65. Evolution of Seagrasses

Organised by Gary Kendrick (U Western Australia) and Michelle Waycott (James Cook U) to be held at the Biodiversity Conservation Centre, Kings Park, Perth. First meeting 8-11 December, 2009

PARTICIPANTS Gary Kendrick - U Western Australia - recruitment and landscape ecology of seagrasses, spatially explicit modeling of clonal growth in seagrasses Michelle Waycott - James Cook U - seagrass genetics and evolution Tim Carruthers - U Maryland, Center for Environmental Science (USA) - experience in Ruppia recruitment ecology, specialist in synthesis and integration skills across terrestrial and marine ecosystems Kor-jent Van Dijk - James Cook U - population genetics of tropical seagrasses Siegy Krauss - Kings Park and Botanic Garden, WA - genetics of terrestrial plants, population genetics, paternity and dispersal studies Paul Lavery - Edith Cowan U - seagrass physiology and ecophysiology Don Les - U Connecticut (USA) - evolution of aquatic angiosperms, reproductive traits and evolution Ryan Lowe - U Western Australia - hydrodynamic modeler interested in spatially explicit particle and seed dispersal models Robert J. Orth - Virginia Institute of Marine Science (USA) - seed dispersal and recruitment ecology of the genera Zostera and Posidonia Elizabeth Sinclair - Kings Park and Botanic Garden, WA - population and evolutionary geneticist, temperate Australian Posidonia species Jennifer Verduin - Murdoch U - hydrodynamics of pollination and seed dispersal in Amphibolis species

Dec 09>

GOAL

One of the most important unanswered questions in plant ecology concerns the role of long distance seed dispersal in the population dynamics of plant species (Ouborg et al. 1999; Nathan et al. 2002). Long distance seed dispersal is recognised as critical in colonisation, in metapopulation biology, and in plant migrations in relation to climate change, both in terrestrial and marine plant populations (Cain et al. 2000). The frequency (how often) and extent (how far) of long distance dispersal and its implications for plant population dynamics can be addressed via (1) molecular markers that provide genetic fingerprinting of individuals, and associated statistical procedures such as population assignment and likelihood methods (Ouborg et al. 1999; Cain et al. 2000), and (2) the development of coupled hydrodynamic and biological models (sensu Kendrick et al. 2005) that can, in combination with understanding of the physics and biology of pollen, fruits, spathes, seeds and viviparous seedlings and genetic fingerprinting, create a more synthetic outcome (Higgins et al. 2003).

The specific aims of this working group are to:
1. compare and contrast the unique strategies that seagrasses exhibit for pollination, seed dispersal and recruitment;
2. identify how these strategies interact with the hydrodynamic environment to result in recruitment success; and
3. assess the influence that these strategies have on the genetic population structure, survival and evolution of seagrasses to a completely submerged existence.

The subject has not had a synthetic treatment and the areas of evolutionary and population genetics, reproductive and recruitment ecology and the physics of fully submerged reproduction and water borne dispersal.

Background
Seagrasses are fundamental to the health and productivity of temperate and tropical coastal marine environments globally, and occur in greatest abundance in sheltered coastal embayments and estuaries (Orth et al. 2006). They have water-borne pollination and seed dispersal mechanisms that have adapted to hydrodynamically active coastal environments (Verduin et al. 2002), and are highly clonal such that rare recruitment success is amplified via vegetative growth alone. There are a range of adaptations to pollination and seed dispersal across the four evolutionary lineages that comprise the seagrasses. The genus Halophila produces hard seeds that are released in situ and through their small size disperse within a local hydrodynamic context. Heterozostera releases spathes that float to the surface and are dispersed by wind-driven waves and surface currents (sensu Orth et al. 2007). Amphibolis produces viviparous seedlings that have a comb anchor, drift on the bottom and entangle in other seagrasses, matte and seaweeds. Posidonia produces floating fruits that enclose a small seed already developing leaves and roots. Clearly, this diversity in seed dispersal alone offers mechanisms for both long distance dispersal and maintenance of populations in hydrodynamically active environments.

Genetically, temperate Australian species range from highly clonal inbred populations to highly outcrossed. For example, in the endemic temperate Australian species, Posidonia australis, a surprisingly wide range of outcrossing rates (t) have been reported which varied from 0 to 0.9 among 7 populations (Waycott & Sampson 1997). This highly variable pattern of outcrossing in this species, with populations ranging from predominantly inbred to predominantly outbred indicates that hydrophily (water pollination) is less uniform than wind pollination and more similar to animal pollination in its variability. More importantly, Waycott & Sampson (1997) suggested that differences in water movement (currents, tides, weather) at the time of pollen dehiscence has a marked effect on mating patterns, as may the physical location of meadow (exposed, protected). These observations suggest that extrinsic forces may have a greater impact on pollen dispersal and mating patterns than in terrestrial systems, and with variation in clonality and effective population size, there is likely no ‘typical’ population (Reusch 2001).

Last Updated March 2010