The gut microbiota and Bergmann’s rule in wild house mice

The extent to which the gut microbiota may play a role in latitudinal clines of body mass variation (i.e., Bergmann's rule) remains largely unexplored. Here, we collected wild house mice from three latitudinal transects across North and South America and investigated the relationship between variation in the gut microbiota and host body mass by combining field observations and common garden experiments. First, we found that mice in the Americas follow Bergmann's rule, with increasing body mass at higher latitudes. Second, we found that overall differences in the gut microbiota were associated with variation in body mass controlling for the effects of latitude. Then, we identified specific microbial measurements that show repeated associations with body mass in both wild‐caught and laboratory‐reared mice. Finally, we found that mice from colder environments tend to produce greater amounts of bacteria‐driven energy sources (i.e., short‐chain fatty acids) without an increase in food consumption. Our findings provide motivation for future faecal transplant experiments directly testing the intriguing possibility that the gut microbiota may contribute to Bergmann's rule, a fundamental pattern in ecology.     

Real-time PCR quantification of the predominant bacterial divisions in the distal gut of Meishan and Landrace pigs

Firmicutes and Bacteroidetes are closely related to body fat in humans and mice, which are the two dominant bacterial divisions of gut microbiota in mammals. Here real-time PCR analysis indicated that Meishan pigs had a 34% reduction in percentage Bacteroidetes (P=0.008) and a significantly lower proportion of Bacteroides (P=0.013) than Landrace pigs. The percentage of Bacteroidetes or Bacteroides had a negative correlation with body fat (R(2) was 0.63 for Bacteroidetes and 0.57 for Bacteroides, P<0.05). There was a trend that the percentage of Firmicutes in Meishan pigs was higher in numerical value than in Landrace pigs, although this difference was not statistically significant (P=0.290) between the two breeds. These suggested that body fat correlated with the percentage of Bacteroidetes division of the gut microbiota in the common pig breeds, and the differences of gut microbial ecology in obese versus lean animals may be analogous.     

Weapon allometry varies with latitude in the New Zealand giraffe weevil

Animal body size commonly shows a relationship with latitude to the degree that this phenomenon is one of the few ‘rules’ discussed in evolutionary ecology: Bergmann's rule. Although exaggerated secondary sexual traits frequently exhibit interesting relationships with body size (allometries) and are expected to evolve rapidly in response to environmental variation, the way in which allometry might interact with latitude has not been addressed. We present data showing latitudinal variation in body size and weapon allometry for the New Zealand giraffe weevil (Lasiorhynchus barbicornis). Males display an extremely elongated rostrum used as a weapon during fights for access to females. Consistent with Bergmann's rule, mean body size increased with latitude. More interestingly, weapon allometry also varied with latitude, such that lower latitude populations exhibited steeper allometric slopes between weapon and body size. To our knowledge, this is the first study to document a latitudinal cline in weapon allometry and is therefore a novel contribution to the collective work on Bergmann's rule and secondary sexual trait variation.     

成年与未成年圈养林麝粪便菌群多样性的比较

本研究旨在解析林麝未成年组(n=10)和成年组(n=10)之间的菌群差异。收集林麝新鲜粪便,提取总DNA,利用带标签的通用引物扩增16S rRNA V3-V4区,使用Illumina Miseq 300PE测序平台对扩增产物进行Miseq双端测序,通过计算ACE和Shannon等多样性指数,以及微生物组成成分和距离聚类分析,揭示组成结构与差异。α多样性分析表明成年组微生物的多样性丰富度略高于未成年组,但不存在显著差异性(P>0.05)。未成年组和成年组均是厚壁菌门(Firmicutes)、拟杆菌门(Bacteroidetes)和变形菌门(Proteobacteria)所占的比例较高。成年组Proteobacteria比例明显高,而Firmicutes比例较低。LEfSe分析表明有12个显著差异的细菌分类。两组在Firmicutes门存在显著差异的细菌较少,而在Proteobacteria上存在显著差异的细菌较多。本研究证明在不同年龄阶段,微生物的丰富度和多样性不存在显著差异,细菌的组成成分也相同。但是在组成比例上存在差异性,间接反映了不同年龄阶段营养吸收的不同需求。     

