Isolation of 11 polymorphic tri- and tetranucleotide microsatellite loci in a North American sedge (Carex scoparia: Cyperaceae) and cross-species amplification in three additional Carex species

We report on the isolation and evaluation of 11 microsatellites from a widespread eastern North American wetland sedge, Carex scoparia. Loci exhibit 3-9 alleles over five populations and significant F(IS) (0.204-0.717) in most populations. All primers cross-amplify in at least two other species, and 10 cross-amplify in the more distantly related C. stipata. These markers will be used to examine population genetics and patterns of chromosomal diversification in this ecologically important sedge species and its relatives.     

Discordance between phylogenetics and coalescent-based divergence modelling: exploring phylogeographic patterns of speciation in the Carex macrocephala species complex

We fit a molecular data set, consisting of the rpL16 cpDNA marker and eight microsatellite loci, to the isolation-with-migration model as implemented in IM a to test a well-supported phylogenetic hypothesis of relationships within the Carex macrocephala species complex (Cyperaceae). The phylogenetic hypothesis suggests C. macrocephala from North America is reciprocally monophyletic and is sister to a reciprocally monophyletic clade of C. kobomugi . The North American C. macrocephala and C. kobomugi clade form a sister clade with a lineage of Asian C. macrocephala , thereby forming a paraphyletic C. macrocephala species. Not only does the phylogenetic hypothesis suggest C. macrocephala is paraphyletic, but it also suggests that the two lineages which share a partially overlapping distribution, Asian C. macrocephala and C. kobomugi , are not the most closely related. To test these relationships, we used coalescent-based population genetic models to infer divergence time for each lineage pair within the species complex. The coalescent-based models account for the stochastic forces which drive population divergence, and can account for the lineage sorting that occurs prior to lineage divergence. A drawback to phylogenetic-based phylogeographical analyses is that they do not account for stochastic lineage sorting that occurs between gene divergence and lineage divergence. By comparing the relative divergence time of the three main lineages within this group, Asian C. macrocephala , North American C. macrocephala , and C. kobomugi , we concluded that the phylogenetic hypothesis is incorrect, and the divergence between these lineages occurred during the Late Pleistocene epoch.     

The vertical distribution of nitrogen and photosynthetic activity at different plant densities in Carex acutiformis

Shoots of the monocotyledonous perennial Carex acutiformis were grown in open (28 shoots m⁻²) and dense stands (280 shoots m⁻²). For fully grown stands the distribution of relative PPFD and leaf nitrogen per unit leaf area over canopy depth was determined. Light response of photosynthesis was measured on leaf segments sampled at various heights in the stands. Relations between parameters of these curves and leaf nitrogen were investigated. Simulations showed that in the open stand daily canopy photosynthesis was not affected by nitrogen redistribution in the canopy. For the dense stand however, a uniform nitrogen distribution would lead to only 73% of the maximum net carbon gain by the stand under optimal nitrogen distribution. The actual canopy photosynthesis was only 7% less than this theoretical maximum; the actual nitrogen distribution of the dense stand clearly tended to the optimal distribution. The vertical pattern of the nitrogen distribution was to a large extent determined by the minimum leaf nitrogen content. The relatively high minimum leaf nitrogen content found for Carex leaves may perhaps be necessary to maintain the physiological function of the basal parts of the leaves.     

The effect of female body size on male mounting behaviour in Dermacentor variabilis and D. andersoni

Abstract. This study was undertaken to determine if body size of female ticks was an important factor in eliciting the mating behaviour of Dermacentor variabilis and D. andersoni males. Dummy female ticks (DFTs) representing varying sizes of feeding females were prepared from plastic beads. Size of DFT was shown to be important in determining both the time spent by males in contact with DFTs and the extent of male mating response released. Dermacentor varlabilis males preferred the smaller-sized DFT, whereas D. andersoni males preferred the larger sizes. Males of both species were able to discriminate between size of DFT only when mounting sex pheromone (MSP) was present.
Size of the DFT was more important than the composition of the MSP extract in determining the time males spent in contact with DFTs.
Males of both species were sensitive to variations in concentration of extract, and spent 2–6 times longer in contact with DFTs when the concentration was optimal than when it was not. No significant difference in the male's mating response was seen in response to variation in concentration of heterospecific extract.
Male mating response, i.e. the behaviour of the male as it progresses through the initial contact, climbing onto the dorsal surface and turning onto the venter, was shown not to be dependent upon how long the male spent in contact with the DFT. Male D. andersoni had a much lower mating response to DFTs than D. variabilis males, suggesting that some further stimulus may be required.     

