Tracking evolutionary paths

Tracking Evolutionary Paths in Colonizing EventsTemporal changes in life-history traits,

microsatellites and inversions in Drosophila subobscura

Josiane SantosSupervised by Margarida Matos and Marta Pascual

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?

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)


• Genetic differentiation in molecular markers between 2 foundations from neighbouring populations was assessed in laboratory experiments (Simões et al. 2008a)

• FCT = 0.013CI 95% = [0.008; 0.018]

But the experimental design did not allow disentangle differentiation caused by origin vs. founder effects.

SintraArrábida

2001


• 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

Evolution of chromosomal polymorphism after colonization

Reduce recombination within and nearby them in heterokaryotypes

• The role of inversions on adaptation is well documented


• 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)

• 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


• Analysing the dynamics of inversions together with their genetic content by real-time evolution may give insights favouring one of the hypotheses

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)

• 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)

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)

Sampling effects at foundation were excludedFounder effects took place during early steps of laboratory colonization

FWAf

FWBfNARAf

NARBf

FWA1

FWA2FWA3

FWB1

FWB2

FWB3

NARA1

NARA2

NARA3

NARB1NARB2NARB3

Axis

2 (3

9.21

% o

f var

iatio

n ex

plai

ned)

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

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)

Founder effects impact adaptationHigher 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

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*

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

**

** ***

AST

A2 E1+2+9+12

OST O3+4+7U1+2

U1+8+2

7/23 chromosomal arrangements changed frequency consistently along colonization, not expected by drift alone

General maintenance of polymorphismConvergence to

TW



9 frequency G4-G282 in O3+4 LD with inversion G28

Chromosomal inversions and adaptation

197inside

116outside

No LD among both alleles within

inversion

Favours Local Adaptation Hypothesis

Epistatic selection not involved

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).

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!!

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Tracking evolutionary paths