转基因鲤鱼与对照鲤肠道微生物群落差异研究

以转“全鱼”生长激素基因鲤(Cyprinus carpio L.)和野生对照鲤为对象, 采用454高通量测序技术对其肠道微生物16S rRNA基因进行测序并分析了3个不同发育阶段微生物群落结构的变化, 进而探讨了转基因鲤与对照鲤肠道微生物群落的差异。基于转基因鲤和对照鲤不同发育时期(6日龄、2月龄、5月龄)肠道微生物群落组成的DCA排序分析显示, 2月龄转基因鲤与对照鲤肠道微生物组成不同。Alpha多样性及均匀度都显示转基因鲤肠道微生物多样性高于对照鲤。从门水平的比较分析发现, 转基因鲤肠道中存在较多的厚壁菌门(Firmicutes)细菌, 而对照鲤中拟杆菌门(Bacteroidetes)细菌较多, 其中2月龄转基因鲤肠道内Bacteroidetes/Firmicutes比值低于对照鲤。研究结果表明, 在所分析的3个发育时期, 转基因鲤的肠道微生物组成与对照鲤相比发生了改变, 且在2月龄时存在差异。该研究为进一步揭示转基因鱼肠道微生物与宿主的相互影响和作用机制提供了很好的参考。     

A Reassessment of Bergmann's Rule in Modern Humans

It is widely accepted that modern humans conform to Bergmann''s rule, which holds that body size in endothermic species will increase as temperature decreases. However, there are reasons to question the reliability of the findings on which this consensus is based. One of these is that the main studies that have reported that modern humans conform to Bergmann''s rule have employed samples that contain a disproportionately large number of warm-climate and northern hemisphere groups. With this in mind, we used latitudinally-stratified and hemisphere-specific samples to re-assess the relationship between modern human body size and temperature. We found that when groups from north and south of the equator were analyzed together, Bergmann''s rule was supported. However, when groups were separated by hemisphere, Bergmann''s rule was only supported in the northern hemisphere. In the course of exploring these results further, we found that the difference between our northern and southern hemisphere subsamples is due to the limited latitudinal and temperature range in the latter subsample. Thus, our study suggests that modern humans do conform to Bergmann''s rule but only when there are major differences in latitude and temperature among groups. Specifically, groups must span more than 50 degrees of latitude and/or more than 30°C for it to hold. This finding has important implications for work on regional variation in human body size and its relationship to temperature.     

Urbanization disrupts latitude‐size rule in 17‐year cicadas

Many ectotherms show a decrease in body size with increasing latitude due to changes in climate, a pattern termed converse Bergmann's rule. Urban conditions—particularly warmer temperatures and fragmented landscapes—may impose stresses on development that could disrupt these body size patterns. To test the impact of urbanization on development and latitudinal trends in body size, we launched a citizen science project to collect periodical cicadas (Magicicada septendecim) from across their latitudinal range during the 2013 emergence of Brood II. Periodical cicadas are long‐lived insects whose distribution spans a broad latitudinal range covering both urban and rural habitats. We used a geometric morphometric approach to assess body size and developmental stress based on fluctuating asymmetry in wing shape. Body size of rural cicadas followed converse Bergmann's rule, but this pattern was disrupted in urban habitats. In the north, urban cicadas were larger than their rural counterparts, while southern populations showed little variation in body size between habitats. We detected no evidence of differences in developmental stress due to urbanization. To our knowledge, this is the first evidence that urbanization disrupts biogeographical trends in body size, and this pattern highlights how the effects of urbanization may differ over a species’ range.     

