The title pretty much says it all. Plants are a far cry from the passive green and brown things you thought they were.
**Bizarre Botany will be a four-part series covering the weird world of plants.
Let’s go over some of the strange things that plants do, shall we? This post is going to be all about the sex life of one of my favourite types of plants – the orchid.
In a way, yes. Let’s go over the basics of plant reproduction first of all. Seed producing plants comprise two main types: Gymnosperms and Angiosperms. Gymnosperms are characterised by their ‘naked seeds’ – in the form of cones. So these include things like conifers and cycads. Angiosperms, which evolved later on in the evolutionary scale, are characterised by encapsulating their seeds into ovaries, within flowers. The divergence of angiosperms from the ancestor allowed for a diversity explosion in not only plants, but other life too. They quickly became the dominant type of plant existing on Earth.
So the general consensus is that the flowering angiosperms reproduce via the transfer of male gametes to female gametes, much like animals do. However, the immobile nature of plants requires them to utilise mobile life forms or things like wind or ocean currents, to act as a vessel between two individuals. Whether by bird or bee, pollen grains (which contains male sperm, produced by the microsporangium) falls on the stigma of a different flower. They travel down the style to the ovary, where the female gametes are located.
And orchids do follow this method – for the most part. However, there are some orchid deceptionists out there who taken matters into a rather…different direction.
Orchids, like all other plants, use insects to pollinate them. But in one group of orchids, they don’t attract insects by visual or olfactory cues, like most plants do. Oh no. Some orchids have evolved to attract insects using sexual cues. Mmhmm…
Take the Mirror Bee Orchid (Ophrys speculum) below.
Kind of odd-looking for an orchid, isn’t it? I hear you. That weird blue shiny bit and the furry brown fringe have evolved to *look* like the unfortunate wasp pollinator of the species; Dasyscolia cilliata. It may not fool us, but to an insect’s visual system the similarities are indiscernible. Furthermore, the natural scent of the flowers have evolved to mimic the mating pheromones of the female wasps. Gasp! Deception!
You can probably guess what happens next. A male wasp picks up the scent. He heads eagerly towards it, buzzing with sexual excitement. He’s about to get laid! …or so he thinks. 😦 He arrives at the plant, clambers onto the flower, and–
Mr Male Wasp mates with what he thinks is a female wasp. It’s really just the flower. The motions of the male wasp during the act allows him to be coated in pollen from the orchid flower. This pollen is then passed on to the next flower he lands on, which kicks off the reproductive process for the orchid. Dear me!
But isn’t this a bit counter-productive for the poor wasps? It all seems like an incredible waste of precious sperm, which of course required energy to produce and could have been put to better use elsewhere. Not to mention, the energy costs involved in actually getting to the flower and ‘mating’ with them. The orchid does its job so well that wasps have been observed leaving a real female – during the act – to go mate with the flower instead. Why haven’t the male wasps of duped species evolved measures which would allow them to identify the flower frauds? And how are real female wasps actually getting sperm if it is all wasted on flowers?
This has been a long term research topic of one of my favourite lecturers from my time at university, Dr Anne Gaskett. It’s unknown as of yet why males haven’t developed the ability to detect these femme fatales, but she has found indication that the females of the majority of those species that are used by orchids are able to reproduce without the use of sperm or males. It’s called Parthenogenesis, and will be covered in a future post.
So, even if male wasps have their happy ending in the throes of passion with a flower, there is little loss to the species on a whole. Yay!
Featured image is sourced from http://conservingorchids.org/wp-content/uploads/2013/07/bee-orchid.jpg.