Contributed
Papers
USING PHYLOGENY TO INVESTIGATE THE HISTORY
OF MORPHOLOGICAL EVOLUTION IN HETEROSPOROUS FERNS
Kathleen Pryer, Harald
Schneider, Rick Lupia
ABSTRACT: Throughout the evolutionary history of plants on land
there have been repeated re-invasions of aquatic environments by terrestrial
plants from distantly related groups. In order to survive these very
different physical conditions, these plants have had to dramatically
modify their vegetative, reproductive, and dispersal systems. Few living
ferns are aquatic, most are terrestrial and homosporous. The exceptions
are heterosporous ferns, with morphologically distinct spores producing
unisexual gametophytes. Heterosporous ferns are monophyletic and comprise
two extant families, the semi-aquatic Marsileaceae and the aquatic Salviniaceae.
Except for very recent interest in the relationships among the five
extant heterosporous genera, these ferns have been largely ignored in
systematic studies and infrageneric relationships are virtually unknown.
Similarly, our knowledge of the history of the morphological character
evolution that accompanied the transition of these ferns to their aquatic
environments is limited. Heterosporous ferns are relative newcomers
that diversified during the Cretaceous, at the same time as flowering
plants, and the fossil record has preserved a rich history of these
ferns, mostly in the form of microfossils with a remarkable diversity
of ornamented spores. Together we are reconstructing a comprehensive
phylogeny for the heterosporous aquatic ferns. Our study will be among
the first to include both living and fossil members of a group, incorporating
data from multiple genes, morphology, and developmental studies for
the living taxa, and integrating ultrastructural morphological data
from fossil taxa. Understanding the history of character evolution in
these ferns requires integration of fossil taxa, necessarily using morphology
pertinent to the spores. Understanding the development and structure
of the spore wall, primarily through electron microscopy, is critical
to this project because the character-rich spore wall is well preserved
in fossils and will permit fossil taxa to be integrated into the phylogeny.
We hope to understand better the morphological character state transitions
associated with the ecological specialization of these ferns to aquatic
habitats.
RATE HETEROGENEITY AMONG LINEAGES OF TRACHEOPHYTES:
INTEGRATION OF MOLECULAR AND FOSSIL DATA AND EVIDENCE FOR MOLECULAR
LIVING FOSSILS
Pamela S. Soltis,
Douglas E. Soltis, Vincent Savolainen, Peter R. Crane, and Timothy G.
Barraclough
ABSTRACT: Many efforts to date evolutionary divergences using
a molecular clock have yielded age estimates that are grossly inconsistent
with the paleontological evidence. Such discrepancies are often attributed
to the inadequacy of the fossil record, but many potential sources of
error can affect molecular-based estimates. In this study, we minimize
the potential error due to inaccurate topology and uncertain calibration
times by using a well-supported tree, multiple genes, and multiple well-substantiated
dates to explore the correspondence between the fossil record and molecular-based
age estimates for major clades of tracheophytes. Age estimates varied
due to gene effects, codon position, lineage effects, method of inferring
branch lengths, and whether or not rate constancy was assumed. However,
even methods designed to ameliorate the effects of rate heterogeneity
among lineages could not accommodate the substantially slower rates
observed in Marattia + Angiopteris and in the tree ferns. Both of these
clades of ferns have undergone dramatic decelerations in their rates
of molecular evolution and are "molecular living fossils",
consistent with their relative morphological stasis for the past 165-200
million years. Similar discrepancies between the fossil record and molecular-based
age estimates noted in other studies may also be explained in part by
violations of rate constancy among lineages.
THE ROOT OF THE ANGIOSPERMS REVISITED
Michael J. Zanis, Douglas
E. Soltis, Pamela S. Soltis
ABSTRACT: Most recent phylogenetic analyses of basal angiosperms
have converged upon the placement of Amborella as sister to all other
extant angiosperms. However, certain recent studies suggested that Amborella
and Nymphaeales (water lilies) form a clade sister to all remaining
angiosperms or that Nymphaeales alone are the sister to the remaining
angiosperms. We report here (i) maximum parsimony, maximum likelihood,
and Bayesian phylogenetic analyses of 11 genes (> 15,000bp/taxon)
for 16 taxa, (ii) maximum parsimony analysis for a subset of these genes
for 104 taxa, and (iii) tests of alternative rootings using the non-parametric
bootstrap and the likelihood ratio test using the parametric bootstrap.
In addition, we use simulation analyses to examine the amount of bias
that may be present in our methods of phylogeny estimation. Amborella
continues to receive strong bootstrap support as the sister to all other
extant angiosperms, and three of four tests reject alternative hypotheses
of the angiosperm root. Although we cannot conclusively choose between
Amborella vs. Amborella + Nymphaeales as sister to all other angiosperms,
most analyses favor the former rooting.
COMBINING FAST EVOLVING CHLOROPLAST DNA SEQUENCES
FOR PHYLOGENETIC ANALYSIS IN BASAL ANGIOSPERMS
Khidir W. Hilu 1, Thomas Borsch
2, Kai Müller 2
1 Department of Biology, Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061.
2 Botanisches Institut und Botanischer Garten, Friedrich-Wilhelms-Universität
Bonn, Germany.
ABSTRACT: Our understanding of flowering plant phylogeny has
been enhanced considerably by recent information from gene sequences.
