Population genetics of liothyrella neozelanica in breaksea sound
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Population genetics of Liothyrella neozelanica in Breaksea Sound. Erik Suring University of Otago, Dunedin, New Zealand. Marine Science 480 Research Project. Marine Gene Flow. Gene flow occurs by larval dispersal Larval life history characteristics Larval type – passive or swimming

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Population genetics of Liothyrella neozelanica in Breaksea Sound

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Population genetics of liothyrella neozelanica in breaksea sound

Population genetics ofLiothyrella neozelanicain Breaksea Sound

Erik Suring

University of Otago,

Dunedin, New Zealand

Marine Science 480

Research Project


Marine gene flow

Marine Gene Flow

  • Gene flow occurs by larval dispersal

  • Larval life history characteristics

    • Larval type – passive or swimming

    • Duration of planktonic phase

    • Settlement characteristics

    • Spawning time

  • Geographic factors

    • Past or present physical barriers to genetic exchange

    • Fiord hydrography may limit gene flow


Fiord dynamics

Fiord Dynamics

Special type of estuarine flow (Stanton and Pickard 1981)


Liothyrella neozelanica

Liothyrella neozelanica

  • Brachiopoda:Articulata:Terebratulidae

    • Reported in Fiordland as far north as Doubtful Sound

    • Found attached on overhangs

    • Aggregated distribution (Richardson 1981)

    • Lecithotrophic, brooded larvae (Chuang 1994)

    • Found at depths below 20 meters


Terebratella sanguinea

Terebratella sanguinea

  • Articulate brachiopod

    • The most common and widely ranged brachiopod in Fiordland

    • Less gregarious(Richardson 1981)

    • Attached or free-lying

    • Found between 5 and 35 meters


Sample locations

Sample Locations

  • Inner and Outer locations from Breaksea Sound

    • 32 animals from inner location

    • 27 animals from outer location

    • Collected during summer, 1999

Doubtful

Sound

Breaksea Sound

Dusky Sound


Breaksea sound

Breaksea Sound


Genetic differentiation

Genetic Differentiation

  • No genetic exchange – populations equilibrate at different allele frequencies

    • Longer and more complete isolation causes increased fixation of differences

  • Genetic markers quantify the amount of genetic variation

    • Different markers record different processes and show different scales of variation


Population questions

Population Questions

  • How much genetic variation is there in L. neozelanica?

  • Is the population structure of an inner fiord site different from an outer fiord site in Breaksea Sound?

  • Is the genetic differentiation (Fst) between inner and outer populations different between species?

  • How differently do separate genetic markers resolve genetic population structure?


Allozyme electrophoresis

Allozyme Electrophoresis

  • Indirect measure of sequence variation

    • Based on electrophoretic changes in proteins that represent allelic changes - phenotypes

    • Some loci can be affected by selection, does not register all variation

  • Technique is well documented

    • Relatively cheap and easy, though polymorphic enzyme systems can be hard to find (Parker et al. 1998)


Allozyme electrophoresis methods

Allozyme Electrophoresis Methods

  • Cellulose-acetate gels

    • Homogenize tissues

    • Add to gel

    • Run gel

    • Stain gel

  • Hexokinase (Hk)

  • Glucose-Phosphate Isomerase (Pgi)

  • Peptidase (Pep)


Amplified fragment length polymorphism aflp

Amplified Fragment Length Polymorphism (AFLP)

  • Also an indirect measure of sequence variation

    • Cut entire genome with restriction enzymes

    • Amplify cut fragments

    • Compare size and number of fragments

  • AFLP resolves finer differences than allozyme electrophoresis


Allozymes hardy weinburg equilibrium

Allozymes – Hardy-Weinburg Equilibrium


Allozymes peptidase allele frequencies

Breaksea Inner

Breaksea Outer

Allozymes – Peptidase Allele Frequencies

Allele frequencies in each group for HK and PGI were very similar


Allozymes f st

Allozymes – Fst

* p = 0.05, ** p = 0.01


F st comparisons

Fst Comparisons


Population genetics of liothyrella neozelanica in breaksea sound

AFLP

  • Bands were visible for some animals but overall the gel was underdeveloped

  • This could be remedied by

    • Using increased radioactivity

    • Using a different DNA extraction method

  • We have some of the problems have been worked out and may have useful data soon…


Heterozygosity

Heterozygosity

  • Two loci, especially peptidase, were not in Hardy-Weinburg equilibrium

    • Banding patterns may not represent allelic variation

    • Banding may have been improperly scored

    • Natural selection may favor certain alleles

    • Inbreeding

    • Small populations

    • Small sample size

  • No conclusions can be made about disequilibrium without further tests


Genetic differentiation1

Genetic Differentiation

  • There is significant population structure within Breaksea Sound in L. neozelanica.

  • Not much allozyme allelic variation (except in peptidase)

  • There are also indications that L. neozelanica may have greater within fiord population differentiation than T. sanguinea

    • Perhaps because of short planktonic phase and aggregated distribution limits gene flow


Technique comparison

Technique Comparison

  • Allozymes may evolve too slowly to be informative in this situation

    • Fiords have been inundated for less than 10,000 years (Pickrill et al. 1992)

  • AFLP may show finer genetic differentiation

  • In Lingula anatina DNA sequences have revealed genetic structure not seen with allozymes (Endo et al. 2001)


Further work

Further Work

  • Find a technique with greater resolution

    • L. neozelanica seems to have low variability

  • Analyze a greater number of sites

    • More inner and outer fiord replicates

    • More sites within the fiord

  • Make comparisons with different species

    • Species with planktotrophic larvae

    • Underway by Cecile Perrin and Gigi Ostrow


Conclusions

Conclusions

  • There is significant population structure within Breaksea Fiord

  • L. neozelanica has low allozyme variability

  • L. neozelanica may have greater within fiord differentiation than T. sanguinea

  • Further study of the interactions between the fiord environment and larval life histories is promising


Thank you

Thank you!

Gigi Ostrow

Dr. Stephen Wing

Dr. Michael Roy

Everyone else in

Marine Science


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