Biology Reference
In-Depth Information
30
Fig. 11.11
Attack rates and
relatedness in the
polyembryonic
wasp
C. floridanum
.
Giron
et al
. (2004).
Photograph of a
female parasitizing
a
Trichoplusia ni
egg. Photo © Paul
Ode.
25
20
15
10
5
0
Sisters
(r ~1)
Brothers
(r ~ 0.25)
Unrelated
females
(r ~ 0)
Unrelated
males
(r ~ 0)
Morphotype of prey
Soldiers
preferentially
attack larvae to
which they are
relatively less
related
wasp larvae. Giron
et al
. labelled the introduced larvae with a fluorescent tracer
and assessed the rate at which they were attacked, measuring how many of the
resident soldiers ingested labelled larval tissue. As predicted they found that the
soldiers were more likely to attack larvae to which they are less related (Fig. 11.11).
In a follow up study, Giron and Strand (2004) showed that the cue used for kin
discrimination is the extraembryonic membrane surrounding each larva during its
development in the caterpillar host. In a series of extremely elegant experiments,
they showed that attack rates correlated negatively with kinship when the membrane
was present, but not when the membrane was removed. In addition, by transplanting
membranes between larvae they were able to fool the soldiers, whose attack rates
correlated negatively with their relatedness to the membrane donor but not with the
larva encased inside.
(3)
There is strong competition for local resources, and considerable variation in relatedness,
such that substantially closer relatives can benefit from the harming of others
. The limited
resources provided by a moth caterpillar only allow a fraction of the wasp larvae to
complete development and emerge as adults. This leads to intense competition for
resources among the larvae within the host, which can be reduced by the killing
behaviour of the soldiers. However, it is also key that the relatedness of those that
benefit from this killing is sufficiently different from those killed. This occurs with
these wasps because, by killing brothers, the soldiers free up resources for clonal
sisters, to whom they are more closely related.
The membrane
surrounding each
larvae is the cue
for relatedness
The soldiers are
closely related to
the larvae that
benefit from
reduced
competition than
they are to those
killed
Chemical warfare in bacteria
Another example of spiteful behaviour is provided by the antagonistic interactions
between different strains of bacteria. Many bacteria produce anti-microbial compounds
that are termed bacteriocins, which are lethal to members of the same species unless
they carry an immunity gene which encodes a factor that deactivates the bacteriocin.
