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. 2018 Feb 14;285(1872):20172457.
doi: 10.1098/rspb.2017.2457.

Wound Treatment and Selective Help in a Termite-Hunting Ant

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Free PMC article

Wound Treatment and Selective Help in a Termite-Hunting Ant

Erik T Frank et al. Proc Biol Sci. .
Free PMC article

Abstract

Open wounds are a major health risk in animals, with species prone to injuries likely developing means to reduce these risks. We therefore analysed the behavioural response towards open wounds on the social and individual level in the termite group-hunting ant Megaponera analis During termite raids, some ants get injured by termite soldiers (biting off extremities), after the fight injured ants get carried back to the nest by nest-mates. We observed treatment of the injury by nest-mates inside the nest through intense allogrooming at the wound. Lack of treatment increased mortality from 10% to 80% within 24 h, most likely due to infections. Wound clotting occurred extraordinarily fast in untreated injured individuals, within 10 min. Furthermore, heavily injured ants (loss of five extremities) were not rescued or treated; this was regulated not by the helper but by the unresponsiveness of the injured ant. Interestingly, lightly injured ants behaved 'more injured' near nest-mates. We show organized social wound treatment in insects through a multifaceted help system focused on injured individuals. This was not only limited to selective rescuing of lightly injured individuals by carrying them back (thus reducing predation risk), but, moreover, included a differentiated treatment inside the nest.

Keywords: myrmecology; prosocial behaviour; rescue behaviour; social immunity.

Conflict of interest statement

We declare we have no competing interests.

Figures

Figure 1.
Figure 1.
Injury severity dependent help. (a) Rescue behaviour in nest-mates of M. analis to differently injured individuals. Light: lightly injured individual (two cut-off legs); heavy: heavily injured individual (five cut-off legs); broken: ant with incapacitated legs; phero: heavy injured ant coated with synthesized help pheromone (DMDS/DMTS); dummy: frozen dead ant coated with synthesized help pheromone. Positive values show clear attempts of help by picking up the ant and dropping it again (black) or carrying it back to the nest (grey). Negative values show behaviour in which the ant was disposed of (dragged away from the raiding column). Fisher's exact test for count data between neutral treatment (zero help) and the other categories for carried ants (see electronic supplementary material, table S1 for detailed statistical results); n = 20. Data for light and dummy trials from Frank et al. [3]. (b) Investigation time by nest-mates on injured individual. Dead: frozen dead ant; helped: time of investigation for ants that were helped. LMM followed by a least-square means analysis; n = 20. See electronic supplementary material, table S2 for detailed statistical results.
Figure 2.
Figure 2.
Context-specific behaviour of injured ant. Running speed of healthy and injured (−2 legs) ants depended on the presence/absence of the raiding column. Dashed line: mean returning raid column speed (2.2 cm s−1, n = 82 raids). LMM followed by a least-square means analysis; n = 20. See also electronic supplementary material, table S3 for detailed statistical results.
Figure 3.
Figure 3.
Treatment of handicapped and injured ants inside the nest. (a) Number of times wound grooming by nest-mates on injured ants (two cut-off limbs) was observed; n = 10. (b) Number of times interactions with the clinging termite by nest-mates was observed. Pulling: nest-mates were pulling on the termite. Biting: nest-mates were biting the termite (no significant difference); n = 10. GLMM followed by a least-square means analysis (see also electronic supplementary material, tables S5 and S6 for detailed statistical results).
Figure 4.
Figure 4.
Survival probability of injured ants. Kaplan–Meier cumulative survival rates of workers in isolation that received different treatments. Control: healthy ant kept on unsterile soil; sterile control: healthy ant kept on sterile soil; injured: ant with two removed limbs kept on unsterile soil; sterile injured: ant with two removed limbs kept on sterile soil; 1 h treatment: ant with two removed limbs kept in the nest for 1 h before being isolated on unsterile soil. N = 20 for all experiments. ***p < 0.001. Statistical significance tested with a mixed-effects Cox proportional hazards regression model (electronic supplementary material, table S8) followed by a post hoc least-square means analysis.

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