Body size phenotypes comprehensively assess cardiometabolic risk and refine the association between obesity and gut microbiota.

OBJECTIVE: The gut microbiota associates with obesity and related disorders, but recent meta-analyses have found that this association is, at best, of small effect. We argue that such analyses are flawed by the use of body mass index (BMI) as sole proxy for disease, and explore a classification method that distinguishes the cardiometabolic health status of individuals to look for more comprehensive associations between gut microbes and health. DESIGN: We analyzed a 441 community-dwelling cohort on which we obtained demographic and health information, anthropometry and blood biochemistry data that served to categorize participants according to BMI, cardiometabolic health status and body size phenotypes. In addition, the participants donated fecal samples from which we performed 16S rRNA gene sequencing to analyze the gut microbiota. RESULTS: We observed that health-related variables deteriorate with increased BMI, and that there are further discrepancies within a given BMI category when distinguishing cardiometabolically healthy and unhealthy individuals. Regarding the gut microbiota, both obesity and cardiovascular disease associate with reductions in α-diversity; having lean, healthy individuals the most diverse microbiotas. Moreover, the association between the gut microbiota and health stems from particular consortia of microbes; the prevalence of consortia involving pathobionts and Lachnospiraceae are increased in obese and cardiometabolically abnormal subjects, whereas consortia including Akkermansia muciniphila and Methanobrevibacter, Oscillospira and Dialister have higher prevalence in cardiometabolically healthy and normoweight participants. CONCLUSIONS: The incorporation of cardiometabolic data allows a refined identification of dissimilarities in the gut microbiota; within a given BMI category, marker taxa associated with obesity and cardiometabolic disease are exacerbated in individuals with abnormal health status. Our results highlight the importance of the detailed assessment and classification of individuals that should be carried out prior to the evaluation of obesity treatments targeting the gut microbiota.

Self-fertilization, long-distance flash invasion and biogeography shape the population structure of Pseudosuccinea columella at the worldwide scale.

Population genetic studies are efficient for inferring the invasion history based on a comparison of native and invasive populations, especially when conducted at species scale. An expected outcome in invasive populations is variability loss, and this is especially true in self-fertilizing species. We here focus on the self-fertilizing Pseudosuccinea columella, an invasive hermaphroditic freshwater snail that has greatly expanded its geographic distribution and that acts as intermediate host of Fasciola hepatica, the causative agent of human and veterinary fasciolosis. We evaluated the distribution of genetic diversity at the largest geographic scale analysed to date in this species by surveying 80 populations collected during 16 years from 14 countries, using eight nuclear microsatellites and two mitochondrial genes. As expected, populations from North America, the putative origin area, were strongly structured by selfing and history and harboured much more genetic variability than invasive populations. We found high selfing rates (when it was possible to infer it), none-to-low genetic variability and strong population structure in most invasive populations. Strikingly, we found a unique genotype/haplotype in populations from eight invaded regions sampled all over the world. Moreover, snail populations resistant to infection by the parasite are genetically distinct from susceptible populations. Our results are compatible with repeated introductions in South America and flash worldwide invasion by this unique genotype/haplotype. Our study illustrates the population genetic consequences of biological invasion in a highly selfing species at very large geographic scale. We discuss how such a large-scale flash invasion may affect the spread of fasciolosis.