Biology Reference
In-Depth Information
The cost (or not) of handicaps and other signals
In the previous section we showed how the honesty of a relatively cost-free signal could
be maintained by a social cost (handicap) imposed on dishonest signallers. The key
point here is that the handicap principle requires that the marginal cost of producing a
larger signal would be greater for lower quality individuals, not that the signal is costly
for all to produce. Consequently, honest handicap signals are not necessarily costly to
produce. However, it is also true that when a signal is costly, it will not necessarily be a
handicap. To illustrate this it is useful to distinguish between the efficacy and strategic
costs of signals (Guilford & Dawkins, 1991). Efficacy costs are those required to ensure
the information is reliably perceived, such as the energy required for a toad to croak or
a human to speak. Strategic costs are those required to maintain the honesty of a
handicap signal. Consequently, all forms of signal (index, handicap and common
interest) will have some efficacy costs, the importance of which will vary, whereas only
handicaps will entail strategic costs.
Other possible examples of handicap signalling are discussed in Chapter 7, in the
context of sexual selection, and Chapter 8, in the context of offspring begging for food
from their parents. This is still a very active area of research, where it has often proved
much harder to decisively distinguish between indices and handicaps in empirical
studies than in theoretical models.
Honest handicap
signals need not
be costly …
… and costly
signals are not
necessarily
handicaps
Efficacy costs …
… and strategic
costs
Common interest
Honest signalling
and common
interest
The final possible explanation for honest signalling is that the sender and receiver have
a common interest, such that there is no benefit to be had from deceiving the receiver.
The easiest way in which this can occur is if the sender and receiver are genetically
related, such that the sender gains a kin selected benefit by signalling honestly to the
receiver.
A breathtaking example of this phenomenon is provided by the waggle dance of the
honeybee (Fig. 14.14). When a foraging honeybee returns to its colony, it performs a
dance to inform the other workers in the colony where food (pollen) can be found. The
duration and the orientation of the dance provide information on both the distance and
direction of the food source. That honeybees are selected to signal this information
honestly is not surprising, because the worker gains a kin selected benefit telling other
workers where to find food: those workers will then feed to relatives of the dancer. Whilst
the waggle dance provides an example of a signal that can be explained by common
interest, it does not allow the influence of relatedness to be tested directly, as honeybees
are related and dance in all colonies. However, it has been possible to examine the
consequences of variation in relatedness with a form of signalling between bacteria
that is termed quorum sensing.
Genetic
relatedness (kin
selection) is one
way to get
common interest
Quorum sensing in bacteria
Quorum sensing is a form of between cell signalling in bacteria, used to regulate the
production of molecules which are then released into the environment to aid growth. In
many bacterial species, cells produce small diffusible signalling molecules that they
