Age-dependent genetic effects on a secondary sexual trait in male Alpine ibex, Capra ibex

Secondary sexual traits, such as horns in ungulates, may be good indicators of genetic quality because they are costly to develop. Genetic effects on such traits may be revealed by examining correlations between multilocus heterozygosity (MLH) and trait value. Correlations between MLH and fitness traits, termed heterozygosity-fitness correlations (HFC), may reflect inbreeding depression or associative overdominance of neutral microsatellite loci with loci directly affecting fitness traits. We investigated HFCs for horn growth, body mass and faecal counts of nematode eggs in wild Alpine ibex (Capra ibex). We also tested if individual inbreeding coefficients (f') estimated from microsatellite data were more strongly correlated with fitness traits than MLH. MLH was more strongly associated with trait variation than f'. We found HFC for horn growth but not for body mass or faecal counts of nematode eggs. The effect of MLH on horn growth was age-specific. The slope of the correlation between MLH and yearly horn growth changed from negative to positive as males aged, in accordance with the mutation accumulation theory of the evolution of senescence. Our results suggest that the horns of ibex males are an honest signal of genetic quality.     

A strong genetic footprint of the re‐introduction history of Alpine ibex (Capra ibex ibex)

A population’s neutral genetic variation is a composite of its size, degree of isolation and demographic history. Bottlenecks and founder events increase genetic drift, leading to the loss of genetic variation and increased genetic differentiation among populations. Gene flow has the opposite effects. Thus, gene flow can override the genetic patterns caused by founder events. Using 37 microsatellite loci, we investigated the effects of serial bottlenecks on genetic variation and differentiation among 42 Alpine ibex populations in Switzerland with known re‐introduction histories. We detected a strong footprint of re‐introduction events on contemporary genetic structure, with re‐introduction history explaining a substantial part of the genetic differentiation among populations. As a result of the translocation of a considerable number of individuals from the sole formerly surviving population in northern Italy, most of the genetic variation of the ancestral population is now present in the combined re‐introduced Swiss populations. However, re‐introductions split up the genetic variation among populations, such that each contemporary Swiss population showed lower genetic variation than the ancestral population. As expected, serial bottlenecks had different effects on the expected heterozygosity (He) and standardized number of alleles (sNa). While loss of sNa was higher in the first bottlenecks than in subsequent ones, He declined to a similar degree with each bottleneck. Thus, genetic drift was detected with each bottleneck, even when no loss of sNa was observed. Overall, more than a hundred years after the beginning of this successful re‐introduction programme, re‐introduction history was the main determinant of today’s genetic structure.     

A Novel Approach for Choosing Summary Statistics in Approximate Bayesian Computation

The choice of summary statistics is a crucial step in approximate Bayesian computation (ABC). Since statistics are often not sufficient, this choice involves a trade-off between loss of information and reduction of dimensionality. The latter may increase the efficiency of ABC. Here, we propose an approach for choosing summary statistics based on boosting, a technique from the machine-learning literature. We consider different types of boosting and compare them to partial least-squares regression as an alternative. To mitigate the lack of sufficiency, we also propose an approach for choosing summary statistics locally, in the putative neighborhood of the true parameter value. We study a demographic model motivated by the reintroduction of Alpine ibex (Capra ibex) into the Swiss Alps. The parameters of interest are the mean and standard deviation across microsatellites of the scaled ancestral mutation rate (θ_anc = 4N_eu) and the proportion of males obtaining access to matings per breeding season (ω). By simulation, we assess the properties of the posterior distribution obtained with the various methods. According to our criteria, ABC with summary statistics chosen locally via boosting with the L₂-loss performs best. Applying that method to the ibex data, we estimate θ^anc≈1.288 and find that most of the variation across loci of the ancestral mutation rate u is between 7.7 × 10⁻⁴ and 3.5 × 10⁻³ per locus per generation. The proportion of males with access to matings is estimated as ω^≈0.21, which is in good agreement with recent independent estimates.     