RAD‐seq linkage mapping and patterns of segregation distortion in sedges: meiosis as a driver of karyotypic evolution in organisms with holocentric chromosomes

Meiotic drive, the class of meiotic mechanisms that drive unequal segregation of alleles among gametes, may be an important force in karyotype evolution. Its role in holocentric organisms, whose chromosomes lack localized centromeres, is poorly understood. We crossed two individuals of Carex scoparia (Cyperaceae) with different chromosome numbers (2n = 33^II = 66 × 2n = 32^II = 64) to obtain F1 individuals, which we then self‐pollinated to obtain second‐generation (F2) crosses. RAD‐seq was performed for 191 individuals (including the parents, five F1 individuals and 184 F2 individuals). Our F2 linkage map based on stringent editing of the RAD‐seq data set yielded 32 linkage groups. In the final map, 865 loci were located on a linkage map of 3966.99 cM (linkage groups ranged from 24.39 to 193.31 cM in length and contained 5–51 loci each). Three linkage groups exhibit more loci under segregation distortion than expected by chance; within linkage groups, loci exhibiting segregation distortion are clustered. This finding implicates meiotic drive in the segregation of chromosome variants, suggesting that selection of chromosome variants in meiosis may contribute to the establishment and fixation of chromosome variants in Carex, which is renowned for high chromosomal and species diversity. This is an important finding as previous studies demonstrate that chromosome divergence may play a key role in differentiation and speciation in Carex.     

The cole-moore effect in nodal membrane of the frogRana ridibunda: Evidence for fast and slow potassium channels

Summary The K conductance (g _K) kinetics were studied in voltage-clamped frog nodes (Rana ridibunda) in double-pulse experiments. The Cole-Moore translation forg _K–t curves associated with different initial potentials (E) was only observed with a small percentage of fibers. The absence of the translation was found to be caused by the involvement of an additional, slow,g _K component. This component cannot be attributed to a multiple-state performance of the K channel. It can only be accounted for by a separate, slow K channel, the fast channel being the same as then ⁴ K channel inR. pipiens.The slow K channel is characterized by weaker sensitivity to TEA, smaller density, weaker potential (E) dependence, and somewhat more negativeE range of activation than the fast K channel. According to characteristics of the slow K system, three types of fibers were found. In Type I fibers (most numerous) the slow K channel behaves as ann ⁴ HH channel. In Type II fibers (the second largest group found) the slow K channel obeys the HH kinetics within a certainE range only; beyond this range the exponential decline of the slowg _K component is preceded by anE-dependent delay, its kinetics after the delay being the same as those in Type I fibers. In Type III fibers (rare) the slow K channel is lacking, and it is only in these fibers that the Cole-Moore translation of the measuredg _K–t curves can be observed directly.The physiological role of the fast and slow K channel in amphibian nerves is briefly discussed.     

Elemental concentrations and correlations in winter micropopulations of Stephanodiscus rotula: an autecological study over a period of cell size reduction and restoration

The population of Stephanodiscus rotula in a temperate eutrophic lake was studied over a 2 month period (January to early March). Although during the study period nutrient concentrations in the lake water remained far in excess of phytoplankton requirements, no notable increase in chlorophyll levels was recorded. This suggests that algae were limited by shortage of light and low temperatures. Frequency distribution analysis of cell diameters showed a dramatic size reduction at the end of winter, followed by restoration of higher values by early spring. Electron probe X-ray microanalysis spectra from Stephanodiscus cells routinely showed peaks of Ca, K, Si, P, S, Fe, Al, Mn, Mg, Na and Cl, with substantial variation in elemental concentrations both between and within samples. End-of-winter reduction in the cell size coincided with a considerable depletion of intracellular chemical levels of Si, P, Cl and K and could be related to the concurrent decrease in dissolved organic C and increase in intracellular Al. Correlation and factor analysis of intracellular elemental concentrations showed that statistical elemental associations within Stephanodiscus cells were mainly determined by three factors, with P, Cl, Si and K showing higher loadings on the first, Ca, Mn and S on the second, and Fe, Ca and Al on the third factor. Significant correlations among the elements of the first association may indicate the importance of P (ATP), K (through involvement in P metabolism) and Cl (possibly charge balance) in the active Si uptake during the study period.     