A global assessment of Bergmann's rule in mammals and birds

Bergmann's rule states that endotherms have a large body size in high latitudes and cold climates. However, previous empirical studies have reported mixed evidence on the relationships between body size and latitude, raising the question of why some clades of endotherms follow Bergmann's rule, whereas others do not. Here, we synthesized the interspecific relationships between body size and latitude among 16,187 endothermic species (5422 mammals and 10,765 birds) using Bayesian phylogenetic generalized linear mixed models to examine the strength and magnitude of Bergmann's rule. We further assessed the effect of biological and ecological factors (i.e., body mass categories, dietary guild, winter activity, habitat openness, and climate zone) on the variations in the body mass–latitude relationships by adding an interaction term in the models. Our results revealed a generally weak but significant adherence to Bergmann's rule among all endotherms at the global scale. Despite taxonomic variation in the strength of Bergmann's rule, the body mass of species within most animal orders showed an increasing trend toward high latitudes. Generally, large-bodied, temperate species, non-hibernating mammals, and migratory and open-habitat birds tend to conform to Bergmann's rule more than their relatives do. Our results suggest that whether Bergmann's rule applies to a particular taxon is mediated by not only geographic and biological features, but also potential alternate strategies that species might have for thermoregulation. Future studies could explore the potential of integrating comprehensive trait data into phylogenetic comparative analysis to re-assess the classic ecogeographic rules on a global scale.     

Interrelations of global macroecological patterns in wing and thorax size,sexual size dimorphism,and range size of the Drosophilidae

Support for macroecological rules in insects is mixed, with potential confounding interrelations between patterns rarely studied. We here investigate global patterns in body and wing size, sexual size dimorphism and range size in common fruit flies (Diptera: Drosophilidae) and explore potential interrelations and the predictive power of Allen's, Bergmann's, Rensch's and Rapoport's rules. We found that thorax length (r² = 0.05) and wing size (r² = 0.09) increased with latitude, supporting Bergmann's rule. Contrary to patterns often found in endothermic vertebrates, relative wing size increased towards the poles (r² = 0.12), a pattern against Allen's rule, which we attribute to selection for increased flight capacity in the cold. Sexual size dimorphism decreased with size, evincing Rensch's rule across the family (r² = 0.14). Yet, this pattern was largely driven by the virilis–repleta radiation. Finally, range size did not correlate with latitude, although a positive relationship was present in a subset of the species investigated, providing no convincing evidence for Rapoport's rule. We further found little support for confounding interrelations between body size, wing loading and range size in this taxon. Nevertheless, we demonstrate that studying several traits simultaneously at minimum permits better interpretation in case of multiple, potentially conflicting trends or hypotheses concerning the macroecology of insects.     

The converse to Bergmann's rule in bumblebees,a phylogenetic approach

Two patterns commonly emerge when animal body size is analyzed as a function of latitudinal distribution. First, body size increases with latitude, a temperature effect known as Bergmann's rule, and second, the converse to Bergmann's rule, a pattern in which body size decreases with latitude. However, other geographic patterns can emerge when the mechanisms that generate Bergmann's and the converse to Bergmann's clines operate together. Here, we use phylogenetic comparative analysis in order to control for phylogenetic inertia, and we show that bumblebees exhibit the converse to Bergmann's rule. Bumblebee taxa are distributed worldwide in temperate and tropical regions. The largest species are found in places with high water availability during the driest time of the year. Nonetheless, large body size is constrained by extreme temperatures. Bumblebees’ body size could be related to a higher extent to the size of food rewards to be harvested than to the energetic advantages of thermoregulation. Moreover, we found that the body size of eusocial and cuckoo species responded in the same way to environmental variables, suggesting that they have not diverged due to different selective pressures.     

Body size explains interspecific variation in size–latitude relationships in geographically widespread beetle species

1. In most birds and mammals, larger individuals of the same species tend to be found at higher latitudes, but in insects, body size–latitude relationships are highly variable. 2. Recent studies have shown that larger‐bodied insect species are more likely to decrease in size when reared at increased temperature, compared with smaller‐sized species. These findings have led to the prediction that a positive relationship between body size and latitude should be more prevalent in larger‐bodied insect species. 3. This study measured the body size of > 4000 beetle specimens (12 species) collected throughout North America. Some beetle species increased in size with latitude, while others decreased. Importantly, mean species body size explained c. 30% of the interspecific variation in the size–latitude response. 4. As predicted, larger‐bodied beetle species were more likely to show a positive relationship between body size and latitude (Bergmann's rule), and smaller‐bodied species were more likely to show a negative body size–latitude relationship (inverse Bergmann's rule). 5. These body size–latitude patterns suggest that size‐specific responses to temperature may underlie global latitudinal distributions of body size in Coleoptera, as well as other insects.     

