Monday, 1 June 2009

Seeds at Sea

The unfloatable (but once thought to be floatable) Coco de Mer (Lodoicea maldivica) among other fruits and seeds in the recent display by our Volunteer Guides for their 'Native Fruit and Nuts' talk and walk.

With long-distance dispersal becoming cool, and indeed necessary - how else do you get protea relatives from Australia to South Africa after the split of Gondwana (see my previous posting about the work of Peter Weston and colleagues) - it's time to look at oceanic journeys by plant seeds.

Let's turn our focus then from Seeds in Space to Seeds at Sea.

A neat PhD study on this topic is described in the latest issue of the Friends of Kings Park quarterly magazine 'For People & Plants'. It's the work of student Lydia Guja, guided by David Merritt and Kingsley Dixon of (Kings Park) Botanic Gardens and Parks Authority and Grant Wardell-Johnson of Curtin University of Technology.

The article starts with some historical context. That well-known botanist Charles Darwin was one of the first to test experimentally whether seeds will survive after floating in sea-water. In his garden at Downe - his laboratory for studies of pollination, climbing and carnivory in plants, among other things - Darwin discovered that some seed capsules and fruits could survive for up to 28 days, and some up to 137 days, as ocean currents washed them from one shore to another.

He figured that you could reasonably expect at least 10% of seeds in any country to travel 1,500 km. Of course most of these plants would occur naturally near the coast and would typically be salt-tolerant anyway.

With a simlar argument to the one used when we sent a few thousands seeds of Australian seeds into space, Lydia and her colleagues point out that no Western Australian coastal plants have ever been given the Darwin treatment.

And so the fruits of 13 WA species were floated in sea water for 70 days, and then the seed germinated. Ten survived the ordeal, with only one suffering a little from the experience. Event the three that germinate were thought to be inhibited by dormancy rather than salt and/or water.

The study will now move into testing the boyancy of different fruits, and into the physiology of surving high salt concentrations.

Does all this help us explain how protea relatives got to South Africa from Australia? Well not really, unless there is a salt tolerant ancestor somewhere in the Proteaceae family tree. Or perhaps a raft-building forebear?


Jarrett said...

Fascinating topic. Of course, if a proto-iguana can get from South America to Fiji by riding a raft of debris, any number of seeds might have made the trip that way as well.

Someone needs to write a novel about that iguana.

Tim Entwisle said...

Or about a seed? Could actually be an interesting way to tell the story of evolution.