Veld & Flora Feature
THIS FEATURE IS FROM THE VELD & FLORA ISSUE 107(4), PAGES 12-15
Colour them beautiful: Saving the Hilton daisy
The Hilton daisy is iconic and endangered – CAROLINA DILLER & ISABEL JOHNSON tried to find out what might help it survive
FEB 19, 2022 | CAROLINA DILLER AND ISABEL JOHNSON. PHOTOGRAPHS: SUPPLIED
Above: In the ’hills around Pietermaritzburg’ during the 1840s, Ferdinand Krauss (1812-1890) collected the first Hilton daisy specimen – it was orange.
MESMERISING, THRILLING, EXHILARATING – these are our memories of our first sightings of Hilton daisies (Gerbera aurantiaca).
For Isabel, that memory has endured more than two decades. This KZN botanist was completely mesmerised by her first glimpse of the charismatic Hilton daisy on the Byrne escarpment in 2000 – and has been studying the mysteries of its colour variation and reproductive strategies ever since.
The thrill of seeing her first Hilton daisy, south of Pietermaritzburg in 2017, in the first population of Hilton daisies that they visited, crowned Carolina’s first field day in Africa. That first site was at the top of a hill, at the end of a narrow dirt road.
Isabel was driving. Carolina had time to savour her excitement when she caught sight of her first Hilton daisy flower – a bright red spot against a luscious green grassland. And then she saw that several more handsome red Hilton daisies closely surrounded this one spot.
Above: The study site in Mpumalanga is a patch of mistbelt grassland surviving amid farming and tree plantations.
Carolina herself had come the long way round to that grassland – she is German born, mainly raised in Argentina and studied in the USA. In KwaZulu-Natal, she found that she could match her passion for conservation genetics with the Hilton daisy project based at UKZN’s Pollination Laboratory & Centre for Functional Biodiversity.
Carolina joined forces with Isabel – who had been studying the daisy for some time and knew where to find them, what their pollinators are and much more – to work out the population genetics of the Hilton daisy and so try to protect it from likely extinction.
To do this, Carolina enjoyed extensive road trips with Isabel, exploring KwaZulu-Natal and even some of Mpumalanga. For a biologist who had never been to South Africa before, Carolina felt very lucky to be teamed up with a research partner with such knowledge about the local flora, local issues and even local history.
Above: The iconic Hilton daisy is best known for its deep red colour – before the daisy disappeared from the Hilton grounds, pupils at Hilton College used to wear it in their buttonholes on Spring Day.
The Hilton daisy is closely related to the Barberton daisy (Gerbera jamesonii) and to the blushing Barberton daisy (Gerbera viridifolia), prized for its subtle pink petals. Together they are the parents of the immensely successful commercial gerbera hybrids.
The Hilton daisy is also an iconic flower – but, by contrast, it has disappeared from most of its range. This flagship species was once common across the Midlands mistbelt grasslands. Now it is declining and is endangered and threatened with extinction. Hilton daisies are found today only in about 30 small mistbelt grassland patches left between commercial plantations, sugar-cane fields and urban development.
Despite the first site looking like a very healthy grassland with a vast number of red-flowered daisies, Isabel found that seed set there had been extremely low year after year for more than 20 years. The Hilton daisy is not able to self-fertilise like many other flowering plants – so it relies on its pollinators to prompt it to set seed and fruits.
These daisies can propagate vegetatively in circular clumps. The plants are clones, with every offshoot and flower genetically identical – so the plants are genetically one individual. This helps the daisies survive short term when pollinators do not appear. However, these clones do not help the species in the long term. Only sexual reproduction through flowers, fruit and seed production gives the genetic variability essential for adapting to any future environmental change.
Left: Male monkey beetles battle to occupy a daisy before using it as a platform for mating.
Above: Isabel Johnson samples data from a Hilton daisy clone – at each site, the researchers collected small leaf samples of 30 plant individuals to extract DNA and to analyse population genetics.
LOST & FOUND
At the next population we visited – north of Pietermaritzburg this time – Carolina had the treat of meeting the Hilton daisy’s iconic pollinator, the monkey beetle. This ‘furry’ and very appealing little beetle with long and strong hind legs is not common worldwide.
Generally, beetles are considered poor pollinators compared to other types of pollinators – but monkey beetles stand out in being efficient pollen carriers across individuals of multiple South African plant species. Their ‘furriness’ helps trap pollen grains when they visit flowers, either to consume pollen or while searching for a mate.
Sometimes these beetles were not the only ones searching. Travelling through the backroads of deep rural Zululand after visiting one of our sites, we were caught in a violent thunderstorm and heavy rain.
