New paper: The whimsical long-proboscid fly and its favourite colour.

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The flowers on one of these plants conceal drops of sticky nectar. The other is a cheating orchid, presenting empty flowers and false promises. Can you tell which is which? Even if you knew which one carried nectar, how can you tell the difference between them? The two plants might look a bit different to human high-res optics, but now try blurring your eyes. Pretty similar, huh?

What about this pair?

Screenshot 2018-10-30 15.09.50If it’s difficult for our brains and eyes to discern the difference between the flower with the reward and the one that’s falsely advertising, then what hope does a nectar-hunting fly with low resolution compound eyes and a smear of a central nervous system have?

Specifically, I’m talking about this fly…

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If this fly looks embarrassed, its because it has orchid pollen stuck to its face.

Until now, you probably thought lion, or elephant, or rhino were the most impressive animals roaming the grasslands of southern Africa. Well you’re wrong, and it’s ok to change your mind after seeing the majestic long-proboscid fly of South Africa. There are several species of these magnificent beasts, and this one is named Prosoeca ganglbaueri.

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That giant proboscis hanging from its face is a tool crafted by evolution for sucking nectar from the bottom of long flower tubes, and it can grow as long as 5 cm (which is longer than the fly’s own body length). Unlike butterflies who coil their proboscises, the long-proboscid flies simply hinge the instrument down, tucking it away underneath their bodies to trail out behind them. And this species isn’t even the most extreme: proboscises in Moegistorhynchus longirostris get up to 8 cm!

Sometimes handling that long instrument can be a challenge…

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In some areas of South Africa, P. ganglbaueri is the only creature capable of extracting nectar from flowers with very long floral tubes, and because of this it has become the exclusive pollinator for 20 species of plant. Altogether, the long-proboscid flies as a group bear the great responsibility as the only pollinator for approximately 130 species of plant, making them a truly important creature for the ongoing survival of many South African plants.

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Figure 1 from Whitehead et al. (2018): Prosoeca ganglbaueri feeding from a variety of nectar sources. (a) Zaluzianskya microsiphon, (b) Scabiosa columbaria, (c) Agapanthus campanulatus, (d) Dianthus basuticus.

An interesting fact about flowers that are pollinated by long-proboscid flies, is that most of them are pink, or white, or some variation in between (with one blue exception). This strong colour preference is a critical feature directing the evolution of the cheating orchid flowers introduced earlier. For a deceptive orchid to attract this fly, the orchids’ flower colour must match the flies’ colour preference, or the mimicry simply won’t work.

In my recent paper, we asked whether the colour preference of flies was something that they learned, like we learn to associate that perfect golden-brown hue of fried food with a mouth-watering culinary experience, or if it was instead a more hardwired innate response, like a moth drawn to a lamp. The answer is important for understanding ultimately what is driving the evolution of false advertisement signals in mimic orchids. So, for example, if flies had an innate bias to pink or white, then cheating orchid flowers would evolve to match that bias, in the same way that any good advertisements are designed to appeal to the fundamental desires of its audience. On the other hand, if flies learned to associate nectar reward with certain colours, their preference should be determined by the colour of their local nectar diet. Under the learned scenario, orchids should be evolving to match local flowers’ colours, not any intrinsic bias of the fly.

To test this, I took advantage of just how easy it is to bamboozle these flies. With a home-made artificial flower, painted to match the pink and white flowers visited by the fly, anyone can fool a fly into attempting to feed. So I mounted a pink and a white model to my “interview stick”, and travelled across the rugged Drakensberg Mountains to interview various populations of flies. In each location, I recorded whether the local flies preferred probing the pink or white model flower, as well as the colour and species of flower that the flies were using for nectar there.


The results were clear. Flies used to feeding mainly on pink flowers preferred the pink model. Flies that fed mainly on white flowers preferred the white model. And flies that fed on both pink, white, and violet flowers, showed no clear preference between pink and white.

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Figure 3 from Whitehead et al (2018): Pink-white preference for flies at seven sites. The x-axis shows colour preference, with pink on the right, white on the left. Measured preference at seven sites is represented, with the colour of local nectar sources depicted in the small pie charts.

This tells us that the flies are very flexible in their preferences, and the strong implication is that these flies are learning to associate colour and reward. A further result showed that as the variation of colours flies fed from increased, this made them less choosy in the pink-white preference choice. So the bottom line is that the colour of their local nectar-buffet strongly controls a fly’s colour preference.

