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.

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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The Toadlet Diaries 2: Gulf country.

In 2010 I was fortunate to accompany herpetologist Dr. Renee Catullo on a trip through Australia’s Top End collecting little brown frogs. Here are some of my field notes along with photography. While my photography has vastly improved, I’m not sure I’ve felt so inspired to write since that trip. I hope this series of vignettes communicate some of the flavour and excitement of the wet season in Australia’s monsoon tropics.

(Part one here)

31 January 2010

I was relieving myself a stone’s throw from the inundated Carpentaria Highway when I saw my first Brolga. Its lanky form drifted indolently against a pastel sky as the tropical sun poured out late afternoon’s final slanting blaze. I finished my business, picked up my binoculars and shovel, tucked the bog roll under my arm, snatched a nearby burrowing frog with my free hand and wandered back to where Steve had left our hired Landcruiser: bogged up to the axles in the soft roadside sludge.

We had been following a map to the “Lost City”, scrawled on a take-away order pad by a gnarly-toothed cook at Cape Crawford’s “Heartbreak Hotel”. (This sentence is entirely true and gives me great pleasure to write). I had hoped to see the exceedingly elusive Carpentarian Grass-wren there, but like Grass-wrens, Lost Cities are difficult to find. Renee planned to make a 200 km push down and back the Tablelands Highway that night so our search for the Lost City was truncated in favour of beginning the evening’s driving. Our U-turn was truncated on the shoulder of the highway, which had been under floodwater for the last 3 or 4 days and needed little persuasion to engulf the hired Landcruiser.

We had been stalking 300 kms of the Carpentaria Hwy for the last two nights and had seen one car in that time. It was 5.30pm on Sunday and we had enough food and water in the car to last us a few nights should it come to that, but in a great fluke of variance the next 30 minutes sent us three different cars. Our eventual saviour rocked up in a big old Landcruiser. As a spry indigenous woman jumped out of the passenger seat to retrieve a rope from the tray, a man as weathered, wide and red as our fair country hopped out of the driver’s seat. Our saviour was in a hurry, the rope quickly linked our cars back to back and he barked some instructions to an unsure Steve behind the wheel of our stricken vehicle. Soon wheels were spinning as his truck revved and squealed, switching about like a hooked barramundi. Steve eventually found 4WD, low range, reverse and our steed was yanked backwards from the muck.

Impeded on the Carpentaria Hwy

Impeded on the Carpentaria Hwy

That was the beginning of one of the most eventful evenings of the trip. We were now running a bit late, but counted ourselves lucky to have gotten away with an hour delay. The drive ahead saw us traveling south down the Tablelands Highway, a road that splits rocky cliffs of rust red upon which the ivory white bark of eucalypts is thrown into dramatic contrast by the light from the setting sun. We stopped on a vast flat grass plain after dark and watched the moon rise, a giant languid yellow disc that was to light the rest of our evening.

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It is worth mentioning that I only refer to the roads by name because there are so damn few of them here in the Top End. Each road takes on a character through its interaction with the elements, the lansdscape, and the idiosyncrasies of the disparate roadhouses, towns and remote communities it links across vast distance. These bitumen ribbons of country and the hours spent on them forms a large part of the Top End experience for residents and visitors alike.

Soon after dark the animals started throwing themselves in front of the car. A remote wet season highway at night is chaos. I’ve never seen so much wildlife ever, and you’ll be pleased to know most of it survived. Bustards, nightjars, owls and curlews appear in the headlights, I brake and they make a flapping flash in my periphery as they fly within centimetres of the windscreen. Agile wallabies bound in groups across the road ahead, or sometimes they just stand on the road shoulder, waiting for us to drive closer before darting out into our path. The road is littered with frogs, only discernable as the car drives on over them. But one can’t look out for them as it is much more important to spot the groups of Brahman cattle from a distance safe enough to slow down. At several points we’re slowed to sub 10 km/h as dozens of cows slowly bumble down the road in front of you for hundreds of meters. There is nothing to do but travel along behind until they find a spot to vacate the bitumen. In addition to the fauna there’s water to watch for, the road is flooded in some points up close to a meter, and the floods have dragged onto the road a flotsam of logs, branches and general crap to drive around.

Tablelands Hwy denizen with biologist for scale - Black-headed python

Tablelands Hwy denizen with biologist for scale – Black-headed python

When we swapped drivers I had run over what I was horrified to hear Renee later estimate as a total of 30 burrowing frogs. At the wheel, Steve the frog lover perhaps avoided a few more than I did, but unfortunately he was unable to avoid a nail tail wallaby. The nail tails are beautiful creatures up close, covered in soft, fine light caramel fur with faint white markings. A dark dorsal line runs from the back of their neck down their spine to the nail protruding from a spray of thick black bristles at the end of the tail.

