The world-wide, rapid urbanization is leading to substantial changes in environmental and habitat conditions. These changes, as well as disturbances accompanying urbanization have considerable effects at various levels of the biological organization on wildlife. Understanding behavioral responses to such changes is essential for identifying which organisms may successfully adapt to the altered conditions. In this study, individuals of a forest specialist ground beetle, Carabus convexus, from rural and urban forest patches were tested for their exploratory and risk-taking behavior. Beetles responded consistently in the different contexts; furthermore, by behaving consistently over time, demonstrated that they had personalities. Agglomerative cluster analysis identified two groups of behavioral traits: the exploratory and the risk-taking dimension of personality. Urban females were significantly more exploratory than urban males which can be an adaptation to find high quality food needed to mature eggs in urban habitats, as well as to select favorable microsites for oviposition. Moreover, urban females and males showed more risk-taking behavior than rural females. Urban beetles with more risk-taking behavior may be better able to cope with frequent urbanization-driven disturbance events.

Urbanization is increasing worldwide and causes substantial changes in environmental parameters, generating various kinds of stress on arthropods, with several harmful consequences. We examined a forest specialist ground beetle, Carabus convexus, in forested habitats to evaluate the changes in four important life history traits between rural and urban populations. Analyzing beetles from the overwintered cohort in their first breeding season, we found no significant differences in body length or body mass between the rural and urban individuals. Body condition, judged by fat reserve scores, was similarly poor in both habitats, indicating that beetles were not able to accumulate substantial fat reserves at either habitat. Females with ripe eggs in their ovaries were first captured at the same time in both areas. The number of ripe eggs, however, was significantly higher in females of the low-density urban population (6.13 eggs/female) than in those of the high-density rural population (4.14 eggs/female), indicating density-dependent fecundity. Altered environmental and habitat conditions by urbanization, however, seemed to cause high mortality during egg hatching and/or larval development, preventing the growth of the urban population to the level of rural one.

Urbanization is creating changes in environmental and habitat conditions, as well as creating disturbance and threats to urban-associated species. Some traits, such as high exploratory and risk-taking behavior, are beneficial to allow colonization of urban habitats and coping with urbanization-derived pressures. In this study the exploratory and risk-taking behavior of rural and urban individuals of three forest-associated rove beetle species were tested during their main reproductive period by five frequently used behavioral measures. Individuals of all studied species were similarly ranked by all behavioral measures, indicating that the studied rove beetles responded consistently in the different contexts. However, the behavior of beetles was consistent over time for all/most studied species only by using two measures of exploratory behavior. These provide evidence for the existence of the exploratory dimension of personality in rove beetles. We found a higher exploratory behavior in males than females in Ocypus nitens which can be explained by the active searching of males for mating partners. There were no urbanization-related differences in the exploratory behavior of individuals, suggesting that behavioral changes (being more exploratory) may not yield additional fitness benefits in these rove beetle species with good dispersal capacity.

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.

Trait-based approaches, particularly those focusing on behavioral traits, have become increasingly important in ecology. However, empirical studies addressing behavioral trait variation in insects remain comparatively scarce. To address this knowledge gap, we investigated the behavior of six wild-living ground beetle species for which no behavioral data have previously been reported. Using standardized behavioral measures, we found that in species occurring in their preferred forest habitats, behavioral traits related to activity, exploration, boldness, and risk-taking showed weak or limited temporal consistency. In contrast, in species inhabiting modified forest habitats, behavioral traits exhibited pronounced and repeatable individual differences, were intercorrelated, and formed behavioral syndromes. Moreover, half of the studied species showed sex-specific differences in personality, reflecting drivers related to reproductive roles and investment. Overall, our findings emphasize that animal personality and behavioral syndromes in ground beetles are not universal species-level properties but emerge from the interaction between intrinsic traits, and sex-specific strategies, underscoring the importance of considering ecological context when interpreting individual-level behavioral variation.