Group phenotypic composition drives task performances in ants

Differences in individual behaviour within a group can give rise to functional dissimilarities between groups, particularly in social animals. However, how individual behavioural phenotypes translate into the group phenotype remains unclear. Here, we investigate whether individual behavioural type affects group performance in a eusocial species, the ant Aphaenogaster senilis. We measured individual behavioural traits and created groups of workers with similar behavioural type, either high-exploratory or low-exploratory workers. We tested these groups in four different, ecologically relevant, tasks: reaction to an intruder, prey retrieval from a maze, nest relocation and tool use. We show that, compared to groups of low-exploratory workers, groups of high-exploratory workers were more aggressive towards intruders, more efficient in collecting prey, faster in nest relocation and more likely to perform tool use. Our results demonstrate a strong link between individual and collective behaviour in ants. This supports the 'behavioural type hypothesis' for group dynamics, which suggests that an individual's behaviour in a social environment reflects its own behavioural type. The average behavioural phenotype of a group can therefore be predicted from the behavioural types of individual group members.

Interspecific attraction between ground-nesting songbirds and ants: the role of nest-site selection

BACKGROUND

Interspecific interactions within ecological networks can influence animal fitness and behaviour, including nest-site selection of birds and ants. Previous studies revealed that nesting birds and ants may benefit from cohabitation, with interspecific attraction through their nest-site choice, but mutual interactions have not yet been tested. We explored a previously undescribed ecological link between ground-nesting birds and ants raising their own broods (larvae and pupae) within the birds' nests in a temperate primeval forest of lowland Europe. We tested whether the occurrence of ant broods within bird nests resulted from a mutual or one-sided interspecific attraction that operated through nest-site choice and was modified by weather conditions.

RESULTS

We found a non-random occupation of bird nests by ants raising their own broods within them, which indicated interspecific attraction driven solely by the ants. The birds' preference to nest near tussocks of vegetation showed little overlap with the most frequent placement of ant colonies among fallen deciduous tree-leaves, dead wood and moss. Additionally, birds did not appear to select forest localities with high densities of ant colonies. The occurrence of ant broods within bird nests was also unrelated to bird nest placement near to specific habitat features. The attractiveness of bird nests to ants appeared to increase with the thermal activity of the birds warming their nests, and also during cool and wet weather when the occurrence of ant broods within bird nests was most frequent. Ants often remained in the nests after the birds had vacated them, with only a slight reduction in the probability of ant brood occurrence over time.

CONCLUSIONS

The natural patterns of bird nest colonisation by ants support the hypothesis of ants' attraction to warm nests of birds to raise their broods under advantageous thermal conditions. Similar relationships may occur between other warm-blooded, nest-building vertebrates and nest-dwelling invertebrates, which depend on ambient temperatures. The findings advance our understanding of these poorly recognised interspecific interactions, and can inform future studies of ecological networks.

The influence of age and development temperature on the temperature-related foraging risk of Formica cinerea ants

Abstract

Climate change and the subsequent increase of global temperature are the most current and important threats to biodiversity. Despite the importance of temperature, our knowledge about the level of behavioural and physiological adaptations of ant species from temperate regions to cope with high temperatures is limited compared to the broad knowledge of typical thermal specialists from warmer regions. In the current study, we investigated the temperature-related foraging risk of xerothermic ant species from the temperate climate in Europe, Formica cinerea. Our aims were to check how an increase in external soil temperature affects the foraging activity of workers and how the temperature during development and worker age affects foraging activity in high temperatures. Based on our results, we can draw the following conclusions: (1) the majority of workers utilize a risk-aversive strategy in relation to foraging in high surface temperatures; (2) pupal development temperature affects the risk taken by adult workers: workers that developed in a higher temperature forage more often but for shorter intervals compared to workers that developed in a lower temperature; (3) age is an important factor in temperature-related foraging activity, as with increasing age, workers forage significantly longer at the highest temperatures. Our study is one of the first to assess the potential factors that can affect the foraging risk of ants from a temperate climate in high ambient temperatures.

Significance statement

Our study is the first direct test of workers' age and the development temperature of pupae on the thermal-related foraging strategy of adult F. cinerea workers. It shows that worker age and the development temperature of pupae interact to promote tolerance of thermal stress. We found that with increasing age, workers are prone to forage significantly longer at the highest and riskiest temperatures. Workers that developed in the high temperature (28°C) foraged more often but for shorter intervals compared to workers that developed in the lower temperature (20°C). Interestingly, the factor of age is more significant for ants that developed in the higher temperature of 28°C; the foraging time of these ants significantly increased with their age.