That was one day in gulf country, out near Boroloola.

The Toadlet Diaries 1: Trench warfare frogging.

In 2010 I was fortunate to accompany herpetologist Dr. Renee Catullo on a trip through Australia’s Top End collecting little brown frogs. Here are some of my field notes along with photography. While my photography has vastly improved, I’m not sure I’ve felt so inspired to write since that trip. I hope this series of vignettes communicate some of the flavour and excitement of the wet season in Australia’s monsoon tropics.

3 February 2010

Birds, wind, insects, all still, all silent. An atmosphere of exhaustion settles in as the temperature draws near 40. Wanda Inn roadhouse sits baking between red clay and the azure expanse of the outback sky. This would be home for the night, and we’d best get some sleep before tonight’s activities.

Littoria caerulea find respite from day's dry heat by hanging out in the toilets.

Littoria caerulea find respite from day’s dry heat by hanging out in the toilets.

The area hadn’t seen rain for a while but on dusk the moodily flashing cumulus clouds in the distance promised a change in the weather. Soon after dark we find ourselves in frogless country, standing on the roof of the Landcruiser captivated by the lightshow of distant electrical storms. As time passes the breeze blows harder, and we drive closer to its origin. Soon we are buffeted by a stiff cool wind, petrichor fills the air, fat drops of rain spatter and we are surrounded on all sides by the intermittent discharge of three kinds of lighting. Coruscating bolts crack somewhere between us and the horizon, leaving their jagged after-image in negative on our retinas, snaking fingers of electrical tracery race bifurcating and branching in the clouds overhead, and distant bolts diffused through cloud and rain suddenly bathe the land in white, turning puddles into mirrors for the silver sky before plunging us back into darkness. The weather is completely in character for the Northern Territory: at once utterly romantic and dangerously thrilling.

We stop periodically to stand on the car and take pictures of the gathering storm (still no frogs calling) but when a blinding bolt cracks too close for comfort we quickly curtail our roof-standing. Discouraged by the lack of frogs, the talk turns to gin and tonic at our next stop, but when we get there, rather than a refreshing drink, the distinctive chip of the Stonemason toadlet greets us and the frogging is on.

And so the wind blows, fat drops spatter our skin as we stride through waist high grass and negotiate ankle-twisting holes, boot-sucking puddles, and mud that cakes to the mud that’s caked on the mud caked on our boots. We wiggle between the slick ground and barbed wire fences while the sky flashes chaotically, rumbling and booming, and we stalk around pools thronging with the disorientating din of burrowing frogs, occasionally glimpsing the wide eyes of the other when the land in an instant becomes awash in the white of a nearby burst of lighting. This was trench-warfare frogging.

Top End storm

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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

Mount Gilboa’s meadows.

This has been my sometimes workplace for the last two weeks:

The slopes of Mt. Gilboa. Watsonia densiflora in the foreground.

The slopes of Mt. Gilboa. Watsonia densiflora in the foreground.

To catch pollinators in action you need fine weather. On those days when the skies are clear and there’s little more than a gentle breeze in the air, Mt Gilboa is an exciting place to be. Gleaming green Malachite sunbirds chase one another between aloes, eagles and vultures wheel overhead, a startled bush buck bounds down the slope and out of view.

On these days the flowering veld is humming with the noise and motion of uncountable beetles, bees, flies and wasps, flitting, buzzing, mating and feeding. Protea heads crawl with furry monkey beetles, massive grasshoppers zoom by on the wing and bees of varied colour, shape and size forage diligently.

The flowering veld

The flowering veld

I come here to collect long tongue flies. As you prowl among the Watsonia inflorescences you first hear the telltale loud buzz, then look for the hovering fly probing a flower with its long proboscis.

Philoliche aethiopica foraging on Watsonia densiflora

Philoliche aethiopica is a specialist forager on Watsonia densiflora. This fly’s thorax is completely covered in pollen.

Netting the flies is not too difficult—they are lazy fliers. Keeping them alive in my flight-cage back closer to sea level has proved to be the big challenge. With the season wrapping up for this site, I’m unfortunately looking at the possibility of coming away with little more than just jars of dead flies.

Watsonia lepida, common veld iris and long tongue fly host plant.

Watsonia lepida, common veld iris and long tongue fly host plant.

Despite the setback there are other research avenues to pursue as the Summer field season unfolds. The luxury of a long field season is one factor that makes this veld such a productive place to study pollination.