Biology Reference
In-Depth Information
Worker policing in the honeybee
Francis Ratnieks and Kirk Visscher studied conflict over who should produce males in
the honeybee,
Apis mellifera
. The possibility for this conflict arises in many species of
ants, bees and wasps because whilst workers never mate they are able to lay unfertilized
eggs which, being haploid, develop into males (drones). On the basis of genetic
relatedness, it is possible to calculate, all other things being equal, which colony
members would benefit from worker egg laying. Let us look at the benefits for the queen,
the worker that lays an egg and the other workers.
In the honeybee, queens mate multiply with 10-20 males during their nuptial flight.
If we assume that offspring are half-siblings, who only share genes through their
mother, the relatedness coefficients in Box 13.2 show that:
(1)
The queen would prefer her sons to her grandsons (the sons of the workers/her
daughters) (
r
Workers would
rather rear their
own sons, than
those of the
queen
0.25).
(2)
The laying worker would prefer her sons to her brothers (the sons of the queen)
(
r
=
0.5 >
r
=
0.25).
(3)
Other workers would prefer their brothers (the sons of the queen) to their nephews
(the sons of other workers) (
r
=
0.5 >
r
=
0.125) [remember that multiple mating
reduces the relatedness between sisters from 0.75 to 0.375].
=
0.25 >
r
=
When a queen
mates multiply,
workers would
rather rear the
queen's sons,
than those of
their sisters
These analyses show that, queens are expected to try and suppress worker reproduction
(result 1). However, the more interesting result is that while workers can be favoured to
produce sons (result 2), other workers will be selected to suppress this reproduction (result
3) (Woyciechowski & Lomnicki, 1987; Ratnieks, 1988).
Ratnieks and Visscher (1989) showed that such 'worker policing' occurs in the
honeybee. They experimentally introduced male eggs that had been laid by either the
queen or a worker into colonies and found that while the worker-laid eggs were quickly
removed and eaten, the majority of the queen-laid eggs were not (Fig.13.14). The
possibility that the queen was responsible for this removal was excluded because
Ratnieks and Visscher placed a wire mesh around the combs with their introduced
eggs - the workers could pass through but not the larger queens. It is not known how
workers determine whether an egg has been laid by the queen or another worker,
although it is probably a chemical cue on the queen laid eggs (Martin
et al
., 2005).
Worker policing provides an explanation for worker laid eggs being very rare (<0.1% of
males) in species such as the honeybee - although workers can and do lay eggs, they are
destroyed by other workers. More generally, worker policing in the honeybee was
predicted before it was observed, so this provides a nice example of how theory can lead
to the discovery of new, amazing natural history.
A further prediction that follows from kin selection theory is that worker policing is
not predicted when a queen only mates once. In this case, using the relatedness
coefficients given in Table 13.1, whilst results (1) and (2) from above still hold, result (3)
does not. The reason for this is that the workers will now be full sisters, related by
r
In honeybees,
workers remove
or 'police' the
eggs laid by other
workers
0.75, meaning that a worker would prefer the sons of the other workers (nephews)
to the sons of the queen (brothers) (
r
=
0.25). Consequently, if the queen
only mates once workers are not expected to police the sons produced by other workers.
=
0.375 >
r
=
