Demographic consequences of age-structure in extreme environments: population models for arctic and alpine ptarmigan

Organisms living in arctic and alpine environments are increasingly impacted by human activities. To evaluate the potential impacts of global change, a better understanding of the demography of organisms in extreme environments is needed. In this study, we compare the age-specific demography of willow ptarmigan (Lagopus lagopus) breeding at arctic and subalpine sites, and white-tailed ptarmigan (L. leucurus) breeding at an alpine site. Rates of egg production improved with age at the alpine and subalpine sites, but the stochastic effects of nest and brood predation led to similar rates of annual fecundity among 1-, 2-, and 3+-year-old females. All populations had short generation times (T<2.7 years) and low net reproductive rates (R ₀<1.2). Stable age distributions were weighted towards 1-year-old females in willow ptarmigan (>59%), and to 3+-year-old females in white-tailed ptarmigan (>47%). High damping ratios (ρ>3.2) indicated that asymptotic estimates were likely to match natural age distributions. Sensitivity and elasticity values indicated that changes in juvenile survival would have the greatest impact on the finite rate of population change (λ) in willow ptarmigan, whereas changes to the survival of 3+-year-old females would have a greater effect in white-tailed ptarmigan. High survivorship buffers white-tailed ptarmigan in alpine environments against the potential effects of climate change on annual fecundity, but may make the species more sensitive to the effects of pollutants or harvesting on adult survival. Conversely, processes that reduce annual fecundity would have a greater impact on the population viability of willow ptarmigan in arctic and subalpine environments. If these same demographic patterns prove to be widespread among organisms in extreme environments, it may be possible to develop general recommendations for conservation of the biological resources of arctic and alpine ecosystems.     

Tissue remodeling in Guinea pig lateral prostate at different ages after estradiol treatment

Estrogen seems to have an essential role in the fibromuscular growth characteristic of benign prostatic hyperplasia (BPH). This paper describes the effects of chronic estradiol treatment on Guinea pig prostatic stroma at different ages. Tissues from experimental animals were studied by histological and histochemical procedures, morphometric-stereological analysis and transmission electron microscopy (TEM). Marked fibromuscular hypertrophy was observed after estradiol treatment in animals of pre-pubertal and adult ages. Increases in the density and thickness of the collagen and elastic fibers were observed by histochemistry. TEM revealed wide distributions of collagen fibrils and large elastic fibers adjacent to the epithelial basal lamina and between the stromal cells, establishing contacts between them. These results indicate that the Guinea pig prostate simulates the stromal modifications observed in BPH in some aged animals after estrogen treatment at different ages, making it a good model for this disease.     

Engyprosopon vanuatuensis, a new species of bothid flounder (Pleuronectiformes: Bothidae) from off Vanuatu, South West Pacific

A new bothid flounder, Engyprosopon vanuatuensis, is described on the basis of 15 specimens (9 males and 6 females, 41.1–55.8mm in standard length) collected from deep waters (163–165m) off Vanuatu Island in 1994 during the French exploratory cruise MUSORSTOM 8. The new species clearly differs from its congeners in having a short body, big eyes, large scales, and many gill rakers without serrations. Remarkable sexual dimorphism appears in interorbital width, anterior curve of head profile, rostral and orbital spines, length of ocular-side pectoral fin, small dots on eyes, and pigmentation of blind-side body.     

A huge,undescribed soil ciliate (Protozoa: Ciliophora) diversity in natural forest stands of Central Europe

