Browsing by Subject "divergence times"
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Item Open Access Phylogenetic relationships and evolution of extant horsetails, Equisetum, based on chloroplast DNA sequence data (rbcL and trnL-F)(International Journal of Plant Sciences, 2003-01-01) Des Marais, DL; Smith, AR; Britton, DM; Pryer, KMEquisetum is a small and morphologically distinct genus with a rich fossil record. Two subgenera have been recognized based principally on stomatal position and stem branching: subg. Equisetum (eight species; superficial stomates; stems branched) and subg. Hippochaete (seven species; sunken stomates; stems generally unbranched). Prior attempts at understanding Equisetum systematics, phylogeny, and character evolution have been hampered by the high degree of morphological plasticity in the genus as well as by frequent hybridization among members within each subgenus. We present the first explicit phylogenetic study of Equisetum, including all 15 species and two samples of one widespread hybrid, Equisetum x ferrissii, based on a combined analysis of two chloroplast markers, rbcL and trnL-F. Our robustly supported phylogeny identifies two monophyletic clades corresponding to the two subgenera recognized by earlier workers. The phylogenetic placement of Equisetum bogotense, however, is ambiguous. In maximum likelihood analyses, it allies with subg. Hippochaete as the most basal member, while maximum parsimony places it as sister to the rest of the genus. A consensus phylogeny from the two analyses is presented as a basal trichotomy (E. bogotense, subg. Hippochaete, subg. Equisetum), and morphological character evolution is discussed. We detected rate heterogeneity in the rbcL locus between the two subgenera that can be attributed to an increased rate of nucleotide substitution (transversions) in subg. Hippochaete. We calculated molecular-based age estimates using the penalized likelihood approach, which accounts for rate heterogeneity and does not assume a molecular clock. The Equisetum crown group appears to have diversified in the early Cenozoic, whereas the Equisetaceae total group is estimated to have a Paleozoic origin. These molecular-based age estimates are in remarkable agreement with current interpretations of the fossil record.Item Open Access PLEUROCARPOUS MOSSES IN SPACE AND TIME: BIOGEOGRAPHY AND EVOLUTION OF THE HOOKERIALES(2012) Pokorny Montero, Cristina IsabelMorphological characters from the gametophyte and sporophyte generations have been used in land plants to infer relationships and construct classifications, but sporophytes provide the vast majority of data for the systematics of vascular plants. In bryophytes both generations are well developed and characters from both are commonly used to classify these organisms. However, because morphological traits of gametophytes and sporophytes can have different genetic bases and experience different selective pressures, taxonomic emphasis on one generation or the other may yield incongruent classifications. The moss order Hookeriales has a controversial taxonomic history because previous classifications have focused almost exclusively on either gametophytes or sporophytes. The Hookeriales provide a model for comparing morphological evolution in gametophytes and sporophytes, and its impact on alternative classification systems. Sometimes, placement of certain groups within Hookeriales remains challenging even at the molecular level. That is the case of the genus Calyptrochaeta. We study diversification dynamics in this genus to elucidate possible mechanisms obscuring its placement and we address biogeographic questions using the Tropical Conservatism scenario as our null hypothesis. Furthermore, to better understand biogeographic patterns in the Southern Hemisphere, infraspecific molecular patterns are compared in two species of the genus Calyptrochaeta (i.e., C. apiculata and C. asplenioides) and vicariance and recent long distance dispersal are tested to explain the disjunct distributions observed in these species.
In this study we reconstruct relationships among pleurocarpous mosses in or associated to the Hookeriales, in Calyptrochaeta, and within Calyptrochaeta. Six molecular markers are explored in total from all three genome compartments to reconstruct the evolution of morphological characters and habitat preferences in our phylogenies. Divergence times are estimated in a Bayesian framework using a relaxed molecular clock, and diversification rates are calculated on the chronograms resulting from these estimations.
As a result, we found that the Hookeriales, as currently circumscribed, are monophyletic and that both sporophyte and gametophyte characters are labile. We documented parallel changes and reversals in traits from both generations. We show that diversification rates in Calyptrochaeta have changed through its history. Also, though we lack support to clearly reject the tropical conservatism hypothesis, our data point to a more complex scenario where both temperate and tropical species can be ancient and give rise to one another, since shifts between tropical and temperate regions seem to be possible in any direction. Finally, we have show that recent long distance dispersal best explains the distribution of both C. apiculata and C. asplenioides in the Southern Hemisphere.