Increased Risk Proneness or Social Withdrawal? The Effects of Shortened Life Expectancy on the Expression of Rescue Behavior in Workers of the ant Formica cinerea (Hymenoptera: Formicidae)

Life expectancy in ants explains variation in helpfulness regardless of phylogenetic relatedness

Rescue behavior aims to free a relative from danger. Ants are particularly known for such helpfulness and, perhaps not coincidentally, also show the highest level of social organization in the animal kingdom, i.e. eusociality. However, even among social species such as ants, there is a huge variation in rescue proneness, and little is understood about the underlying causes of this variation. In this study, we explore the relationship between helpfulness in the form of rescue and life expectancy, focusing on 14 ant species with diverse phylogenetic backgrounds. We posit that species with longer worker life expectancies are more prone to engaging in rescue actions. To test this, we assessed worker lifespan in each species and conducted behavioral tests simulating entrapment scenarios involving a nestmate ensnared by an artificial obstacle. Observed behaviors involved contact with the nestmate, digging around it, pulling at its body parts, and biting the entrapping obstacle. Our findings reveal that species with longer worker life expectancies exhibit higher proneness to rescue endangered nestmates, irrespective of phylogenetic relatedness. Furthermore, we found no trace of a phylogenetic signal in the life expectancies or helpfulness of workers belonging to different species. The results underscore the significance of life expectancy as a key factor influencing the likelihood of rescue behavior in ants. This phenomenon warrants further investigation, given the varied physiologies, life histories, and ecologies observed among species. Nevertheless, the impact of life expectancy on behavioral patterns in social insects suggests that this parameter is likely significant across diverse taxa.

Do They Know What They Are Doing? Cognitive Aspects of Rescue Behaviour Directed by Workers of the Red Wood Ant Formica polyctena to Nestmate Victims Entrapped in Artificial Snares

Ant rescue behaviour belongs to the most interesting subcategories of prosocial and altruistic behaviour encountered in the animal world. Several studies suggested that ants are able to identify what exactly restrains the movements of another individual and to direct their rescue behaviour precisely to that object. To shed more light on the question of how precise the identification of the source of restraint of another ant is, we investigated rescue behaviour of red wood ant Formica polyctena workers, using a new version of an artificial snare bioassay in which a nestmate victim bore two wire loops on its body, one (acting as a snare) placed on its petiole and an additional one on its leg. The tested ants did not preferentially direct their rescue behaviour towards the snare. Moreover, the overall strategy adopted by the most active rescuers was not limited to precisely targeted rescue attempts directed towards the snare, but consisted of frequent switching between various subcategories of rescue behaviour. These findings highlight the importance of precise identification of cognitive processes and overall behavioural strategies for better understanding of causal factors underlying animal helping behaviour in light of new facts discovered by testing of various successive research hypotheses.

Small workers are more persistent when providing and requiring help in a monomorphic ant

The common sand-dwelling Formica cinerea ants possess monomorphic workers, yet with considerable and easily identified size variation. Considering the importance of body size in polymorphic ants and other animals, we test whether size-dependent differences in behaviour occur in this species. We focus on the behaviour of large and small foragers in the context of rescue occurring between nestmates when one of them is entrapped and requires help. We show that workers of different sizes are characterized by a similar frequency of rescue activity and time delay to the first act of rescue. However, small workers rescue for longer than large workers. These results indicate that, although there is no size-related rescue specialization in F. cinerea foragers, small rescuers behave differently than large ones in terms of rescue persistence. Additionally, we show that small workers are more active when trapped. We suggest that variation in behavioural persistence of differently-sized workers may increase the efficiency of rescue actions. This study is the first to find a connection between body size and rescue behaviour in ants and the first to quantify and analyze the behaviour of individuals in need of rescue. These findings add substantially to our understanding of social insects and, more generally, highlight the need to study among-individual behavioural variation in social animals, including those in which body size is judged minute and irrelevant.

Injury shortens life expectancy in ants and affects some risk-related decisions of workers

The Formica cinerea ants are known to be highly territorial and aggressively defend their nest and foraging areas against other ants. During the foraging, workers engage in large-scale battles with other colonies of ants and injuries often occur in the process. Such injuries open the body up to pathologies and can lead to costs expressed in lower survival. Here, we addressed the significance of injury in dictating decisions related to engagement in risky behavior in ants (i.e., rescue and aggression). We manipulated the life expectancies of F. cinerea workers by injury and found that the survival of injured workers was shorter compared to the intact individuals. Furthermore, we found that injured workers discriminated between the intact and injured nestmates and showed more rescue behavior toward intact individuals. These rescue actions were expressed as digging around the trapped ant in need of rescue, pulling at its body parts, transporting the sand covering it, and biting the thread entrapping it. In turn, intact and injured workers showed similar and high levels of aggression toward heterospecifics. Our findings highlight the role of behavioral context in the studies devoted to the decision-making processes among social insects and the importance of life expectancy in their behavioral patterns.

