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A Study of Tamarix , a Invasive Desert Species or,

A Study of Tamarix , a Invasive Desert Species or, Another Juicy Hypothesis Bites the Dust Greg Wadsworth and Candace Collmer. Assumption: US Tamarix population is the result of

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A Study of Tamarix , a Invasive Desert Species or,

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  1. A Study of Tamarix, a Invasive Desert Species or, Another Juicy Hypothesis Bites the Dust Greg Wadsworth and Candace Collmer

  2. Assumption: US Tamarix population is the result of the introduction of a single plant in the 19th century. Prediction: Haplotypes of US Tamarix would be tightly clustered relative to Asia haplotypes Expected phylogeny A A U U A A A A A A A A A A

  3. Big Tree U51 A51 UA3 A3 UA1 A4 U52 UA50 A6 UA2 U50 U53 Phylogram of US and Asian haplotypes. Type A found only in Asia, type U found only in US, type UA found in both US and Asia. (Note: US haplotypes not tightly clustered)

  4. Frequency of three genotypes of Tamarix in the US and Eurasia USAsia 1/1 20.6 9.6 2/2 19.3 24.6 1/2 21.3 0

  5. The two most abdundant haplotypes in the US (1 and 2) represent two different species in Eurasia with overlapping ranges – eastern T.chiensis (2/2) and western T. ramosissima (1/1) Hypothesis: the first plant introduced into the US was a 1/2 hybrid created artificially by the ornamental industry

  6. Hypothesis: Genotype 1/2 is under positive selection is the U.S. Prediction: Frequency of 1/2 genotype in the U.S. is greaterthan the value predicted by Hardy-Weinberg equilibrium from the haplotypic frequencies

  7. i.e. If f(1) = p = 0.395 f(2) = q = 0.372 Then f(1/2) = 2pq = 2 (.395)(.372) = 0.29 = expected frequency of genotype 1/2 Observed frequency = 32/155 = 0.206

  8. Therefore, the hypothesis that genotype 1/2 is currently under positive selective pressure in the U.S. is not supported by the data

  9. US Tree Can introduction of single hybrid account for diversity of US haplotypes? Not Likely.

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