North American populations of

Entoleuca mammata

are genetically more variable than populations in Europe

Introduction

•

What is E. mammata?

• A damaging pathogen in

Populus tremuloides

,

P. grandidentata

in North America, and

Populus alba, P.trichocarpa, P.tremula

and the hybrid aspen in Europe • Major cause of aspen death http://www.glfc.cfs.nrcan.gc.ca/treedisease/photos/Pg%2052-c.JPG

Locations •

NA locations:

• North-east, Great Lakes region, North-western prairies • Noticeably absent in Rocky mountains, Alaska (abundance of aspens?) • Thought to be restricted to NA •

EU locations:

• Noticed in France(1975) • Isolated regions in the French Alps • 2 races of

P. tremula,

mountains and plains • No serious outbreaks • Coexistance? Coevolution?

Objective and Hypothesis

• Objective: to investigate relationship btw NA and EU • Hypothesis: • 1) NA and EU are conspecific • 2) Fungus was introduced btw continents resulting in both founder and bottleneck effect • To prove: • 1) should have identical alleles and no phylogenetic grouping according to geographic origin. • 2) measure genetic variability btw continents

Materials and Methods

• Samples from both EU and NA collected • 63 samples collected to analyze • Wood surface sterilized and incubated • Isolates incubated • Ascospore isolations • Most isolations of hyphae from canker margins http://www.na.fs.fed.us/spfo/pubs/fidls/hypoxylon/hypox_fig1.jpg

http://www.forestpathology.org/hypoxylo.gif

Hypothesis of Conspecificity

• Alleles determined by sequencing= • Several identical alleles • Consensus trees, phenograms, bootstrap programs, and calculations= • Lack of phlyogenetic grouping of alleles • Therefore species conspecific

Direction of Introduction

• Introduced continent = lower genetic diversity • Nei’s, Chao-estimates, rarefaction curves • EU lower diversity than NA • NA had unique genotypes • EU had identical genotypes • Therefore, • NA→EU

Testing introduction hypothesis

• Measured genetic differentiation • Founder effect→ Fst and Gst calculated • High Fst= low gene flow • Low Fst= high gene flow (high differentiation) • Gst close to 0= variation within population • Gst close to = populations different • Results • Fst=0.193 (low) • Gst= 0.160 (low) • Therefore, high differentiation

within

population http://www.umbc.edu/bioclass/biol100/powerpoints/lecture10/img032.jpg

Bottleneck effect?

• Bottleneck effect • Population reduced by atleast 50% • New mutations in a small population • Should of produced unique alleles • Reduce NA and EU identical alleles • No unique EU alleles • Therefore, no bottleneck effect • Introduction effect favoured http://www.uri.edu/artsci/bio/twombly/BIO113/images/drift2a.jpg

Possible introduction events?

• Wide variety of hosts • Carried by humans • Long-distance air dispersal • Insects and birds http://www.rspb.org.uk/Images/great%20spotted%20 woodpecker%20on%20tree%20stump%20180_tcm3 27242.jpg

http://www.canadianbiodiversity.mcgill.ca/english/sp ecies/insects/agromyzidae.jpg

Summary

•

E. Mammata

• Conspecific between NA and EU • Native to NA • Introduced to EU • Founder effect