The mottled brown colour of seedlings matches the background leaf litter, says the study.This may have been a defence against New Zealand's largest herbivore, the now extinct moa.
Credit: Kevin Burns
SYDNEY: One species of New Zealand tree evolved camouflage to escape being eaten by the now extinct giant moa, says a new study.
Although camouflage is common in animals such as insects, snakes, and fish, this is the first time it has been reported for a tree. The finding is published this month in the journal New Phytologist.
"There isn't much quantitative evidence for camouflage in plants, so our result for seedlings is new. The mottled colour of the margins of leaves make their true size and shape difficult to distinguish," said lead researcher Kevin Burns, an ecologist at Victoria University of Wellington in New Zealand.
Metamorphosis
Plants have long been known to use defences such as poisonous chemicals – including cyanide and strychnine – or nasty thorns to deter predators. But matching colours to the background environment has rarely been recorded.
The New Zealand native araliaceae tree Pseudopanax crassifolius undergoes several colour transitions throughout its life cycle, from blotchy brown leaves as a seedling; to brown leaves, with green highlighted spikes as a sapling; to plain dark green leaves as an adult.
While this variation could be due to changes in the environment, Burns and his team suspected it evolved to help the young trees evade the now extinct moa, a giant bird that inhabited New Zealand until around 750 years ago.
Prior to the arrival of people, the islands had few native land mammals and were instead home to a wide variety of flightless birds, including the moa a giant relative of the ostrich and emu.
Moa adaptations
To test the theory, they collected one leaf from 10 seedlings, 10 saplings, and two adult araliaceae trees on both the mainland and the Chatham Islands, which were never home to the giant bird. The leaves were compared to both each other and the leaf litter in their natural environment.
On the mainland, the mottled brown colour of seedling leaves matches the background leaf litter, said Burns, while in saplings, defensive leaf spines are bright green and clearly distinguishable from the brown leaf litter background.
Leaves from adult plants – which are taller than moa's maximum height of three metres – were spineless and plain dark green, he said.
Chatham Island tree leaves did not show the same pattern of changing colour and clearly stood out against the leaf litter, which suggest that aliaceae leaf patterns could be adaptations to the presence of moa, said Burns.
