A comparative study of relatedness in the invasive wasp species Polistes dominulus

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A comparative study of relatedness in the
invasive wasp species Polistes dominulus

• Stephanie Newton
• Providence College

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Evolutionary Background

• In 1859, Darwin introduced the concepts of
  descent with modification from common ancestors,
  and survival of the fittest through natural
  selection of hereditary variations.
• Hamilton expanded upon these ideas in 1964 with
  the inclusive fitness theory, which modified
  Darwins ideas to account for social behavior in
  animals.

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Characteristics of Social Insects

• Participate in indirect reproduction
• At any time, at least two life stages are capable
  of working in the colony
• Cooperative brood care
• Reproductive division of labor

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Polistes dominulusof the order Hymenoptera

• Primitively eusocial
• High degree of parental and worker care
• No caste differentiation, yet demonstrate
  reproductive division of labor
• Distinguished by the haplodiploid genetic system
• Diploid (2n) females
• Haploid (n) males

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Haplodiploid pedigree
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Consequences of Haplodiploidy in P. dominulus

• Worker policing (Starr, 1984)
• Workers will prevent other workers from laying
  male eggs (collective worker control) when the
  relatedness of workers to the queens offspring
  is higher than to the other workers offspring
• Relatedness
• Among queen, workers, and brood
• Sex ratios

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Colony cycle of P. dominulus

• Nest started by foundress(es) fertilized at end
  of previous cycle
• Workers produced
• Reproductive males and queens are produced
• Queens hibernate, next spring start new nest

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What are microsatellites?

• Tandem repeats of DNA sequences,
• 2-6 base pairs long
• Alleles differ in number of tandem repeats
• Abundant, highly polymorphic, uniformly
  distributed throughout the genome
• Length of polymorphisms amplified with polymerase
  chain reaction (PCR)

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Why microsatellites?

• Highly polymorphic
• Can be used to estimate relatedness, determine
  sex, and determine mother of brood
• Analyzed by Autoradiography
• Radioactive 35S labeled nucleotides
• 1 size ladder per certain samples
• or Automatic Sequencer
• Flourescently labeled primers
• 1 size ladder per each individual sample

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Comparison of Sequencing Methods

• Autoradiography
• 1 size ladder per 16 samples
• Many hours needed to get results
• Faint bands hard to interpret
• Only 1 size primer can be run at a time
• Results subject to human error

• Automatic Sequencer
• Internal lane size ladder
• Gel run and results obtained in few hours
• Useful data from faint bands
• Different primer size ranges can be run together
• Computerized results

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Autoradiography
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Automatic Sequencing
Rice University, Joan Strassmanns Lab
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Focus P. dominulus in New England

• Genus is endemic to Western Europe, first
  reported in Cambridge, MA in 1981
• Determine the effect of queen removal on
  relatedness, nest size, and worker policing
• Compare nest size, foundress number, length of
  nest cycle, and genetic variability of
  microsatellites with European P. dominulus

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New England Study

• Nests in Scituate, RI
• 4 control, 4 experimental nests
• Foundresses were marked
• Colonies observed from 6/8/01-7/20/01
• Foundress behavior
• Colony growth
• Production of offspring
• Collect queens from experimental nests 6/29/01
• Extract DNA from adults, analyze microsatellites
  with autoradiography

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Physical Characteristics of Queens
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Control nest 1- New England
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Nest Size
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Average Nest Size in NEvs. Italian Nests
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Old World vs. New World
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Microsatellite primers used in this study

• We used 2 variable microsatellite primers,
  PACO3434 and Pann80, out of 13
• PACO3434 has 8 alleles, Pann80 has 14 alleles
  which have been described

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Microsatellite allele frequencies for PACO3434
NE and Italy both have 5 alleles
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Microsatellite allele frequencies for Pann80
NE has 7 alleles, while Italy has 12
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Conclusion

• A founder effect probably occurred as the species
  moved to New England, reducing variability of
  alleles
• Due to less stringent new environment, the cycle
  length was longer, and nest size was smaller
  compared to Italy
• Since nests were primarily monogynous,
  relatedness among workers was high and worker
  policing did not occur
• Experimental nests were smaller in size due to
  the disturbance of queen removal
• Although more time-consuming, autoradiography is
  more reliable than automatic sequencing when DNA
  amounts are small (such as in eggs)

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Acknowledgments

• Thanks to Dr. Elisabeth Arévalo, Dr. Joan
  Strassman, Dr. David Queller, Wendy Castle, Eva
  Toth, Tony Izzo, Melany Gomes, and George Dekki