Urbanization is rapidly shaping and transforming natural environments, creating networks of modified land types. These urbanization‐driven modifications lead to local extinctions of several species, but the surviving ones also face numerous novel selection pressures, including exposure to pollutants, habitat alteration, and shifts in food availability and diversity. Based on the assumption that the environmental pool of microorganisms is reduced in urban habitats due to habitat alteration, biodiversity loss, and pollution, we hypothesized that the diversity of bacterial microbiome in digestive tracts of arthropods would be lower in urban than rural habitats. Investigating the gut bacterial communities of a specialist ground beetle, Carabus convexus, in forested rural versus urban habitats by next generation high‐throughput sequencing of the bacterial 16S rRNA gene, we identified 3839 bacterial amplicon sequence variants. The composition of gut bacterial samples did not significantly differ by habitat (rural vs. urban), sex (female vs. male), sampling date (early vs. late spring), or their interaction. The microbiome diversity (evaluated by the Rényi diversity function), however, was higher in rural than urban adults. Our findings demonstrate that urbanization significantly reduced the diversity of the gut bacterial microbiome in C. convexus.

The responses of earthworms to excess soil element concentrations are well studied. However, published information on the metallic element accumulation in individuals is controversial. In this paper, the published data on earthworm As, Cd, Cr, Cu, Ni, Pb, and Zn whole body concentrations were evaluated in individuals collected from contaminated and uncontaminated (control) soils, using meta-analyses. The role of soil pH and exposure time as potential influencing factors on metal accumulation was also assessed. Based on the evaluations, the accumulation of each metallic element was significantly (p < 0.05) more intensive in individuals collected from contaminated soils than in ones from control soils, with minor differences in the order of accumulation intensity among the studied metallic elements. Further, major interspecific differences were indicated in the accumulation, with different species being the most intensive accumulators for individual metallic elements. Among the studied metals, Cu concentration in earthworm bodies increased significantly with increasing soil pH. As for the exposure time-dependent accumulation, Pb concentration was found to decrease significantly with time in whole body tissues of earthworms. These results suggested a high variability in metal- and species-specific accumulation-excretion patterns of earthworms, influenced also by other external factors. Based on the results highlighted in this meta-analysis, accumulation schemes raise the need for further analyses involving other additional variables (e.g., soil type, organic matter content, climatic condition) to get a better understanding of element cycle-earthworm relations.

Urbanization has a significant impact on abiotic and biotic factors in nature. We examined the morphometric characters of four carabid species (Abax parallelepipedus, Carabus scheidleri, Carabus violaceus, and Pterostichus oblongopunctatus) along urbanization gradients in and around the cities of Vienna (Austria) and Debrecen (Hungary). We found significant differences among urban, suburban, and rural areas in the parameters of antennomers, the maxillary palpus, the labial palpus, and the length of the tibia and the elytra of the carabids studied. We also found significant differences between males and females based on the parameters of antennomers, the maxillary palpus, the labial palpus, the femur, and the elytra. An interaction between urbanization and sex was found in the case of antennomers, the maxillary palpus, the labial palpus, the femur, and the elytra. Our findings suggested that in the cases of species from Carabini tribus the parameters of antennomers, the maxillary palpus, and the elytra could be useful for assessing the effects of urbanization because these morphometric characters responded sensitively to the environmental stress, whereas the most useful parameters are those of antennomers and the tibia for the species of Pterostichini tribus. Our findings also revealed that females are more sensitive to environmental stress than males.

Urbanization causes significant environmental and structural changes in habitats, one of them being increased fragmentation. Traits associated with increased locomotory capacity may be advantageous in such situations, as individuals with those traits may expand their home range or have a chance to escape the patch where conditions threaten their survival. Individuals of the forest specialist, flightless ground beetle Carabus convexus in urban habitats may respond to urbanization by increasing their locomotory capacity (increased muscle mass) with respect to their conspecifics in rural habitats. In order to test this hypothesis, morphological traits standardized for body size were assessed using linear mixed-effects models. Pronotum volume (as a proxy for muscle mass) showed no significant difference between urban and rural individuals. The size of the tibia and femur of the front, middle, and hind legs (a proxy for leg muscle mass) significantly differed between sexes, with males having significantly larger tibiae and femora than females. Furthermore, urban males had significantly larger hind tibiae than rural conspecifics. Sex-specific differences in tibia and femur size is expected because males usually have higher locomotory activity than females. Larger tibiae of urban males can be advantageous to extend their home range, ensuring that males find mating partners even in low-density urban populations.

Biological interactions, including symbiotic ones, have vital roles in ecological and evolutionary processes. Microbial symbionts in the intestinal tracts, known as the gut microbiome, are especially important because they can fundamentally influence the life history, fitness, and competitiveness of their hosts. Studies on the gut-resident microorganisms of wild animals focus mainly on vertebrates, and studies on species-rich invertebrate taxa, such as ground beetles, are sparse. In fact, even among the species-rich genus Carabus, only the gut microbiome of two Asian species was studied, while results on European species are completely missing. Here, we investigated the gut bacterial microbiome of a widespread European Carabus species, targeting the V3 and V4 regions of the 16S ribosomal RNA genes by next-generation high-throughput sequencing. We identified 1138 different operational taxonomic units assigned to 21 bacterial phyla, 90 families, and 197 genera. Members of the carbohydrate-degrading Prevotellaceae family, previously not detected in ground beetles, were the most abundant in the gut microbiome of the carnivorous C. convexus. Presumably, individuals from the studied wild populations also consume plant materials, especially fruits, and these carbohydrate-degrading bacterial symbionts can facilitate both the consumption and the digestion of these supplementary foods.