This document summarizes a thesis on tracking evolutionary paths during colonization events in Drosophila subobscura populations. The author studied: 1) founder effects on genetic differentiation between populations, finding early genetic drift impacts adaptation, 2) associations between genetic variability and adaptive responses, showing variability predicts evolutionary potential, and 3) the role of chromosomal inversions in adaptation, providing evidence for local adaptation within inversions. The research improves understanding of how selection and drift interact during colonization to impact genetic composition and adaptive trajectories.
1. Tracking Evolutionary
Paths in Colonizing
Events Temporal changes in life-history traits, microsatellites
and inversions in Drosophila subobscura
Josiane
SantosSupervised by
Margarida Matos and Marta Pascual
2. Colonizing Events and Adaptation
• Evolution of colonizer populations counts both with stochastic effects
due to reduction of Ne and with selection due to the new
environment
– How do selection and genetic drift interplay along adaptation to
the new colonized environment?
– What is the biological level of their action?
– How is the genetic composition of colonizer populations affected
?
– Can one predict the evolutionary consequences of colonization?
3. Genetic variability and response to selection
• Experimental evaluation of the interplay of:
effective size genetic variability
response to selection
Previously it was shown that
though there is convergence
and repeatability of
evolutionary patterns in life
history traits, some
evolutionary contingencies
affect those patterns
(Matos et al. 2000, 2002, 2004;
Simões et al. 2007, 2008a, 2008b)
4. Genetic variability and response to selection
• Genetic differentiation in molecular markers between 2
foundations from neighbouring populations was assessed in
laboratory experiments (Simões et al. 2008a)
•
FCT = 0.013
CI 95% = [0.008; 0.018]
But the experimental design did not allow disentangle
differentiation caused by origin vs. founder effects.
Sintra
Arrábida
2001
5. Genetic variability and response to selection
• What is the impact of founder effects on the evolution
following colonization?
Can one predict the evolutionary potential of populations
adapting to a new environment based on non-codifying markers?
• We need to characterize more foundations in
several generations both for temporal changes in
genetic variability of non-codifying markers and
in life-history traits
genetic variability of non-codifying markers
adaptive rate of fitness related traits
Suggestion of a
relation
(Simões et al. 2008a)
Only two foundations
Founders were not
analysed
6. Evolution of chromosomal polymorphism
after colonization
Reduce recombination
within and nearby them in
heterokaryotypes
• The role of inversions on adaptation is well documented
7. Evolution of chromosomal polymorphism
after colonization
• Why do inversions evolve after colonizing a new
environment?
Is it due to direct selective value, heterokaryotype advantage,
reduction of recombination?
Is their genetic content involved in the response to selection?
Several inversions respond to
selection during lab adaptation
(Fragata et al. 2014)
8. • Two main hypotheses focused on reduction of recombination
to explain the evolution of inversions :
– Co-adaptation hypothesis (Dobzhansky 1943, 1970)
Epistatic effects of co-adapted alleles
– Local adaptation hypothesis (Kirkpatrick and Barton 2006)
Locally adapted alleles which might have only additive
effects,
though epistasis is not excluded
Evolution of chromosomal polymorphism
after colonization
•Analysing the dynamics of inversions together
with their genetic content by real-time evolution
may give insights favouring one of the
hypotheses
9. The main aim of this thesis was to study the adaptive dynamics of
colonizing events
• To localize 72 microsatellites by FISH in the chromosomes of
Drosophila subobscura and determine position relative to inversions
(Santos et al. Chrom Res 2010)
• To disentangle causes of genetic differentiation during colonization:
origin (space and time) vs. stochastic effects at foundation (Santos et
al. J. Genet. 2013)
• To prospect for an association between the adaptive dynamics of life
history traits following colonization with both the initial genetic
molecular variability and its changes along the process (Santos et al.
