Population structure and dynamics of wood mouse Apodemus sylvaticus in Iceland

Five-year-studies of two wood mouse populations (Apodemus sylvaticus L.) were carried out outside the village Vík. S. Iceland, and in a birch forest close to the lake Mývatn, N. Iceland. The population at Vík was studied on a 1.10 ha grid on a slope covered with Angelica archangelica L., the seeds of which constituted a major food resource for the mice. Altogether 948 individuals were caught, marked and followed during 1973–1978. No other free-living small mammals occur in Iceland, and predator pressure is low and considered non-existent on the Angelica slope. The population density was extremely high; highest autumn density recorded was 150 ind ha^?1. Like other Apodemus populations, the one at Vík showed a typical seasonal pattern in numbers: a winter decrease, relatively stable numbers in late summer, and an autumn peak. Breeding started in late April or early May and ended in late September; no winter breeding was observed. Three or four litters were produced, and the last litter(s) of the season greatly contributed to the autumn increase. The output of young per reproductive female throughout the year was negatively correlated with spring density, and autumn peak density with the number of females in August. Also overwinter success and weight changes appeared to be associated with population density (and weather). Survival rates did not vary much between years and seasons and were consistently rather high. Autumn survival of juveniles was positively correlated with mean minimum temperatures. Juvenile survival was, at least at times, negatively affected by the presence of adult males. Trapping outside the main grid did not indicate any marked dispersal, though some immigration to the grid must have occurred, especially in spring and early summer. Among the factors governing the population density and dynamics of wood mouse at Vík we emphasize the absence of interspecific competition and predation, the rich and dependable food resources (mainly Angelica seeds), the mild (though moist and windy) climate, the shelter of dense Angelica stands, the abundance of crevices (e.g. nest-sites), and the social interactions. The birch forest in northern Iceland was low productive and the wood mouse population differed from the Vík population by exhibiting low density, short breeding season, and high vagility; characteristics we consider to be representative for most Apodemus populations in Iceland.     

Influence of sexual intercourse on genital tract microbiota in infertile couples

Several studies have suggested the association of disturbed genital tract microbiota with infertility. Our aim was to clarify the influence of sexual intercourse on partner’s genital tract microbiota in infertile couples. Seventeen couples were studied, and in 5 men inflammatory prostatitis (IP) was diagnosed. Semen samples were collected during menstruation of the female counterpart, two self-collected vaginal samples were taken 3–5 days later – before intercourse and 8–12 h after intercourse. Ureaplasma parvum was found in 59% of women, its prevalence was higher in women whose partner had IP, as well as in half of their male partners. Sexual intercourse caused significant shifts in vaginal microbiota – increase of Nugent score and shifts in cultured microbiota (emergence and disappearance of several species). These changes were less expressed in the presence of normal vaginal microbiota but more prominent in the partners of IP men. These changes may interfere with fertilization.     

Host density predicts presence of cuckoo parasitism in reed warblers

In some hosts of avian brood parasites, several populations apparently escape parasitism, while others are parasitized. Many migratory specialist brood parasites like common cuckoos, Cuculus canorus , experience a short breeding season, and in order to maintain local parasite populations host densities should be sufficiently high to allow efficient nest search. However, no studies have investigated the possible effect of host density on presence of cuckoo parasitism among populations of a single host species. Here, we investigated possible predictors of common cuckoo parasitism in 16 populations of reed warblers, Acrocephalus scirpaceus , across Europe. In more detail, we quantified the effect of host density, number of host breeding pairs, habitat type, mean distance to nearest cuckoo vantage point, predation rate and latitude on the presence of cuckoo parasitism while controlling for geographical distance among study populations. Host density was a powerful predictor of parasitism. We also found a less pronounced effect of habitat type on occurrence of parasitism, while the other variables did not explain why cuckoos utilize some reed warbler populations and not others. This is the first study focusing on patterns of common cuckoo-host interactions within a specific host species on a large geographic scale. The results indicate that if host density is below a specific threshold, cuckoo parasitism is absent regardless of the state of other potentially confounding variables.     

A nondestructive method for extracting maternally derived egg yolk carotenoids

ABSTRACT.   Maternally deposited carotenoids are a prominent component of egg yolk and are vital for the development and growth of the embryo. In most studies of avian yolk carotenoids, eggs are destructively sampled and this may limit both the number of clutches studied and the research questions addressed. We describe an empirical field trial for a nondestructive biopsy method to extract small samples (0.05 ml) of egg yolk for high-performance liquid chromatography (HPLC) analysis of yolk carotenoid concentrations. We sampled 180 clutches ( N = 44 biopsies) of two species of introduced thrushes (genus Turdus ) from agricultural habitats in central North Island, New Zealand. Once the protocol was established, all biopsied eggs from clutches that were not depredated or deserted before candling were found to be developing normally after 3–5 d of incubation ( N = 28) and all hatched. Biopsy samples (>0.02 g) produced concentrations of yolk carotenoids (and variances) that were statistically indistinguishable from whole yolk destructive samples. In addition, our samples (>0.02 g) confirmed previously reported differences in yolk carotenoid concentrations between the two thrush species and revealed a significant decline in yolk carotenoid concentration with laying order. Further examination of how variability in yolk carotenoid concentration and identity influences offspring sex, success, and survival or, later in life, reproductive success and ability to efficiently incorporate dietary carotenoids into both integument and immune tissues will require larger sample sizes. Studies to date have been restricted by the number of destructive samples that investigators are willing (or permitted) to obtain from wild species. Thus, we hope that our nondestructive method of sampling yolk will promote further examination of the links between carotenoid uptake from the environment and maternal investment in the avian yolk.     