Geographical distribution and diversity of bacteria associated with natural populations of Drosophila melanogaster

Drosophila melanogaster is one of the most widely used model systems in biology. However, little is known about its associated bacterial community. As a first step towards understanding these communities, we compared bacterial 16S rRNA gene sequence libraries recovered from 11 natural populations of adult D. melanogaster. Bacteria from these sequence libraries were grouped into 74 distinct taxa, spanning the phyla Proteobacteria, Bacteroidetes, and Firmicutes, which were unevenly spread across host populations. Summed across populations, the distribution of abundance of genera was closely fit by a power law. We observed differences among host population locations both in bacterial community richness and in composition. Despite this significant spatial variation, no relationship was observed between species richness and a variety of abiotic factors, such as temperature and latitude. Overall, bacterial communities associated with adult D. melanogaster hosts are diverse and differ across host populations.     

Host genetic determinants of the gut microbiota of wild mice

Identifying a common set of genes that mediate host–microbial interactions across populations and species of mammals has broad relevance for human health and animal biology. However, the genetic basis of the gut microbial composition in natural populations remains largely unknown outside of humans. Here, we used wild house mouse populations as a model system to ask three major questions: (a) Does host genetic relatedness explain interindividual variation in gut microbial composition? (b) Do population differences in the microbiota persist in a common environment? (c) What are the host genes associated with microbial richness and the relative abundance of bacterial genera? We found that host genetic distance is a strong predictor of the gut microbial composition as characterized by 16S amplicon sequencing. Using a common garden approach, we then identified differences in microbial composition between populations that persisted in a shared laboratory environment. Finally, we used exome sequencing to associate host genetic variants with microbial diversity and relative abundance of microbial taxa in wild mice. We identified 20 genes that were associated with microbial diversity or abundance including a macrophage‐derived cytokine (IL12a) that contained three nonsynonymous mutations. Surprisingly, we found a significant overrepresentation of candidate genes that were previously associated with microbial measurements in humans. The homologous genes that overlapped between wild mice and humans included genes that have been associated with traits related to host immunity and obesity in humans. Gene–bacteria associations identified in both humans and wild mice suggest some commonality to the host genetic determinants of gut microbial composition across mammals.     

Patterns of size variation in bees at a continental scale: does Bergmann's rule apply?

Body size latitudinal clines have been widley explained by the Bergmann's rule in homeothermic vertebrates. However, there is no general consensus in poikilotherms organisms in particular in insects that represent the large majority of wildlife. Among them, bees are a highly diverse pollinators group with high economic and ecological value. Nevertheless, no comprehensive studies of species assemblages at a phylogenetically larger scale have been carried out even if they could identify the traits and the ecological conditions that generate different patterns of latitudinal size variation. We aimed to test Bergmann's rule for wild bees by assessing relationships between body size and latitude at continental and community levels. We tested our hypotheses for bees showing different life history traits (i.e. sociality and nesting behaviour). We used 142 008 distribution records of 615 bee species at 50 × 50 km (CGRS) grids across the West Palearctic. We then applied generalized least squares fitted linear model (GLS) to assess the relationship between latitude and mean body size of bees, taking into account spatial autocorrelation. For all bee species grouped, mean body size increased with higher latitudes, and so followed Bergmann's rule. However, considering bee genera separately, four genera were consistent with Bergmann's rule, while three showed a converse trend, and three showed no significant cline. All life history traits used here (i.e. solitary, social and parasitic behaviour; ground and stem nesting behaviour) displayed a Bergmann's cline. In general there is a main trend for larger bees in colder habitats, which is likely to be related to their thermoregulatory abilities and partial endothermy, even if a ‘season length effect’ (i.e. shorter foraging season) is a potential driver of the converse Bergmann's cline particularly in bumblebees.     

