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

Abstract

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.

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].…”