The effect of different media and culture techniques on plating efficiency of strawberry mesophyll cells in culture

Mesophyll cells of strawberry were isolated mechanically by a hand homogenizer, One g healthy, fully-expanded leaves yielded 10⁷ cells. The agar culture method was the only culture technique found suitable to obtain any quantitative data.     

The genetics of adaptive shape shift in stickleback: pleiotropy and effect size

The distribution of effect sizes of genes underlying adaptation is unknown ( Orr 2005 ). Are suites of traits that diverged under natural selection controlled by a few pleiotropic genes of large effect (major genes model), by many independently acting genes of small effect (infinitesimal model), or by a combination, with frequency inversely related to effect size (geometric model)? To address this we carried out a quantitative trait loci (QTL) study of a suite of 54 position traits describing body shapes of two threespine stickleback species: an ancestral Pacific marine form and a highly derived benthic species inhabiting a geologically young lake. About half of the 26 detected QTL affected just one coordinate and had small net effects, but several genomic regions affected multiple aspects of shape and had large net effects. The distribution of effect sizes followed the gamma distribution, as predicted by the geometric model of adaptation when detection limits are taken into account. The sex‐determining chromosome region had the largest effect of any QTL. Ancestral sexual dimorphism was similar to the direction of divergence, and was largely eliminated during freshwater adaptation, suggesting that sex differences may provide variation upon which selection can act. Several shape QTL are linked to Eda, a major gene responsible for reduction of lateral body armor in freshwater. Our results are consistent with predictions of the geometric model of adaptation. Shape evolution in stickleback results from a few genes with large and possibly widespread effects and multiple genes of smaller effect.     

The role of extracellular potassium dynamics in the different stages of ictal bursting and spreading depression: A computational study

Experimental evidences point out the participation of nonsynaptic mechanisms (e.g., fluctuations in extracellular ions) in epileptiform bursting and spreading depression (SD). During these abnormal oscillatory patterns, it is observed an increase of extracellular potassium concentration [K⁺]_o and a decrease of extracellular calcium concentration [Ca²⁺]_o which raises the neuronal excitability. However, whether the high [K⁺]_o triggers and propagates these abnormal neuronal activities or plays a secondary role into this process is unclear. To better understand the influence of extracellular potassium dynamics in these oscillatory patterns, the experimental conditions of high [K⁺]_o and zero [Ca²⁺]_o were replicated in an extended Golomb model where we added important regulatory mechanisms of ion concentration as Na⁺-K⁺ pump, ion diffusion and glial buffering. Within these conditions, simulations of the cell model exhibit seizure-like discharges (ictal bursting). The SD was elicited by the interruption of the Na⁺−K⁺ pump activity, mimicking the effect of cellular hypoxia (an experimental protocol to elicit SD, the hypoxia-induced SD). We used the bifurcation theory and the fast-slow method to analyze the interference of K⁺ dynamics in the cellular excitability. This analysis indicates that the system loses its stability at a high [K⁺]_o, transiting to an elevated state of neuronal excitability. Effects of high [K⁺]_o are observed in different stages of ictal bursting and SD. In the initial stage, the increase of [K⁺]_o creates favorable conditions to trigger both oscillatory patterns. During the neuronal activity, a continuous growth of [K⁺]_o by outward K⁺ flow depresses K⁺ currents in a positive feedback way. At the last stage, due to the depression of K⁺ currents, the Na⁺-K⁺ pump is the main mechanism in the end of neuronal activity. Thus, this work suggests that [K⁺]_o dynamics may play a fundamental role in these abnormal oscillatory patterns.     

