Transcript Changing habitats, changing populations?

Changing habitats,
changing populations?
Life-history evolution of coexisting
Drosophila species in a heterogeneous
environment.
Paul Brakefield
Jan Sevenster
Bas Zwaan
Kim van der Linde
Institute for Evolutionary and Ecological Sciences,
Section Animal Ecology and Section Evolutionary Biology,
Leiden University,
Leiden, The Netherlands.
Life cycle of a Drosophila
Between 9 and 15 days.
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Up to >30 days.
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A life history trade-off and community
structure in variable environments.
• The availability of a certain resource in the environment varies through
the year.
• Species differ in life-history.
• A short development time is an advantage when fruit is abundant.
• A good starvation resistance (survival time under food stress) is an
advantage when fruit is scarce.
• A trade-off between development time and starvation resistance allow
different species to have a competitive advantage during different times
of the year!
Sevenster JG & van Alphen JJM (1993) Lecture notes in Biomatics 98: 155-172.
Sevenster JG & van Alphen JJM (1993) Journal of Animal Ecology 62: 720-736.
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Graphical representation
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48
44
40
36
32
28
24
20
16
12
8
4
0
Fruit abundance
Fast species
Slow species
Weeks
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Philippines 1994
• Are there differences between habitats?
• Does the habitat shape the realized trade-off between the traits?
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Different habitats
• Habitats differ in year round breeding substrate availability.
• Local populations are likely to adapt to those differences.
• Expected result is that populations of the same species from different
habitats will show differences in the life-history traits.
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Methods
• Collecting flies from four habitats: secondary forest, forest edge,
kaingin (slash and burn agriculture) and grassland: P generation.
• Bring them to the common environment of the lab: F1 generation.
• Measuring development time and starvation resistance: F2 generation.
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Starvation resistances
3.5
Starvation resistance (days)
3
2.5
2
1.5
1
0.5
0
D. ananassae
D. atripex
1.98
1.27
2.2
1.9
2.45
2.05
Forest edge
Grassland
Kaingin
Secondary forest
D. bipectinata
D. eugracilis
1.5
2.68
D.
D. malerkotliana pseudoananass
ae
1.92
1.42
2.25
2.08
D. sulfurigaster
D. takahashii
3.18
2.29
2.91
1.9
2.56
1.84
2.04
2.79
1.83
Species
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Development times
11.50
11.00
10.50
Average dev. time (days)
10.00
9.50
9.00
8.50
8.00
7.50
7.00
D. ananassae
D. atripex
Grassland
9.74
11.01
8.44
Kaingin
8.97
8.67
8.23
Forest edge
Secondary forest
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D. bipectinata
D. eugracilis
9.50
8.69
8.21
D.
D. malerkotliana pseudoananass
ae
9.59
9.61
8.50
D. takahashii
9.94
8.53
9.75
8.72
8.83
8.51
8.29
Changing habitats, changing
populations?
D. sulfurigaster
10.08
8.50
9
3000
25
89
26
65
Monte-carlo
simulation
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15
12
18
2000
Frequency
Observed value
2500
1500
0
3
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3
47
23
1
31
500
7
79
0
1000
5
7
9 11 13 15 17 19
Combined measure of concordance
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Pilot experiment
(Philippines, 1994)
Conclusions:
– There is variation between habitats in both traits for several
species.
– Concordant effect of habitat on development time (8 species,
monte carlo simulation, p=.028).
– Variation has the same pattern for all (7) species of the Sophophora
subgenus (p=.0012).
– No effect on starvation time (p=1.0).
– Effect of the environment on the expression of development time
and starvation resistance unknown.
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Questions?
• How are life-history traits expressed under natural circumstances?
• Are there genetic correlations that can pose a barrier to ecological
optimisation?
• How do ecological and genetic aspects of life-history variation among
and within species relate to properties of the natural habitats?
• Evaluate theory on the relationship between life-history trade-offs and
coexistence and community structure in heterogeneous environments.
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Common environment versus real
environment
.
10.5
10
9.5
Development time
9
8.5
8
7.5
7
1
2
3
4
Habitat (random)
Observ ed v alues
Smoothening effect
Amplified effect
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Panama 1998
1
2
3
4
Expression of life-history traits in the original habitat
Transplantation experiment, offspring of many females
Transplantation experiment, offspring of a single female
Common environment in the lab in Leiden
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Unfortunately, the results are not
yet available.
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Genetic correlation's in D. melanogaster
Development time
+
0
+
0
Body size
0
±
Longevity
+
+
Starvaton resistance / fat content
Source: Zwaan, BJ (1993) Genetical and environmental aspects of aging in Drosophila
melanogaster. Ph.D. thesis, Groningen
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