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Premise of research. Hybridization is a mechanism frequently invoked to account for the spectacular radiations observed in oceanic islands, but, surprisingly, there is little empirical support for its ecological role in island plant radiations. Theory predicts that hybridization should provide individuals with the phenotypic novelty required for habitat shifts, thus promoting conditions for subsequent speciation. In this article, we studied the first stages of this process using two hybridizing species of Dubautia (Asteraceae), the most diversified genus of the Hawaiian silversword radiation. Methodology. Phenotypic and habitat differentiation were investigated in two recently derived species (Dubautia arborea and Dubautia ciliolata) and a hybrid zone. Morphological trait expression and physiological trait expression under field and common garden conditions and microclimatic variation were analyzed to address the patterns of differentiation among parental species and hybrids. Pivotal results. Our analyses showed that parental species occupied contrasting habitats and represented the extremes of phenotypic variation. Conversely, hybrids displayed novel phenotypes outside parental ranges, generating a continuum of intermediate phenotypes in the study system. We also found a strong relationship between morphological and physiological variation and plant performance, which suggests that broad phenotypic variation in hybrids could be favored by the environmental heterogeneity of the hybrid zone. Conclusions. The initial expectations for the ecological role of hybridization in adaptive radiations are confirmed in this Dubautia system, in which hybrids of closely related species display novel morphological and physiological variation associated with the colonization of a new habitat. To understand the evolutionary processes creating an unusual degree of variation within particular lineages, molecular studies revealing cases of hybridization in island radiations should be complemented with ecological studies. © 2013 by The University of Chicago. All rights reserved.

The ecological, morphological, and genetic differentiation in a small clade consisting of four East Maui-endemic species of Dubautia such as D. Menziesii, D. platyphylla, D. reticulata and D. waianapanapaensis is discussed. Results show that ecological and morphological diversification has driven genetic divergence at fast evolving microsatellite loci.

Several different self-incompatibility (SI) syndromes have been previously reported from Polemoniaceae, including differences in genetic control, timing of the response, and the location of pollen tube inhibition. In order to examine the evolutionary linkage between genetic control and site of pollen tube inhibition, crossing experiments and microscopic analyses were performed on an additional species of Polemoniaceae, Ipomopsis tenuifolia. Thirteen individuals from a natural population were used for the parental crosses; three F1 full-sibling arrays were grown to maturity. Strong self-incompatibility was found in the parental population on the basis of significant differences in the percentages of seed set in self- versus outcross matings. In the F1 arrays, none of the outcrosses or backcrosses was completely incompatible, leading to a large number of mating types. On the basis of the number of mating types in the F1 arrays, self-recognition in this species must be based on full allelic matching of at least three loci. Pollen tubes were observed inside the ovary after both cross- and self-pollination using SEM and fluorescent microscopy, suggesting that self-pollination recognition takes place in the ovule, representing a late-acting SI system. The large number of different SI mechanisms reported in the Polemoniaceae suggest that this family may be particularly labile in its breeding system. [ABSTRACT FROM AUTHOR]

Many plant species have high contents of polysaccharides, polyphenols, or other secondary metabolites that can interfere with DNA extraction and purification. These contaminating compounds can lead to poor DNA yield and prevent access by modifying enzymes, such as restriction endonucleases and Taq polymerase. A number of factors, including choice of plant tissue, tissue preparation, and modifications of the extraction buffer, can help in DNA extraction for difficult plant species. This chapter presents some of the DNA extraction protocols developed for various plants.