Conflicts of Interest in Polistes dominulus: Queen Succession after Queen Removal

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Conflicts of Interest in Polistes dominulus
Queen Succession after Queen Removal
Mark Brady, Providence College
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Topics

• Evolution Genes
• Polistes dominulus as a model system
• Methods
• Results
• Conclusions

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Evolution Genes

• Darwin recognized problem of explaining natural
  selection within species with non-reproducing
  individuals
• Hamiltons inclusive fitness hypothesis explained
  altruism as a selfish strategy for passing on
  ones genes
• Dawkins argued that the evolution is about
  passing on your genes to the next generation

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Eusocial Insects

• individuals cooperate in caring for young
• the queen dominates reproduction
• generations overlap so offspring help their
  parents

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P. dominulus as a model system

• Primitively eusocial Old World paper wasp with
  well studied nest cycle and social order
• All females can potentially reproduce
• Haplodiploid- Incentives for altruism
• 50 genes between female and offspring identical
  by descent
• 75 genes between sisters identical by descent
• only 25 genes between sister and brother
  identical, giving incentive to lay male eggs

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Haplodiploid pedigree
haploid (no allele)
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Other Factors

• Haplodiploidy does not alone explain the
  evolution of altruism in eusociality
• other eusocial diploid systems (naked mole rat
  and termites)
• inbreeding increases inclusive fitness
• ecological factors benefits against predators,
  specialization of tasks, high cost of leaving
  nest to start new nest or invade another nest,
  season not long enough start a new nest very far
  in

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Other Factors (continued)

• Female workers accept complete reproductive
  subjugation by their queen -- despite being
  completely unrelated to either her or her
  offspring (Queller 2000)
• lie and wait
• invade
• sneaky egg laying

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Conflicts of Interest

• With the death of a queen, many latent conflicts
  arise that are suppressed by the presence of a
  queen
• Who should be the next successor?
• Who should lay the male eggs?
• What should the sex ratio be?

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Big Question

• How are the conflicting genetic interests of
  separate individuals resolved so that they are
  merged into a single more successful whole?

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Hypotheses

• Upon removal of the queen from the experimental
  nests
• The successor will be one of the original queens
  daughters because she will be most related to the
  rest of the daughters (R.75)
• The sex ratio will become biased in favor of more
  males eggs because it is in every females
  genetic interest to produce males

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Hypotheses (continued)

• There will be a higher relatedness among female
  offspring than male offspring due to a greater
  interest of even full sisters in producing males
  (R .5 versus .25)
• As a cost of conflict in determining succession,
  the sizes of the experimental nests will be
  smaller than the controls

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Methods

• Field Work
• Behavioral observation to determine the queen to
  be removed and counting the number of cells and
  individuals in each nest

• Lab Work
• Dissections to determine fecundity
• Genotyping using microsatellites

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Colony cycle of Polistes dominulus in Italy
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Collection Site
Cavriglia, Italy
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Field Site
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Checkingthe Nests

• Half of the nests, considered experimental, had
  the behavioral queen removed.
• The other half was left intact and considered
  control.
• Numbers of adult wasps, brood and cells were
  recorded every three days for one month. At the
  end of that time, all the colonies and the
  associated wasps were collected.

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Reproductive statusOvarian development
Egg-laying female
Non-reproductive female
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Spermatheca
Spermatheca with Sperm 25x
Sperm ball 50x
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Genotyped samples
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Microsatellites
Pdom 122 AAT

• Thirteen trinucleotide microsatellites were used
  that ranged from 5 to 19 alleles.
• They were used to
• Estimate relatedness
• Determine sex of the brood
• Determine the mother of the male brood

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Polistes dominulus microsatelliteallele
frequencies
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Relatedness Calculation
x indexes individuals, k indexes loci and l
indexes allelic position. The variables in the
ratio are Px The frequency within the current
x individual of the allele found at xs locus k
and allelic position l. Py The frequency of
that same allele in the set of partners of x
the individual(s) to which you want to measure
xs relatedness. P The frequency of the
allele in the population at large, with all
putative relatives of x excluded.
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Relatednesses( standard errors jackknifed over
loci)
Average relatedness over colonies estimated by
Relatedness v 5.0 based on microsatellite loci
(Goodnight and Queller, 1989)
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Relatednesses( standard errors jackknifed over
loci)
Average relatedness over colonies estimated by
relatedness program (Goodnight and Queller, v 5.0)
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Number of Cells Per Nest
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Conclusions

• A full sister of the original Queen was the
  successor in the experimental nests. This is
  counter- intuitive because it suggests that the
  hierarchical structure is based more on age than
  relatedness.
• The number of male brood in the experimental nest
  increased almost twofold, as expected from the
  genetic benefit to every female of laying males.

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Conclusions (continued)

• Male egg laying in the experimental nests may be
  being monopolized by one individual, but further
  genotyping is necessary to make this
  statistically clear.
• Decrease in nest size shows the cost of conflict
  and suggests an incentive for having a mechanism
  to reduce the cost.

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Acknowledgements

• Dr. Elisabeth Arevalo, Colleen Brown, and Ruth
  Lambert (Providence College)
• Joan Strassmann and David Queller (Rice
  University) for their support in experimental
  design and in part of the lab work.
• Rita Cervo and Francesca Zacchi (Università di
  Firenze) for field assistance in Italy.
• Financial support was provided by research grants
  to EA (BIR-940643, BIR-9612687, and IBN-9900975).

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Team P.dom
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Applications for understanding more complex
systems???