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?


Does biodiversity lead to more biodiversity?New species should give rise to new niches for other organisms.



Does biodiversity lead to more biodiversity?New species should give rise to new niches for other organisms.


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 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 Wasp:

Diachasma alloeum

parasitoid on all of these Rhagoletis species larvae


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



Hypothesis: Different groups of wasps may have specialized to each of these groups of flies.



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.


Determine sequences of a 21 microsatellites. 9 were useful as they showed host-related correlations.

red = hawthorngreen = appleblue = blueberryblack = snowberry


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.


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?



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


Y-Tube Olfactometer

Fruit odor in one flask. Second flask was empty.

Add wasp at red arrow.

Record wasp movement.


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?


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)?

discussion of sequential sympatric speciation across trophic levels by

Documents

apple wasps

hawthorn wasps

snowberry wasps

blueberry wasps

different groups of

thesegroups of wasps

apple trees hypothesis

different trees