What does this mean for orchid cheats? Well, the colour of nectar cheats is all important, and what matters most for the success of a deceptive orchid is the colour composition of the surrounding nectar-rich floral community.

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Post-script:
Still wondering about which flowers in the opening images were cheats, and which had nectar?

In both cases the deceptive orchid is on the left. The first image features Disa nivea (left), and Zaluzianskya microsiphon (right), the second features Disa pulchra (left) and Watsonia lepida (right).

Reference:

Whitehead MR, Gaskett AC, Johnson SD. (in press) Floral community predicts pollinators’ color preference: implications for Batesian floral mimicry. Behavioral Ecology 

New paper: Plants and their very variable sex lives.

Plants mate. In a manner far more elegant than our own mammalian shenanigans, and far more important for the ongoing survival of the Earth’s ecosystems, plants are out there constantly having sex. And it is a deeply interesting thing involving insects, and wind, and stigmas, and stamens, and enough puzzling evolutionary biology to fill journal articles and occupy a small handful of academic careers.

My latest paper is about plant mating, and rather than wade through meadows of blooms to collect the data for this effort, I remained desk-bound in Milwaukee, wading through 30 years of plant mating literature with the intention of assembling a dataset to help us see plant mating in a new light.

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A mint-bush (Prostanthera lasianthos), caught in the act of mating.

As you may know, the flowers of many plant species are hermaphrodite, i.e. they bear both male and female sexual organs. This means plants can have sex with themselves. It’s called self-pollination, or “selfing”, and it can happen in two ways. First, pollen can move from the male parts of a flower to the female parts of the same flower. Second, on a single plant, pollen can move from the male parts of one flower to the female parts of a different flower.

“But isn’t this inbreeding??” I hear you ask, recoiling in horror at the moral and population genetic gutter down which I have so suddenly led you. Yes! Seed fertilized in a selfed flower is about as inbred as it gets, even more so than sibling mating. But you see, inbreeding is not always a bad thing—in fact inbreeding can actually be beneficial in some circumstances—and here’s where things get messy.

Genes are selfish. As such, they will do whatever it takes to get themselves propagated into another body. Consider then the selfish genes of a mother plant, which want to get into the next generation, and into as many individuals as possible. If a mother plant mates with a genetically different plant (an “outcross” mating event), its seeds each inherit approximately 50% of the mother’s genetic variation. This is because they combine with (and are diluted by) the genes of the pollen donor during pollination and sexual reproduction. On the other hand, if a mother self-fertilizes its own seeds, it transmits closer to 100% of its genetic legacy into each offspring. In the eyes of natural selection, this is a huge difference, and offers a great advantage to selfing over outcrossed reproduction.

So why aren’t all plants selfing all the time? This is because the huge advantage in transmitting genes via selfing is offset by the drawbacks of inbreeding. You can’t often get away with inbreeding without cost, and the cost is that inbred offspring are commonly less fit than their “outbred” siblings. Called “inbreeding depression”, this occurs because breeding from related individuals vastly raises the probability of combining rare genetic variants that harm the individual they are in. In the long run, inbreeding also reduces genetic variation that is essential for adapting to changing environments.

Evolutionary biologists have been pondering this tension for decades, and it led to the hypothesis that plants should be driven by natural selection into two polar opposite strategies: selfing plants should be favoured by natural selection when inbreeding depression is weak, and outcrossing plants should be favoured by natural selection when inbreeding depression is strong. Anything in the middle should not be adaptive, and should therefore be rare in nature. Sounds sensible, except numerous studies have now measured selfing/outcrossing across hundreds of plant species, and there is a curious and difficult-to-explain preponderance of plants that are neither exclusively selfing or outcrossing. These plants are having it both ways, seemingly hedging between strategies, and we call them the “mixed maters”.

Now for the problem my study addresses… Over the last 30 years, loads of studies have been measuring the selfing/outcrossing rate of plants in the wild. There have also been important studies which collect all these outcrossing estimates into big global datasets and generate observations like the one above: that mixed-mating is inexplicably common. For 30 years however, much of this discussion on global patterns was centred around average outcrossing per species, and using this to classify a species as a “selfer”, “outcrosser”, or “mixed mater”. We know evolution doesn’t work on a “species level” though. What is more appropriate is what is happening in a population context. And perhaps by averaging away all the variation within each species, my co-authors and I thought we might be missing an important perspective on the data.

What my co-authors and I did then was to collect all the outcrossing estimates from published papers containing three or more population outcrossing estimates. Going back 30 years, we collected data for 105 species and measured the variation in outcrossing within a species, among populations.

