Manipulation and Spite Flashcards
One individual may be ‘tricked’ or ‘coerced’ into behaving cooperatively towards another…
…what looks like altruistic cooperation is actually manipulation
there are many instances where individuals manipulate others to invest heavily in them without the donors receiving any apparent gain,
a classic example being brood parasitism where parasites exploit the parental care of their hosts. In this lecture, we will look at how parasites are able to manipulate the provisioning rules of their hosts in order to trick them into being altruistic.
Interspecific brood parasitism
has evolved independently many times in many different taxa where hosts provide care, e.g. cuckoo catfish, slave-making ants and 100 species of birds. Like the hosts of intraspecific parasites, many interspecific hosts have evolved egg recognition, and parasites have evolved egg mimicry to trick parents (see APS209 lecture on brood parasitism).
But, how do parasites subvert host defences and manipulate host provisioning rules to be altruistic towards them, often at a very substantial cost?
e.g. reed warbler parents v. cuckoo chicks (Kilner et al. 1999 Nature 397: 667-672) - Reed warbler parents integrate information from nestlings’ brightly coloured gapes and their begging calls (which indicate hunger) when deciding how often to feed their own chicks. A single cuckoo chick has a much smaller gape than a brood of reed warblers, but they compensate for this signalling deficiency by begging at a much higher rate than reed warbler chicks. Thus, cuckoos induce a high feeding rate from their foster parents by exploiting host provisioning rules that integrate visual and auditory cues. See also Tanaka & Ueda (2005) Science 308: 653 for another strategy to persuade hosts to provision a cuckoo chick at a high rate.
e.g. great-spotted cuckoos v. magpie hosts (Canestrari et al. 2014 Science 343: 1350-1352) – Cooperative interactions are inherently unstable and often lapse into exploitation when one individual takes advantage of their social partner.
In other words, there is a continuum of symbiotic associations (e.g. we saw how mutualisms may lapse into parasitism in the last lecture). This is a remarkable case where parasitism has lapsed into mutualism because the parasitic chick (which is reared alongside host chicks) actually benefits the host by producing a foul-smelling cloacal secretion that deters predators and thus increases the chance that the host brood fledges.
Brood parasites include many wonderful examples of the coevolution of host defences and parasite offences. The outcome of such evolutionary games, in terms of who wins
, the strategies employed, etc are extremely variable and illustrate the remarkable power of intra- and inter-specific conflict in generating adaptations to manipulate others to be altruistic towards them, and for resistance to the manipulative behaviour of others.
Spite is a rather neglected aspect of Hamilton’s classification of social interactions. He predicted that natural selection can also favour spiteful harming behaviour by an actor towards a recipient
. Its relative neglect is probably because the idea that harming another individual, at a cost to oneself, in order to benefit a third party seems intuitively unlikely. Indeed, it does seem to be rare in nature, so there are not lots of obvious examples of such behaviour.
Thinking in terms of Hamilton’s rule, spiteful behaviour is costly to the actor, so C is positive. It is also costly or harmful to the recipient, so B is negative. Therefore, for Hamilton’s rule to apply, i.e. for rB > C, then a negative relatedness between the actor and recipient is required.
This sounds odd, but in reality it is quite possible for this to happen because relatedness is a relative concept – i.e. the relatedness between two individuals should be measured relative to that of the population as a whole. This is often termed the geometric view of relatedness, and, formally, it means that the coefficient of relatedness, r, is defined statistically as the genetic similarity between social partners relative to the rest of the population. This is not only a theoretical position, but is also how software packages estimate r in real populations – i.e. with respect to the allelic composition of the population from which those individuals are drawn.
Taking a gene’s perspective, a gene for spiteful behaviour that harms individuals that do not possess that gene may spread through a population if that harmful effect benefits other carriers of the spiteful gene, for example, by reducing competition.
In other words, spite could be directed at non-relatives thereby benefitting relatives. This is the equivalent of altruism towards kin by harming their competitors.
e.g. Spiteful soldiers in polyembryonic parasitoid wasps (Giron et al. 2004 Nature 430: 676-679; Gardner et al. 2007 American Naturalist 169: 519-533) – The bizarre natural history of this system results in thousands of clonal female and male larvae occupying a single host moth. Some larvae (usually female) develop as a precocious sterile soldier caste and these soldiers attack other larvae within the host, preferentially directing their harmful behaviour towards males (r = 0.25) and not females (r = 1).
This is interpreted as spiteful behaviour because soldiers are sterile, their harmful behaviour is directed towards relatively distant kin (males) and it benefits close kin (females) who have reduced competition for the resources provided by the moth host.
See also:
Chemical warfare in bacteria and other possible examples in Gardner & West (2006 Current Biology16: R662-R664).
Spite is likely to be rare in nature for several reasons. Among these are, first, a spiteful act towards non-kin incurs a cost for the actor and may benefit a relative, but it may also benefit other individuals in the population to whom the actor is not related. If this is the case, the actor may derive a net cost from their spite.
Second, while an individual may be able to recognize the relatively small number of close kin in a population towards whom they should direct cooperative behaviour (for kin-selected benefits), it will generally be much harder to identify individuals with negative relatedness in the population from the many individuals that are distant relatives. Therefore, there will be a risk that spiteful behaviour is directed towards distant kin as well as individuals of negative relatedness.
