(Phys.org, 19, Aug 2013) - Manipulation is often thought of
as morally repugnant, but it might be responsible for the evolutionary origins
of some helpful or altruistic behaviour, according to a new study.
Journal article: Evolution of manipulated behavior (apologies, article not live at time of publishing)
In evolutionary biology, manipulation occurs when an
individual, the manipulator, alters the behaviour of another individual in ways
that is beneficial to the manipulator but may be detrimental to the manipulated
individual. Manipulation not only occurs in humans and animals but also at the
cellular level, such as among cells in a multicellular organism, or in
parasites, which can alter the behaviour of their hosts.
Consider the case of the parasitic roundworm (Myrmeconema neotropicum), which once
ingested by the tropical ant (Cephalotes
atratus) in Central and South America, causes the ant to grow a bright red
abdomen, mimicking berries. This bright abdomen constitutes a phenotype
manipulated by the roundworm. Birds eat the "berries," or infected
ants, and then spread the parasite in their droppings, which are subsequently
collected by foraging Cephalotes atratus and fed to their larva, and the cycle
of manipulated behaviour begins anew.
In the study published this week in the journal American
Naturalist, the researchers developed a mathematical model for the evolution of
manipulated behaviour and applied it to maternal manipulation in eusocial
organisms, such as ants, wasps, and bees, which form colonies with reproductive
queens and sterile workers. In the model, mothers produce two broods, and they
manipulate the first-brood offspring to stay in the maternal site and help
raise the second brood.
Mothers can do this by disrupting the offspring's
development in some way, for example through poor feeding or aggressive behaviour.
Manipulated offspring of the first-brood stay and help to raise the second
brood. Alternatively, first-brood offspring can resist manipulation and leave.
The researchers show that an offspring's resistance to
manipulation may often fail to evolve, if the costs of resistance are high. In
a sense, then, helping or altruistic behaviour is coerced through manipulation.
"The evidence in so-called primitive eusociality, where
helping is often coerced through aggression or differential feeding, appears
consistent with these results," said lead author Mauricio Gonzalez-Forero,
who conducted the study while a graduate research assistant at the National
Institute for Mathematical and Biological Synthesis.