Sparrowhawks Accipiter nisus affect the spacing behaviour of wintering Turnstone Arenaria interpres and Redshank Tringa tetanus

The presence of a Sparrowhawk induces short-term abandonment of territories by wintering Redshank and increases both the density within flocks and the ranging behaviour of wintering Turnstone. The latter effect is thought to be due to the disturbance caused by hawk attacks, and the results suggest benefits for flocking beyond predator detection.     

Causes and consequences of marine mammal population declines in southwest Alaska: a food-web perspective

Populations of sea otters, seals and sea lions have collapsed across much of southwest Alaska over the past several decades. The sea otter decline set off a trophic cascade in which the coastal marine ecosystem underwent a phase shift from kelp forests to deforested sea urchin barrens. This interaction in turn affected the distribution, abundance and productivity of numerous other species. Ecological consequences of the pinniped declines are largely unknown. Increased predation by transient (marine mammal-eating) killer whales probably caused the sea otter declines and may have caused the pinniped declines as well. Springer et al. proposed that killer whales, which purportedly fed extensively on great whales, expanded their diets to include a higher percentage of sea otters and pinnipeds following a sharp reduction in great whale numbers from post World War II industrial whaling. Critics of this hypothesis claim that great whales are not now and probably never were an important nutritional resource for killer whales. We used demographic/energetic analyses to evaluate whether or not a predator–prey system involving killer whales and the smaller marine mammals would be sustainable without some nutritional contribution from the great whales. Our results indicate that while such a system is possible, it could only exist under a narrow range of extreme conditions and is therefore highly unlikely.     

Occurrence and population densities of yeast species in a fresh-water lake

Quantitative studies of yeasts present in surface and deep water samples from a fresh water body (Douglas Lake, Michigan) revealed 12 species (Candida parapsilosis, C. pulcherrima, Cryptococcus albidus, Cr. diffluens, Cr. gastricus, Cr. laurentii, Rhodotorula glutinis, R. pilimanae, R. rubra, Trichosporon cutaneum, Debaryomyces sp., black yeasts). In two regions of surface sampling the population densities averaged 39.6 and 5.5 cells per 100 ml respectively, whereas the average deep water count was 40.3 cells per 100 ml. Yeasts of the genusRhodotorula predominated.     

Sixty years of anthropogenic pressure: a spatio-temporal genetic analysis of brown trout populations subject to stocking and population declines

Analyses of historical samples can provide invaluable information on changes to the genetic composition of natural populations resulting from human activities. Here, we analyse 21 microsatellite loci in historical (archived scales from 1927 to 1956) and contemporary samples of brown trout ( Salmo trutta ) from six neighbouring rivers in Denmark, to compare the genetic structure of wild populations before and after population declines and stocking with nonlocal strains of hatchery trout. We show that all populations have been strongly affected by stocking, with admixture proportions ranging from 14 to 64%. Historical population genetic structure was characterized by isolation by distance and by positive correlations between historical effective population sizes and habitat area within river systems. Contemporary population genetic structure still showed isolation by distance, but also reflected differences among populations in hatchery trout admixture proportions. Despite significant changes to the genetic composition within populations over time, dispersal rates among populations were roughly similar before and after stocking. We also assessed whether population declines or introgression by hatchery strain trout should be the most significant conservation concern in this system. Based on theoretical considerations, we argue that population declines have had limited negative effects for the persistence of adaptive variation, but admixture with hatchery trout may have resulted in reduced local adaptation. Collectively, our study demonstrates the usefulness of analysing historical samples for identifying the most important consequences of human activities on the genetic structure of wild populations.     

Autotetraploids of Vicia cracca show a higher allelic richness in natural populations and a higher seed set after artificial selfing than diploids

Background and Aims

Despite the great importance of autopolyploidy in the evolution of angiosperms, relatively little attention has been devoted to autopolyploids in natural polyploid systems. Several hypotheses have been proposed to explain why autopolyploids are so common and successful, for example increased genetic diversity and heterozygosity and the transition towards selfing. However, case studies on patterns of genetic diversity and on mating systems in autopolyploids are scarce. In this study allozymes were employed to investigate the origin, population genetic diversity and mating system in the contact zone between diploid and assumed autotetraploid cytotypes of Vicia cracca in Central Europe.

Methods

Four enzyme systems resolved in six putative loci were investigated in ten diploid, ten tetraploid and five mixed-ploidy populations. Genetic diversity and heterozygosity, partitioning of genetic diversity among populations and cytotypes, spatial genetic structure and fixed heterozygosity were analysed. These studies were supplemented by a pollination experiment and meiotic chromosome observation.

