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A Study of Tamarix , a Invasive Desert Species or,

This study by Greg Wadsworth and Candace Collmer explores the genetic diversity of Tamarix, an invasive desert species. By examining haplotypes and genotypes from the US and Asia, the study challenges assumptions about the origins and evolution of Tamarix populations. The analysis reveals unexpected patterns that raise questions about the introduction and spread of Tamarix species in different regions. The researchers investigate the hypothesis that a single hybrid plant introduced in the 19th century can account for the diversity of Tamarix haplotypes in the US. Through genetic analyses, the study dissects haplotype frequencies, genotype selections, and the potential impact of artificial hybridization in shaping the genetic landscape of Tamarix populations.

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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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