Evolution of Wound care behaviours in ants: from amputations to antimicrobials

Animals developed different behavioural adaptations to help injured individuals. In ants

permanently injured individuals that lost an extremity are carried back to safety to allow them

to recover. In case of an infection, different behavioural strategies have evolved to combat the

pathogens. Ants often use the metapleural gland, but some genera lost this gland in their

evolutionary history. Here we compare two different behaviours to combat an infected

wound, one with the metapleural gland and one without. The ant Megaponera analis treats

infected wounds with antimicrobial compounds secreted from the metapleural gland, thereby

reducing mortality of infected ants by 90%. Further analyses of the metapleural gland

secretions of M. analis revealed over 121 chemical compounds and 41 proteins, almost half of

which have an antimicrobial effect. However, ants from the genus Camponotus do not have

this gland at their disposal. Remarkably, we observed that workers amputated the infected leg

by biting it off at its base. This behaviour halted the infection and guaranteed the survival of

the injured ant. The large phylogenetic distance between Megaponera and Camponotus and

their strikingly different natural history (Megaponera a group-hunting predator, Camponotus

a solitary foraging generalist) also suggest that wound care behaviour could be much more

widespread in social insects than previously thought. Overall, we reveal a multifaceted care

system, which not only allows to differentiate between sterile and infected wounds but also to

treat them either with antimicrobial compounds or amputation of the infected leg. Thereby

allowing M. analis and Camponotus to combat opportunistic pathogenic pressures present on

their frequently inflicted wounds with two very different strategies.