Key Results and Conclusions

Weak evidence of fixed heterozygosity, a low proportion of unique alleles and genetic variation between cytotypes similar to the variation among populations within cytotypes supported the autopolyploid origin of tetraploids, although no multivalent formation was observed. Tetraploids possessed more alleles than diploids and showed higher observed zygotic heterozygosity than diploids, but the observed gametic heterozygosity was similar to the value observed in diploids and smaller than expected under panmixis. Values of the inbreeding coefficient and differentiation among populations (ρ_ST) suggested that the breeding system in both cytotypes of V. cracca is mixed mating with prevailing outcrossing. The reduction in seed production of tetraploids after selfing was less than that in diploids. An absence of correlation between genetic and geographic distances and high differentiation among neighbouring tetraploid populations supports the secondary contact hypothesis with tetraploids of several independent origins in Central Europe. Nevertheless, the possibility of a recent in situ origin of tetraploids through a triploid bridge in some regions is also discussed.     

Tillering in grain sorghum over a wiide range of population densities: modelling dynamics of tiller fertility

The prediction of tillering is poor or absent in existing sorghum crop models even though fertile tillers contribute significantly to grain yield. The objective of this study was to identify general quantitative relationships underpinning tiller dynamics of sorghum for a broad range of assimilate availabilities. Emergence, phenology, leaf area development and fertility of individual main culms and tillers were quantified weekly in plants grown at one of four plant densities ranging from two to 16 plants m(-2). On any given day, a tiller was considered potentially fertile (a posteriori) if its number of leaves continued to increase thereafter. The dynamics of potentially fertile tiller number per plant varied greatly with plant density, but could generally be described by three determinants, stable across plant densities: tiller emergence rate aligned with leaf ligule appearance rate; cessation of tiller emergence occurred at a stable leaf area index; and rate of decrease in potentially fertile tillers was linearly related to the ratio of realized to potential leaf area growth. Realized leaf area growth is the measured increase in leaf area, whereas potential leaf area growth is the estimated increase in leaf area if all potentially fertile tillers were to continue to develop. Procedures to predict this ratio, by estimating realized leaf area per plant from intercepted radiation and potential leaf area per plant from the number and type of developing axes, are presented. While it is suitable for modelling tiller dynamics in grain sorghum, this general framework needs to be validated by testing it in different environments and for other cultivars.     

种群密度对加拿大一枝黄花生长与繁殖的影响

加拿大一枝黄花种子可以通过风传播扩散,其地下根茎可以进行无性克隆,具有极强的繁殖能力。为探讨加拿大一枝黄花生长及繁殖规律,2006—2008年在杭州下沙国家级经济开发区内对自然生长状态下不同密度的加拿大一枝黄花定点进行调查,结果表明:90～120株.m-2的高密度状况下,植株平均株高高于其他密度,最大的差距为57.6cm;60～80株.m-2的中密度下,茎粗最大,达到10.3mm,比低密度条件下平均值粗2mm;中密度条件下加拿大一枝黄花叶片的增长数最多,平均日增长量最多达3.4片;高密度时加拿大一枝黄花最早开花,分别比中密度、低密度条件下提前约8和3d;高密度条件下种子扩散的时间最早,分别比中密度、低密度条件下提前约7和2d;中密度条件下平均每株产生种子数量最多,平均种子量达到77896颗.株-1,且种子的发芽率最高。本研究明确了自然生长状况下加拿大一枝黄花的营养及繁殖生长特性,可为加拿大一枝黄花的防控措施的制定提供科学依据。     

Understanding population change in migratory songbirds: long-term and experimental studies of Neotropical migrants in breeding and wintering areas

Effective conservation and management of migratory bird species requires an understanding of when and how their populations are limited and regulated. Since 1969, my colleagues and I have been studying migratory songbird populations in their breeding quarters at the Hubbard Brook Experimental Forest in north-central New Hampshire, USA, and since 1986, in their winter quarters in the Greater Antilles (Jamaica). Long-term data on the abundance and demography of these populations, coupled with experimental tests of mechanisms, indicate that processes operating in the breeding area (e.g. density-dependent fecundity, food limitation) are sufficient to limit and regulate the local abundance of these species. At the same time, limiting factors operating in the non-breeding season (e.g. climate-induced food limitation in winter quarters and especially mortality during migration) also have important impacts on migrant populations. Furthermore, recent studies have shown that limiting processes during the winter period can carry over into the breeding season and affect reproductive output. These findings clearly demonstrate that to understand changes in abundance of long-distance migrant species requires knowledge of events operating throughout the annual cycle, which presents a challenge to researchers, managers and others concerned with the welfare of these species.     

