Prickly holly leaves are a traditional Christmas decoration, from wreaths adorning homes, to greeting card scenes. Yet, look closer at a holly tree and while some leaves are prickly, others are not. Scientists writing in the Botanical Journal of the Linnean Society believe variations within a single tree are the combined result of herbivore activity and molecular responses to environmental change.
"The ability of an organism to change its characteristics in response to environmental variations is known as phenotypic plasticity and it is a key driving factor in the evolution of a species," said Dr Carlos Herrera from National Research Council of Spain (CSIC) in Seville. "In plants this is often seen in eye-catching changes to leaves and flowers related to variable growing conditions. Every gardener knows that leaves produced in deep shade and under full sun are often very different in size and shape."
However, this variation of leaf forms can also take place within a single tree of many different species, and it is known as heterophylly. Dr Herrera partnered with Ms Pilar Bazaga, also from CSIC, to explore this phenomenon in European holly (Ilex aquifolium) a pioneer species, with a strong ability to accommodate to changing conditions.
"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 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."
"Heterophylly is a widespread phenomenon occurring in many different types of plants," Dr Mike Fay, Chief Editor of the Botanical Journal of the Linnean Society. "By coincidence it is also a conspicuous feature of ivy (Hedera helix), another plant associated with Christmas decorations."
|Contact: Ben Norman|