Planning for pollination in Australia’s largest orchid translocation
It’s not often you get the chance to increase the size of a threatened species’ population in one month, let alone the population of 3 threatened species. Yet this is what the wild orchids project achieved in July this year.
Prior to this project, just 1,809 sand-hill spider-orchids (Caladenia arenaria), 1,122 Oaklands diuris (Diuris callitrophila) and 603 crimson spider-orchids (Caladenia concolor) were known to be left in the wild. Now, the population of each of these orchids has been increased by more than 1,600 individuals for the sand-hill spider orchid, a whopping 4,000 individuals for the Oaklands diuris and over 430 individuals for the crimson spider orchid.
While most of the actual planting took place over just two weeks in a flurry of activity involving volunteers and project partners, it was far from a simple case of planting the orchids in the ground and leaving them to their own devices. This work was the culmination of years of research and overcoming challenges and has resulted in some astounding discoveries about the private lives of these enigmatic plants.
Translocation involves moving a species around the environment to ensure populations are sustainable in the long term. This can be done by creating new populations and reinforcement (adding to) existing populations. It can be particularly helpful in cases where genetic diversity is low within a species.
'Seed was collected from existing wild populations and propagated by the Royal Botanic Gardens, Victoria,' says Anna Murphy, Senior Threatened Species Officer with Saving our Species (SoS).
This process all sounds simple enough, but germination presented the first major hurdle. Most plants get nutrients from their roots. However, these orchids also rely on a symbiotic relationship with mycorrhizal (literally means fungus root) fungi to germinate in the wild and to aid in uptake of nutrients from the soil. So unique are these relationships that the mycorrhizal fungi are often specific to the genus or species of orchid.
Dr Noushka Reiter, Senior Research Scientist at the Royal Botanic Gardens Victoria, set out to understand which fungus was associated with which orchid, and how to grow that fungus in the lab to germinate and propagate these highly threatened orchids.
‘It was very exciting to see these orchids germinating symbiotically in their petri dishes in the lab and later growing these in the nursery, a process which took many years,’ says Dr Reiter.
It’s also a very complex process to choose a translocation site. You don’t want to go to all the effort of collecting seed, isolating the mycorrhizal fungus, and germinating and growing the orchids only to plant them where they won’t survive. Typically, this process involves assessing the vegetation that occurs around existing populations and then finding sites that match this vegetation community and have pollinators present (more on that in a second). As the plants are grown symbiotically with their fungi, the fungi are transferred to the site with the orchid.
Plant–pollinator interactions also play an essential role in the long-term survival of these populations. The absence of the most effective pollinator can make or break the success of an orchid translocation, but identifying an orchid’s pollinator can be a notoriously hard research question to crack.
Research into plant pollinator interactions identified some amazingly specialised evolutionary relationships between orchids and their pollinators. Most orchids have a one-to-one relationship with a pollinator species. However, some can be generalists, attracting multiple pollinator species.
Before this project, the pollinator relationships for these 3 orchid species were shrouded in mystery. One thing was certain, though – they required a pollinator in order to set seed, and without pollination the next generation of plants couldn’t be produced and the translocation would not be successful in the long term.
The first step in uncovering this mystery was to identify which insect species pollinate the orchids and whether they were present at the proposed translocation sites. This was done through a process called ‘pollinator baiting’ – where the potted orchids are placed in the wild to see if they’re visited by their pollinators and observe how these pollinators are interacting with the orchids.
‘We found some really unique pollination strategies with each of the species,’ says Dr Reiter.
‘The crimson spider orchid was a particularly tricky pollinator relationship to unpack, because it’s pollinated by one species of tiny little wasp. Insects are normally active between 10am and 4pm, but we weren’t getting any pollinator action during those times.’
Dr Reiter happened to be out later than usual one day – and that’s when it all clicked. She observed the wasps flying and crawling over the plants in the evening before coming together in groups to roost on the plants overnight. This is when the pollination was occurring.
‘It was about understanding a new way to survey for these pollinators, and from that critical moment it became quite easy,’ says Dr Reiter.
‘We could take potted plants out on a warm day and leave them there overnight, come back early in the morning when it was very cold and these little pollinators were all sleeping on the plants so we were able to confirm the locations they were present at.’
The sand-hill spider orchid was a bit easier to figure out. This orchid provides a nectar reward for pollinators and was visited by 2 species of thynnid wasp and one species of native bee, which made it far easier to find translocation sites.
In contrast, the Oaklands diuris produces a tiny amount of nectar, definitely not enough to reward its pollinators. Research by the Royal Botanic Gardens Victoria showed that one of Australia’s favourite bees, the blue-banded bee (Amegilla chlorocyanea), is the key pollinator for this species. The Oaklands diuris doesn’t waste energy on providing a reward to encourage a bee visit Instead, it has evolved to trick its bee pollinator into pollination with a bit of botanical subterfuge.
We think the orchid uses ‘generalised food deception’ by resembling other rewarding species such as chocolate lilies through the similar colour and smell of its flowers, tricking the blue-banded bees into pollinating the orchid!
For such tiny little creatures, bees have very complex brains and will not be tricked too many times. Luckily, the Wild Orchids team were planning their own botanical subterfuge.
‘The Oaklands diuris are planted in rows, and between these rows we’ll be planting bee-pollinated plants such as chocolate lilies that will help attract and feed the pollinators. We hope that, as the bees travel between these host plants, they’ll make some mistakes along the way and visit the orchids,’ says Ms Murphy. The team will also continue their pollinator research to help boost plant recruitment.
‘As pollinators receive little or no benefit from visiting these flowers, pollination is just a bit of an accident for them, but for the orchids it represents thousands of years of evolution.’
Conserving a complex web
No species exists in isolation. Threatened species recovery benefits more than individual species, and threatened species ecologists work to preserve the complex web of interactions that exist within an ecosystem, from pollinators and fungi to predators and prey. If an orchid is lost to extinction, so too are the amazing and complex relationships that it supports.
The Wild Orchids Project started in 2016 and is coordinated by Murray Local Land Services in partnership with the department’s Saving our Species program. The project is also supported by the NSW Environmental Trust, Royal Botanic Gardens Victoria, Forestry Corporation NSW, NSW National Parks and Wildlife Service, the Australian Network for Plant Conservation, Crown Lands, Parklands Albury Wodonga and Australasian Native Orchid Society.