Sex Changing Trees?
During November of last year researchers discovered that the Fortingall Yew in Perthshire, one of Europe’s oldest trees, was undergoing a change in sex. The 5,000 year old tree that was thought to be male began fruiting; A process only seen in female yews. This sparked many a debate about the in’s and out’s of trees and their gender, including how and why some trees undergo a “sex change”.
Many plants are hermaphroditic, able to produce both sets of gametes from both male and female reproductive structures. Other plants are what is known as monoecious, meaning it produces flowers containing male reproductive structures, and flowers containing female reproductive structures. Most coniferous trees and some deciduous shrubs, much like humans, are entirely male or female depending on the individual organism. These species are known to be diecious.
Changing sex in the natural world is not unheard of, and is commonly known as ‘sequential hermaphroditism’. Thought to be caused by environmental pressures, this is a process that involves undergoing a change in genetic and morphological characteristics to become the opposite sex. Although commonly found in invertebrate and gastropod species, it can occur in plants too.
It is generally thought that monoecious plant species that are able to change sex, do so to avoid self-pollination due to them having flowers closely positioned next to one another. Close arrangements of flowers on a plant can mean pollinators often fertilise flowers on the same plant rather than on other individuals. As inbreeding can raise a variety of problems, a change in sex may be beneficial. Cleverly, some plants are able to position flowers with female structures below flowers with male structures. This means that insects ascending up the plant are unable to spread pollen from male to female flowers.
Sequential hermaphroditism in diecious plants is less common and still remains somewhat of a mystery to scientists. In the case of the Fortingall Yew, it has been suggested that instead of a complete change in sex, it simply produced what is known as a lusus or a “sport”. This is a portion of the tree that differs morphologically to the rest of the plant. Nectarine trees have sometimes been known to grow sports that produce peaches, therefore it is not too farfetched to believe that the Fortingall Yew could produce a female sport. Although it is not quite the spectacular and intriguing “sex change” that media outlets reported, “sporting” is still a fascinating process and worthy of further investigation.
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