The Myrmecofauna (Hymenoptera: Formicidae) of Hungary: Survey of Ant Species with an Annotated Synonymic Inventory

Simple Summary

Abundance is a hallmark of ants (Hymenoptera: Formicidae). They are exceedingly common in both natural and artificial environments and they constitute a conspicuous part of the terrestrial ecosystem; every 3 to 4 out of 10 kg of insects are given by ants. Due to their key role in natural habitats, they are at the basis of any nature conservation and pest management policy. Thus, the first step in developing adequate management strategies is to build a precise faunistic inventory. More than 16,000 valid ant species are registered worldwide, of which 126 are known to occur in Hungary. Thanks to the last decade’s efforts in the Hungarian myrmecological research, and because of the constantly changing taxonomy of several problematic ant genera, a new checklist of the Hungarian ants is presented here. A comparison of the Hungarian myrmecofauna to other European countries’ ant fauna is also provided in this paper. The current dataset is a result of ongoing work on inventorying the Hungarian ant fauna, therefore it is expected to change over time and will be updated once the ongoing taxonomic projects are completed.

Abstract

Ants (Hymenoptera: Forimicidae) are exceedingly common in nature. They constitute a conspicuous part of the terrestrial animal biomass and are also considered common ecosystem engineers. Due to their key role in natural habitats, they are at the basis of any nature conservation policy. Thus, the first step in developing adequate conservation and management policies is to build a precise faunistic inventory. More than 16,000 valid ant species are registered worldwide, of which 126 are known to occur in Hungary. Thanks to the last decade’s efforts in the Hungarian myrmecological research, and because of the constantly changing taxonomy of several problematic ant genera, a new checklist of the Hungarian ants is presented here. The state of the Hungarian myrmecofauna is also discussed in the context of other European countries’ ant fauna. Six species (Formica lemani, Lasius nitidigaster, Tetramorium immigrans, T. staerckei, T. indocile and Temnothorax turcicus) have been reported for the first time in the Hungarian literature, nine taxon names were changed after systematic replacements, nomenclatorial act, or as a result of splitting formerly considered continuous populations into more taxa. Two species formerly believed to occur in Hungary are now excluded from the updated list. All names are nomenclaturally assessed, and complete synonymies applied in the Hungarian literature for a certain taxon are provided. Wherever it is not self-evident, comments are added, especially to explain replacements of taxon names. Finally, we present a brief descriptive comparison of the Hungarian myrmecofauna with the ant fauna of the surrounding countries. The current dataset is a result of ongoing work on inventorying the Hungarian ant fauna, therefore it is expected to change over time and will be updated once the ongoing taxonomic projects are completed.

A small number of workers with specific personality traits perform tool use in ants

Ants use debris as tools to collect and transport liquid food to the nest. Previous studies showed that this behaviour is flexible whereby ants learn to use artificial material that is novel to them and select tools with optimal soaking properties. However, the process of tool use has not been studied at the individual level. We investigated whether workers specialise in tool use and whether there is a link between individual personality traits and tool use in the ant Aphaenogaster senilis. Only a small number of workers performed tool use and they did it repeatedly, although they also collected solid food. Personality predicted the probability to perform tool use: ants that showed higher exploratory activity and were more attracted to a prey in the personality tests became the new tool users when previous tool users were removed from the group. This suggests that, instead of extreme task specialisation, variation in personality traits within the colony may improve division of labour.

Protective behavior or 'true' tool use? Scrutinizing the tool use behavior of ants

In the genus Aphaenogaster, workers use tools to transport liquid food to the colony. During this behavior, ants place or drop various kinds of debris into liquids or soft food, and then, they carry the food-soaked tools back to the nest. According to some authors, this behavior is not "true" tool use because it represents two separate processes: a defense response to cover the dangerous liquid and a transport of food. Here, we investigated the debris dropping and retrieving behavior of the ant Aphaenogaster subterranea to establish which of the two hypotheses is more probable by conducting manipulative experiments. We tested the responses of eight colonies (a) to liquid food (honey-water) and nonfood liquids (water) in different distances from the nest and (b) to nonthreatening liquids previously covered or presented as small droplets. We also tested whether the nutritional condition of colonies (i.e., starved or satiated) would affect the intensity and rate of debris dropping. Our results were consistent with the tool-using behavior hypothesis. Firstly, ants clearly differentiated between honey-water and water, and they directed more of their foraging effort toward liquids farther from the nest. Secondly, ants performed object dropping even into liquids that did not pose the danger of drowning or becoming entangled. Lastly, the nutritional condition of colonies had a significant effect on the intensity and rate of object dropping, but in the opposite direction than we expected. Our results suggest that the foraging behavior of A. subterranea is more complex than that predicted by the two-component behavior hypothesis and deserves to be considered as "true" tool use.

