Evolution in Plants of Southern South America

Much is known about mechanisms of speciation and species-level biogeography in the floras of North America and Europe. Very little is known about these same processes in the temperate flora of southern South America. This region, dissected by the Andes mountains, contains numerous vegetation zones that have been shaped by interactions with climatic changes, especially during the Pleistocene. Chile is the most isolated portion of southern South America, confined on the west by the Pacific Ocean, to the north by the extremely dry Atacama Desert, on the east by the towering Andes chain, and to the south by frigid Antarctica. Within this island-like country are contained three princi-pal environmental zones: the northern deserts and semideserts, the central Mediterranean- like region, and the southern Magellanic forests. This proposal seeks to understand mechanisms of speciation in plants of these different environments of Chile. The genus selected for detailed analysis is Hypochaeris (Compositae) , which has 22 species endemic to the country and that occur in all the three major habitats. The genus is well suited for studies on speciation due to its herbaceous habit, low chromosome number (n = 4), and large chromosomes (2-8) with a distinctive bimodal karyotype. Phylogenetic analysis will be completed on these Chilean species using morphological and DNA sequence data (ITS regions of nrDNA, and trnL and intergenic spacer sequences atpB-rbcL of cpDNA) to test the hypothesis that the group is monophyletic and to determine which species are close relatives. Related species groups will be examined with isozymes and RAPDs for alternative views of relationship. Detailed chromosomal studies emphasizing karyotypic analysis with fluorochrome staining and in situ DNA hybridization will be done to determine chromosomal homologies. Total DNA content calibrations will be done as a correlate to observed karyotypic alterations. Breeding systems will be determined from living plants in greenhouse experiments. All these data will be used to test the hypotheses of phylogenetic reconstruction established through DNA sequence data, and conversely, to gain insights on character evolution within the group. The present and past ecological data will be synthesized for a view on present parameters for explaining distributions of species and to suggest possible changes of distributions through time. These biogeographic hypotheses will be compared with molecular clock assumptions taken from DNA sequence information. The results of this study will provide the first detailed and modern view of speciation in the flora of southern South America.

The results from this grant can be summarized into three major areas of investigation within Hypochaeris of South America: (1) results from phylogenetic studies; (2) results from biogeographic studies; and (3) results bearing on populational differentiation and modes of speciation. In general, all combined studies have: helped to define the monphyletic character of the South American taxa; indicated considerable about relationships among these species based on DNA sequences and cytogentic markers; and revealed detailed affinities and patterns of genetic variation at the populational level based on AFLP markers. During the field investigations, 2147 plants in 114 populations have been collected for analysis. The phylogenetic structure of Hypochaeris is now becoming much clearer. DNA sequences have included nuclear ITS and chloroplast trnL-trnF and matK, and they reveal that: (1) the South American species of Hypochaeris are clearly monophyletic, suggesting that they may have originated from a single original introduction; (2) based on outgroup rootings, the South American taxa have originated from Europe, rather than the reverse; (3) the strongest ties between the South American species and those from Europe are with Sect. Achyrophorus and Sect. Metabasis, with patristic distances being shorter with the former, which is a new hypothesis supplanting the earlier on that H. robertia in Sect. Robertia might be ancestral; and (4) wuite unexpectedly, the European species of Hypochaeris interdigitate between Leontodon and the other outgroups. Leontodon also appears to be biphyletic. A number of studies have been initiated and completed on biogeographic aspects within Hypochaeris. These studies have tested: (1) the concept of isolation by distance within species that have broad distributional patterns along the southern Andes; (2) that newly originated populations on volcanic peaks should originate from the closest source populations and contain less genetic variation in comparison to source populations; and (3) that populations in newly glaciated areas should have lowered genetic variation in comparison to those in unglaciated regions. That genetic variation is partitioned geographically (isolation by distance) has been tested in four populational systems in Hypochaeris: H. acaulis, H. apargioides, H. palustris, and H. tenuifolia. The results show that all species confirm the general pattern of isolation by distance, with north-south distributional patterns of populations based on genetic AFLP data.