Grey mistletoe (Amyema quandang) in New South Wales, Australia
SHOWY MISTLETOES
The showy mistletoes (family Loranthaceae) are mostly aerial stem parasites that belong to the sandalwood order. The family has a Gondwanan origin and are most diverse in the Tropics and the Southern Hemisphere, extending into subtropical temperate regions of the Northern Hemisphere. All Loranthaceae are obligate hemiparasites, unable to survive without connecting to the vascular system of their host. The degree of host specificity in mistletoe-host interactions is thus a fundamental determinant of mistletoe diversity, persistence, geographic distribution, and abundance. Additionally, their floral displays and fleshy fruits link them with their animal pollinators and avian dispersers. Mistletoe patches in host canopies increase complexity in canopy structure and are a focal point in distinctive plant-animal interaction networks. We are building a phylogenetic framework to study the evolution, biogeography, and ecological interactions of Australasian showy mistletoes.
MacDonnell Ranges cycad (Macrozamia macdonnellii) near the entrance to Standley Chasm, Northern Territory, Australia
CYCAD PHYLOGENETICS
Cycads are a small but iconic Paleozoic lineage that first appeared in the fossil record about 320 million years ago (Ma), during the Carboniferous, and are one of a handful of seed plant lineages to have persisted through the Mesozoic. Cycad diversity, however, was greatly decreased by extinctions through the Mesozoic; living cycads are now distributed among ten genera, but at least twice as many fossil genera are known. For this reason, reconstructing phylogenetic relationships for cycads using genetic data is akin to putting together a jigsaw puzzle without all the pieces. It is easy to make errors and the completed puzzle will have holes. Similarly, molecular phylogenies may be erroneous and they give an incomplete picture of the evolutionary history of cycads. To address this issue and we are using analyses that integrate both fossil and molecular data.
Image modified from Mathews & Tremonte 2012 depicts evolution of phytochrome-controlled far-red high irradiance response in seed plants.
PHYTOCHROME EVOLUTION
Phytochrome photoreceptors enable plants to detect neighbors and to determine whether they are in open or shaded environments through their capacity to measure the ratio of red to far-red light in their environment. Land plants inherited a single phytochrome gene from their algal ancestors, which over the course of land plant evolution, independently diversified into small gene families, once each in mosses, ferns, and seed plants. In seed plants, divergence of gene duplicates led to two distinct functional types that have complementary and antagonistic roles in open versus shaded environments. One of our research goals is to use phylogenetic insights to design functional experiments that test whether divergence in phytochrome function helped plants better adapt to canopy shade.