CLARK, CURTIS. Biological Sciences Department, California State Polytechnic University, Pomona, CA 91768. - The phylogeny of Encelia (Asteraceae: Heliantheae).

Encelia consists of nineteen species and subspecies of arid western North and South America. Cladistic methods were applied to information from gross morphology, micromorphology, and phytochemistry to derive a cladogram for the group. The genus is diagnosed by rounded shoulders of the achene converging on a narrowed apical notch. Encelia nutans, generally treated as an Enceliopsis, shares only that feature with the rest of the genus. The remaining taxa form two clades. One is diagnosed by UV-reflecting ray corollas, a unique benzofuran-benzopyran dimer, and the presence of moniliform trichomes. The color of the disk corollas and stigmas, morphology of leaf trichomes, and disposition of the capitula establish kinship within the clade. The other is diagnosed by erect fruiting heads and the absence of resin ducts and their associated secondary metabolites. Within this clade, the presence of broad-based trichomes and the absence of all benzopyrans and benzofurans are additional apomorphies. Three species are of hybrid origin, one involving a parent from each of the two clades. The resulting cladogram provides insight into the evolution and ecology of the genus.

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CLARK, CURTIS. Biological Sciences, California State Polytechnic University, Pomona CA 91768. - A phylogenetic view of climatic tolerance in the Encelia alliance (Asteraceae: Heliantheae).

Cumulative monthly and annual precipitation and mean temperature were obtained from climatic reporting stations within the ranges of all the species of Encelia, Enceliopsis, and Geraea, which together constitute a monophyletic group. From these I calculated mean annual temperature, a measure of the warmth of climate, mean annual range of temperature, which distinguishes continental from oceanic climates, and total precipitation for winter, spring, fall, and summer, to distinguish seasonal differences. Outgroup comparison suggests that the ancestral climatic regime for the alliance was continental, with winter temperatures below freezing, and a primary rainy season in the summer. In all three genera there has been a trend toward drier climates with much less summer rain. Within Encelia, the E. californica clade shows a tendency toward oceanic climates, and the E. frutescens clade toward continental. The understanding of climatic tolerances afforded by this study will allow prediction of the distribution of these species in the recent past by comparison with vegetation from woodrat middens.

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The Encelia alliance consists of the genera Encelia, Enceliopsis, and Geraea. A previous cladogram based on 21 phenotypic characters showed the latter two genera to be sister taxa, and supported two major clades within Encelia. Cladograms derived from sequences of the internal transcribed spacers (ITS) of rDNA support these major groupings, but differ from the phenotypic cladogram in the arrangements within the groups. Some characters that are congruent homologies in the phenotypic cladogram appear homoplastic on ITS cladograms. Because of tautology, character evolution cannot be studied in the context of phylogenies that are based in part on the character in question. Consideration of all the phenotypic characters in the context of a phylogeny based on ITS alone avoids tautology, but throws away phylogenetically useful features. However, removing one phenotypic character at a time from a combined analysis often yields cladograms with different topologies. A consensus cladogram of all these analyses provides a framework for studying character evolution. Another approach involves calculating for each node of the shortest tree based on all characters (phenotypic and ITS) the percentage of the analyses with one phenotypic character removed that include that node (this is similar to the ubiquitous bootstrap analysis, but is a jackknife technique). Although the preferred outcome will involve sequences of additional DNA regions, the techniques outlined here provide a method for studying character evolution without discarding data.

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Most well-documented cases of homoploid hybrid speciation follow the recombinational model, in which the new species passes through a period of genetic rearrangement and reduced fertility. An alternate model has been presented, in which external barriers to gene flow prevent genetic swamping of the new species by the parent species. The two documented cases of hybrid speciation in Encelia (E. virginensis and E. asperifolia) appear to follow this model. In both cases, the species of hybrid origin are generally intermediate to the parents, and E. virginensis is also similar to artificial F1 hybrids. In both cases, the species of hybrid origin share random amplified polymorphic DNA (RAPD) markers with each of the parent species. A single sampled individual of each species of hybrid origin shares the nrDNA internal transcribed spacer (ITS) sequence of one of the parents. All North American Encelia species are obligate outcrossers with n = 18 chromosomes, and in cultivation they form fertile hybrids apparently in all combinations. In the natural environment, plants of F1 phenotype are locally common, but backcross progeny are rare, being confined primarily to areas of human disturbance, and there is no evidence of introgression. Progeny tests in one case of natural hybridization suggested that backcross progeny are eliminated after seed dispersal. This suggests that the F1 phenotype represents a "local optimum" on the selective landscape, and that the selection against backcrosses strongly reduces gene flow between the incipient hybrid species and the parents.

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Most well-documented cases of homoploid hybrid speciation follow the recombinational model, in which the new species passes through a period of genetic rearrangement and reduced fertility. An alternate model has been presented, in which external barriers to gene flow prevent genetic swamping of the new species by the parent species. The two documented cases of hybrid speciation in Encelia (E. virginensis and E. asperifolia) appear to follow this model. In both cases, the species of hybrid origin are morphologically intermediate to the parents, and E. virginensis is also similar to artificial F1 hybrids. In both cases, the species of hybrid origin share random amplified polymorphic DNA (RAPD) markers with each of the parent species. A single sampled individual of each species of hybrid origin shares the nrDNA internal transcribed spacer (ITS) sequence of one of the parents. All North American Encelia species are obligate outcrossers with n = 18 chromosomes, and in cultivation they form fertile hybrids apparently in all combinations. In the natural environment, plants of F1 phenotype are locally common, but backcross progeny are rare, being confined primarily to areas of human disturbance, and there is no evidence of introgression. Progeny tests in one case of natural hybridization suggested that backcross progeny are eliminated after seed dispersal. This suggests that the F1 phenotype represents a "local optimum" on the selective landscape, and that the selection against backcrosses strongly reduces gene flow between the incipient hybrid species and the parents.

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Allan, Gerard J. 1995. Distribution of parental DNA markers in Encelia virginensis (Asteraceae: Heliantheae) a diploid species of putative hybrid origin. M.S. Thesis, Claremont Graduate University. vii + 38 p.

The importance of natural hybridization in the evolution of homoploid plant species is a subject of considerable interest and concern. Traditional analyses of putative hybrid species hae been unable to provide sufficient resolution for elucidating the role hybridization plays in homoploid hybrid speciation. Recently developed molecular methods, however, are capable of a more direct genetic approach for testing hypotheses of hybrid origin. In this study, information from chloroplast DNA and RAPDs is used to investigate the hypothesis that Encelia virginensis originated from genetic stabilization of hybrids between E. actoni and E. frutescens. Restriction fragment analysis of cpDNA showed no variation among any Encelia species making a hypothesis of hybrid origin untestable. Analysis of RAPD amplifications of nuclear DNA, however, revealed that E. virginensis exhibits additivity of RAPD markers from both parent species, and has no unique ones. This information, along with that from morphology, ecology and geography is consistent with a hypothesis of hybrid origin, and is less easily accounted for by a divergent model of speciation.

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