Large-plaque mutants of Sindbis virus show reduced binding to heparan sulfate, heightened viremia, and slower clearance from the circulation

Laboratory strains of Sindbis virus must bind to the negatively charged glycosaminoglycan heparan sulfate in order to efficiently infect cultured cells. During infection of mice, however, we have frequently observed the development of large-plaque viral mutants with a reduced ability to bind to heparan sulfate. Sequencing of these mutants revealed changes of positively charged amino acids in putative heparin-binding domains of the E2 glycoprotein. Recombinant viruses were constructed with these changes as single amino acid substitutions in a strain Toto 1101 background. All exhibited decreased binding to heparan sulfate and had larger plaques than Toto 1101. When injected subcutaneously into neonatal mice, large-plaque viruses produced higher-titer viremia and often caused higher mortality. Because circulating heparin-binding proteins are known to be rapidly sequestered by tissue heparan sulfate, we measured the kinetics of viral clearance following intravenous injection. Much of the parental small-plaque Toto 1101 strain of Sindbis virus was cleared from the circulation by the liver within minutes, in contrast to recombinant large-plaque viruses, which had longer circulating half-lives. These findings indicate that a decreased ability to bind to heparan sulfate allows more efficient viral production in vivo, which may in turn lead to increased mortality. Because Sindbis virus is only one of a growing number of viruses from many families which have been shown to bind to heparan sulfate, these results may be generally applicable to the pathogenesis of such viruses.     

Heterosexual men and women both show a hypothalamic response to the chemo-signal androstadienone

The odorous steroid compound 4,16-androstadien-3-one (androstadienone), found in axillary sweat, was previously reported to evoke hypothalamic activation in heterosexual women, but not in heterosexual men. However, subjects were exposed to the pure crystalline form of androstadienone, which raised the question whether the observed hypothalamic response is physiologically relevant. Therefore, in the present study, we asked whether sexually dimorphic hypothalamic responses could be measured when subjects were exposed to lower, more physiologically relevant concentrations of androstadienone. A total of 21 women and 16 men, all heterosexual, participated in our functional magnetic resonance imaging study (fMRI). Three different concentrations of androstadienone diluted in propylene glycol (10 mM "high," 0.1 mM "medium" and 0.001 mM "low") were delivered to the subjects' nostrils using a computer-controlled stimulator. When exposed to the "high" androstadienone concentration, women showed stronger hypothalamic activation than men. By contrast, men showed more hypothalamic activation when exposed to the "medium" androstadienone concentrations in comparison to women. Thus, we replicated that smelling the chemo-signal androstadienone elicits a hypothalamic activation. However, this effect does not seem to be gender-specific, because androstadienone activated the hypothalamus in both men and women, suggesting that androstadienone exerts specific effects in heterosexual individuals of both sexes.     

Isolated populations of a rare alpine plant show high genetic diversity and considerable population differentiation

Background and Aims

Gene flow and genetic variability within and among alpine plant populations can be greatly influenced by the steep environmental gradients and heterogeneous topography of alpine landscapes. In this study, the effects are examined of natural isolation of alpine habitats on genetic diversity and geographic structure in populations of C. thyrsoides, a rare and isolated European Alpine monocarpic perennial with limited seed dispersal capacity.

Methods

Molecular diversity was analysed for 736 individuals from 32 populations in the Swiss Alps and adjacent Jura mountains using five polymorphic microsatellite loci. Pollen flow was estimated using pollen grain-sized fluorescent powder. In addition, individual-based Bayesian approaches were applied to examine population structure.

Key Results

High within-population genetic diversity (H_E = 0·76) and a relatively low inbreeding coefficient (F_IS = 0·022) were found. Genetic differentiation among populations measured with a standardized measure was considerable (G′_ST = 0·53). A significant isolation-by-distance relationship was found (r = 0·62, P < 0·001) and a significant geographic sub-structure, coinciding with proposed postglacial migration patterns. Altitudinal location and size of populations did not influence molecular variation. Direct measures of pollen flow revealed that insect-mediated pollen dispersal was restricted to short distances within a population.