We investigated 12 natural forest stands in eastern Austria for soil ciliate diversity, viz., eight beech forests and two lowland and Pinus nigra forests each. The stands span a wide range of climatic (e.g., 543–1759 mm precipitation, 160–1035 m above sea-level) and abiotic (e.g., pH 4–7.4) factors. Samples were taken twice in autumn and late spring and analysed with the non-flooded Petri dish method. Species were identified in vivo, in silver preparations, and in the scanning electron microscope. A total of 233 species were found, of which 30 were undescribed, a surprising number showing our ignorance of soil ciliate diversity, even in Central Europe. Species number varied highly from 45 (acidic beech on silicate) to 120 (floodplain forest) and was strongly correlated with pH and overall habitat quality, as measured by climate, the C/P quotient (ratio of r-selected colpodean and k-selected polyhymenophorean ciliates), and the proportion of mycophagous ciliate species; multivariate analysis showed further important variables, viz., the general nutrient status (glucose, nitrogen, C/ N ratio) and microbial (urease) activity. The highest species number occurred in one of the two floodplain soils, supporting the intermediate disturbance hypothesis. The three main forest types could be clearly distinguished by their ciliate communities, using similarity indices and multidimensional scaling. Individual numbers varied highly from 135^–1 (lowland forest) to 10,925 ml^–1 (beech on silicate) soil percolate and showed, interestingly, a weak correlation with soil protozoan phospholipid fatty acids. Eight of the 30 new species found and a forgotten species, Arcuospathidium coemeterii (Kahl 1943) nov. comb., are described in detail, as examples of how species were recognized and soil protozoan diversity should be analyzed: Latispathidium truncatum bimicronucleatum, Protospathidium fusioplites, Erimophrya sylvatica, E. quadrinucleata, Paragonostomum simplex, Periholosticha paucicirrata, P. sylvatica, and Australocirrus zechmeisterae.     

SC-435, an ileal apical sodium-codependent bile acid transporter inhibitor alters mRNA levels and enzyme activities of selected genes involved in hepatic cholesterol and lipoprotein metabolism in guinea pigs

We have demonstrated that SC-435, an apical sodium codependent bile acid transporter (ASBT) inhibitor, lowers plasma low-density lipoprotein cholesterol (LDL-C) concentrations in guinea pigs. The purpose of this study was to further examine the hypocholesterolemic effects of SC-435, by measuring the activity and RNA expression of regulatory enzymes of hepatic cholesterol and lipoprotein metabolism. In addition, the use of a combination (COMBO) therapy with simvastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, was also tested. Male Hartley guinea pigs were randomly allocated to one of three diets (n=10 per group), for 12 weeks. The control diet contained no ASBT inhibitor or simvastatin. The monotherapy diet (ASBTi) contained 0.1% of SC-435. The COMBO therapy consisted of a lower dose of SC-435 (0.03%) and 0.05% simvastatin. Cholesterol ester transfer protein (CETP) and HMG-CoA reductase mRNA abundance were determined using RT-PCR techniques. Hepatic HMG-CoA reductase and cholesterol 7-hydroxylase (CYP7) activities were measured by radioisotopic methods. Compared to the control group, CETP activity was 34% and 56% lower with ASBTi and COMBO, respectively. Similarly, CETP mRNA expression was reduced by 36% and 73% in ASBTi and COMBO groups, respectively. Cholesterol 7-hydroxylase and HMG-CoA reductase activities were increased 2-fold with ASBTi and COMBO treatments, respectively. Likewise, HMG-CoA reductase mRNA expression was increased 33% with ASBTi treatment. These results suggest that both SC-435 monotherapy and combination therapy lower LDL cholesterol concentrations by altering both hepatic cholesterol homeostasis and the intravascular processing of lipoproteins in guinea pigs.     

Patterns of Allozyme Variation at Two Stages of the Life History in Wild Rice <Emphasis Type="Italic">Oryza rufipogon</Emphasis> and Conservation Genetic Implications

Oryza rufipogon Griff. occurs widely in aquatic ecosystem of tropics and subtropics of monsoon Asia as well as Southern China. It is a vital gene source for rice breeding programs. Many populations of the species, unfortunately, have drastically diminished because of the disappearance of aquatic habitats as a result of human disturbance. In order to determine patterns of genetic variation at two stages of the life-cycle in the wild rice species, we investigated allozyme variation of four natural populations in China. Two southern populations have significant asexual reproduction while two other northern marginal populations show a mixed reproduction in China. At 22 allozyme loci, a significantly lower genetic diversity was observed in the ratoons than in the seeds of the two southern populations, whereas a significantly higher genetic diversity was found in the ratoons than in the seeds of the two northern marginal populations. The results suggest that the variation of reproductive system is probably associated with their patterns of genetic variation in the species. Moreover, a significantly higher genetic differentiation among populations found in the ratoons than in the seeds may stem from pollen-mediated gene flow among them. Finally, we propose suggestions for conservation management of the endangered species.     

