Samplings: October 2009

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Lancewood tree grows from a speckled seedling, left, into a thorny sapling, right.

Kevin Burns

The lancewood, Pseudopanax crassifolius, is a New Zealand tree that goes through an unusual changing act as it grows. Seedlings’ leaves are mottled; saplings’ leaves have conspicuous pale green thorns; and adults’ leaves are an unremarkable thornless green. Could the leaves’ transformation be a vestigial defense against munching by now-extinct moas, as various researchers have proposed? Those giant, wingless birds were New Zealand’s main herbivores until people extirpated them 700 years ago.

The mottling would have camouflaged vulnerable seedlings against a background of leaf litter, and the thorns would have discouraged swallowing, if their color hadn’t already warned the birds away. Once the trees made it to ten feet tall—the maximum reach of an adult moa—they no longer needed extraordinary protection.

To test that idea, graduate student Nik Fadzly and his advisor Kevin C. Burns, of Victoria University of Wellington, New Zealand, along with two collaborators, measured the colors of the leaves and compared them with the visual capacity of ostriches, the moas’ closest living relatives. They found that seedling leaves would indeed be concealed to an ostrich’s (and presumably, a moa’s) eye, whereas thorny sapling leaves would be conspicuous. Critically, the leaves of P. chathamicus, a cousin of the lancewood that evolved 500 miles away on the moa-free Chatham Islands, showed neither camouflage nor contrast coloration.

Many animals deploy color to hide from or deter their predators. The lancewood is the first documented case of a plant doing both. (New Phytologist)

Related link:

Dr. H. Martin Schaefer - Research group on the evolution and function of visual signals