Biology Reference
In-Depth Information
It is not known why some larvae are discriminators and some not. Perhaps under
some conditions, such as harsher competition for resources, or when there is a lack of
non-relatives, it could pay to eat kin.
Spite
Bill Hamilton (1970) pointed out that Hamilton's rule, whilst explaining altruism, also
has a more sinister interpretation, because it shows how natural selection can favour
spiteful harming behaviours, which are costly to both the actor and recipient (Box 11.1).
In terms of Hamilton's rule, this means that
C
is positive (the behaviour is costly to the
actor),
B
is negative (the behaviour is costly or harmful to the recipient). Consequently,
for
rB
−
C
Spite: cost to
others, cost to
actor
0 to occur, a negative relatedness (
r
) is required. Negative relatedness may
seem like a bizarre concept, but it simply means that the recipient of a particular
behaviour is less related to the actor than an average member of the population
(Box 11.5).
To consider how spite can be favoured, it is useful to take a gene's eye view and
consider a gene that will lead to a costly harming behaviour being directed at
individuals who do not have this gene. If this harming of individuals who do not carry
the spiteful gene frees up resources or reduces competition in a way that benefits other
carriers of the spiteful gene, then this gene can spread. One way of conceptualizing
this is that spite is favoured when it can be directed at non-relatives, and that this
harming of the non-relatives frees up resources (or reduces competition) for relatives
of the actor. Spite can, therefore, also be thought of as altruism towards a secondary
recipient or recipients - harming an individual can be favoured if this provides a
benefit to a closer relatives (Fig. 11.10). The key thing here is relative relatedness, as
what is required is that the actor is more closely related to the secondary recipient who
benefits from the reduced competition than it is to the individual that it actually harms
(primary recipient).
It has long been assumed that spite did not occur in the natural world, because it
would be hard to obtain situations where harming an individual is the most efficient
way of helping another individual. While several possible examples of spite had been
given, these were all much more easily explained as selfish behaviours which provide a
benefit to the actor in the long term (Table 11.3). For example, birds can engage in
aggressive encounters with other individuals over territories. While this aggression
may appear costly to the actor, this is only in the short term, and can be explained
through the longer-term direct benefits of reducing competition for resources.
Consequently, such behaviours are selfish not spiteful. However, it has recently been
discovered that spite does occur in the real world.
>
For spite to
evolve, a negative
relatedness is
required
Spite as secondary
altruism
Many behaviours
that were thought
to be spiteful
actually provide a
direct benefit in
the long term,
and so are selfish
Murderous soldiers in polyembryonic parsitoid wasps
Mike Strand and colleagues studied the parasitoid wasp
Copidosoma floridanum
, which
lays its eggs into the eggs of moths. The wasp larvae then develop within the moth
caterpillar, consuming it from the inside as it grows. It is often the case that a female will
lay two eggs in a host, one male and one female. Each of these eggs divides asexually to
produce thousands of larvae, leading to the situation where a caterpillar will contain a