基于高通量测序技术研究水貂远端肠道细菌群落组成

【目的】研究水貂远端肠道微生物群落组成及其多样性。【方法】通过高通量测序技术研究水貂远端肠内容物细菌的组成和多样性。【结果】从10只健康水貂远端肠道内容物样品中得到146 287高质量序列代表17个菌门、167个细菌属。水貂肠道细菌以厚壁菌门(59.99%)、拟杆菌门(16.2%)、梭杆菌门(11.5%)、放线菌门(5.9%)和变形菌门(5.3%)为主,其中厚壁菌门最为丰富。厚壁菌门中的梭菌目是最丰富的目,而梭菌目中的链球菌占有50%以上的OTUs,是最大的细菌属。【结论】水貂肠道内存在复杂的微生物区系,这对进一步研究水貂对营养物质吸收利用提供了理论基础。     

取食不同食物对小菜蛾幼虫肠道细菌多样性的影响

【目的】植食性昆虫肠道细菌的组成与其食物密切相关。本研究旨在探究小菜蛾Plutella xylostella幼虫肠道细菌多样性与其取食食物之间的关系以及它们之间相互适应的过程。【方法】本研究选取小菜蛾人工饲料品系(S)及其转寄主到结球甘蓝Brassica oleracea var. capitata、结球白菜Brassica rapa subsp. pekinensis和花椰菜Brassica olerocea var. botrytis饲养后第1代(分别为G1C, G1CC和G1WC)和第3代(分别为G3C, G3CC和G3WC)的4龄幼虫,提取小菜蛾肠道细菌基因组DNA,利用Illumina MiSeq二代高通量测序技术,分析其肠道细菌多样性和丰度。【结果】α多样性指数分析发现,取食不同食物的小菜蛾4龄幼虫肠道细菌多样性高低顺序为G1WC>G1CC>S>G1C。在菌群组成上,以人工饲料为食的S样品肠道细菌主要由厚壁菌门(Firmicutes)组成,转寄主植物后的G1C, G1CC和G1WC肠道中厚壁菌门(Firmicutes)相对丰度显著下降,G1C和G1CC小菜蛾肠道中变形菌门(Proteobacteria)相对丰度显著上升成为优势菌群,G1WC肠道中拟杆菌门(Bacteroidetes)成为优势菌群。在寄主植物上连续饲养3代后,与第1代相比,小菜蛾肠道细菌α多样性指数没有显著性改变,但在结球甘蓝和结球白菜上小菜蛾肠道菌群结构却发生了变化,相比G1C,G3C肠道中芽孢杆菌目(Bacillales)的相对丰度显著下降;相比G1CC, G3CC肠道中放线菌门(Proteobacteria)、芽单胞菌门(Gemmatimonadetes)和硝化螺旋菌门(Nitrospirae)的相对丰度均显著上升。【结论】取食人工饲料和不同寄主植物的小菜蛾幼虫肠道细菌多样性和群落构成存在显著差异,寄主植物对小菜蛾肠道微生物的结构组成具有重要的影响,且小菜蛾肠道微生物对寄主植物可能存在一个长期适应的过程。本研究为进一步探讨影响小菜蛾肠道细菌变化的因素,以及后续研究肠道细菌与寄主植物之间的互作奠定了良好的基础。     

Interactions between multiple helminths and the gut microbiota in wild rodents

The gut microbiota is vital to host health and, as such, it is important to elucidate the mechanisms altering its composition and diversity. Intestinal helminths are host immunomodulators and have evolved both temporally and spatially in close association with the gut microbiota, resulting in potential mechanistic interplay. Host–helminth and host–microbiota interactions are comparatively well-examined, unlike microbiota–helminth relationships, which typically focus on experimental infection with a single helminth species in laboratory animals. Here, in addition to a review of the literature on helminth–microbiota interactions, we examined empirically the association between microbiota diversity and composition and natural infection of multiple helminth species in wild mice (Apodemus flavicollis), using 16S rRNA gene catalogues (metataxonomics). In general, helminth presence is linked with high microbiota diversity, which may confer health benefits to the host. Within our wild rodent system variation in the composition and abundance of gut microbial taxa associated with helminths was specific to each helminth species and occurred both up- and downstream of a given helminth''s niche (gut position). The most pronounced helminth–microbiota association was between the presence of tapeworms in the small intestine and increased S24–7 (Bacteroidetes) family in the stomach. Helminths clearly have the potential to alter gut homeostasis. Free-living rodents with a diverse helminth community offer a useful model system that enables both correlative (this study) and manipulative inference to elucidate helminth–microbiota interactions.     

