Genetic differences on a local scale

Testing Drosophila life-history in the field

Paul M. BrakefieldJan G. SevensterJacques J.M. van AlphenBas J. Zwaan

Leiden University,Institute for Biology,Sections Animal Ecology & Evolutionary Biology,The Netherlands.

Kim van der Linde

Deforestation

The beginning…... …. and the end

Habitat change: local effects

• Abiotic: microclimatic changes– Higher day temperatures– Dryer– Higher light intensity at the forest floor– ...

• Biotic– Vegetation composition and structure– Resource abundance– Species composition– ...

Research questions

• Does variation between habitats over short distances result in local adaptation in the resident populations?

• And if so, what is the relative importance of:– Genetic differences?– Environmental variation?– GxE interactions?

Where?• Panama canal zone

– Easy access– Established situation

• Two transects with each three habitats:– Forest– Intermediate– Grassland

• Distance between habitats within a transect 1-2 km• Distance between transects 10 km

Which model system?• Panamanian Drosophila

– Ecologically well studied: Sevenster (1987-1992), Krijger (1996-2000)

– Many species:30+ within Panama canal zone, 12 used in this experiment• Elimination of lucky choice• Robustness of effect

– Short generation time: 8-15 days

– Easy to collect and culture

• Three ecological relevant life-history traits– Body size– Development time– Starvation resistance

Field set-up

• Large roofed cages to work in• Small cages with fine netting for development times• Petridishes with agar and covered with fine netting for

starvation resistance• Dead flies for body size

Experiments• Collection of flies

– Maintained in open air laboratory for several generations

• Field experiment 1: expression of life-history traits in the original collection habitat– 12 species, 5941 individuals

• Field experiment 2: transplantation experiment– 4 species, 5629 individuals

• Common environment experiment: expression of life-history traits in the laboratory environment– 12 species, 15802 individuals

Starvationresistance

Overall variation

Maria transect

Summit transect

Habitat: F(2, 2921) = 9.2673, p < 0.001

Transect: F(1, 2921) = 0.41939, p = 0.52

Location (habitat*transect): F(2, 2921) = 10.569, p < 0.001

Original AND experimental habitat

Sta

rvat

ion

resi

stan

ce re

sidu

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Forest Intermediate Grassland

Field experiment 1: original environment

Conclusions

• First field experiment (original environment):– Habitat and location effect on starvation resistance– Forest populations do better then grassland populations

• Second field experiment (transplantation experiment):• Common environment experiment:

Transect 2

Forest Inter-mediate

Grass-land

Transect 1

Forest Inter-mediate

Grass-land

Experiment

Transect 2

Forest Inter-mediate

Grass-land

Transect 1

Forest Inter-mediate

Grass-land

Stocks

Field experiment 2: transplantation

Degree of SS Freedom MS F p

Intercept .0673 1 .067 .330 0.56Transect 1.3706 1 1.370 6.730 0.01Origin (OR) .8766 2 .438 2.152 0.12Experimental (EX) 26.9426 2 13.471 66.157 <0.001Transect*OR 3.4590 2 1.729 8.493 <0.001Transect*EX 1.1549 2 .577 2.835 0.06OR*EX 8.6395 4 2.159 10.607 <0.001Transect*OR*EX 7.3454 4 1.836 9.018 <0.001Error 593.5638 2915 0.203

Degree of SS Freedom MS F p

Intercept .0673 1 .067 .330 0.56Transect 1.3706 1 1.370 6.730 0.01Origin (OR) .8766 2 .438 2.152 0.12Experimental (EX) 26.9426 2 13.471 66.157 <0.001Transect*OR 3.4590 2 1.729 8.493 <0.001Transect*EX 1.1549 2 .577 2.835 0.06OR*EX 8.6395 4 2.159 10.607 <0.001Transect*OR*EX 7.3454 4 1.836 9.018 <0.001Error 593.5638 2915 0.203

Field experiment 2: transplantation

Original versus experimental habitat

MariaEugenia

SummitGardens

Experimental habitat

-0.3

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0.0

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ForestIntermediate

Grassland

Original habitat

Sta

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ForestIntermediate

Grassland

Field experiment 2: transplantation

Subdivision into components

Genetic: 9 %Environmental: 58 %GxE interactions: 33 %

Field experiment 2: transplantation

Summary of conclusions• First field experiment (original environment):

– Habitat and location effect on starvation resistance– Forest populations do better then grassland populations

• Second field experiment (transplantation):– Strong environmental impact– Original by experimental location effect indicates gxe

interaction for 4 species at population level• Common environment experiment:

Overall variationCommon environment experiment

MariaEugenia

SummitGardens

Habitat: F(2, 9040) = 10.872, p < 0.001

Transect: F(1, 9040) = 25.092, p < 0.001

Location (habitat*transect): F(2, 9040) = 2.5096, p = 0.08

Original habitat

Sta

rbat

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resi

stan

ce re

sidu

als

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0.00

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Forest Intermediate Grassland

Summary of conclusions• First field experiment (original environment):

– Habitat and location effect on starvation resistance– Forest populations do better then grassland populations

• Second field experiment (transplantation):– Strong environmental impact– Original by experimental location effect indicates GxE interaction for 4

species at population level

• Common environment experiment:– Habitat and location related genetic differences– Grassland population are better adapted to stress

Variation in thefield?

Variation in thelaboratory?

GeneticEnvironmentalGxE

Body size Yes, butinconsistent

Yes, andconsistent atlocation level

32.7%35.8 %31.4 %

Developmenttime

Yes, andconsistent atlocation level

Yes, andconsistent atlocation level

19.8 %40.9 %39.4 %

Starvationresistance

Yes, andconsistent athabitat level

Yes, andconsistent athabitat level

9.0 %58.0 %33.0 %

Variation in thefield?

Variation in thelaboratory?

GeneticEnvironmentalGxE

Body size Yes, butinconsistent

Yes, andconsistent atlocation level

32.7%35.8 %31.4 %

Developmenttime

Yes, andconsistent atlocation level

Yes, andconsistent atlocation level

19.8 %40.9 %39.4 %

Starvationresistance

Yes, andconsistent athabitat level

Yes, andconsistent athabitat level

9.0 %58.0 %33.0 %

Comparison with other traits

Final conclusions

• Local adaptation does take place

• The results are robust and are duplicated between species

• Extensive GxE interaction present in all three traits

• Extrapolating the results from one common environment to general conclusions about the field is tricky

Questions?

• van der linde, K. 2003. Testing Drosophila life-history theory in the field: local adaptation in body size, development time and starvation resistance. Ph.D.-Thesis. Leiden university, Leiden