Monday 24 June 2019

How an Irish bog plant learned to catch flies

Jim Hurley - Nature Trail

The Round-leaved Sundew is the most common insectivorous plant found in bogs and wet, acid ground throughout Ireland. It has round leaves covered with crimson-coloured, sticky, gland-tipped hairs, each topped with a drop of dew-like glue to attract, trap and digest insects. But, how did the sundew 'learn' how to catch flies? The reasoning goes something like this.

Since bogs are poor in nutrients, especially nitrogen and phosphorus, many plants do not grow well in these habitats. In the distant past, after it had rained, drops of rainwater clung to the leaves of bog plants. Tiny insects got caught in the raindrops by the water's surface tension. Some drowned, died and started to rot resulting in a drop of nutrient-rich soup. The sundews absorbed the nutrients through their leaves, giving them a little boost in the harsh environment they were trying to survive in.

Sundews, like people, differ. Individuals that happened to have traits that facilitated absorbing nutrients from insects grew and reproduced better than their neighbours. Traits that aided holding raindrops and enhanced insect-catching included having hairy leaves rather than smooth ones, having slightly concave leaves rather than flat ones, having a colour other than green, being sticky, having the ability to curl inwards, etc.

All these tiny advantages working in combination over millions of years resulted in those with the best and most advantageous traits surviving and thriving and those without dying out. The gene pool got refined over very many generations as natural selection and random mutations dictated that the fittest survived and those less fit perished.

The most important thing about the less fit perishing was that by dying they failed to breed. Their demise took their unsuitable genes out of circulation.

The strongest evidence that the above sequence of events was the likely process that produced insectivorous plants is the fact that totally unrelated species of plants growing in bogs on different continents all evolved techniques for catching insects.

The conclusion must be that the challenges that a habitat poses, drives different life forms in different places to independently adopt similar solutions to overcoming the challenges posed by growing in a nutrient-poor environment.

The phenomenon is called 'convergent evolution'. Life forms evolve or change in ways that converge or come together to address similar challenges posed by an environment. So, the Round-leaved Sundew never 'learned' to catch flies; it is simply the product of the forces of nature at work over long periods of time.