CHANDLER, GREGORY THOMAS1*, MICHAEL DOUGLAS CRISP2, and RANDALL JAMES BAYER3. 1Department of Biology, Virginia Commonwealth University, PO Box 842012, Richmond VA 23284-2012, USA; 2Division of Botany and Zoology, The Australian National University, Canberra ACT 0200, Australia; 3Australian National Herbarium, CSIRO Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia. - Character evolution, toxicity, co-evolution, and relationships in the endemic Australian genus Gastrolobium (Fabaceae: Mirbelieae).
Gastrolobium (Fabaceae: Mirbelieae) is endemic throughout the
south west of Western Australia, and is important both ecologically
and economically. It forms a large and important part of the
understorey of different ecosystems, from forest and woodland to
heathland and rock outcrops. It also produces sodium
monofluoroacetate, a highly toxic compound to all animals. This has
led to large stock losses over time, and also to a program of
eradication in many farmland areas. Gastrolobium has had an
unstable taxonomy, and was recently expanded to include three other
genera, Brachysema, Jansonia and Nemcia, based on
two molecular phylogenetic studies. This leads us to examine and
question evolutionary traits within this group, as many previously
important morphological characters have been shown to be homoplastic.
These include inflorescence structure, pollination syndrome, ovule
number, and fluoroacetate production, which, at some point, have all
been used to help define the generic limits of the genera in this
group. In general, fluoroacetate levels are reduced in the more
derived groups of Gastrolobium, and are presumed to be absent
in the derived, putatively bird-pollinated lineage, which includes
Brachysema, Jansonia and some species of Nemcia,
and are highest towards the more basal, putatively bee-pollinated
lineages. This provides us with a unique look into the evolution of
several traits in the Gastrolobium group, particularly toxicity
and pollination syndrome, and the apparent tradeoff that occurs
between these two traits, and allows the exploration of the
co-evolution of Gastrolobium and the development of
fluoroacetate tolerance in native animals.
Key words: Australia, Fabaceae, fluoroacetate, Gastrolobium, Mirbelieae, molecular phylogenetics