical realms. Supergroup A strains differed between mycophagous and non‐mycophagous Diptera more than expected by chance, suggesting that ecological associations can facilitate horizontal transmission of Wolbachia within mycophagous fly communities. For Supergroup B, there were no significant associations between strain similarity and host phylogeny, biogeography, or ecology. We identified only two cases in which closely related hosts carried closely related Wolbachia strains, evidence that Wolbachia‐host co‐speciation or early introgression can occur but may not be a major contributor to overall strain diversity. Our results suggest that horizontal transmission of Wolbachia can be influenced by host ecology, thus leading to partial restriction of Wolbachia strains or strain groups to particular guilds of insects.