Beneficial modulation of the gut microbiota

The human gut microbiota comprises approximately 100 trillion microbial cells and has a significant effect on many aspects of human physiology including metabolism, nutrient absorption and immune function. Disruption of this population has been implicated in many conditions and diseases, including examples such as obesity, inflammatory bowel disease and colorectal cancer that are highlighted in this review. A logical extension of these observations suggests that the manipulation of the gut microbiota can be employed to prevent or treat these conditions. Thus, here we highlight a variety of options, including the use of changes in diet (including the use of prebiotics), antimicrobial-based intervention, probiotics and faecal microbiota transplantation, and discuss their relative merits with respect to modulating the intestinal community in a beneficial way.     

Estimating handling times for herbivore diets: a statistical method using the gamma distribution

1. We present a statistical model for the prediction of handling times for different diet items of herbivores foraging in heterogeneous environments, based on the distribution of time intervals between bites.
2. We propose the gamma distribution as a convenient and appropriate model for foraging data and illustrate its use with field observations of foraging Nubian ibex ( Capra ibex nubiana Linnaeus 1758) in the Negev Desert of Israel.
3. Specifically, we demonstrate how to estimate handling times from skewed frequency data of intervals between bites within patches.
4. We compared two mathematically equivalent gamma models and found a pronounced difference in the numerical results in fitting empirical data.
5. Estimated handling times varied with bite size, but not with plant category or sex of the foraging animal.
6. Fitting a gamma model to foraging data allows the efficient estimation of minimum handling constraints, mean handling times and within-patch cropping rates, which should be useful for models of the herbivore foraging process.     

Foraging behaviour of coypus Myocastor coypus: why do coypus consume aquatic plants?

Foraging behaviour of wild coypu was studied to examine two hypotheses that had been previously proposed to explain the species’ preference for aquatic plants. First, the nutritional benefit hypothesis which states that aquatic plants are more nutritional than terrestrial plants. Second, the behavioural trade-off hypothesis which states that coypus avoid foraging far from the water because of the costs associated with other types of behaviour. In order to test the nutritional benefit hypothesis, we studied the diet composition of coypus in relation to the protein content of the diet and of the plants available in the environment. Fieldwork was conducted seasonally from November 1999 to August 2000 at one study site located in the Province of Buenos Aires, east central Argentina. Behavioural observations showed that coypus remained foraging in the water and microhistological analysis of faeces indicated that their diet was principally composed of hygrophilic monocotyledons (Lemna spp. and Eleocharis spp.) throughout the year. We did not find support for the nutritional benefit hypothesis: nutritional quality (based on nitrogen content) of hygrophilic plants was not higher than that of terrestrial plants, and seasonal changes in diet quality did not match either fluctuations in vegetation quality or proportion of hygrophilic plants in the diet. Although not directly tested, the behavioural trade-off hypothesis may explain why coypus prefer to forage in or near the water as a mechanism for reducing predation risk.     

增氮对青藏高原东缘高寒草甸土壤甲烷吸收的早期影响

研究大气氮沉降对青藏高原高寒草甸土壤CH4吸收的影响,对于揭示氮素调节土壤CH4吸收的机制和评价氮沉降增加背景下大气CH4收支平衡至关重要.通过构建多形态、低剂量的增氮控制试验,测定土壤CH4净交换通量和相关土壤理化性质,分析高寒草甸土壤CH4通量变化特征及其主要驱动因子.研究结果表明:自然状态下高寒草甸土壤是大气CH4汇,CH4平均吸收量为(35.40±1.92) μg· m-2· h-1.土壤CH4吸收主要受水分驱动,其次为土壤NH4+-N和NO3-N含量.NH4+-N抑制CH4吸收,NO3--N促进CH4吸收;不同剂量氮素输入对土壤CH4吸收影响也不尽相同,低氮处理促进土壤CH4吸收,而中氮和高氮处理抑制土壤CH4吸收.结果显示青藏高原高寒草甸土壤是重要的大气CH4汇,在未来大气氮沉降加倍的情景下CH4汇功能增强,但当氮沉降量增加两倍以上时CH4汇功能将会减弱.