Whitton, J , Olson, Teika E .
Chromosomal rearrangements are not primary barriers to gene flow in the Calycadenia paucifloracomplex(Asteraceae).
The classical theory of chromosomal speciation proposed that chromosomal rearrangements can act as primary barriers to gene flow and thus contribute directly to reproductive isolation and speciation. More recent treatments of chromosomal speciation postulate an indirect role for rearrangements in reproductive isolation, yet few empirical studies have examined patterns of gene flow in plants that exhibit chromosomal rearrangements. We studied patterns of genetic divergence among populations of known chromosomal race within the Calycadenia pauciflora complex (Asteraceae). This complex is known to include at least 12 chromosomal races that differ by a series of reciprocal translocations and pericentric inversions. We surveyed variation in 88 polymorphic RAPD markers assessed in 23 populations of the complex to evaluate patterns of divergence. Neighbor-Joining trees based on genetic distances as well as multivariate analysis of RAPD variation revealed two main clusters of populations; one primarily containing individuals with yellow ray florets and the other containing individuals with white rays. We also surveyed one population that was polymorphic for ray flower colour and detected a strong pattern of divergence between white and yellow rayed individuals. In most cases, populations did not cluster according to chromosomal race. Furthermore, in three of the nine races examined, different populations of the same race separated into each of the two distinct genetic clusters. We conclude that chromosomal rearrangements do not serve as the primary barriers to gene flow in the Calycadenia pauciflora complex, but rather that patterns of gene flow are best explained as a function of geographical isolation and flowering time differences.
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1 - University of British Columbia, Botany Department, 3529-6270 University Boulevard, Vancouver, British Columbia, V6T 1Z4, Canada
Presentation Type: Oral Paper
Date: Monday, August 15th, 2005
Time: 3:15 PM