Contrasting dynamics of cold resistance traits in field-fresh Myrmica ants during the active season

Functional magnetic resonance imaging multivoxel pattern analysis reveals neuronal substrates for collaboration and competition with myopic and predictive strategic reasoning

Competition and collaboration are strategies that can be used to optimize the outcomes of social interactions. Research into the neuronal substrates underlying these aspects of social behavior has been limited due to the difficulty in distinguishing complex activation via univariate analysis. Therefore, we employed multivoxel pattern analysis of functional magnetic resonance imaging to reveal the neuronal activations underlying competitive and collaborative processes when the collaborator/opponent used myopic/predictive reasoning. Twenty‐four healthy subjects participated in 2 × 2 matrix‐based sequential‐move games. Searchlight‐based multivoxel patterns were used as input for a support vector machine using nested cross‐validation to distinguish game conditions, and identified voxels were validated via the regression of the behavioral data with bootstrapping. The left anterior insula (accuracy = 78.5%) was associated with competition, and middle frontal gyrus (75.1%) was associated with predictive reasoning. The inferior/superior parietal lobules (84.8%) and middle frontal gyrus (84.7%) were associated with competition, particularly in trials with a predictive opponent. The visual/motor areas were related to response time as a proxy for visual attention and task difficulty. Our results suggest that multivoxel patterns better represent the neuronal substrates underlying the social cognition of collaboration and competition intermixed with myopic and predictive reasoning than do univariate features.

Comparison of thermal traits of Polistes dominula and Polistes gallicus, two European paper wasps with strongly differing distribution ranges

The two paper wasps, Polistes dominula and Polistes gallicus, are related species with strongly differing distribution ranges. We investigated thermal tolerance traits (critical thermal limits and metabolic response to temperature) to gain knowledge about physiological adaptations to their local climate conditions and to get evidence for the reasons of P. dominula’s successful dispersion. Body and ambient temperature measurements at the nests revealed behavioural adaptations to microclimate. The species differed clearly in critical thermal minimum (P. dominula −1.4 °C, P. gallicus −0.4 °C), but not significantly in critical thermal maximum of activity (P. dominula 47.1 °C, P. gallicus 47.6 °C). The metabolic response did not reveal clear adaptations to climate conditions. At low and high temperatures, the metabolic rate of P. dominula was higher, and at intermediate temperatures, we determined higher values in P. gallicus. However, the species exhibited remarkably differing thermoregulatory behaviour at the nest. On average, P. gallicus tolerated a thoracic temperature up to ~41 °C, whereas P. dominula already tried at ~37 °C to keep the thorax below ambient temperature. We suggest this to be an adaptation to the higher mean ambient temperature we measured at the nest during a breeding season. Although we determined for P. dominula a 0.5 °C larger thermal tolerance range, we do not presume this parameter to be solely responsible for the successful distribution of P. dominula. Additional factors, such as the thermal tolerance of the queens could limit the overwintering success of P. gallicus in a harsher climate.

Chill coma temperatures appear similar along a latitudinal gradient, in contrast to divergent chill coma recovery times, in two widespread ant species

Populations of widely distributed ectotherms demonstrate different cold resistance corresponding to the local climate. However, efficiently thermoregulating ectotherms could avoid divergence in cold resistance. Two species of ants, previously shown to even out latitudinal differences of mean summer temperatures in their nests, were used to test this hypothesis by comparing the temperature dependence of cold resistance in three distant populations (from 50°, 60° and 67°N). The species differ in habitat preferences, one (Myrmica rubra) being less stenotopic than the other (M. ruginodis). Therefore, three different predictions were made about their cold resistance: along the latitudinal gradient, it might be similar within the two species (because of thermoregulation within nests/habitats) or similar only in M. rubra (as a result of thermoregulation among habitats), or divergent at least in M. rubra (no effect of thermoregulation). Among populations of both species, neither differences nor latitudinal trends in chill coma temperature were statistically significant after 11 months of standard conditions, with or without cold hardening. In contrast, recovery time significantly differed among populations in both species, although its latitudinal trends were strongly curvilinear: in M. rubra, the intermediate population tended towards the slowest recovery, and in M. ruginodis, it tended towards the fastest. After 22 months, the patterns remained the same, except that M. ruginodis showed a significant linear latitudinal trend in chill coma temperature (with no significant populational differences). Hence, thermoregulation, both within and among habitats, apparently does keep chill coma temperatures similar. Recovery rate demonstrates divergence, but its curvilinear trends suggest a connection with climates experienced by ancestral populations.

The Inclusion of Functional Connectivity Information into fMRI-based Neurofeedback Improves Its Efficacy in the Reduction of Cigarette Cravings

Real-time fMRI (rtfMRI) neurofeedback (NF) facilitates volitional control over brain activity and the modulation of associated mental functions. The NF signals of traditional rtfMRI-NF studies predominantly reflect neuronal activity within ROIs. In this study, we describe a novel rtfMRI-NF approach that includes a functional connectivity (FC) component in the NF signal (FC-added rtfMRI-NF). We estimated the efficacy of the FC-added rtfMRI-NF method by applying it to nicotine-dependent heavy smokers in an effort to reduce cigarette craving. ACC and medial pFC as well as the posterior cingulate cortex and precuneus are associated with cigarette craving and were chosen as ROIs. Fourteen heavy smokers were randomly assigned to receive one of two types of NF: traditional activity-based rtfMRI-NF or FC-added rtfMRI-NF. Participants received rtfMRI-NF training during two separate visits after overnight smoking cessation, and cigarette craving score was assessed. The FC-added rtfMRI-NF resulted in greater neuronal activity and increased FC between the targeted ROIs than the traditional activity-based rtfMRI-NF and resulted in lower craving score. In the FC-added rtfMRI-NF condition, the average of neuronal activity and FC was tightly associated with craving score (Bonferroni-corrected p = .028). However, in the activity-based rtfMRI-NF condition, no association was detected (uncorrected p > .081). Non-rtfMRI data analysis also showed enhanced neuronal activity and FC with FC-added NF than with activity-based NF. These results demonstrate that FC-added rtfMRI-NF facilitates greater volitional control over brain activity and connectivity and greater modulation of mental function than activity-based rtfMRI-NF.

Cold resistance depends on acclimation and behavioral caste in a temperate ant

Adjusting to low temperatures is important for animals living in cold environments. We studied the chill-coma recovery time in temperate ant workers (Temnothorax nylanderi) from colonies collected in autumn and spring in Germany. We experimentally acclimated these ant colonies to cold temperatures followed by warm temperatures. As expected, cold-acclimated workers recovered faster from freezing temperatures, but subsequent heat acclimation did not change the short recovery times observed after cold acclimation. Hence, either heat acclimation improves cold tolerance, possibly as a general response to stress, or at least it does not negate enhanced cold tolerance following cold acclimation. Colonies collected in spring showed similar cold tolerance levels to cold-acclimated colonies in the laboratory. Next, we compared the chill-coma recovery time of different worker castes and found that exterior workers recovered faster than interior workers. This difference may be related to their more frequent exposure to cold, higher activity level, or distinct physiology. Interior workers were also heavier and showed a higher gaster-to-head ratio and thorax ratio compared to exterior workers. An obvious difference between exterior and interior workers is activity level, but we found no link between activity and cold tolerance. This suggests that physiology rather than behavioral differences could cause the increased cold tolerance of exterior workers. Our study reveals the importance of acclimation for cold tolerance under natural and standardized conditions and demonstrates differences in cold tolerance and body dimensions in monomorphic behavioral castes of an ant.