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ABN 46 006 591 304Moa Affected Plant Evolution
The feeding habits of the moa may have inluenced the evolution of warning and
defence mechanisms by a plant species in New Zealand.
As part of his PhD studies at Victoria University of Wellington, Patrick
Kavanagh looked at the colour and shape of the lancewood. “The lancewood is
pretty amazing and unique,” he said. “It starts out with rigid, saw-like leaves when
it’s juvenile, but at about 3 metres in height the leaves become wider and more
rounded in shape. It’s no coincidence that 3 metres is the same as the maximum
height that the largest moa species was able to reach.”
While this theory has been around for some time, Kavanagh has added weight
to the argument by examining colour changes in the lancewood leaves as the plant
matures, arguing that they are used as a warning signal to deter moa from eating
the developing saplings.
Kavanagh explains that the lancewood leaves “possess spines down their margins
that are largest when plants are saplings, potentially to deter New Zealand’s largest
known herbivore – the moa”.
Small green spots on the tops of the leaves are associated with these spines.
“These spots are most conspicuous when the plant is poorly developed and there-
fore most vulnerable to predators. The spots act as a kind of untruthful signal to
deter moa and other herbivores from eating it.”
Kavanagh “also noticed that the underside of the lancewood leaf changes colour
as the plant develops. Small seedlings are light green underneath the leaf, but that
turns dark red when it reaches sapling stage. It changes back to green when the
plant is fully grown.”
All warning colours and leaf spines are absent in adults, after they grow above
the height of the largest moa species.
Kavanagh used spectral analysis techniques to test whether the dark red coloura-
tion makes the sapling’s leaves more conspicuous to herbivores looking up from
below. “The higher contrast of dark red against the other green foliage happens
when the leaves are most spikey and therefore best defended. In this phase of the
plant’s life, it’s a more truthful warning to any bird planning to eat it – there’d be
painful consequences.”
In contrast, “spots on the upper side of leaves were strongest when plants were
small and poorly defended, providing a dishonest warning signal”.
Kavanagh says that the production of honest and dishonest warning signals as
the lancewood plant grows vertically relects the changing visual perspective of herbi-
vores, and is therefore an example of how the moa has shaped the evolution of plants
in New Zealand.
The research was published in the Biological Journal of the Linnean Society
(tinyurl.com/jqvn3v8).
Left: Upper (A) and lower (B) leaf surfaces of typical lancewood leaves as the
plant matures from seedling to adult. The inset box in panel (A) magnifies the
lateral leaf spines and associated spots of brightly coloured tissue.
Credit: Kavanagh et al.