Size and temperature dependent foraging capacities and metabolism: consequences for winter starvation mortality in fish

The foraging related capacities, energy requirements and the ability of individuals to withstand starvation are strongly dependent on body size and temperature. In this study, we estimated size-dependent foraging rates and critical resource density (CRD) in small Arctic char ( Salvelinus alpinus ) under winter conditions and compared these with previous observations under summer conditions. We investigated if starvation mortality is size-dependent in the laboratory, and we assessed the potential for winter growth and the occurrence and size dependency of winter mortality both in a large scale pond experiment and in natural lakes. The efficiency of foraging on macroinvertebrates increased with size but was lower at 4 than 12°C, still CRD was lower at 4 than 12°C as metabolic rates decreased faster than foraging efficiency with temperature. When starved, small char died before large and at rates which suggest that YOY char need to feed during winter to avoid starvation. Results from both our pond experiment and field study indicate that survival of YOY char over winter is high, despite severe winter conditions, because YOY char are able to feed and grow during winter. In seasonal environments with declining resources, the size scaling and temperature dependency of foraging and metabolic demands may provide conditions which can favour either small or large individuals. This size advantage dichotomy relates to that larger individual's by having a higher CRD are more likely to start starving, but once resource levels are below CRD for all size classes, small individuals starve to death at a higher rate. Negative size-dependent winter mortality from starvation is suggested to be more pronounced in species that are not adapted to feed at low temperatures and in species feeding on zooplankton, since zooplankton abundance, in contrast to macroinvertebrate abundance, is generally low during winter.     

Air temperature triggers the recovery of evergreen boreal forest photosynthesis in spring

The timing of the commencement of photosynthesis (P^*) in spring is an important determinant of growing‐season length and thus of the productivity of boreal forests. Although controlled experiments have shed light on environmental mechanisms triggering release from photoinhibition after winter, quantitative research for trees growing naturally in the field is scarce. In this study, we investigated the environmental cues initiating the spring recovery of boreal coniferous forest ecosystems under field conditions. We used meteorological data and above‐canopy eddy covariance measurements of the net ecosystem CO₂ exchange (NEE) from five field stations located in northern and southern Finland, northern and southern Sweden, and central Siberia. The within‐ and intersite variability for P^* was large, 30–60 days. Of the different climate variables examined, air temperature emerged as the best predictor for P^* in spring. We also found that ‘soil thaw’, defined as the time when near‐surface soil temperature rapidly increases above 0°C, is not a useful criterion for P^*. In one case, photosynthesis commenced 1.5 months before soil temperatures increased significantly above 0°C. At most sites, we were able to determine a threshold for air‐temperature‐related variables, the exceeding of which was required for P^*. A 5‐day running‐average temperature (T₅) produced the best predictions, but a developmental‐stage model (S) utilizing a modified temperature sum concept also worked well. But for both T₅ and S, the threshold values varied from site to site, perhaps reflecting genetic differences among the stands or climate‐induced differences in the physiological state of trees in late winter/early spring. Only at the warmest site, in southern Sweden, could we obtain no threshold values for T₅ or S that could predict P^* reliably. This suggests that although air temperature appears to be a good predictor for P^* at high latitudes, there may be no unifying ecophysiological relationship applicable across the entire boreal zone.     

Secondary chemistry and ribosomal DNA data congruencies in Arnica (Asteraceae)

To investigate possible congruencies between DNA sequence data and secondary chemistry, we compared nuclear ribosomal DNA (nrDNA) sequence data, sesquiterpene lactone (STL) contents, and cytometric data from 35 accessions of 16 Arnica (Asteraceae) species and two outgroup taxa ( Layia hieracioides and Madia sativa ), using phylogenetic inference and principal component analysis (PCA). Several groups supporting multiple accessions of the same species (of A. montana , A. longifolia , A. gracilis , and A. chamissonis ) are congruent between the phylogenetic trees based on nrDNA and STL data. Sesquiterpene lactone profiles were found to be highly consistent within multiple samples of A. montana and A. longifolia respectively . Moreover, sesquiterpene lactone data support subspecies classifications of A. chamissonis and A. parryi , with additional support from DNA sequence data and cytometric data. Morphology, STL data (PCA), cytometric data and DNA sequence data suggest a hybrid origin of one accession ( A. gracilis  ×  longifolia ). In A. gracilis , A. latifolia , and Layia hieracioides , previously not investigated for STLs, we found large amounts of xanthalongin derivatives. This is the first time STLs have been reported from subtribe Madiinae.
© The Willi Hennig Society 2009.