Caught between hostile land and sea, an oyster's life is a daily battle against the elements, predators, and disease.
Now a team, including Peter Holland of Oxford University’s Department of Zoology, has decoded the oyster's genome to gain a better understanding of one of life's great survivors. The work is reported in this week's Nature.
I asked Peter what their genes tell us about these marvellous molluscs, their evolution, and how they might be farmed more efficiently…
OxSciBlog: What makes the seashore so challenging for life?
Peter Holland: The seashore looks tranquil enough, but spare a thought for the animals living in the intertidal zone, between land and sea. Twice a day, every day, as tides move in and out, these animals are plunged between two different worlds. It is hard to know which is more hostile.
An animal such as an oyster must cope with searing heat and desiccation when the tide goes out, and then coolness, high salinity and crushing currents when the tide washes back over it. Its gills are adapted to extract oxygen under water, but cannot absorb oxygen from dry air. The sea is also a breeding ground for innumerable parasites and pathogens. This is an environment where environmental stress is fact of daily life.
OSB: What do the oyster's genes tell us about how it evolved to cope?
PH: All animals have genes for coping with environmental stress, but the oyster genome has many more than other species studied so far.
Take the hsp70 genes, involved in protecting cellular proteins from heat. The oyster has over 80 of these genes, and this heat protection system is indeed switched on when the animal is exposed to high temperatures. The oyster also has extra genes involved in protection against oxidative stress and for defence against pathogens.
Even in these days when genome sequencing is becoming almost routine, it is rare that we can 'see' the biology of the animal in the genome so clearly. The genome shows us how the oyster genome has been adapted over millions of years to allow life in this hostile environment.
Not all of the oyster genome is so easy to understand, however. We found changes to the genes that control embryo and larval development, such as homeobox genes, and can only guess the underlying reasons. There are also unexpected genes used in formation of the oyster shell, suggesting that formation of mollusc shells is more variable and more complex than previously thought.
OSB: How does the oyster's 'genetic survival kit' compare with the genes of other intertidal species?
PH: We don't yet know how recently the oyster's genetic adaptations arose. Are they shared with all bivalves (the molluscs with two shells)? Or are they older, shared with all molluscs? Or more recent, and specific to oysters? More genome sequencing is needed to find out how many different routes there are to intertidal adaptation.
OSB: How might these insights help to boost oyster farming?
PH: Oyster farming is quite inefficient, with many animals dying before they become fully developed. Most often, the causes are unknown.
Now that the full set of oyster genes is known, it will be possible to see which genes respond to which stresses, or indeed which pathogens, and then see if there is variation between individuals. This might allow oyster farming to choose strains if oysters that are better suited to local conditions.
This would be a boost for the economics of oyster farming and hope it succeeds, but personally, I won't be partaking. I may have been part of the consortium that studied the genome, but I'm allergic to oysters.