What we found was huge variation! There was commonly so much variation in mating within a species, that species averages felt inadequate for expressing where mating system variation lies. The data also showed that variation was difficult to predict. For example, there was an old hypothesis floating about that wind-pollinated plants were less variable in their outcrossing/selfing rate than animal pollinated species. The reason being that animals were thought to fluctuate more in their abundance and service between sites and seasons, while wind was a more consistent, reliable force for pollination. For the first time we were able to test this, and our analysis did not support the hypothesis. We also tested whether mating variation was evolving in a predictable fashion, but found that the relationship of plant species had no bearing on the variation we found in those species’ mating patterns.

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Arabis alpina: revealed in our study as a species with one of the most variable mating systems measured. By Hedwig Storch CC BY-SA 3.0, from Wikimedia Commons.

Ultimately, our study can’t solve the mystery of why we have so many mixed-mating plants. What it does do though is present a new way to look at the known range of variation in plant mating. There are other analyses waiting to be done with the data collected here, and we have highlighted where more studies are needed to answer interesting questions. For example, do different kinds of animal pollinators result in more or less variable outcrossing? Or do populations on the fringe of a species’ range experience more or less variable outcrossing?

As the body of knowledge on plant mating systems continues to grow, this dataset will grow too, and this population-level perspective on plant mating will hopefully provide the basis for the next insights into evolution’s influence on plant mating.

 

Full reference:

Whitehead MR, Lanfear R, Mitchell RJ, Karron JD. (2018) Plant mating systems often vary widely among populations. Frontiers in Ecology and Evolution, 6:38.

Further reading:

Goodwillie C, Kalisz S, Eckert CG. (2005) The evolutionary enigma of mixed mating systems in plants: occurrence, theoretical explanations, and empirical evidence. Annu. Rev. Ecol. Evol. Syst., 36:47-79.

Schemske, DW and Lande, R. (1985) The evolution of self‐fertilization and inbreeding depression in plants. II. Empirical observations. Evolution, 39:41-52.

Barrett, SC and Harder, LD. (2017) The Ecology of Mating and Its Evolutionary Consequences in Seed Plants. Annual Review of Ecology, Evolution, and Systematics, 48:135-157.

First video of bird pollination in Astroloma stomarrhena

I’m thrilled to share this never-before seen sequence of birds feeding on Astroloma stomarrhena, a winter-flowering shrub endemic to Western Australia.

Earlier this year, I decided A. stomarrhena looked like a perfect candidate for my new study on pollinators and gene flow. What I needed was a bird-pollinated species of plant, closely related to an insect-pollinated species. This one seemed to match all the criteria I needed, except there was no evidence that it was bird-pollinated. But with those long, tapered corolla tubes, and that pink-red coloration, I believed that birds absolutely had to be the pollinator.

The danger was, that while birds might be visitors, the plant could be somewhat “generalized”, and also use insects. This is pretty common, especially in places like Australia where European Honeybees (Apis mellifera) have invaded ecosystems that evolved in their absence, and honeybees will visit absolutely everything whether the plants are adapted to bees or not.

By deploying a new camera-trapping method that I am developing to record insect visitation, I was able to gather several days of pollinator observations, despite some very bad weather. After initially being baffled as to what honeyeater might visit such a low ground-hugging shrub, I got my answer after day one, when I captured video of my new favourite bird: the Tawny-crowned Honeyeater (Gliciphila melanops) feeding on the flowers. Furthermore, the recordings of honeybee fly-bys are sufficient to rule them out as pollinators.

This little result is a win on two fronts: a successful trial of new pollinator-monitoring cameras, and vindication of predicting pollinators from flower morphology.

Click here for the full HD video.

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Bumping into old floral friends, and pollination with a hug.

Rare plants nurseries are like second hand bookshops. It’s always so tempting to browse on the off chance you find that little treasure. I recently visited a charming rare plants nursery in Mt Macedon (boutique-y town outside Melbourne, Australia) where I discovered these for sale:

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Hello old friend! (Hesperantha coccinea)

The last time I saw this elegant iris, it was flowering on stream banks 10,000 km away in the Drakensberg Mountain range in South Africa. There in its natural habitat, it is pollinated in some areas by a very special butterfly: the Mountain Pride (Aeropetes tulbhagia). In other places, it is pollinated by the amazing long-tongue fly (Prosoeca ganglbaueri). The two forms are a wonderful example of “pollination ecotypes”, where different populations are undergoing adaptation to their unique pollinators. The fly-serviced ones are a pink hue with narrow petals, while the butterfly-pollinated ones are much redder with broader petals.

