Non-transferable
signal on ant queen eggs prevents policing evasion by cue scrambling

Abstract

How biological systems resolve internal conflicts
is a major evolutionary question. Social insect
workers cooperate but also pursue individual interests,
such as laying male eggs. The rewards of this individual
selfishness can be reduced by policing, such as by killing
worker-laid eggs. However, selfish individuals may evade
policing. What factors prevent individuals from being able
to evade policing? In the ant Pachycondyla inversa,
workers kill (police) worker-laid eggs. Because the colony
keeps eggs in piles and worker-laid and queen-laid eggs are
chemically distinct, worker-laid eggs might become more
acceptable once placed in the egg pile by odour transfer
from touching queen-laid eggs. Here, we show that such
“cue scrambling” does not occur. Worker-laid eggs that
were sandwiched between three queen-laid eggs for 45 min
were not more acceptable in a policing bioassay than
control worker-laid eggs. Chemical analyses also showed
that the surface hydrocarbon profile of these eggs was
unchanged. Policing, therefore, is stable against this potential cheating mechanism probably because queen-laid eggs are made chemically distinct using chemicals that are not easily transferred by physical contact.