JEB 2012)
• To screen for an evolutionary response of chromosomal
arrangements and of their genetic content during colonization, sorting
out effects of selection vs. genetic drift (Accepted with revisions in
JEB)
10. • FISH with digoxigenin-labelled probes
revealed to be an efficient technique for
detection of microsatellite loci on the
polytene chromosomes
• Adequate markers to identify each
chromosomal element or specific
regions within them
Microsatellite localization
FISH
Filter for Rhodamine
Filter for DAPI in BW
Overlapp using Photoshop
Useful tools to characterize genetic
variability of populations and the
genetic basis of chromosomal inversion
evolution
(Santos et al. Chrom Res 2010)
11. Founder effects cause genetic differentiation
50 Km
Sintra
Arrábida
• 9 Microsatellites
(Founders and G3)
• 2 Years
• 2 Locations
• 6 Foundations
• 2 Samples in 2005
(Santos et al. J. Genet. 2013)
12. Sampling effects at foundation were excluded
Founder effects took place during early steps o
laboratory colonization
FWAf
FWBfNARAf
NARBf
FWA1
FWA2
FWA3
FWB1
FWB2
FWB3
NARA1
NARA2
NARA3
NARB1NARB2NARB3
Axis2(39.21%ofvariationexplained)
Axis 1 (43.52% of variation explained)
Principal coordinates analysis for pairwise FST values including generation
three and the founders (2005 populations)
Founder effects cause genetic differentiation
The 6 founder populations (G0)
were not differentiated
(independent of sample, location, year)
As in 2001, all foundations were
genetically differentiated at generation
3
Fast genetic differentiation was due
to founder effects G1-G2
2005
13. Founder effects impact adaptation
Foundations show a
decoupling of genetic
variability G0-G15 and
even G0-G3
We cannot predict
molecular genetic
changes along colonizing
events from founders
9 microsatellites (Founders, G3, G15)
life-history traits (20-21Gen)
6 foundations
(Santos et al. JEB 2012)
14. Founder effects impact adaptation
Higher early variability at G3 was associated
with higher rate of adaptation
(not G0)
G3 can be used for prediction of
evolutionary potential of
populations
G0 is not a good proxy for
quantitative genetic variation of
fitness
Adaptation to the
laboratory differed across
foundations
15. Founder effects impact adaptation
Higher loss of Allelic
Richness (dA)
between G0-G3 and
G0-G15 correlates with
lower adaptive rate
Not between G3-G15
Confirms founder effects between G0-G3 play an important
role in the adaptive dynamics
This relation was mediated by effective population size
Correlations between pairwise differences in slopes of life-
history traits and variability decline in three generation
ranges (six foundations). Significance of Mantel tests is
given.
generation
range
Slopes of life-history traits
A1R F1-7 F8-12 RF Cphen
dA
G0-3 -0.60** -0.80** -0.29 0.56 -0.81*
G3-15 0.15 -0.26 -0.28 0.1 -0.12
G0-15 -0.47** -0.83** -0.38 0.54 -0.78*
dHE
G0-3 -0.73** -0.87** -0.86** 0.15 -0.46
G3-15 0.22 0.02 -0.09 0.15 0.02
G0-15 0.10 -0.32 -0.40* 0.18 -0.17
* 0.01<P-value<0.05; ** 0.001<P-value<0.01.
dA – decline in allelic richness; dHE – decline in gene diversity.
16. Chromosomal inversions play a role on
adaptation
• 1 New foundation from Sintra (3-fold replicated)
• Life-history traits (33Gen)
• Inversions (G4, G14, G28)
• 22 Microsatellites (G4 and G28)
(Santos et al. accepted with revisions JEB 2016)
Populations clearly adapted
to the laboratory following
colonization
17. *
*
** *
**
AST
A2
E1+2+9+12
OST O3+4+7
U1+2
U1+8+2
7/23 chromosomal arrangements
changed frequency consistently
along colonization, not expected
by drift alone
General maintenance
of polymorphism
Convergence to
TW
Chromosomal inversions play a role on
adaptation
19. Chromosomal inversions and adaptation
197
inside
116
outside
No LD among both
alleles within inversion
Favours Local Adaptation Hypothesis
Epistatic selection not
involved
20. Final remarks
The cytological localization of microsatellite loci is a helpful tool
for evolutionary genetic studies.
Genetic drift plays a major role on evolution following colonization
of a new environment.
Early stochastic effects during colonization of a novel
environment affect the genetic composition of populations.
There is an association between early genetic variability for non-
codifying markers and phenotypes related to fitness.
Laboratory populations do not provide a useful guide to the
properties of the wild populations from which they derive.
There is an adaptive value of inversions and their allelic
composition (not involving epistatic selection).
21. I want to thank…
To my supervisors Margarida Matos e Marta Pascual
To L. Serra, J. Balanya, E. Solé, M. R. Rose, M. Lima, B. Kellen,
M. A. Santos, A. Marques, M. Lopes-Cunha and specially to P.
Simões, I. Fragata
To CBA/cE3c
To Departament de Genêtica, Universitat de Barcelona
To FCT, Portugal:
• PhD scholarship (SFRH/BD/28498/2006)
• project POCI-PPCDT/BIA-BDE/55853/2004 (with
coparticipation of FEDER)
• project PTDC/BIA-BDE/65733/2006
To Ministerio de Ciencia y Tecnología (MCYT, Spain) and the EU
(FEDER) for project CGL2006-13423-C02-02
To Generalitat de Catalunya (Spain) for project SGR2009-636
To my Friends and Family
Thank you all!!