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Hesperantha coccinea at home in South Africa with its pollinator (Prosoeca ganglbaueri).

Fast forward two weeks, and I’m home walking the dog in my quite unremarkable Melbourne suburb, when who should I see?

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Hello old friend! (Diascia sp.)

It’s winter here, with very little in flower, but these brilliant little pink blooms volunteering themselves from underneath a fence in suburban Melbourne really made my day. The last time I saw a Diascia, it was growing amongst the boulders on creek beds and on cliffs in the Drakensberg Mountains. These are Diascia, or “twinspur” and its this common name that alludes to their fascinating pollination story.

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Hug-pollination by oil-collecting bee (Rediviva sp.) in Diascia.

Diascia have two spurs on the back of the flower, which is distinct from the usual arrangement of a single nectar-spur. The difference is that these flowers don’t reward pollinators with sugary secretions, instead they provide oil to specialised oil-collecting bees in the genus Rediviva. The bees use this oil to line their nests and provision their young. In order to collect the nectar, they must reach deep into the twin spurs with their lanky forelimbs, and comb it out. In so doing, they effectively hug the reproductive parts of the Diascia flower and effect pollination.

In Spring, I plan to take some cuttings from this little Diascia. Keeping species with special personal significance is a deeply satisfying part of cultivating plants. A plant can be kept like a souvenir or memento marking a time in one’s life, just like a photo or trinket. But plants have an advantage over these inanimate reminders. Because biological reproduction requires the physical donation of part of the mother’s cells to the daughter cells, my keepsake plant can be viewed as a physical part of the plant that appears in my fond memory. If I could see in four dimensions, I could literally look down the line of cell-divisions all the way back to where the Hesperantha in the nursery physically intersects as the same individual with the Hesperantha I observed flowering in the Autumn sun of the Drakensberg Mountains in South Africa.

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The Drakensberg Mountains, South Africa, Autumn 2014.

 

Australia’s sexual swindlers.

Seduction. Pollination. Deception.

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I recently wrote an article for Wildlife Australia about Australian sexually deceptive orchids, their evolutionary biology, and historical and current research about them. You can download and read the article here: PDF. Thanks to Carol Booth for her collaboration and editorial guidance.

The latest of Australia’s sexually deceptive orchids that I have seen (below) are Caleana major, the Flying Duck orchid (left), and a spider orchid Caladenia clavigera (right). Both were photographed last week in Brisbane Ranges NP, Victoria.

Flowering this year is one of the best seasons of recent times both east and west of the country. So if you’re in Australia, don’t miss the chance to get out bush and enjoy it.

Sex, lies and pollination. Australia’s remarkable sexual swindlers.

Article reposted from original publication with The Territories.

Rather than luring its pollinator with the promise of food this flower uses an equally, if not more, powerful motivator: sex.

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In shades of dusky green and claret red, the bird orchid’s subdued palette hints at its alternative lifestyle. The usual strategy for flowers attempting to catch the compound eye of a passing insect is to advertise proudly. Petals are used as panels for saturated colour, assembled en masse into conspicuous aggregate displays exuding exotic scents. In this way, nectar-filled flowers loudly broadcast the promise of their reward to entice would be pollinators into servicing them.

 

A deviant among flowering plants, the bird orchid eschews these typical hallmarks of floral advertisement. Crouched modestly on the forest floors of eastern Australia, its stature belies its status as one of the supreme specialists amongst the world’s flowering plants. Like those other showy flowers, the bird orchid needs the service of a pollinator from time to time, however unlike most other flowers, it attracts its pollinator without the payment of any reward. The orchid flower in fact completely lacks nectar.

 

Rather than luring its pollinator with the promise of food this flower uses an equally, if not more, powerful motivator: sex. Undetectable to human senses, the orchid’s advertisement is a precise chemical mimicry of a female wasp’s sex pheromone. This is targeted marketing at its finest, as the use of a signature sex pheromone ensures that the orchid attracts only males of a specific species of wasp.

 

Skimming by on wide zig-zagging flights, the wasps are interminably attracted when the ruse takes hold. They alight onto the flower with fervor, probing and hunting for the mate that their senses scream must be there. Bucking back into the column of the flower (the reproductive parts of an orchid flower are fused in this special structure), they make contact with the anthers and a large packet of pollen is deposited on them. The wasp disengages eventually and leaves, but soon, elsewhere, he will catch on the breeze the smell of a mate, and if fooled again, fulfill his role as duped courier for an orchid’s reproductive ends.