Rescue specialists in Cataglyphis piliscapa ants: The nature and development of ant first responders

Previous research in our laboratories has demonstrated that, within each colony of Cataglyphis piliscapa (formerly C. cursor) ants, only some individuals are capable of performing a complex sequence of behavioral patterns to free trapped nestmates-a sequence that not only is memory-dependent but also is responsive to the particular circumstances of that entrapment and how the rescue operation unfolds. Additionally, this rescue behavior is inherited patrilineally from but a few of the many males that fertilize the eggs of the colony's single queen. Here, we describe three experiments to explore rescue behavior further-namely, whether rescuers are in any way selective about which nestmates they help, how the age of rescuers and the victims that they help affect the quantity and quality of the rescue operation, and when this complex behavior first emerges in an ant's development. Taken together with the previous heritability analysis, these behavioral experiments provide clear evidence that the ability to rescue nestmates in distress should be recognized as a specialization, which together with other specialized tasks in C. piliscapa, contributes to a division of labor that increases the efficiency of the colony as a whole and, thus increases its reproductive success.

"O Sister, Where Art Thou?"-A Review on Rescue of Imperiled Individuals in Ants

Altruism is defined as an action that decreases the lifetime direct fitness of an actor and benefits one or more recipients. This phenomenon, which is generally difficult to understand and explain, requires special research attention. The subject of this review, rescue, is a type of altruistic behavior in which the actor puts itself at risk to save another individual, the recipient, that is in danger. The highest numbers of published empirical works have been devoted to rescue behavior in ants and they have enormous potential for further study. We review studies devoted to the subject and group them into four main areas of research on ant rescue actions: (1) variation in rescue behavior activity on a between-individual scale, (2) factors contributing to the evolution of rescue behavior on a between-species scale, (3) rescue behavior releaser signals and (4) rescue behavior benefits and costs. We highlight the progress in research on rescue behavior in ants, indicate that this behavior is probably much more common than previously thought yet thus far demonstrated in only a few species, and uncover research gaps and open questions that remain unexplored. We additionally point out some gaps in knowledge that become evident when research devoted to rescue behavior in rats, the second most studied group of animals in this context, is briefly overviewed. We hope to help navigate among studies on rescue behavior and provide the most up-to-date summary of the relevant literature. Moreover, we hope to encourage and facilitate researchers in behavioral ecology and other subdisciplines to further experimentally analyze rescue behavior, not only in ants but also in other taxa.

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.

Comparative analysis of experimental testing procedures for the elicitation of rescue actions in ants

Rescue behavior is observed when 1 individual provides help to another individual in danger. Most reports of rescue behavior concern ants (Formicidae), in which workers rescue each other from various types of entrapment. Many of these entrapment situations can be simulated in the laboratory using an entrapment bioassay, in which ants confront a single endangered nest mate entrapped on a sandy arena by means of an artificial snare. Here, we compared numerous characteristics of rescue actions (contact between individuals, digging around the entrapped individual, pulling at its body parts, transport of the sand covering it, and biting the snare entrapping it) in Formica cinerea ants. We performed entrapment tests in the field and in the laboratory, with the latter under varying conditions in terms of the number of ants potentially engaged in rescue actions and the arena substrate (marked or unmarked by ants’ pheromones). Rescue actions were more probable and pronounced in the field than in the laboratory, regardless of the type of test. Moreover, different test types in the laboratory yielded inconsistent results and showed noteworthy variability depending on the tested characteristic of rescue. Our results illustrate the specifics of ant rescue actions elicited in the natural setting, which is especially important considering the scarcity of field data. Furthermore, our results underline the challenges related to the comparison of results from different types of entrapment tests reported in the available literature. Additionally, our study shows how animal behavior differs in differing experimental setups used to answer the same questions.

Leg or antenna injury in Cataglyphis ants impairs survival but does not hinder searching for food

Injury is common in nature resulting, for example, from fighting, partial predation, or the wear of body parts. Injury is costly, expressed in impaired performance, failure in competition, and a shorter life span. A survey of the literature revealed the frequent occurrence of injury in ants and its various causes. We examined whether leg or antenna injury impacts food-discovery time and reduces the likelihood of reaching food in workers of the desert ant Cataglyphis niger. We examined the search-related consequences of injury in groups of either 4 or 8 workers searching for food in a short arena, a long arena, and a maze. We conducted a small field survey to evaluate the prevalence of injury in the studied population. Finally, we compared the survival rates of injured versus uninjured workers in the laboratory. Injury was common in the field, with almost 9% of the workers collected out of the nest, found to be injured. Injured workers survived shorter than uninjured ones and there was a positive link between injury severity and survival. However, we could not detect an effect of injury on any of the searching-related response variables, neither in the arenas nor in the mazes tested. We suggest that workers that survive such injury are only moderately affected by it.

Social immunity behaviour among ants infected by specialist and generalist fungi

Social insects are distinguished by their lifestyle of living in groups with division of labour, cooperative brood care, and reproduction limited to a few colony members. Social insects often build large colonies with remarkable densities of highly related individuals and this can lead to an increased pathogen pressure. Our review focuses on interactions of ants with two important taxonomic groups of fungi infecting ants: Hypocreales (Ascomycota) and Entomophthorales (Entomophthoromycotina), and their different infection strategies, including host manipulation for optimal spore dispersal in the specialised ant pathogens. In social insects such as ants, resistance to pathogens is present at the colony level, with social immunity in addition to the individual resistance. We describe how ants use both organizational and behavioural defence strategies to combat fungal pathogens, with emphasis on highly specialised fungi from the genera Ophiocordyceps and Pandora.