Mitochondrial haplotypes and the New Zealand origin of clonal European Potamopyrgus, an invasive aquatic snail

The small aquatic snail Potamopyrgus antipodarum is an important invading species in Europe, Australia and North America. European populations are generally believed to derive from accidental introductions from New Zealand, probably dating back to the mid-19th century. We have employed mitochondrial DNA sequences to test the proposed New Zealand origin of European Potamopyrgus, and to learn more about its genealogical history. Using a 481-bp region of the 16S ribosomal RNA gene, we identified 17 distinct haplotypes among 65 snails from New Zealand. In marked contrast, only two haplotypes were found across all European samples, which cover a large geographical area. Importantly, these two haplotypes are shared with snails from the North Island of New Zealand. Due to sampling limitations we cannot rule out a South Island origin for one of the haplotypes, but our results clearly demonstrate the New Zealand origin of European populations. The marked divergence among the two European haplotypes implies the successful colonization by two distinct mitochondrial lineages, which is consistent with previous data based on nuclear markers.     

Variation for neutral markers is correlated with variation for quantitative traits in the plant pathogenic fungus Mycosphaerella graminicola

We compared genetic variation and population differentiation at RFLP marker loci with seven quantitative characters including fungicide resistance, temperature sensitivity, pycnidial size, pycnidial density, colony size, percentage of leaves covered by pycnidia (PLACP) and percentage of leaves covered by lesions (PLACL) in Mycosphaerella graminicola populations sampled from four regions. Wide variation in population differentiation was found across the quantitative traits assayed. Fungicide resistance, temperature sensitivity, and PLACP displayed a significantly higher Q(ST) than G(ST), consistent with selection for local adaptation, while pycnidial size, pycnidial density and colony size displayed a lower or significantly lower Q(ST) than G(ST), consistent with constraining selection. There was not a statistical difference between Q(ST) and G(ST) in PLACL. We also found a positive and significant correlation between genetic variation in molecular marker loci and quantitative traits at the multitrait scale, suggesting that estimates of overall genetic variation for quantitative traits in M. graminicola could be derived from analysis of the molecular genetic markers.     

Ancient DNA from pollen: a genetic record of population history in Scots pine

Assessments of plant population dynamics in space and time have depended on dated records of fossil pollen synthesized on a subcontinental scale. Genetic analyses of extant populations have revealed spatial relationships that are indicative of past spatial dynamics, but lack an explicit timescale. Synthesis of these data requires genetic analyses from abundant dated fossil material, and this has hitherto been lacking. Fossil pollen is the most abundant material with which to fill this data gap. Here we report genetic analyses of fossil pollen retrieved from Holtjärnen postglacial lake sediment in Sweden and show that plastid DNA is recoverable from Scots Pine and Norway spruce pollen grains that are 100 and 10 000 years old. By sequencing clones from two short plastid PCR products and by using multiple controls we show that the ancient sequences were endogenous to the fossil grains. Comparison of ancient sequences and those obtained from an extant population of Scots pine establishes the first genetic link between extant and fossil samples in this species, providing genetic continuity through time. The finding of one common haplotype present in modern, 100-year old and 10 000-year old samples suggests that it may have persisted near Holtjärnen throughout the postglacial period. This retrieval of ancient DNA from pollen has major implications for plant palaeoecology in conifer species by allowing direct estimates of population dynamics in space and time.     

Geographic variation in diapause incidence, life-history traits, and climatic adaptation in Drosophila melanogaster

In Drosophila melanogaster, exposure of females to low temperature and shortened photoperiod can induce the expression of reproductive quiescence or diapause. Diapause expression is highly variable within and among natural populations and has significant effects on life-history profiles, including patterns of longevity, fecundity, and stress resistance. We hypothesized that if diapause expression is associated with overwintering mechanisms and adaptation to temperate environments, the frequency of diapause incidence would exhibit a latitudinal cline among natural populations. Because stress resistance and reproductive traits are also clinal in this species, we also examined how patterns of fecundity and longevity varied with geography and how stress resistance and associated traits differed constitutively between diapause and nondiapause lines. Diapause incidence was shown to vary predictably with latitude, ranging from 35% to 90% among natural populations in the eastern United States Survivorship under starvation stress differed between diapause and nondiapause lines; diapause phenotypes were also distinct for total body triglyceride content and the developmental distribution of oocytes in the ovary following stress exposure. Patterns of longevity, fecundity, and ovariole number also varied with geography. The data suggest that, for North American populations, diapause expression is functionally associated with overwintering mechanisms and may be an integral life-history component in natural populations.