Genetic specificity of invasive species 1'

1
Genetic specificity of invasive species 1.

• Invasive species experience
• a colonization phase (small population size)
• an invasion phase (rapid growth and colonization
  of new habitats)

What are the genetic consequences of these
demographic particularities? Can we detect
demographic events using molecular data? Can we
retrace the history of an invasion from molecular
data?
2
Genetic drift
Binomial sampling (2N, pt)
?
gamete pool
3
Time to fixation increases with population size
Variance in allelic frequency
Mean time to fixation
It takes on average 4N generations for an allele
that appeared from mutation to go to fixation
4
The founder events (genetic bottlenecks)
Most of the genetic diversity is lost by drift
during the bottleneck. If a species experiences
several independent founder events, the genetic
compositions of newly founded populations might
differ.
5
Linkage (gametic) disequilibrium
2 genes, 2 alleles per genes 4 possible types
of gamete
during a bottleneck, some combinations might be
lost
A statistical association between alleles is
then created. If a species experiences several
independent founder events, the statistical
associations might differ between the different
newly founded populations.
6
Linkage (gametic) disequilibrium
Within a population, D decreases with time, the
rate of decrease depending on the rate of
recombination between loci.
7
Post-glacial recolonization of Europe by Quercus
spp.
8
Post-glacial recolonization of Europe by Quercus
spp.
9
Invasion of America by Bromus tectorum
Novack, S. J., R. N. Mack, and P. S. Soltis.
1993. Genetic variation in Bromus tectorum
(Poaceae) introduction dynamics in North
America. Canadian Journal of Botany 711441-1448.
10
Another way of looking at Genetic drift the
coalescence theory
Time of coalescence (T)
11
Time of coalescence increases with population size
When k is large, E(T)?4N
12
Coalescent tree and the detection of rapid
population growth
A star like coalescent tree indicates recent
and rapid population growth rate (i.e. recent
colonization?)
Slatkin, M. Hudson, R. 1991 Pairwise
comparisons of mitochondrial DNA sequences in
stable and exponentially growing populations.
Genetics 129, 555-562
13
Coalescent tree and the detection of rapid
population growth (a case study Birgus latro)
Lavery, S., Moritz, C. Fielder, D. R. 1996
Genetic patterns suggest exponential growth in a
declining species. Mol. Biol. Evol. 13, 1106-1113.
14
Quantifying genetic differentiation
p 0.5, HT 0.5, FST 0
p 0.5 , HT 0.5, FST 1
FST in a metapopulation is determined in part by
gene flow between populations. In an island model
at equilibrium