As darkness fell in the slippery road next to the roaring Tugela river, we realised that we were driving in circles. It didn’t help that our GPS guided us to a mythical bridge.
Luckily, some locals easily recognised that we were lost. They helped us find our way back to the main road, after negotiating a steep winding road with high-speed flying taxis coming down on the wrong side. We finally got home safely after midnight.
Left: Carolina Diller in the field – at every site, the researchers also measured several floral characteristics such as flower colour to help inform their analyses. Right: Like all daisies, the Hilton daisy is a flowerhead made up of little florets – what are often thought of as petals are, in fact, ray florets.
Hilton daisy sites that we visited north of Pietermarizburg were all strikingly different. Unlike the more southern populations we had first seen, there were daisy clumps of different shades of orange, not just red, with the proportion of red to orange varying from site to site.
When we mapped the daisies’ colour variations, we confirmed that the southernmost populations are predominantly red or orange red. The central populations in Zululand are entirely yellow. The northernmost populations in Mpumalanga are multicoloured.
At one site, the daisies had an immensely diverse colour palette – flowers in different shades of red, orange, yellow, pink and even flowers with a mix of red and yellow petals together! As the site also had a healthy community of pollinators, both monkey beetles and solitary bees, it became our main study site.
We had found no relationship between flower colour and factors such as rainfall, temperature or soil chemistry but colour change in various other species is often related to the colours that their pollinators prefer.
Bees, both honeybees and solitary bees, frequently visited the yellow-flowered populations but we seldom saw them in the red populations – possibly because red is reflected in long wavelengths that are close to the upper limits of what bees can see. Monkey beetles, however, chose red, yellow or orange flowers equally often in our study of the multicoloured population.
Unravelling what drives flower colour variation in Hilton daisies is one of Isabel’s main research questions. We decided it was time to go into the lab.
Left: This map shows how the Hilton daisies changed colour between areas – locations are not disclosed as plant collectors and breeders are a threat to the species. Right: This population has daisies of different shades and mixtures of red, orange, yellow and pink – some are even streaked or have a few striped petals.
We started with extensive DNA paternity tests on a vast number of individual plants from our study site. We hope that this will confirm Isabel’s findings on the daisy’s reproductive and pollination system, which are based on classical cross experiments.
We recorded the flower colour of each parent in the crossing experiment so we shall also know whether some flower colours are more successful at producing seeds than others because pollinators prefer them and whether offspring are produced by similarly coloured parents or dissimilar.
Ultimately, the answer to these questions will reveal how pollinators affect the evolution of different flower colours among Hilton daisies and help to maintain this diversity.
Above: This Hilton daisy clone is part of an exclusively yellow population in Mpumalanga – the daisies’ colour varies according to how much red (anthocyanin) overlies the yellow (carotene) in the petals’ upper surface.
Alarmingly, very few populations of the Hilton daisy sites that we visited are protected – only two of the 25 known populations are are in Ezemvelo KZN Wildlife protected areas (Queen Elizabeth Park and Blinkwater Nature Reserve). Five more are on properties where declaration as protected areas under the KZN Biodiversity Stewardship Programme is being negotiated. One is situated in a Department of Forestry, Fisheries and the Environment wilderness area.
Even when grassland areas are formally protected, many are increasingly threatened by uncontrolled grazing and burning, encroachment by invasive alien plant species and, of course, climate change.
Throughout our road trip, it was remarkable how we had to travel several kilometres between Hilton daisy sites. Then we were able to survey all the plants present in less than half an hour. Such very small and highly fragmented populations are two important red flags for survival.
Sheer low numbers of individuals threaten the survival of any endangered species because small, fragmented populations mean fewer mates are available and genetic variation within and among populations decreases. Healthy genetic variation within a population increases the chances of a plant receiving pollen from mates genetically distinct from itself. Such genetic variation allows new adaptations to evolve and long term would increase the Hilton daisy’s chances of coping with environmental changes.
Carolina Diller was a post-doc at the Pollination Lab & Centre for Functional Biodiversity at the University of KwaZulu-Natal in Pietermaritzburg from 2017 to 2020. She is now a post-doc at the Swedish University of Agricultural Sciences in Alnarp. Isabel Johnson is a botanical conservation consultant to BotSoc and affiliated to the Pollination Lab and Centre for Functional Biodiversity at the University of KwaZulu-Natal in Pietermaritzburg.
They thank the Botanical Education Trust for funding for this project.
This article was first featured in Veld & Flora in the December 2021 edition. Veld & Flora is only available to BotSoc members.
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