| Agathis
is a genus of tropical conifers found in
lowland and montane forest, and
occasionally in scrublands, throughout
much of Malesia and in the southwest
Pacific islands. By virtue of its
long history of taxonomic confusion, its
paucity of discrete macromorphological
characters, the availability of
appropriate molecular markers, and its
intrinsic importance as a major
timber-producing tree, it is an ideal
genus within which to explore a number of
issues relating to the principles,
methods, and utility of different types
of data in species delimitation. Despite over
forty years of heated discussion within
systematics over the methods employed in
the reconstruction of phylogeny, and much
recent interest in “species
concepts”, the methods for detection
and delimitation of species – the
other principal task of systematics
– have received remarkably little
attention. Recent work by Wiens
& Servedio (2000) on a statistical
approach to species delimitation and to
quantifying levels of confidence in
delimitation decisions has offered a
start, but the underlying mathematics
needs to be extensively developed in
order to deal with the complexities of
continuous rather than discrete data, and
to understand the spatial components to
taxonomically significant variation
Previous
accounts of the genus Agathis (de
Laubenfels 1972, 1988; Whitmore 1980)
have differed widely on species
boundaries and on the extent and nature
of inter- and intraspecific variation,
and about a thousand herbarium specimens
have been examined from major US and
European herbaria in an effort to
understand and identify potentially
useful characters. Morphometric
analyses have enabled an understanding of
the nature of variation in continuously
varying vegetative characters in some
parts of the genus, and offered an
insight into current delimitations, but
an insufficiency of specimens and
inadequate geographic data makes it
difficult to assess variation in cone
size and shape in a statistically
rigorous manner. Additionally, a
number of characters that are useful in
the field – such as tree
architecture – are not easily
understood from herbarium specimens.
Accordingly,
a particular subgroup of the genus –
the putatively monophyletic New
Caledonian group of species – is
being intensively studied to understand
patterns of both molecular and
morphological differentiation across
landscapes and between and within
populations of putatively separate
species, with two months fieldwork in New
Caledonia this spring. Chloroplast
microsatellite markers originally
developed for forestry work by the
University of Queensland, and for
analysis of the genus Araucaria by
the team at RBG Edinburgh, as well as a
number of others developed for conifers,
are being assayed for their
transferability to the Agathis
genome and their variability, and a suite
of morphometric characters that may
discriminate between species and allow
the estimation of tree-architectural
parameters is being developed (discussion
and data online soon).
I've so
far been successful in amplifying a few
informative sequences from a range of
taxa in the genus: the following pairs of
primers taken from the conifer population
genetics literature have been
investigated accross a range of Agathis
species. Those which successfully amplify
and show a degree of variation between
and within species are marked A
in the right hand column:
ID
|
Sequences
of primers
|
Success? |
Pt110048
|
5'-TAAGGGGACTAGAGCAGGCTA-3'
5'-TTCGATATTGAACCTTGGACA-3'
|
A
|
psbAf-trnHr
|
5'-GTTATGCATGAACGTAATGCTC-3'
5'-CGCGCATGGTGGATTCACAATC-3'
|
A
|
Pr~cpSSR1
|
5'-CAACAGAAGCCCAAGCTTATGG-3'
5'-TGTATTGTATGCGGAATCAACTGG-3'
|
|
Pt30204
|
5'-TCATAGCGGAAGATCCTCTTT-3'
5'-CGGATTGATCCTAACCATACC-3'
|
|
Anyone interested
in more details of these microsatellites
should contact me. I'm hoping to
test a range of microsatellites developed
for other conifer species (these have
largely been developed from pine genomes)
for their transferability, variability
and utility in the New Caledonian species
of Agathis.
|
