Heterophylly in Holly: Science and Season’s Greetings!
⁕ From ancient tree-worshipping Druids to Romans celebrating Saturnalia, from the pagan rituals of Solstice to Hallmark cards of Christmas cheer, the prickly leaves of the Holly (Ilex aquifolium) are a familiar tradition of the season.
⁕ But not all holly leaves are picturesquely prickly. A botanist or gardener knows that the leaves can be smooth or variably serrated, even within a single bush. This is called heterophylly. Scientists took a trip to a forest in southeastern Spain where they noticed a correlation between the grazing pattern of herbivores and the location of prickly leaves- there were more prickly leaves at heights under 2.5 m, the average reach of an adult deer. They then compared the DNA in smooth and prickly leaves from the same plants. Genetically, they were identical, so what explained the difference in appearance?
⁕ Epigenetics is the science that describes how DNA is chemically modified to turn on or off genes. Within the same branch, smooth leaves showed more DNA methylation compared to prickly leaves. These differences were not randomly distributed, but were confined to specific regions of the genome. This suggested that the Holly responded to hungry herbivores by changing which genes were turned on (a process known as transcription) to make more painfully prickly leaves. What’s nice about this swift molecular tit-for-tat is that it does not depend on the slow process of natural selection to respond to immediate pressures in the environment.
Here’s wishing you Season’s Greetings with this science-y sprig of Holiday Holly!
#ScienceEveryday when it’s not #ScienceSunday .
⁕ REF: Epigenetic correlates of plant phenotypic plasticity: DNA methylation differs between prickly and nonprickly leaves in heterophyllous Ilex aquifolium (Aquifoliaceae) trees
Carlos M. Herrera and Pilar Bazaga