Using gravel for environmental enrichment in salmonid hatcheries: The effect of gravel size during egg incubation,endogenous and first feeding in rainbow trout

Environmental enrichment aims for a deliberate increase in structural complexity in otherwise plain rearing units, helping to reduce aberrant traits and promote welfare of fish kept in captivity. Before putting enrichment protocols into practice, however, practitioners like hatchery managers need clear guidelines on enrichment measures and on the substrates used. In the present study, we used rainbow trout as a model species for salmonid rearing and investigated the use of a single layer of three different gravel types, i.e., small (4–8 mm), medium (8–16 mm) and large (16–32 mm), for environmental enrichment during egg incubation, endogenous and first feeding of rainbow trout and compared this to a barren control. From the egg stage onwards, we determined mortality, fungal prevalence as well as growth of larvae and fingerlings. We found that gravel size significantly affected mortality and fungal prevalence with the smallest gravel size and the control showing the lowest incidents. Growth of larvae and fingerlings was not affected by gravel, both when compared between gravel types and to the barren control. When using gravel for environmental enrichment in salmonid hatcheries, a small gravel size should be used. Small gravel provides the fish with a more natural environment without compromising practical feasibility of enrichment in hatcheries, still allowing for easy visual inspection and manual control of the reared fish.     

The effect of xanthoxylin (2-oxy, 4-6-dimethoxyacetophenone) on potassium-dependent acid: extrusion in wheat and maize root segments

Abstract. Xanthoxylin is a cytotoxic and fungicidal compound with the characteristics of a typical phytoalexin. At a concentration of 0.3 mol m⁻³ it inhibits K⁺-dependent acid extrusion and K⁺ net uptake (or uptake of equivalent alkaline cations such as Rb⁺ and CS⁺) by up to about 80% and hyperpolarizes by about 20% the membrane electrical potential. Its inhibition of the acid extrusion does not depend on altered ion exchange involving the anions in the media, a reduction of the metabolic energy available, or detectable changes in the permeability of the cell membrane to H⁺ ions. The drop in K⁺ net uptake depends on a decrease in the influx of K⁺ into the cell. In functional terms, xanthoxylin is an inhibitor of the K⁺ permeation mechanism and does not appear to interact with the mechanisms creating the electrochemical energy gradient.     

The prevalence of male homosexuality: the effect of fraternal birth order and variations in family size

The prevalence of male homosexuality probably varies over time and across societies. One reason for this variation may be the joint effect of two factors: (1) variations in fertility rate or family size; and (2) the fraternal birth order effect, the finding that the odds of male homosexuality increases with each additional older brother. Because of these effects, the rate of male homosexuality may be relatively high (at least in terms of sexual attraction if not behavior) in societies that have a high fertility rate, but this rate has probably declined somewhat in some, particularly western, societies. Thus, even if accurately measured in one country at one time, the rate of male homosexuality is subject to change and is not generalizable over time or across societies.     

The causes and consequences of variation in offspring size: a case study using Daphnia

Offspring size can have large and direct fitness implications, but we still do not have a complete understanding of what causes offspring size to vary. Daphnia (water fleas) generally produce fewer and larger offspring when food is limited. Here, we use a mathematical model to show that this could be explained by either: (1) an advantage of producing larger eggs when food is limited; or (2) a lower boundary on egg volume (below which eggs do not have sufficient resources to be viable), that is similar in volume to the evolutionarily stable egg volume predicted by standard clutch size models. We tested the first possibilities experimentally by placing offspring from mothers kept at two food treatments (high and low - leading to relatively small and large eggs respectively) into two food treatments (same as maternal treatments, in a fully factorial design) and measuring their fitness (reproduction, age at maturity, and size at maturity). We also tested survival under starvation conditions of offspring produced from mothers at low and high food treatments. We found that (larger) offspring produced by low-food mothers actually had lower fitness as they took longer to reproduce, regardless of their current food treatment. Additionally, we found no survival advantage to being born of a food-stressed mother. Consequently, our results do not support the hypothesis that there is an advantage to producing larger eggs when food is limited. In contrast, data from the literature support the importance of a lower boundary on egg size.     

