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)

Abstract

In social insects behavioral consequences of shortened life expectancy include, among others, increased risk proneness and social withdrawal. We investigated the impact of experimental shortening of life expectancy of foragers of the ant Formica cinerea achieved by their exposure to carbon dioxide on the expression of rescue behavior, risky pro-social behavior, tested by means of two bioassays during which a single worker (rescuer) was confronted with a nestmate (victim) attacked by a predator (antlion larva capture bioassay) or immobilized by an artificial snare (entrapment bioassay). Efficacy of carbon dioxide poisoning in shortening life expectancy was confirmed by the analysis of ant mortality. Rescue behavior observed during behavioral tests involved digging around the victim, transport of the sand covering the victim, pulling the limbs/antennae/mandibles of the victim, direct attack on the antlion (in antlion larva capture tests), and snare biting (in entrapment tests). The rate of occurrence of rescue behavior was lower in ants with shortened life expectancy, but that effect was significant only in the case of the entrapment bioassay. Similarly, only in the case of the entrapment bioassay ants with shortened life expectancy displayed rescue behavior after a longer latency and devoted less time to that behavior than ants from the control groups. Our results demonstrated that in ant workers shortened life expectancy may lead to reduced propensity for rescue behavior, most probably as an element of the social withdrawal syndrome that had already been described in several studies on behavior of moribund ants and honeybees.

“O Sister, Where Art Thou?”—A Review on Rescue of Imperiled Individuals in Ants

“…This demonstrated that, at least in some ant species, the detection of rescue behavior might depend on the test type used for detection. Taken together with the results of another study demonstrating differences between test types [ 43 ], these findings showed that the context of rescue action, in terms of the source of endangerment to the victims, matters to potential rescuers.…”

“…Using laboratory tests with F. cinerea victims caught by predatory antlions and ensnared by nylon threads, Miler et al [ 43 ] tested whether potential rescuers with differing life expectancies display different levels of rescue behavior. In the previous study on life expectancy, but from the perspective of the victims [ 38 ], the two reasons for the effect of life expectancy gave similar predictions; here, the predictions diverged.…”

“…It thus seemed that, generally, shortened life expectancy somewhat increased social withdrawal in these ants, which was well documented in ants in other contexts (e.g., [ 46 , 47 ]). Importantly, however, neither study focusing on the subject of life expectancy [ 38 , 43 ] controlled for changes in other types of behavior, and therefore, the studies did not fully exclude other explanations. For example, the detected effects might have stemmed from general deterioration of activity after CO 2 poisoning and not an increase in social withdrawal specifically.…”

Dyadic Nestmate Reunion Test in the Research on Ant Social Behavior

“…Therefore, it might have been expected that ants with shortened life expectancy will show higher propensity to engage in risky rescue behavior, However, many studies reported, that in ants shortened worker life expectancy may also lead to social withdrawal (Hölldobler and Wilson 1990;korczyńska 2001;uGelviG and creMer 2007;Heinze and Wal-Ter 2010;Bos et al 2011;diez et al 2015; leclerc and deTrain 2017). The findings of Miler (2016) and Miler et al (2017b) can thus be interpreted, too, in terms of the induction of social withdrawal. If so, these findings suggest that experimental studies of ant rescue behavior may prove to be of importance for comparative research devoted to causal factors underlying social withdraw-should also be generally suited to the circumstances, and should not be inherently rewarding or beneficial to the rescuer (noWbaHari and Hollis 2010; Hollis and noWbaHari 2013a).…”

“…A series of experiments of Miler and his coworkers explored various factors influencing nestmate rescue behavior of workers of F. cinerea during bioassays with antlion larvae (Miler 2016) and artificial snares (Miler and kuszeWska 2017), and during both these types of bioassays (Miler et al 2017a(Miler et al , 2017b. These studies revealed, among others, that workers of F. cinerea with life expectancy experimentally shortened by exposure to carbon dioxide less efficiently triggered rescue behavior of their nestmates during the bioassays with antlion larvae (Miler 2016), and less readily engaged in rescue behavior in response to a nestmate entrapped in an artificial snare (Miler et al 2017b). These findings were surprising, as in ants shortened life expectancy often leads to increased readiness to engage in risky tasks (Moroń et al 2008(Moroń et al , 2012.…”