Anna MacDonald, Stephen Sarre and Nancy FitzSimmons

Institute for Applied Ecology University of Canberra

Sex chromosome microsatellite markers:

A new tool for macropod population ecology

•  A short DNA motif is repeated in tandem

•  Microsatellite variation is due to different numbers of repeats in different individuals

•  Each different version of the microsatellite is called an allele

What are microsatellites?

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-------GTGTGTGTGTGTGT---------

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Microsatellites as genetic markers

•  High mutation rates generate high levels of genetic variation

•  Mendelian inheritance

•  PCR-based genotyping allows amplification from small / degraded samples

----------------GTGTGTGTGTGTGTGT----------------- ----------------CACACACACACACACA-----------------

PCR primer 1

PCR primer 2

Application of microsatellites to population ecology

•  Genetic structure within a population

•  Gene flow between populations •  Mating systems

Sex chromosome microsatellites would provide different evolutionary perspectives when used in conjunction with autosomal / mitochondrial DNA

Sex chromosome microsatellites

X Y X X

X chromosome •  Diploid in females, haploid in males •  Passed from mother to son •  Effective population size 2/3 that of autosomes

Marsupial sex chromosomes

Y Chromosome •  Male-specific, passed from father to son •  Effective population size 1/4 that of autosomes

1 2 3 4 5 6 7 XX XY

Chromosome-specific microsatellites developed from tammar wallaby DNA sequences

9 X chromosome microsatellites

10 Y chromosome microsatellites

Picture courtesy of Amber Alsop

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MeY01 MeY03 MeY04 MeY06 MeY27 MeY28 MeY36 MeY37 MeY56 MeY57

Num

ber o

f alle

les

M. eugenii (n=25) M. rufrigriseus (n=10)M. giganteus (n=10) P. xanthopus (n=10)

Tammar Y chromosome microsatellites tested in other species

MacDonald et al. (2006) Molecular Ecology Notes: In press

Applying sex chromosome microsatellites to

population ecology

Sex-biased dispersal

Eriksson et al. (2006) Molecular Ecology 15: 939-949

Bonobos •  Population dynamics studied: - Y chromosome microsatellites - mtDNA sequence

•  Haplotype diversity greater for mtDNA than Y chromosome

•  Negligible male-mediated gene flow between populations

•  Low male effective population size

Population Origins / Founder Effect

Scandinavian wolves

•  1970’s: population extinct

2002 recovered: c.100 individuals •  Only two initial founders:

1 Y chromosome haplotype = 1 male ≤ 3 alleles at X chromosome microsatellites = 1 male + 1 female

•  Allele frequencies support Eastern origin of migrants

Vila et al. (2003) Proc. R. Soc. Lond. B 270: 91-97

Admixture when ranges overlap

Freeman et al (2006) Genetics: published online ahead of print

1 2 3 4 1 2 3 4

1 2 3 4 1 2 3 4

Lineage A Lineage B

Ancient admixture

1 2 3 4

Recombination event

Linked X chromosome microsatellites used in males to investigate introgression of Bos indicus into Africa

Recent admixture

X chromosome: Recombines in females: measure of admixture over time Haploid in males: haplotypes easily determined

Mating systems / Parentage analysis

Juvenile males

Potential fathers

Y chromosome loci show paternal contribution:

a single locus can exclude many potential fathers

MeY01

Conclusion

•  New microsatellite markers have been identified from the tammar wallaby X and Y chromosomes

•  These markers could be optimised for use in other macropod species

•  Sex chromosome microsatellites will bring a different evolutionary perspective to the study of macropod population ecology

Acknowledgements ARC Centre for Kangaroo Genomics Amber Alsop Terry Fletcher Jenny Graves Barbara Harriss Danielle Hickford Edda Koina Marilyn Renfree Natasha Sankovic Geoff Shaw Anne Thompson Katherine Thompson Matthew Wakefield Lee Webley Kejun Wei Kyall Zenger

University of Canberra Niccy Aitken Oliver Berry Lachlan Farrington Marion Höhn Rachel Walsh All from Applied Ecology! CSIRO Lyn Hinds University of Western

Australia Brian Chambers University of Newcastle Merrilee Harris