He might be endearing with his cheeky smile and seasonally inappropriate antlers, but Rudolph and his more nasally-challenged cousins could be the reason why holly scratches you. It doesn’t have to happen as, if you look closely, you’ll see not all holly leaves are prickly. What causes the spiky leaves? New research in the Botanical Journal of the Linnean Society blames a combination of herbivore activity and epigenetics for Holly’s spikes.
“Heterophylly is often witnessed in holly trees, where some leaves are prickly, a defense against herbivores, while others are non-prickly, with smooth margins and no defense,” said author Dr Herrera. “We wanted to find out if this variation was a response to environmental changes and if this took place without wider genetic change, that is, without alteration of the organism’s DNA sequence.”
They studied the grazing by goats and deer and the reaction of European holly Ilex aquifolium. The result was that there were many more prickly leaves between 0 and 2.5 metres, the range of a hungry red deer. The study showed that the results correlated with epigenetic driving the growth of prickly leaves.
“An increasing number of studies support the idea that the presence of spines and prickles in plants is a response to herbivore activity, and our research suggests this is the case with holly,” concluded Dr Herrera. “The ability of plants to respond to environmental changes through quick epigenetic modifications makes also one to feel a bit more optimistic about plant survival in a quickly changing world.”
You can read more at the Linnean Society’s site or read the paper, possibly for free, at Wiley.
Herrera C.M. & Bazaga P. (2013). Epigenetic correlates of plant phenotypic plasticity: DNA methylation differs between prickly and nonprickly leaves in heterophyllous (Aquifoliaceae) trees, Botanical Journal of the Linnean Society, n/a-n/a. DOI: 10.1111/boj.12007