Geography of Speciation Allopatric – Peripatric Parapatric Sympatric.
Discussion of Sequential Sympatric Speciation Across Trophic Levels by
description
Transcript of Discussion of Sequential Sympatric Speciation Across Trophic Levels by
Discussion of
Sequential Sympatric Speciation Across Trophic Levels
byAndrew A. Forbes, Thomas H.Q. Powell, Lukasz L. Stelinski, James J. Smith and
Jeffrey L. Feder
Department of Biological Sciences, University of Notre Dame
Department of Entomology and Nematology, University of Florida
Department of Entomology, Michigan State University
Science323:776-779
February 6, 2009
BIO101, Nov. 18, 2011
What’s the overall question?
What’s the overall conclusion?
What’s the overall question?
Does biodiversity lead to more biodiversity?New species should give rise to new niches for other organisms.
What’s the overall conclusion?
What’s the overall question?
Does biodiversity lead to more biodiversity?New species should give rise to new niches for other organisms.
What’s the overall conclusion?
Evidence demonstrates that the wasp Diachasma alloeum has sympatrically speciated into two new species, preying on different
groups of flies (which feed on different trees).
The Cast of Characters:
Plants:Hawthorne – small trees
native to North America and Europe
Apple Trees – small treesintroduced to North America from Europe
around 1625same Family as Hawthorn
Snowberry and Blueberrysmaller shrubs
The Cast of Characters:
The Flies:
Rhagoletis pomonella“apple maggot”larvae damages tree fruittwo distinct groups living on Hawthorne or Apple Trees
R. mendaxliving on blueberry
R. zephyrialiving on snowberry
The Cast of Characters:
The Wasp:
Diachasma alloeum
parasitoid on all of these Rhagoletis species larvae
The Cast of Characters:
Three trophic levels: Wasp
Fly
Plant
Evolutionary Changes
Two “races” of R. pomonella have emergedone (ancestral) is adapted to live on hawthorn treesone (recent) is adapted to live on apple trees
Evolutionary Changes
Two “races” of R. pomonella have emergedone (ancestral) is adapted to live on hawthorn treesone (recent) is adapted to live on apple trees
Hypothesis: Different groups of wasps may have specialized to each of these groups of flies.
Evolutionary Changes
Two “races” of R. pomonella have emergedone (ancestral) is adapted to live on hawthorn treesone (recent) is adapted to live on apple trees
Hypothesis: Different groups of wasps may have specialized to each of these groups of flies.
Are there detectable genetic differences among thesegroups of wasps?
Collect wasps Several locations Several hosts
Genetic Analyses of Wasps
Determine sequences of a mitochondrial gene and compare vs. host plants.Three distinct sequences (haplotypes) detected.
Genetic Analyses of Wasps
Determine sequences of a 21 microsatellites. 9 were useful as they showed host-related correlations.
red = hawthorngreen = appleblue = blueberryblack = snowberry
Genetic Analyses of Wasps
Alleles 196, 200 and 204 at microsatellite DA003 were exceptionally helpful.
196 was common in apple wasps (29%), blueberry wasps (18%) and snowberry wasps (26%)but absent in 385 hawthorn wasps.
Genetic Analyses of Wasps
Alleles 196, 200 and 204 at microsatellite DA003 were exceptionally helpful.
196 was common in apple wasps (29%), blueberry wasps (18%) and snowberry wasps (26%)but absent in 385 hawthorn wasps.
What’s more important:
location or host plant?
Genetic Analyses of Wasps
Genetic Analyses of Wasps
Are the genetic changes
consistent with a new wasp
species, specializing on apple-
dwelling flies?
Behavioral Analyses of Wasps
How do the wasps know what trees to go to?
Flies use volatile compounds from fruits to find the right plants.Do wasps?
Proc. Natl. Acad. Sci. USA 100:11490
Behavioral Analyses of Wasps
Y-Tube Olfactometer
Fruit odor in one flask. Second flask was empty.
Add wasp at red arrow.
Record wasp movement.
Behavioral Analyses of Wasps
Positive values indicate that the wasp was moving towards the scent.Negative values indicate that the wasp was moving away.
** P<0.01, *** P <0.001, others not statistically significant
Conclusion?
Behavioral Analyses of Wasps
Positive values indicate that the wasp was moving towards the scent.Negative values indicate that the wasp was moving away.
** P<0.01, *** P <0.001, others not statistically significant
Is this a prezygotic barrier to gene flow?
Life Histories
Typical life cycle of insects:
These flies lay eggs in fruit.
Larvae emerges and eats fruit.
Fruit falls from the tree.Larvae leaves the fruit and over- winters as pupae in soil (diapause).
Adult emerges from pupae (eclosion) in next summer.
Only one generation per year.
Adult lives only about 28 days.
Life Histories
Typical life cycle of insects:
These wasps lay eggs in fly larva.
Eggs hatch and wasp larvae eats fly pupae.
Wasp spends winter as pupae.
Emerges in summer (eclosion).
Also one generation per year.
Adults live for an average of 13 days.
Life Histories
Does eclosion timing differ with different groups of wasps?
Field-collected wasps were allowed to lay eggs in matching flies.
Chilled to 4oC for 4 months (to simulate winter).
Warmed to 21oC and daily monitored for eclosion.
Life Histories
Does eclosion timing differ with different groups of wasps?
Life Histories
Does eclosion timing differ with different groups of flies and wasps?
Life Histories
If adults live an average of 13 days, is this causing a barrier to gene flow?
Life Histories
Variation in eclosion timing may be partially explained by genotype at locus DA003
Model:
Hawthorn
Model:
HawthornApple
~300 years ago
Model:
HawthornApple
~300 years ago
~150 years ago
Model:
HawthornApple
~300 years ago
~150 years ago
Currently seeing sympatric
speciation of wasps
Model:
Currently seeing sympatric speciation of wasps.
Major evidence:
• Genetic differences in wasp populations.
• Behavioral differences that could lead to a prezygotic barrier to gene flow.
• Life history differences that could be a prezygotic barrier to gene flow.
Model:
Currently seeing sympatric speciation of wasps.
Major evidence:
• Genetic differences in wasp populations.
• Behavioral differences that could lead to a prezygotic barrier to gene flow.
• Life history differences that could be a prezygotic barrier to gene flow.
So is D. alloeum one species?
Or do we break it into two (D. alloeum-apple and D. alloeum-hawthorn)?