In the last blog, I discussed one
of the driving mechanisms behind the evolution of socialism in hymenoptera –
kin selection. In this entry I will look at another major driving force of
socialism – maternal (or parental) manipulation.
Queens manipulate their offspring
via genetic, physiological and behavioural avenues to ensure they remain within
the colony to assist with raising their siblings (Gauld & Bolton, 1988). By
doing this individuals forfeit their own breeding potential, form worker castes
& enhance the queens reproduction potential (Gauld & Bolton, 1988). Much
like the kin selection theory – the maternal manipulation theory requires
prolonged mother-daughter relationships and overlapping generations (Gauld
& Bolton, 1988).
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| Image 1 - Yellowjacket (Vespula spp.) queen, gyne, and males. |
In order for mothers to be able
to manipulate their offspring without driving them away from the colony, the
mother needs to move from basic parental care (such as that in pre-social
wasps) into controlling the early development of her daughters so they will
remain in the colony and assist in brood care (Brian, 1983). This manipulation
may be driven by multiple factors including:
- Sex control that ensures a sterile worker caste and an exclusion of males until required (also derived from haplodiploidy)
- Moothers producing more offspring than required – a method which requires large numbers of substandard offspring to develop into a sterile worker caste through domestication – but this does not ensure that females will not leave the colony to create their own. This would require further manipulation through the development of a kin-help allele.
- The establishment of a gene which creates a sensitive phase during early development that can imprint a caste on the individual.
(Brian, 1983)
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| Image 2 - Red fire ant (Solenopsis invicta) castes and developmental stages. Worker, male, and queen (top to bottom) adult, pupa, and larva (left to right). |
Dawkins (1976) argues that even
though the Queen has unchallenged control over her juvenile offspring, there
must be some genetic symmetry otherwise the lack of any gain to the worker
would allow cheat or non-cooperation genes to spread in offspring (Brian, 1983).
Two other theories have been hypothesised
- one being polygyne families where many queens copulate but only the fittest
queens are socially selected to produce brood and the least fit individuals are
excluded after their brood is found to be inferior (Brian, 1983).
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| Image 3 - Multiple queens in a colony of big-headed ants (Pheidole megacephala) in St. Lucia, South Africa. Image courtesy of Alex Wild. |
The other is
group selection where a population is split into sections (demes) that only
come into genetic contact with each other briefly and rarely (Brian, 1983).
Within the small population of the demes there is interbreeding which allows for
random drift in allele frequency – this may lead to demes with unfavourable
alleles dying off and demes with favourable alleles surviving (Brian, 1983). While
these alleles may benefit a group they may be a disadvantage for the individual
(e.g. sterility) however it has been found that the survival of a group is a
direct function of the proportion of kin-help alleles (Brian, 1983).
It seems that none of the theories
surrounding the development of socialism in the hymenoptera are mutually exclusive
and both kin selection and maternal manipulation have been a starting points
for wasp and bee species to evolve into the complex societies we see today (Brian,
1983).
Video - Life Cycle of a Queen Honey Bee (Apis mellifera)
References:
Gould, I & Bolton, B 1988, The hymenoptera, Oxford University Press, Oxford.
Brian, MV 1983, Social Insects: ecology and behavioural
biology, Chapman and Hall, London.
Dawkins, R 1976, The selfish gene, Oxford University
Press, Oxford.
Image 1 – Yellowjacket (Vespula spp.) queen, gyne, and males on Goodisman
Research Group, viewed 11 April 2015, <http://www.goodismanlab.biology.gatech.edu/Images_for_photos/Vmac%20queen,%20gyne,%20and%20males%20in%20nest.LG.jpg>
Image 2 - Red fire ant, Solenopsis
invicta, castes and developmental stages on Goodisman Research
Group, viewed 11 April 2015, <http://www.goodismanlab.biology.gatech.edu/Images_for_photos/Fire%20Ant%20Caste%20Development.AA3.Nov%202%202010.LG.jpg>
Image 3 – Multiple queens in a
colony of Pheidole megacephala big-headed ants St. Lucia, South Africa, viewed 11 April 2015
< http://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Pheidole/i-8BHB924/2/XL/megacephala14-XL.jpg>
Video - Life Cycle of a Queen Honey
Bee, youtube, viewed 11 April 2015 <https://www.youtube.com/watch?v=aNoqN-IX5qs>
The idea of parental manipulation is really cool. Some other ways parents can manipulate offspring in other species is via coercion and punishment, as well as reproductive suppression. Do hymenopteran queens ever punish their workers / offspring? Do some species show reproductive suppression (as opposed to controlling development to drive sterility)? Fascinating.
ReplyDeleteQueens producing pheromones to suppress reproduction is believed to be widespread, it has been found in Apis mellifera and black garden ant Lasius niger. it is thought that it is due to chemicals the queen produces that differ from that of the worker - the primer pheromone 3-MeC31 is expected to be the main pheromone in social insects that drives reproduction suppression and aggressive behaviour in workers (Holman et al 2010, ‘Identification of an ant queen pheromone regulating worker sterility’, Proc. R. Soc. B).
ReplyDeleteCoercion is seen in eusocial species through “egg policing” where worker-laid eggs are killed by the queen/sisters and fertile workers are muscled into not laying. This is very effective in controlling and deterring workers from trying to rear their own offspring. If workers are spending time and energy reproducing, they are not spending those resources on working which reduces the efficiency of a social colony (Ratnieks, FLW & Helantera, H 2009, ‘The evolution of extreme altruism and inequality in insect societies’, Phil. Trans. R. Soc. B, vol. 364, pp. 3169-3179).