Impacts of climate change stressors on marine life history stages - studies
Tropical Invertebrates: Biology, Ecology & Phylogeny
Evo-Devo and Echinoderm Development
- Evo-Devo and the Asterinidae
- Evolution of Maternal Provisioning in Echinoderms
- CNS Specification & Pentamery in Echinoderms / Neurogenesis in Echinoderm Larvae
- Evolution of Viviparity in Asterinids
- Evo-Devo & the Ophiuroidea
Population biology, ecology and genetic connectivity
Molluscan Biology and Evolution
As the oceans simultaneously warm, acidify, increase in pCO2 and decrease in carbonate saturation due to climate change, prospects for marine biota are of concern, particularly early life history stages. These factors are deleterious to marine life and are likely to have negative interactive effects, which are not understood.
In carefully controlled multistressor experiments we investigate the synergistic impacts of climate change stressors on calcifying and non-calcifying life stages of ecologically important marine invertebrates. Investigation of species from the tropics to the poles will generate key insights into biological responses and tipping points in a changing ocean.
Our research in tropical Australia investigates the ecology of echinoderms of the Great Barrier Reef and else where in the Indo-Pacific. Recent studies have involved, molecular phylogeny, biodiversity, species discovery, the population biology of the crown of thorns sea star, larval evolution and reproductive biology of ophiuroids and the ecology of bêche-de-mer sea cucumbers. For the commercial sea cucumbers our research aims to understanding their biodiversity the GBR and for management, conservation and sustainable use of these organisms.
Evo-Devo and Echinoderm Development
Evo-Devo and the Asterinidae
The asterinid sea star family provides a powerful taxon with which to examine developmental processes in evolution because it includes genera (eg. Patiriella, Cryptasterina, Parvulastra) that contain species with indirect (planktotrophic) development through typical feeding larvae and several modes of direct (lecithotrophic) development through non-feeding larvae. A dispersive feeding larva is considered ancestral for the Echinodermata.
We have constructed a robust phylogeny for these genera with calibrated divergence times to map polarity and timing of life history change on an evolutionary time scale. Comparative embryology shows that evolutionary modification of development involved a range of mechanisms including deletion, heterochrony and hypertrophy. Some of the changes were surprisingly fast (< 0.5 Mya). Our results challenge the paradigm that early embryogenesis is constrained against change.
The research is determining what features are conserved and what features are labile to change and the mechanisms involved.
Evolution of Maternal Provisioning in Echinoderms
The egg cell links the adult and larval life stages of marine invertebrates. Acquisition of a large egg appears to have been a crucial preadaptive trait for the shift to direct development in many marine invertebrates. This project investigates evolution of oogenesis in echinoderms and how maternal provisioning differs in species with small and large eggs. Evolution of lecithotrophy involved multiple, independent alterations of oogenesis and these have been fine tuned with respect to egg buoyancy and location (benthic, pelagic) of fertilisation and development. It appears that most of the extra reserves are set aside for the early benthic juvenile.
The nutritive profile of echinoderm eggs in species with different modes of development, the pattern of nutrient utilisation by embryos and the affinities of the yolk protein are being investigated using molecular, Iatraoscan and Proteomic techniques. We have the ability to characterize the details of the lipid classes and the protein profile of individual eggs and trace how these provisions are utilized by embryos and larvae. Egg nutritive composition in closely related species is being compared to identify trends in egg size evolution and phylogenetic hypotheses are used to assess the pathway of change.
Neurogenesis & Evolution of Pentamery in Echinoderms
Understanding the evolutionary origins and development of animal body plans is a fundamental question in evolutionary biology. The pentaradiate echinoderms, derived from a bilateral chordate ancestor, are challenging, as is their bilateral-to-radial transformation as metamorphosis. We investigate the origin of the echinoderm body plan through research on the temporal and spatial expression patterns of neurogenic genes with a focus on the pan-metazoan homeobox genes including: the Hox gene complex, engrailed and Otx.
Metamorphosing Heliocidaris erythrogramma
We are documenting the expression of these genes during the transition to radial symmetry to determine their role in specifying the developing pentameral nervous system. This requires RT-PCR and in situ hybridisation.
Juvenile Parvulastra exigua stained to show location of CNS
Brittle Star - Ophiarachna
Evolution of Viviparity in Asterinids
The evolution of live birth from the parent's reproductive tract involved a profound shift in animal life histories; independent developmental stages were eliminated from the life cycle. Although rare, marine invertebrate clades that contain species with live birth often have several viviparous lineages. The family Asterinidae, a species-rich sea star taxon prone to life history evolution, exemplifies this. Viviparity has evolved independently four times in asterinids through strikingly different evolutionary pathways; by punctuate evolution on the fringe of 'parental' species distributions. This has created a suite of cryptic morphospecies distributed from northern Australia and through Indonesia to Japan. We use molecular phylogeny to discern previously undetected species diversity and phylogenetic hypotheses to reconstruct the direction and number of evolutionary transitions involved with the evolution of live birth in these sea stars. This has lead to the discovery of several new species from the Great Barrier Reef.
Evo-Devo & the Ophiuroidea
The Ophiuroidea is the most-species rich class of the Echinodermata and evolution of development in these echinoderms have evolved a switch to non-feeding development and the evolution of two metamorphic phenotypes (Type I and II development). We investigate the evolution of larval form in ophiuroid genera with Type I and Type II development in species from Australia and the Caribbean. We have discovered that the early larval form is surprisingly variable. The aim of this research is to document the diversity of larval form and ascertain larval homologies with the assistance of molecular phylogeny.
Not surprisingly, this research has led to the discovery of morphospecies complexes where the adults are virtually identical while the larvae differ markedly in morphology and dispersive capacity. A major aim is to determine the clade-specific developmental and life history traits.
The life history basis for the maintenance of populations of benthic marine invertebrates, their genetic connectivity and invasive potential typically involves a dispersive propagule and, for the vast majority of species, these propagules are larvae.
In this project we investigate connectivity of sea star populations in eastern Australia from the Asterinidae, an asteroid family with the greatest diversity of life histories known for the Echinodermata and marine invertebrates in general. Evolution of development, larval form and mating systems have been major forces in speciation in the Asterinidae.
We use this diversity as a model system to investigate the consequences of different systems and larval forms (benthic-planktonic, long and short planktonic duration on population genetic structure.
Molluscan Biology and Evolution
Conservation Biology of Freshwater Bivalves
This project investigates the ecology and conservation biology of freshwater mussels, endemic species currently on the decline in many river systems. The research focuses on the life history to determine the timing of larval release, the identity of the larvae to species and identification of the fish hosts of this parasitic life stage.
Population studies are determining the physical and chemical habitat requirements of freshwater mussels in coastal rivers, presence of mussel populations and population structure. Through this research we will develop a model for mussel distribution based on correlates of biological and physical habitat.
Freshwater Bivalves as Bioindicators
This research investigates bivalves as bioindicators of river health and on the potential to introduce mussels into man made habitats. The impact of toxicants on reproduction and development of bivalves is being examined. The main aims are to determine if the bioaccumulation and reproductive responses of bivalves can be used as monitoring tools to assess the health of freshwater systems and to determination if created habitats can support mussel populations for their conservation.