Thursday, 24 December 2009

Spotty Flowers Survive


Just like dogs, some flowers have spots and other don’t. I’m not sure why dogs have spots but flowers have them to attract pollinators.

In fact pretty much everything to do with a flower is about pollination, preferably moving pollen from one flower to another. Cross-fertilisation, as it is called, is one of the main ways variety is introduced into the genetic makeup of plants.

As circumstances change, the variant most suited to the environment thrives, survives and reproduces. This is how evolution by natural selection works. As Charles Darwin put it, more or less, Nature abhors self-fertilisation.

Many of the odder features of flowers have evolved from competitive evolution with animals. Insects with a particular trait gain extra benefit from a plant, and so thrive and reproduce. Plants with the ability to repel that insect if it’s causing a problem, or to increase the likelihood of it carrying its pollen to anther individual of the same species, will also thrive and reproduce.

A kind of arms war results with quite odd traits evolving such as the development of a 30 cm nectar spur in the orchid flower (Angraecum sesquipedale) illustrated at the top right of my blog.

But back to spots. They appear on the flowers of many species, across many plant families, and have clearly evolved a number of times.

According to a paper in the American Journal of Botany investigating spots on what’s called Beetle Daisy, the prevailing view is that dark petal spots attract pollinators by either ‘intensifying’ the colour and texture, emitting scents, producing nectar, trapping heat, reflecting UV light or creating a guide for navigation. The dark spots may also mimic the pollinator itself, giving the impression of a safe, welcoming flower.

The Beetle Daisy, Gorteria diffusa, has large raised spots at the based of only a few ray florets (daisy flowers are actually a collection of flowers, and what look like ‘petals’ are single specialised flowers). It’s called the Beetle Daisy because the spots were thought to mimic beetles. In fact the main pollinator and attracted insect is a fly.

Meredith Thomas from the University of Cambridge, and colleagues from England and South Africa, studied the development of these spots in great detail. They found that each spot was derived from the fusion of four petals, each with ability to produced part of the spot.

The spots look randomly placed to us and the pollinating flies, but this results from a few predetermined ray florets developing spots and not the rest. Due to the ‘phyllotaxy’ of the flower (i.e. the way and order the bits and pieces in the flower develop, in this case in a Fibonacci series – see earlier blog for background) the spots later appear to be random.

The end result is a flower that looks like it has a couple of flies resting on its petals. All very comforting for the potential pollinator, and all good for the survival of the daisy species.

Image: Image of a Beetle Daisy flower with two prominent spots (the so-called Niew variant) from the American Journal of Botany on-line. For more information see the media release or the full article which is freely available until 17 January 2010.

5 comments:

Greenfingers said...

Fascinating stuff. There's a similar interesting story about 'decoy flowers' in wild carrot that puzzled Darwin - see http://cabinetofcuriosities-greenfingers.blogspot.com/search/label/Daucus%20carota

Tim Entwisle said...

Thanks for the link! It seems from my reading that there is still a lot of conjecture around about what 'random' spots do whenever they occur. Most likely it's for attracting pollinators, and most likely they look like an insect is already on the flower. But as that blogs says, we needs naturalists (and scientists) with time to spare...

Term Papers said...

"Just like dogs, some flowers have spots and other don’t. I’m not sure why dogs have spots but flowers have them to attract pollinators" Well May I know that How flower's attract to a dog?I think dogs are not interested in flower's.I am waiting for your reply.


Term papers

Tim Entwisle said...

I think you are right. Dogs are not attracted much to flowers. They certainly don't pollinate any species I know of!
Why they have spots is presumably quite different to why flowers have spots, but that's for a zoologist to explain.

flower Philippine said...

Good! glad that it still survive, some flowers that has a spots mostly die. Anyway, thanks for sharing this post. Looking forward for your next post.

-pia-