Thermal ecosystem engineering by songbirds promotes a symbiotic relationship with ants

Nesting birds can act as thermal ecosystem engineers by providing warm habitats that may attract arthropods to colonise the nest structure. This cohabitation of birds and nest-dwelling invertebrates may foster symbiotic relationships between them, but evidence is lacking. We investigated whether ants are attracted to bird nests by the heat generated by the hosts, and/or the nests' structural insulation properties, to raise their broods (larvae and/or pupae) in advantageous thermal conditions. We found that the endothermic activity of birds within their nests created 'heat islands', with thermal conditions potentially promoting the survival and development of ant larvae in cool environments. We experimentally confirmed that the presence of heat within bird nests, and not the structure itself, attracted the ants to colonise the nests. As ants might benefit from exploiting warm bird nests, this may be a previously overlooked commensal, mutualistic or parasitic relationship which may be ecologically significant and globally widespread among various nesting birds and reproducing ants. Similar interspecific interactions may exist with other arthropods that reproduce in avian and mammalian nests. Further research is needed to reveal the nature of these relationships between such taxa, and to understand the role of warm-blooded animals as thermal ecosystem engineers.

Habitat features and colony characteristics influencing ant personality and its fitness consequences

Several factors can influence individual and group behavioral variation that can have important fitness consequences. In this study, we tested how two habitat types (seminatural meadows and meadows invaded by Solidago plants) and factors like colony and worker size and nest density influence behavioral (activity, meanderness, exploration, aggression, and nest displacement) variation on different levels of the social organization of Myrmica rubra ants and how these might affect the colony productivity. We assumed that the factors within the two habitat types exert different selective pressures on individual and colony behavioral variation that affects colony productivity. Our results showed individual-/colony-specific expression of both mean and residual behavioral variation of the studied behavioral traits. Although habitat type did not have any direct effect, habitat-dependent factors, like colony size and nest density influenced the individual mean and residual variation of several traits. We also found personality at the individual-level and at the colony level. Exploration positively influenced the total- and worker production in both habitats. Worker aggression influenced all the productivity parameters in seminatural meadows, whereas activity had a positive effect on the worker and total production in invaded meadows. Our results suggest that habitat type, through its environmental characteristics, can affect different behavioral traits both at the individual and colony level and that those with the strongest effect on colony productivity primarily shape the personality of individuals. Our results highlight the need for complex environmental manipulations to fully understand the effects shaping behavior and reproduction in colony-living species.

Behaviours indicating cannibalistic necrophagy in ants are modulated by the perception of pathogen infection level

Cannibalistic necrophagy is rarely observed in social hymenopterans, although a lack of food could easily favour such behaviour. One of the main supposed reasons for the rarity of necrophagy is that eating of nestmate corpses carries the risk of rapid spread of pathogens or parasites. Here we present an experimental laboratory study on behaviour indicating consumption of nestmate corpses in the ant Formica polyctena. We examined whether starvation and the fungal infection level of the corpses affects the occurrence of cannibalistic necrophagy. Our results showed that the ants distinguished between corpses of different types and with different levels of infection risk, adjusting their behaviour accordingly. The frequency of behaviours indicating cannibalistic necrophagy increased during starvation, although these behaviours seem to be fairly common in F. polyctena even in the presence of other food sources. The occurrence and significance of cannibalistic necrophagy deserve further research because, in addition to providing additional food, it may be part of the hygienic behaviour repertoire. The ability to detect infections and handle pathogens are important behavioural adaptations for social insects, crucial for the fitness of both individual workers and the entire colony.

Large- and Small-Scale Environmental Factors Drive Distributions of Ant Mound Size Across a Latitudinal Gradient

Red wood ants are keystone species of forest ecosystems in Europe. Environmental factors and habitat characteristics affect the size of their nest mounds, an important trait being in concordance with a colony’s well-being and impact on its surroundings. In this study, we investigated the effect of large-scale (latitude and altitude) and small-scale environmental factors (e.g., characteristics of the forest) on the size of nest mounds of Formica polyctena in Central Europe. We predicted that the change in nest size is in accordance with Bergmann’s rule that states that the body size of endotherm animals increases with the higher latitude and/or altitude. We found that the size of nests increased along the latitudinal gradient in accordance with Bergmann’s rule. The irradiation was the most important factor responsible for the changes in nest size, but temperature and local factors, like the perimeter of the trees and their distance from the nest, were also involved. Considering our results, we can better understand the long-term effects and consequences of the fast-changing environmental factors on this ecologically important group. This knowledge can contribute to the planning of forest management tactics in concordance with the assurance of the long-term survival of red wood ants.