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Habitat diversity plays a significant role in shaping the genetic structure of cetacean populations. However, the processes involved in defining the genetic differentiation of these highly mobile marine mammals are still largely unknown. Levels of genetic differentiation and dispersal patterns of common bottlenose dolphins (Tursiops truncatus) were assessed in the north‐eastern Mediterranean Sea, with a focus on the Adriatic Sea. This is a region characterized by diverse marine ecosystems and high levels of human‐induced habitat degradation. Although this species seems almost uniformly distributed throughout the Adriatic Basin, genetic evidence rejected the hypothesis of a single stock. Pairwise estimates of genetic differentiation at 12 microsatellite loci, and mitochondrial DNA (entire control region, 920bp), revealed diverse levels of genetic differentiation among five putative populations from the Tyrrhenian Sea to the Aegean Sea. A fine‐scale genetic structure was recorded within the Adriatic Sea, where females appear to be the principal gene flow mediators. The assessment of recent migration rates indicates a relatively high level of gene flow from the North Adriatic towards adjacent areas. Indication of a fine‐scale population structure across the Adriatic Sea is a factor to be carefully considered in the emerging marine management scenario set by the implementation of the EU Marine Strategy Framework Directive (2008/56/CE), particularly when it comes to assessing and managing direct mortality caused by human activities (e.g. fisheries or maritime traffic). A good knowledge of population structure at the basin level is also fundamental for the identification of potential Adriatic Special Areas of Conservation for the bottlenose dolphin under the Habitats Directive (Council Directive 92/43/EEC). Copyright © 2013 John Wiley & Sons, Ltd.

Nest-mate recognition plays a key role in the biology of ants. Although individuals coming from a foreign nest are, in most cases, promptly rejected, the degree of aggressiveness towards non nest-mates may be highly variable among species and relies on genetic, chemical and environmental factors. We analyzed intraspecific relationships among neighboring colonies of the dominant Mediterranean acrobat ant Crematogaster scutellaris integrating genetic, chemical and behavioral analyses. Colony structure, parental relationships between nests, cuticular hydrocarbons profiles (CHCs) and aggressive behavior against non nest-mates were studied in 34 nests located in olive tree trunks. Bayesian clustering analysis of allelic variation at nine species-specific microsatellite DNA markers pooled nests into 14 distinct clusters, each representing a single colony, confirming a polydomous arrangement of nests in this species. A marked genetic separation among colonies was also detected, probably due to long distance dispersion of queens and males during nuptial flights. CHCs profiles varied significantly among colonies and between nests of the same colony. No relationship between CHCs profiles and genetic distances was detected. The level of aggressiveness between colonies was inversely related to chemical and spatial distance, suggesting a ‘nasty neighbor’ effect. Our findings also suggest that CHCs profiles in C. scutellaris may be linked to external environmental factors rather than genetic relationships.

Rhizobia are ecologically important, facultative plant-symbiotic microbes. In nature, there is a large variability in the association of rhizobial strains and host plants of the same species. Here, we evaluated whether plant and rhizobial genotypes influence the initial transcriptional response of rhizobium following perception of a host plant. RNA sequencing of the model rhizobium Sinorhizobium meliloti exposed to root exudates or luteolin (an inducer of nod genes, involved in the early steps of symbiotic interaction) was performed on a combination of three S. meliloti strains and three alfalfa varieties as host plants. The response to root exudates involved hundreds of changes in the rhizobium transcriptome. Of the differentially expressed genes, 35% were influenced by the strain genotype, 16% were influenced by the plant genotype, and 29% were influenced by strain-by-host plant genotype interactions. We also examined the response of a hybrid S. meliloti strain in which the symbiotic megaplasmid (∼20% of the genome) was mobilized between two of the above-mentioned strains. Dozens of genes were upregulated in the hybrid strain, indicative of nonadditive variation in the transcriptome. In conclusion, this study demonstrated that transcriptional responses of rhizobia upon perception of legumes are influenced by the genotypes of both symbiotic partners and their interaction, suggesting a wide spectrum of genetic determinants involved in the phenotypic variation of plant-rhizobium symbiosis. IMPORTANCE A sustainable way for meeting the need of an increased global food demand should be based on a holobiont perspective, viewing crop plants as intimately associated with their microbiome, which helps improve plant nutrition, tolerance to pests, and adverse climate conditions. However, the genetic repertoire needed for efficient association with plants by the microbial symbionts is still poorly understood. The rhizobia are an exemplary model of facultative plant symbiotic microbes. Here, we evaluated whether genotype-by-genotype interactions could be identified in the initial transcriptional response of rhizobium perception of a host plant. We performed an RNA sequencing study to analyze the transcriptomes of different rhizobial strains elicited by root exudates of three alfalfa varieties as a proxy of an early step of the symbiotic interaction. The results indicated strain- and plant variety-dependent variability in the observed transcriptional changes, providing fundamentally novel insights into the genetic basis of rhizobium-plant interactions. Our results provide genetic insights and perspective to aid in the exploitation of natural rhizobium variation for improvement of legume growth in agricultural ecosystems.