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tomato blight

Phytophthora Speciation Lab

Hints for Instructors
Supplies for Lab
Sample results from crosses


Instructor Hints


This is a two part lab that will help students with the concept of pre-zygotic isolating mechanisms as a component of speciation.

The lab uses Phytophthora as a subject species.

PART ONE - Experimental Crosses

In the first part of the lab, students cross various species of Phytophthora to determine which are still capable of interbreeding. A phylogeny of Phytophthora is included  - students should generate expectations of which species will be more likely to cross and then compare the results of actual crosses with expectations generated from the phylogeny.

Fairly exhaustive Phytophthora bibliography (updated 2001)
http://www.btny.purdue.edu/USDA-ARS/Goodwin_lab/results/Phytoph_biblio.html

Encourage students to do some background reading (general speciation / isolating mechanisms and specific to Phytophthora) prior to the exercise.

The results of the crosses from a previous trial of this experiment are included.


PART TWO - Comparing Genetic Similarity using GenBank

The students will use GenBank to examine the genetic similarity of the various strains of Phytophthora. Students should compare the genetic similarities of the strains to the results of the experimental crosses to decide whether genetic distance is a good predictor of  mating compatability.

Ask students how the crosses that were produced in the lab might fair in nature - what additional experiments could be performed to test the suitability of these crosses to living on host species outside the lab?


Other projects could include comparing Drosophila phylogenies and genetic similarities with published accounts of  hybridization.


SUPPLIES FOR PHYTOPHTHORA LABORATORY EXERCISE


Supplies needed for experimental crosses:


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Results from data collected at 7 days after plating samples

                                               
A2 P. infestans (Mexico 6636)
mean
A2 P. infestans (Mexico 510)
mean
A1 P. infestans (Mexico)
12, 1, 8, 80, 15, 8, 104
33.6
0, 31
15.5
A1 P. infestans (The Netherlands)
0, 3, 5, 0, 18, 0, 0
3.7
0
-
A1 P. mirabilis (Mexico)
12, 41, 16, 38, 6, 5, 13, 12
17.9
19, 44, 45, 7, 21, 10, 20, 2
  21
A1 P. parasitica (North Carolina)
 0, 1, 0, 0, 2, 0
0.5
0, 0, 0
-
A1 P. drechsleri (North Carolina)
0, 0, 0, 0, 6, 0, 0
0.86
0, 0, 0, 0, 0, 0, 0
-
A1 P. cinnamomi (North Carolina)
 0, 0, 0, 2, 5, 0
1.2
0, 7, 1
2.7


Data collected at 14 days after plating samples



A2 P. infestans (Mexico 6636)
mean
A2 P. infestans (Mexico 510)
mean
A1 P. infestans (Mexico)
19, 199, 7, 15, 12, 25, 20, 38
 41.8
21, 49, 8, 15, 28, 31
 25.3
A1 P. infestans (The Netherlands)
 10, 7, 3, 0, 3, 2, 5
 4.3
 0, 12, 3, 18, 4, 0
 6.2
A1 P. mirabilis (Mexico)
 5, 4, 1, 79, 48, 14, 12, 25
 23.5
 14, 0, 28, 8, 13, 1, 54
 16.9
A1 P. parasitica (North Carolina)
 9, 0, 0, 3, 0, 0, 0, 2
 1.75
0, 0, 0, 0, 0, 0, 0
 0
A1 P. drechsleri (North Carolina)
 0, 0, 0, 0, 0, 0, 0, 0
0
 3, 0, 0, 0, 0, 0, 0
0.43
A1 P. cinnamomi (North Carolina)
 0, 0, 0, 0, 0, 0, 0, 0
0
0, 10, 0, 2, 0, 0, 0
1.7


Suggested Reading:
Coyne, J. A. and Orr, H. A. 1997. “Patterns of speciation in Drosophila” revisited. Evolution 51:295-303.

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