Curdlan intake changes gut microbial composition,short-chain fatty acid production,and bile acid transformation in mice

Indigestible polysaccharides, such as dietary fibers, benefit the host by improving the intestinal environment. Short-chain fatty acids (SCFAs) produced by gut microbial fermentation from dietary fibers exert various physiological effects. The bacterial polysaccharide curdlan benefits the host intestinal environment, although its effect on energy metabolism and SCFA production remains unclear. Hence, this study aimed to elucidate the effect of curdlan intake on gut microbial profiles, SCFA production, and energy metabolism in a high-fat diet (HFD)-induced obese mouse model. Gut microbial composition of fecal samples from curdlan-supplemented HFD-fed mice indicated an elevated abundance of Bacteroidetes, whereas a reduced abundance of Firmicutes was noted at the phylum level compared with that in cellulose-supplemented HFD-fed mice. Moreover, curdlan supplementation resulted in an abundance of the family Bacteroidales S24-7 and Erysipelotrichaceae, and a reduction in Deferribacteres in the feces. Furthermore, curdlan supplementation elevated fecal SCFA levels, particularly butyrate. Although body weight and fat mass were not affected by curdlan supplementation in HFD-induced obese mice, HFD-induced hyperglycemia was significantly suppressed with an increase in plasma insulin and incretin GLP-1 levels. Curdlan supplementation elevated fecal bile acid and SCFA production, improved host metabolic functions by altering the gut microbial composition in mice.     

Comparative analysis of Korean human gut microbiota by barcoded pyrosequencing

Human gut microbiota plays important roles in harvesting energy from the diet, stimulating the proliferation of the intestinal epithelium, developing the immune system, and regulating fat storage in the host. Characterization of gut microbiota, however, has been limited to western people and is not sufficiently extensive to fully describe microbial communities. In this study, we investigated the overall composition of the gut microbiota and its host specificity and temporal stability in 20 Koreans using 454-pyrosequencing with barcoded primers targeting the V1 to V3 region of the bacterial 16S rRNA gene. A total of 303,402 high quality reads covered each sample and 8,427 reads were analyzed on average. The results were compared with those of individuals from the USA, China and Japan. In general, microbial communities were dominated by five previously identified phyla: Actinobacteria, Firmicutes, Bacteroidetes, Fusobacteria, and Proteobacteria. UPGMA cluster analysis showed that the species composition of gut microbiota was host-specific and stable over the duration of the test period, but the relative abundance of each member fluctuated. 43 core Korean gut microbiota were identified by comparison of sequences from each individual, of which 15 species level phylotypes were related to previously-reported butyrate-producing bacteria. UniFrac analysis revealed that human gut microbiota differed between countries: Korea, USA, Japan and China, but tended to vary less between individual Koreans, suggesting that gut microbial composition is related to internal and external characteristics of each country member such as host genetics and diet styles.     

Comparison of gut-associated and nest-associated microbial communities of a fungus-growing termite (Odontotermes yunnanensis)

Abstract The digestion of cellulose by fungus-growing termites involves a complex of different organisms, such as the termites themselves, fungi and bacteria. To further investigate the symbiotic relationships of fungus-growing termites, the microbial communities of the termite gut and fungus combs of Odontotermes yunnanensis were examined. The major fungus species was identified as Termitomyces sp. To compare the micro-organism diversity between the digestive tract of termites and fungus combs, four polymerase chain reaction clone libraries were created (two fungus-targeted internal transcribed spacer [ITS]– ribosomal DNA [rDNA] libraries and two bacteria-targeted 16S rDNA libraries), and one library of each type was produced for the host termite gut and the symbiotic fungus comb. Results of the fungal clone libraries revealed that only Termitomyces sp. was detected on the fungus comb; no non-Termitomyces fungi were detected. Meanwhile, the same fungus was also found in the termite gut. The bacterial clone libraries showed higher numbers and greater diversity of bacteria in the termite gut than in the fungus comb. Both bacterial clone libraries from the insect gut included Firmicutes, Bacteroidetes, Proteobacteria, Spirochaetes, Nitrospira, Deferribacteres, and Fibrobacteres, whereas the bacterial clone libraries from the fungal comb only contained Firmicutes, Bacteroidetes, Proteobacteria, and Acidobacteris.