 

Called “sexual deception”, this mode of pollination was noticed by Darwin and his contemporaries in an age in which Europe’s natural sciences were in full bloom. It was a naturalist in Blackburn, Victoria however, who was first to discover the phenomenon outside Europe. In 1927, Edith Coleman had turned her great capacity for observation of the natural world to a peculiar native orchid. Resembling more flesh than flower, Cryptostylis, known also as “tongue-orchids” had caught her attention for its magnetic allure to a specific kind of wasp. Through her observations, Coleman was able to discern that male wasps were being attracted to the flower in order to copulate with it. An experiment through a window showed scent to be the primary attractant, and Coleman even observed the ejaculate remaining after having been visited by clearly convinced wasps. She wrote up her notes in a series of papers for the Victorian Naturalist and Transactions of the Royal Society for Entomology, which made quite a splash with the best of botany at the time.

 

We now know this was the tip of the iceberg. Australia is not only home to tongue orchids, but hosts a diverse array of other sexually deceptive orchids including the spider orchids, elbow orchids, hammer orchids, dragon orchids, greenhoods, duck orchids, hare orchids, beard orchids, bird orchids, and the list goes on. Harbouring over 50% of the world’s known examples of sexually deceptive pollination, Australia is certainly the world’s hotspot for this unusual phenomenon. Remarkably, we have several hundred species that employ this unique brand of pollinator attraction, and what is more remarkable, the evidence points to at least six different independent evolutionary occurrences in the Australian orchid family tree. To our eyes, sexual deception seems like a freaky, unlikely strategy and its repeated independent incidence through Australia’s evolutionary history is therefore a startling paradox.

 

Although the reliance on a single species of pollinator for pollination seems precarious, studies have demonstrated that sexual deception comes with the advantage of promoting healthy breeding for our native orchids. In nectar-bearing plants, foraging insects will frequently move between flowers on the same plant and between neighbouring plants. Called “optimal foraging”, exhausting local nectar supplies in a patch before putting energy into finding a new buffet makes economic sense for a nectar-feeding insect. Sexual deception however, has been shown to drive pollinators far from the flower after being fooled, so that pollen escapes the local neighbourhood. As a plant, your neighbours are likely to be related to you, thus deception is a way of ensuring offspring quality by avoiding breeding with your relatives.

 

Another factor supporting the profusion of our sexually deceptive species is Australia’s immense diversity of insects to fool. Although there are examples of gnat and ant sexual deception systems, wasps are the most commonly targeted pollinator for our orchids. Incredibly, we are only now beginning to uncover the immense hidden diversity of Australian wasps. For example, a recent study in a small patch of bush near Margaret River uncovered 28 species of wasps, most of which were previously unknown to science. With each of these species most likely having their own private sex-pheromone cocktail, there is seemingly a kaleidoscope of chemical communication channels available for different orchids to exploit.

 

Despite our deepening understanding of the natural history of sexual deception, its repeated occurrence in Australia remains a true puzzle.

 

Try the Atlas of Living Australia’s region search to discover which orchids (Plant family: Orchidaceae) live near you. [Link: http://biocache.ala.org.au/explore/your-area%5D

New article: The Territories

The Territories is Heath Killen’s new project. The site blends stories of Australia’s natural and cultural history under a unique aesthetic. I encourage you to check it out.

I was happy to make a recent contribution to The Territories, a story and photo gallery about Australia’s abundance of deceptive orchids:

“Sex, Lies and Pollination”

Rather than luring its pollinator with the promise of food this flower uses an equally, if not more, powerful motivator: sex. Undetectable to human senses, the orchid’s advertisement is a precise chemical mimicry of a female wasp’s sex pheromone. This is targeted marketing at its finest, as the use of a signature sex pheromone ensures that the orchid attracts only males of a specific species of wasp.

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Sex, Lies and Nectar: Evolutionary Biology as Written by Flowers

I spoke to the Canberra Skeptics group earlier this week, on a subject most near to my heart. The abstract appears below. It is my aim to soon turn elements of this into a video for online audiences.

In the eyes of evolution, finding a suitable mate for reproduction is one of the most critical stages in any organism’s life. The great majority of flowering plants have outsourced this essential service to animals, giving rise to a fascinating evolutionary dance between plants and pollinators.

