Figs can only be pollinated by female Agaonid wasps that
oviposit inside the fig cavity, and this mutualism is a
model system for studies of co-evolution (Cook &
Rasplus, 2003, Trends Ecol. Evol. 18, 241-248). While this
extraordinary mutualism has received attention for decades,
we are only beginning to reconstruct the phylogeny of both
partners, which is the framework needed to address a
variety of questions concerning patterns and processes in
evolutionary biology.
Morphologically, Ficus
is distinct from
the rest of the Moraceae and is placed in its own tribe
Ficeae. The relationship with the other genera has been
problematic. A recent phylogenetic study of Moraceae by
Datwyler and Weiblen (2004, Am. J. Bot. 91, 767-777) based
on ndhF sequences showed that an expanded tribe Castilleae
is the closest relatives to Ficus.
The South American Poulsenia,
and the Australasian genera Sparattosyce
and
Antiaropsis
were previously
placed in tribe Artocarpae.
An expanded Tribe Castilleae is the closest relatives
to
Ficus
(Datwyler &
Weiblen, 2004, Am. J. Bot. 91, 767-777)
The classification of
Ficus
is based on work by
Corner and Berg over more than half a century. In the most
recent classification by Berg for Flora Malesiana,
Ficus
is divided into six
subgenera and a number of sections (Berg & Corner,
2005. Moraceae (Ficus).
In H. P. Noteboom ed., Flora Malesiana ser. 1, vol.17,
1-730. National Herbarium of Nederland, Leiden, The
Netherlands). This classification is primarily based on
intuitive morphology and indications from previous
molecular studies are largely neglected.
Classification of
Ficus
based on morphology
(Modified
from Berg & Corner, 2005)
Phylogenetic hypotheses are currently
typically based on molecular data, which surpasses
morphological and other types of data in various ways,
particularly in the ability to obtain sufficient amounts of
information for species-level comparison and the need for
phylogenetic hypotheses that are independent of the
biological traits that one may wish to evaluate. However,
large genera, such as Ficus, often display low levels of variation in
the standard makers used. Low-copy nuclear markers provide
a good alternative, but they are often difficult to
amplify.
Previous DNA sequence-based phylogenetic studies of
Ficus
have shown that taxonomic
categories are not natural and revealed several parallel
transitions in growth habit and breeding system (Herre et
al. 1996, J. Biogeogr. 23, 521-530; Weiblen, 2000, Amer. J.
Bot. 87, 1342-1357; Jousselin et al., 2003, Evolution 57,
1255-1269). However, previous studies have only included
limited sampling (less than 50 species, or about 6%) of
this large genus and/or have detected insufficient genetic
variation to allow a detailed estimation of relationships
of fig species, especially at species level.
Ongoing work by Rønsted and co-workers (see for example,
Rønsted et al., 2005, Proc. Roy. Soc. Lond. B, 2593-2599)
aims at producing a robust and comprehensive global
phylogenetic hypothesis for Ficus. We use a two-step approach. First we
sequence three nuclear regions (ITS, ETS and G3pdh) from as
many species of Ficus as we can get hold of (currently over 200
species are included in this matrix). With this
comprehensive sampling, we can identify clades and
problematic taxa. Secondly, we sample additional DNA
regions (Waxy and ncpGS) for a subset of samples,
representing clades and problematic taxa identified in the
three-gene analysis.
A recent phylogenetic tree based on maximum parsimony,
maximum likelihood and Bayesian analysis of five DNA
regions is shown below. For details or an update of the
ongoing work, send an e-mail to Rønsted (contact details on
www.ninaronsted.dk).
Working
molecular phylogenetic classification of
Ficus
(Rønsted et al. 2006. ITS, ETS, G3Pdh, ncpGS, Waxy).
Bootstrap support is indicated
above branches and arrowheads indicate branches
that collapse in the strict consensus of the most
parsimonious trees.