Evolution in Linanthus and Leptodactylon: Phylogenetic relationships and speciation processes

The study of evolution consists of two principal endeavors: (1) inferring the history of evolution and (2) elucidating evolutionary mechanisms. Studies of evolution should therefore involve analysis of both evolutionary patterns and processes. The Polemoniaceae are generally regarded as taxonomically complex at the generic level, and the boundaries between Linanthus and Leptodactylon have been particularly difficult to identify. In a study of evolutionary pattern, a phylogenetic analysis of matK sequences revealed that both Linanthus and Leptodactylon appear to be of para- or polyphyletic origins. However, Linanthus, Leptodactylon, Phlox, and Gymnosteris form a monophyletic lineage within the family. matK sequence data, and external lines of evidence supporting matK relationships, demonstrate the need for re-evaluation of the current taxonomy.;A reliable phylogeny for Linanthus, Leptodactylon, and their relatives allowed me to investigate processes of speciation within Linanthus and Leptodactylon. Linanthus and Leptodactylon represent prime examples of the two most significant modes of plant speciation, polyploidy and geographic divergence. In the study of polyploid speciation in Linanthus sect. Siphonella, matK sequencing revealed the maternal parents of the tetraploid species. Allozyme analysis suggested that tetrasomic inheritance operates in tetraploid Linanthus plants. Unbalanced heterozygotes and complex banding patterns were observed in tetraploid populations; no fixed heterozygosity was observed, and tetraploid populations maintain higher levels of heterozygosity than diploid populations. All of these observations are typical of autopolyploids. Geographic divergence in Leptodactylon californicum was assessed by examining allozymic, ribosomal DNA, and morphologic divergence among populations. Geographic patterns of morphologic and allozymic variation were detected. However, no ribosomal DNA variation exists. Gene flow is restricted among the populations apparently due to geographic barriers and mating system, permitting divergence of populations. Unique alleles are fixed in the most geographically isolated populations, and these populations are those that have diverged morphologically to the greatest extent. The genetic data, coupled with morphology, support a model of geographic divergence in L. californicum and provide the basis for reassignment of subspecific designations within the species.