A number of plastid, nuclear and mitochondrial genes have been used
in deep level phylogenetic reconstruction. Emphasis has been placed
on using slow evolving genes with the notion that levels of homoplasy
will be kept at a minimum. We have been exploring the potential contribution
of the plastid matK gene and the noncoding parts of the trnT-F-region,
both evolving at higher rates than other genes used in angiosperm phylogenetic
reconstruction. These two regions provide robust phylogenies for basal
angiosperms that are congruent with each other and with recent angiosperm
phylogenies based on combined data of gene sequences from the plastid
and nuclear or from all three genomes (Soltis et al., 2000, Qiu et al.,
1999, 2000). Analysis of the combined matK and trnT-F data sets resulted
in a single most parsimonious tree. Statistical support for the majority
of nodes substantially increased compared to previous analyses. The
results of the present study point to the effectiveness of fast evolving
DNA regions in providing strong historical signals that can recover
a reliable and robust phylogeny for angiosperms.
FAGALES OVERVIEW
Paul S. Manos
Department of Botany
Duke University
PHYLOGENETIC ANALYSES OF FAGALES BASED ON
MULTIPLE DNA SEQUENCES FROM THREE GENOMES
Rui-Qi Li, Zhi-Duan
Chen, and An-ming Lu
Laboratory of Systematic and Evolutionary Botany, Institute of Botany,
Chinese Academy of Sciences, Beijing 100093, P. R. CHINA
ABSTRACT: Nucleotide sequences of five genes and one DNA region
from three genomes were used to analyze the inter- and infra-familial
relationships of Fagales. All 31 genera (excluding Ceuthostoma) were
sampled representing eight families of the order. The parsimonious analyses
of combined data set strongly supported the three major clades in the
Fagales, i.e., Nothofagus, Fagaceae and core "higher" hamamelids
as recognized by Manos and Steele (1997). Nothofagus is sister to all
the other Fagales, and Fagaceae is sister to the core "higher"
hamamelids. Two main subclades were resolved in the core "higher"
hamamelids by the combined analysis, one being Myricaceae (Rhoipteleaceae
(Juglandaceae)), the other Casuarinaceae (Ticodendraceae (Betulaceae)).
The latter subclade is strongly supported, while the former is moderately
supported although the positions of Myricaceae are quite different in
each single-gene trees. Fagaceae, Betulaceae and Juglandaceae form their
own clade with 100% bootstrap support, respectively.
Keywords: Fagales, "higher" hamamelids, Myricaceae, phylogeny,
combined analysis
ESTIMATING TIME DIVERGENCE IN THE BIRCH FAMILY
(BETULACEAE): RATE HETEROGENEITY, MULTIPLE CALIBRATION POINTS AND STEM
LINEAGE-CROWN GROUP INTERVAL
Félix Forest,
Vincent Savolainen, Mark W. Chase, Anne Bruneau, and Peter R. Crane
ABSTRACT: We present a phylogenetic analysis of the Betulaceae
including at least one species of each subgeneric division (26 taxa)
of the six genera (Betula, Alnus, Carpinus, Corylus, Ostrya, Ostryopsis).
Parsimony analyses based on ribosomal DNA sequences of 5S gene spacers
and ITS supported the monophyly of the subfamilies and all genera. Likelihood
ratio tests showed rate heterogeneity across lineages, therefore we
made the phylogenetic trees ultra-metric by transforming ML and MP branch
lengths (HKY85 + gamma model of DNA evolution) using the non-parametric
rate smoothing method of Sanderson. We estimated divergence times within
the family using one of the six most parsimonious trees and eight calibration
points from the extensive fossil record of Betulaceae. To assess the
problem of using dates for stem lineages or crown groups in the calibration
procedure, we calculated age estimates by placing each fossil on the
stem lineage node and crown group node, creating an interval. The median
value of those estimates was determined for each node. According to
these results, the ages of the crown groups of the Betulaceae and subfamilies
Coryloideae and Betuloideae are 97.7 Ma, 57.6 Ma and 89.8 Ma respectively.
Taking into account the error estimates, these ages are similar to those
inferred from the fossil record. Deceleration of rates of molecular
evolution is observed in certain clades of the Betulaceae.
FUNCTIONAL FIELD ECOLOGY OF AMBORELLA AND
ITA PLANTS
Taylor Feild
PALEOBOTANICAL DATA AND THE PALEOBIOLOGY DATABASE
INITIATIVE
Hallie J. Sims
ABSTRACT: The Paleobotany Working Group (part of the Paleobiology Database;
see http://www.paleodb.org/) has begun a project to compile locality-based
occurrence data for Phanerozoic land plant localities, using a web-based,
relational database. The database is structured around four tables:
references, collections, occurrences, and taxa. Each collection record
has the geographic coordinates and geologic age of the site, lithologic
and paleoenvironmental context, and taphonomic modification of the remains.
This is linked with a list or lists of taxon occurrences (and abundance
data where available), including which plant parts are present. Taxonomic
names are being linked to tables that allow taxonomic usage to be updated
and plant parts to be associated, recording the opinions of different
workers. Data are drawn from the primary literature, museum collections,
and unpublished field work, and every datum entered is associated with
a reference and an enterer. As a group of specialists (currently fifteen
members), we are updating stratigraphic information and building a table
of valid species, genera, and their synonyms. By making the data publicly
available as a web-searchable database, the paleobotanical community
will be invited (and perhaps incited?) to identify omissions and errors.
The group has several scientific goals, including producing a sampling
standardized plant diversity curve, assessing changes in within-community
diversity over time, and exploring trends in morphological evolution.
However, the lists of valid taxa and occurrence lists from well-constrained
localities, vetted by specialists, can form building blocks for a wide
range of research projects. We hope that this initiative will gain momentum
within the community to maintain and contribute to a public repository
of high-quality paleobotanical data.
MORPHOBANK
Maureen O'Leary