Conclusions

The natural isolation of suitable habitats for C. thyrsoides restricts gene flow among the populations as expected for a monocarpic species with very limited seed dispersal capacities. The observed high within-population genetic diversity in this rare monocarpic perennial is best explained by its outcrossing behaviour, long-lived individuals and overlapping generations. Despite the high within-population genetic diversity, the considerable genetic differentiation and the clear western–eastern differentiation in this species merits consideration in future conservation efforts.Key words: Alpine plant, Campanula thyrsoides, genetic diversity, gene flow, genetic differentiation, glacial history, G′_ST, habitat isolation, microsatellites, monocarpy, SSR     

Immune response and virus population composition: HIV as a case study

Based on the current understanding of the immune response, we present what we believe to be a new model of intrahost virus dynamics. The model takes into account the relationship between virus replication rate and the level of antigen displayed by infected cells, and shows how the cell-directed immune response controls both virus load and virus replication rate. In contrast to conventional wisdom, it shows that the predominant virus variant does not necessarily have the highest replication rate. A strong immune response produces a selective advantage for latent viruses, whereas a deteriorating immune response invites in viruses of higher replication rates. The model is analysed in light of the well-studied HIV/AIDS disease progression, and shows how a wide range of major, seemingly unrelated issues in the study of HIV may be accounted for in a simple and unified manner.     

Amerindians show no association of PC-1 gene Gln121 allele and obesity: a thrifty gene population genetics

PC-1 Gln121 gene is a risk factor for type 2 diabetes, obesity and insulin resistance in European/American Caucasoids and Orientals. We have aimed to correlate for the first time this gene in Amerindians with obesity and their corresponding individuals genotypes with obesity in order to establish preventive medicine programs for this population and also studying the evolution of gene frequencies in world populations. Central obesity was diagnosed by waist circumference perimeter and food intake independent HDL-cholesterol plasma levels were measured. HLA genes were determined in order to more objectively ascertain participants Amerindians origin. 321 Amerindian blood donors who were healthy according to the blood doning parameters were studied. No association was found between PC-1 Gln121 variant and obesity. Significant HDL-cholesterol lower values were found in the PC-1 Lys121 bearing gene individuals versus PC-1 Gln121 bearing gene ones (45.1 ± 12.7 vs. 48.7 ± 15.2 mg/dl, p < 0.05). Population analyses showed a world geographical gradient in the PC-1 Gln121 allele frequency: around 9% in Orientals, 15% in European Caucasoids and 76% in Negroids. The conclusions are: (1) No association of PC-1 Gln121 gene is found with obesity in Amerindians when association is well established in Europeans. (2) PC-1 Gln121 gene is associated to higher levels of HDL-cholesterol than the alternative PC-1 Lys121 allele. This may be specific for Amerindians. (3) Amerindians have an intermediate frequency of this possible PC-1 Gln121 thrifty gene when compared with Negroid African Americans (78.5%) or Han Chinese (7.5%, p < 0.0001). Historical details of African and other groups may support the hypothesis that PC-1 Gln121 is indeed a thrifty gene.     

Distribution and population densities of seven species of bat in northern England

Distribution and minimum population densities for seven UK bat species known to be resident in northern England were calculated in an area covering 2500 km². The species present were pipistrelle ( Pipistrellus pipistrellus ), brown long-eared ( Plecotus auritus ), Daubenton's ( Myotis daubentonii ), whiskered ( Myotis mystacinus ), Natterer's (Myotis nattereri) , noctule ( Nyctalus noctula ) and Brandt's (Myotis brandtii). Data were collected primarily from counts at summer roosts over the period 1983 to 1990. A total of 310 bat roosts were discovered within the study area. Of the 256 roosts at which the species present was identified, the majority, 127 (49.6%) were P. pipistrellus , with a mean maternity roost size of 69.6 bats. A minimum population density of 12.6 batskm⁻² was estimated for P. pipistrellus , based on summer (maternity) roosts. The minimum population density estimate was higher than previous studies in northern England but substantially lower than those reported in Scotland (18.2 bats km-⁻²). The combined density of M. mystacinus, M. brandtii, and P. pipistrellus , which have similar foraging styles (15.8 bats km⁻²), is comparable to Scottish P. pipistrellus densities. The density of M. duubentonii was also lower than in Scotland, although the density of P. auritus was comparable. The majority of summer roosts for all species were found in buildings, except N. noctula and M. duubentonii which used bridges/tunnels or trees.     

