Stretching for about 1,600 km along the western cone coast of South America, the Atacama Desert is the driest place on Earth. Some weather stations there have never recorded precipitation in their entire existence. But it is far from barren: here live many species that are found nowhere else, adapted to the extreme conditions.
And about every 5 to 10 years, from September to mid-November, the Atacama is home to one of the natural world’s most spectacular sights: the “desierto florido” (literally “flowering desert”). This massive bloom, one of which is currently underway in northern Atacama after torrential rainfall earlier this year, often draws media attention from around the world.
But what physiological and evolutionary mechanisms enable the great diversity of colors, shapes and visual patterns of flowers during desiertos floridos? And how do pollinators — in the Atacama, mainly hymenopteras such as solitary wasps and bees — for whose benefit this visual extravaganza evolved, see all this variety? That’s the subject of a new study in Frontiers in Ecology and Evolution.
“Our goal was to shed light on the ecological and evolutionary mechanisms that drive biological diversity in extreme environments such as the Atacama Desert,” said first author Dr. Jaime Martínez-Harms, a researcher at the Institute of Agricultural Research in La Cruz, Chile.
Here we show that flowers of the pussypaw Cistanthe longiscapa, a representative species of desiertos floridos in the Atacama Desert, are highly variable in the color and patterns they present to pollinators. This variability is likely due to several so-called ‘betalain’ ‘-pigments in the petals.”
Martínez-Harms and colleagues studied a desierto florido event near the city of Caldera in northern Chile in late 2021. Despite being smaller than the event currently underway, it was clearly visible to satellites.
A dominant species was C. longiscapa (family Montiaceae), an annual plant up to 20 cm high, which bloomed in two different spots tens of km wide. To human eyes, these patches consisted of uniformly purple and yellow flowers. Between them grew numerous intermediate (i.e. reddish, pink and white) flowers of the same species, strongly suggesting that the purple and yellow morphs are hereditary variants that can interbreed.
Visualize flowers the way insects see them
Insects, with their compound eyes and different sensitivities, see the world very differently than we do. For example, most hymenopterans have three types of photoreceptors, which are maximally sensitive to UV, blue and green.
Martinez-Harms et al. used visible light and UV sensitive cameras and spectrometers to measure the reflection, absorption, and transmission of different wavelengths through the petals of a total of 110 purple, yellow, red, pink, and white C. longiscapa flowers. to measure. This allowed them to create composite images of these variants as seen by their many types of pollinators.
Diversity hidden from human eyes
The results show that it is precisely within this one plant species that the diversity was greater for pollinators than for us. Hymenopterans, for example, like us, can easily distinguish between red, purple, white and yellow varieties. But they can also distinguish flowers with high versus low UV reflectance between yellow and purple flowers. A UV “rose pattern” in the heart of some flowers, which directs pollinators to the nectar and pollen, is invisible to us.
An exception is the UV-reflecting pink and reddish C. longiscapa, which are very different to human eyes, but probably resemble hymenopteras.
This visual diversity of C. longiscapa flowers is probably mainly due to differences between betalains – yellow, orange and purple pigments that are a typical feature of the plant order Caryophyllales to which the kitties belong. Betalains don’t just add color to flowers: they also protect against drought, salt stress and damage from reactive oxygen species under environmental stress – properties that are very beneficial in deserts.
Pollinators send selection for new varieties
The authors hypothesized that the observed standing diversity within C. longiscapa flowers is driven by differences in the sensitivity and preference for different colors and patterns in many pollinator species: an evolutionary experiment currently underway that mostly escapes our view.
“The wide variation in flower color within C. longiscapa can be explained as different species of pollinating insects, through their preference for certain flower colors and patterns, could cause these variants to become reproductively isolated from other individuals of the same plant species. The process could eventually lead to the emergence of new breeds or species,” says Martínez-Harms.
“In our next studies, we will further investigate the chemical identity and biological synthesis pathways of betalains and other flower pigments, as well as their relationship to properties such as the scents produced by the flowers. This should help us understand their role in shaping the interactions. between plants and their pollinators, and in plants’ tolerance to biotic and abiotic stressors under fluctuating climate conditions,” said Martínez-Harms.
Bees use patterns, not just colors, to find flowers
Mechanisms of flower coloring and eco-evolutionary implications of mass blooming events in the Atacama Desert, Frontiers in Ecology and Evolution(2022). DOI: 10.3389/fevo.2022.957318
Quote: The Secret Behind Spectacular Flowers in the World’s Driest Desert (2022, October 21) Retrieved October 21, 2022 from https://phys.org/news/2022-10-secret-spectacular-blooms-world-driest.html
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