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

Abstract

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.

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

“…Various subcategories of rescue behaviour recorded in the present study, such as biting/pulling of various parts of the victim's body, responses to the substrate near the victim (sand digging, removal of small pebbles, responses to the paper disc acting as a part of the snare apparatus) and biting and pulling of the wire loops placed on the victim's body were also already described in numerous studies investigating ant rescue behaviour [28,29,[59][60][61][62][63][65][66][67][68]72,[74][75][76][77].…”

“…This was possible thanks to the application of a novel version of the nestmate rescue test consisting of a confrontation of potential rescuers with a nestmate victim entrapped in an artificial snare. In contrast to earlier studies with the use of the artificial snare bioassay [29,59,61,62,[64][65][66][67][68][69][70][72][73][74][75][76][77], in our study each nestmate victim was bearing on its body not just one, but two wire loops, one placed on its petiole and an additional one placed on its leg. Only the loop on the victim's petiole was acting as a snare, the loop on the leg was not implicated in the victim's entrapment.…”

“…About twenty years ago, Czechowski et al (2002) [28] employed the term "rescue behaviour" in the title and the text of the paper describing rescue behaviour displayed by workers of three ant species (Formica sanguinea, Formica fusca and Formica cinerea) in response to ant victims captured by predatory antlion larvae (Myrmeleon formicarius). This study provided inspiration for further extensive research carried out both in the field and in the laboratory with the use of two main bioassays: antlion larva capture bioassay, during which ant rescue behaviour was elicited in response to an ant captured by an antlion larva [59][60][61][62][63] and artificial snare bioassay, during which ant rescue behaviour was elicited in response to a victim ant entrapped in an artificial snare [29,59,61,62,[64][65][66][67][68][69][70][71][72][73][74][75][76][77].…”

“…Such an artificial snare bioassay has been used in numerous laboratory and field experiments to test a wide range of ant species from the subfamilies Formicinae [29,59,61,62,[64][65][66][67][68][69][70]72,[74][75][76][77], Myrmicinae [59,61,67] and Dolichoderinae [61]. Modified versions of that bioassay consisted of a confrontation of potential rescuers with a victim immobilized by means of duct tape applied to its legs (Odontomachus brunneus, subfamily Ponerinae) [73] and of simultaneous confrontation of potential rescuers with two artificial snares, one empty and one containing a victim, or containing two different victims (Cataglyphis nigra, subfamily Formicinae) [77].…”

“…In these studies, rescue attempts directed precisely to the object responsible for the victim's entrapment were labelled with several similar terms, including such expressions as "precision rescue", "precision rescue behaviour" and "precise rescue behaviour patterns" [19,59,64,65,67,74,102]; "precisely directed rescue behaviour" [29,30,68,102]; "precisely targeted rescue behaviour" [30,66,68,72]; and "precisely tuned rescue behaviour" [80]. Responses to the snare responsible for the entrapment of the victim were also investigated and/or discussed in some other research papers in which these terms were not used [61,62,70,73,75,76], as well as in several review papers [11,19,41,80]. However, surprisingly, in some studies, pulling at the snare and at the victim's appendages were not analysed separately, but pooled together to form a more general subcategory of pulling behaviour [68,77].…”