Natural variation in population densities and vertical transmission rates of a Spiroplasma endosymbiont in Drosophila hydei

A bacterium belonging to the genus Spiroplasma, an endosymbiont of the fly Drosophila hydei, is vertically transmitted through host egg cytoplasm. To infer vertical transmission rates of Spiroplasma in natural populations of D. hydei, the infection status of Spiroplasma was examined for offspring produced by Spiroplasma-positive females that were collected in two geographical populations. In both populations, nearly half of the broods consisted of only infected offspring. Infection frequencies of the rest of the broods ranged from 0.364 to 0.975. Quantitative PCR demonstrated that the Spiroplasma titers in the whole body of wild-caught females were highly variable (1.81?×?10⁶–5.60?×?10⁸ cells per insect). Contrary to our expectations, however, the Spiroplasma titers did not account for the variation in infection frequencies among offspring (i.e., vertical transmission rates). These results suggest that the spatial distribution of Spiroplasma, particularly in somatic tissues and germ tissues, is highly variable among host individuals, which may be caused by environmental stochasticity or some unknown effects.     

Sequences of primate insulin genes support the hypothesis of a slower rate of molecular evolution in humans and apes than in monkeys.

The chimpanzee and African green monkey insulin genes have been cloned and sequenced. These two sequences together with the previously reported sequences for the human and owl monkey insulin genes provide additional support for the hominoid-rate-slowdown hypothesis, i.e., a slower rate of nucleotide substitution in humans and apes than in monkeys. When these sequences and other primate sequences available for the relative-rate test were considered together, the substitution rate in the Old World monkey lineage was shown to be significantly higher than the rates in the human and chimpanzee lineages. This was true regardless of whether the eta-globin pseudogene was included in the analysis. Therefore, in contrast to the claim by Easteal, the hominoid-rate-slowdown is not unique to the eta-globin pseudogene but appears to be a rather general phenomenon. On average, the substitution rate at silent sites is about 1.5 times higher in the Old World monkey lineage than in the human and chimpanzee lineages.     

Mucosal innate immune response associated with a timely humoral immune response and slower disease progression after oral transmission of simian immunodeficiency virus to rhesus macaques

Mucosal transmission is the predominant mode of human immunodeficiency virus (HIV) infection worldwide, and the mucosal innate interferon response represents an important component of the earliest host response to the infection. Our goal here was to assess the changes in mRNA expression of innate mucosal genes after oral simian immunodeficiency virus (SIV) inoculation of rhesus macaques (Macaca mulatta) that were followed throughout their course of disease progression. The SIV plasma viral load was highest in the macaque that progressed rapidly to simian AIDS (99 days) and lowest in the macaque that progressed more slowly (>700 days). The mRNA levels of six innate/effector genes in the oral mucosa indicated that slower disease progression was associated with increased expression of these genes. This distinction was most evident when comparing the slowest-progressing macaque to the intermediate and rapid progressors. Expression levels of alpha and gamma interferons, the antiviral interferon-stimulated gene product 2′-5′ oligoadenylate synthetase (OAS), and the chemokines CXCL9 and CXCL10 in the slow progressor were elevated at each of the three oral mucosal biopsy time points examined (day 2 to 4, 14 to 21, and day 70 postinfection). In contrast, the more rapidly progressing macaques demonstrated elevated levels of these cytokine/chemokine mRNA at lymph nodes, coincident with decreased levels at the mucosal sites, and a decreased ability to elicit an effective anti-SIV antibody response. These data provide evidence that a robust mucosal innate/effector immune response is beneficial following lentiviral exposure; however, it is likely that the anatomical location and timing of the response need to be coordinated to permit an effective immune response able to delay progression to simian AIDS.     

Habits and relative population densities of some hydrophilids in California rice fields

Populations of the hydrophilids Berosus styliferus Horn, Hydrophilus triangularis Say, and Tropisternus lateralis (Fabricius) were observed in northern California rice paddies. Relative adult and larval density for each species was determined using aquatic light traps adjacent to the water margin, and at 5 m and 30 m distances from the levee. Egg cases were monitored by recording numbers per unit area.The seasonal patterns of abundance indicate each species has a univoltine life cycle. All stages of B. styliferus and H. triangularis are more abundant nearer the levees. T. lateralis adults are commonly found at the levees during the first 10 weeks post-flood, whereas T. lateralis larvae and egg cases are most numerous at the 30 m distance.Colonication of the paddies occurs through water connections, flight, and adult overwintering.