Charles Darwin was the first to recognize that flowers were superb teachers of evolution. I will touch on his classic work and explain what we have since learned about remarkable flowers who smell like dung and death, flowers who attract insects with the false promise of sex and a fly with a ridiculously long tongue.

These and other awesome examples of floral evolution would surely have thrilled Darwin, and may even solve his “abominable mystery”: the rapid rise of the spectacular diversity of flowering plants.

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Male thynnid wasp gripping tightly to the lure of the hammer orchid (Drakaea glyptodon).

Pollination, evolution and an orchid’s seductive ruse.

In a PR coup for dumpy little green orchids everywhere, research from my PhD recently landed on the cover of the journal Evolution. But what is it about?

Spring. The Blue Mountains, west of Sydney. Altitude 1000m. Frosty winds whip a swaying eucalypt canopy infiltrated by billowing cloud. Down below, amongst snowgrass tufts, rotting logs and bracken dwell the diminutive bird orchids. Genus: Chiloglottis. They huddle in tight colonies, sporadically sprayed by the high country squall.

Each plant holds two leaves pressed flat to the damp ground. Between the leaves a stem rises, holding aloft a single intricate flower in dusky shades of green and burgundy. When banks of cloud give way to azure sky and the shrike-thrushes resume their piping, these small blooms become irresistible lures.

Their target are the gracile flower wasps. Slim glossy black insects, zooming silently on shimmering wings. They are helplessly drawn to the flower. The bird orchid is emitting a scent, detectable only to wasps, which signals the promise of a mate. Known as ‘sexual deception’, the elaborate ruse uses a precise mimicry of female wasp pheromones to fool male wasps into pollinating the orchid.

However, here on the forest floor there is not only one species of orchid outwitting wasps for its own reproductive ends. Look closer and slight differences in the characteristics of flowers and visiting wasps betray something more complex and interesting. There are actually two species here, looking largely the same, growing in the same places, both deceiving their wasp pollinators through the false promise of sex.

By emitting subtle variations of their chemical trickery, these orchids have “tuned in” to two different pollinator species. This research paper explores this phenomenon as a way of separating the gene pools of closely related organisms. At the heart of it, the story here is about the forces that keep species apart once they split, or reproductive isolation.

First, we show that the different pheromones emitted by the two orchids are responsible for attracting different pollinators. Through arcane powers of chemical synthesis that I do not understand, chemists created synthetic orchid pheromones for us. We took these into the landscape and showed that the two chemicals attract two different wasps. The only perceivable difference between the wasps involved is yellow spangles on the carapace of one of the varieties. What’s more, this specific attraction is exclusive. Chemical A only attracts wasp A, and chemical B only appeals to wasp B.

Next, we take real flowers of both kinds and place them in a row and watch the hapless wasps roll in. We see that wasp A is only attracted to flower A, even when flower B is present just centimetres away. The results are identical to the results of the synthetic pheromone experiment.

On the basis of scent, we therefore expect that orchid A may never mate with orchid B. Exclusive attraction ensures that despite living amongst one another, some orchids may never exchange genes. Despite looking almost the same to us, they may as well exist on separate islands. They distinct separate species.

In order to back this up we then looked at the genetics of the species. By using the same kind of genes used in human DNA fingerprinting we were able to show that the two kinds of orchid exhibit differences in their gene pools of a degree expected if they were different species. Furthermore, analysis showed not a single individual displaying the genetics of a hybrid. Our last tests were to make hand-pollinated hybrids to check that hybrids could indeed form. These crosses showed hybrid offspring germinated and grew faster than pure crosses.

The potential for animals to drive the formation of plant species has long been recognized. This study gives us a strong case study of how that process might look. Our orchids are spectacular examples of the power of pollinators to create and maintain plant species. Through selective pollinator attraction, the orchids have been set upon unique and separate evolutionary journeys.

Further reading:

Whitehead, M. R. and Peakall, R. (2014) Pollinator specificity drives strong prepollination reproductive isolation in sympatric sexually deceptive orchids. Evolution 68: 1561–1575. doi: 10.1111/evo.12382

Rod Peakall and Michael R. Whitehead (2014) Floral odour chemistry defines species boundaries and underpins strong reproductive isolation in sexually deceptive orchids Annals of Botany 113 (2): 341-355 first published online September 19, 2013 doi:10.1093/aob/mct199

Plant pollinator interactions in the South African flora

The slides from my recent departmental seminar at the ANU are below.

The first half of the talk concentrates on plant-pollinator interactions, floral guilds and floral evolution. The second half is a slideshow of vistas, creatures and plants I encountered in my work.