Pollen wall formation in Lilium: The effect of chaotropic agents,and the organisation of the microtubular cytoskeleton during pattern development

Using a combination of electron-microscopic and immunocytochemical techniques the behaviour of the microtubular cytoskeleton has been followed throughout microsporogenesis in Lilium henryi Thunb. Cells treated with colchicine at specific stages and then permitted to develop to near maturity were used to investigate any participation by microtubules in the regulation of pollen wall patterning. The microtubular cytoskeleton assumes four principal forms during the meiotic process; in pre-meiosis it resembles that characteristic of meristematic somatic cells, during meiotic prophase it becomes associated with a nuclear envelope and, perhaps, with the chromosomes and, as the nuclear and cell divisions commence, it takes the form of a normal spindle apparatus. In the young microspores, microtubules assume a radial organisation extending from sites at the nuclear envelope to the inner face of the plasma membrane. No firm evidence was found linking any one of these forms of cytoskeleton with the generation of patterning on the cell surface. Experiments with colchicine revealed that the drug would readily dislocate the colpus, but did not affect the general reticulate patterning. The radial cytoskeleton was present during the deposition of the early primexine, but evidence from these and other studies (J.M. Sheldon and H.G. Dickinson 1983, J. Cell. Sci. 63, 191–208; H.G. Dickinson and J.M. Sheldon, 1984, Planta 161, 86–90) indicates patterning to be imprinted upon the plasma membrane prior to the appearance of this type of cytoskeleton. These results are discussed in terms of a recent model proposed to explain pattern generation on the surface of Lilium pollen grains, based on the self-assembly of patterning determinants within the plasma membrane.Abbreviation MTOC microtubule-organising centre     

Confronting assumptions about spontaneous autogamy in populations of Eulophia alta (Orchidaceae) in south Florida: assessing the effect of pollination treatments on seed formation,seed germination and seedling development

The breeding system of the terrestrial orchid Eulophia alta was investigated in south Florida where it has previously been reported as an auto‐pollinated species. The effect of breeding system on seed viability and germinability and seedling development was also investigated. Incidences of spontaneous autogamy in E. alta were rare at the study site, resulting in only 7.1% of observed flowers forming capsules. In addition, hand pollination resulted in significantly greater capsule formation when flowers were subjected to induced autogamy (46.4%), artificial geitonogamy (64.3%) and xenogamy at both short (pollen source 10–100 m away; 42.9%) and long (pollen source > 10 km away; 67.9%) distances. Pollen source had little effect on seed viability and germinability or seedling growth rates. However, seed resulting from spontaneous autogamy developed more slowly than seed originating from the other treatments. These data indicate that spontaneous autogamy is rare in E. alta and that naturally forming capsules may be the result of unobserved pollination events. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161 , 78–88.     

The influence of landscape configuration and environment on population genetic structure in a sedentary passerine: insights from loci located in different genomic regions

The study of the factors structuring genetic variation can help to infer the neutral and adaptive processes shaping the demographic and evolutionary trajectories of natural populations. Here, we analyse the role of isolation by distance (IBD), isolation by resistance (IBR, defined by landscape composition) and isolation by environment (IBE, estimated as habitat and elevation dissimilarity) in structuring genetic variation in 25 blue tit (Cyanistes caeruleus) populations. We typed 1385 individuals at 26 microsatellite loci classified into two groups by considering whether they are located into genomic regions that are actively (TL; 12 loci) or not (NTL; 14 loci) transcribed to RNA. Population genetic differentiation was mostly detected using the panel of NTL. Landscape genetic analyses showed a pattern of IBD for all loci and the panel of NTL, but genetic differentiation estimated at TL was only explained by IBR models considering high resistance for natural vegetation and low resistance for agricultural lands. Finally, the absence for IBE suggests a lack of divergent selection pressures associated with differences in habitat and elevation. Overall, our study shows that markers located in different genomic regions can yield contrasting inferences on landscape‐level patterns of realized gene flow in natural populations.