The driest place on Earth is the Atacama Desert, which is located along the western coast of the South American Cone and stretches for about 1,600 km. Some of the weather stations there have never recorded any rain in all their years of operation.
But it’s far from lifeless; many species that are unique to this region and have adapted to its harsh conditions can be found here. In addition, the Atacama is home to one of the most breathtaking natural phenomena on average once every five to ten years, from mid-September to mid-November: the “desierto florido” (literally, “flowering desert”) ).
Following heavy rains earlier this year, one of these massive blooms, which is currently occurring in the northern Atacama, is frequently covered by media around the world.
However, what physiological and evolutionary processes allow for the enormous variety of flower colors, shapes, and visual patterns found in desiertos floridos? And how do pollinators, mostly hymenoptera like solitary wasps and Atacama bees, who are the beneficiaries of this visual extravagance, perceive all this variety? A recent study published in Frontiers in Ecology and Evolution addresses this question.
“Our goal was to shed light on the ecological and evolutionary mechanisms that cause biological diversity in extreme environments like the Atacama Desert,” said first author Dr. Jaime Martinez-Harms, a researcher at the Institute of agricultural research in La Cruz, Chile.
“Here we show that the flowers of the kitty Cistanthe longiscapa, a representative species of the desiertos floridos in the Atacama Desert, are highly variable in the color and patterns they present to pollinators. This variability likely results from different so-called pigments” betalains” in flower petals.”
Model species
In late 2021, a Florida desert event was investigated by Martnez-Harms and colleagues close to the city of Caldera in northern Chile. Although it was smaller than the current event, satellites could clearly see it. A dominant species was the annual plant C. longiscopa (family Montiaceae), which flowered in two separate patches tens of kilometers apart and reached a height of 20 cm. In the eyes of man, these spots consisted exclusively of purple and yellow flowers. Many intermediate flowers of the same species – reddish, pinkish and white – have grown between them, providing strong evidence that the purple and yellow forms are hereditary variations capable of reproducing.
See flowers as insects see them
Insects, with their compound eyes and different sensitivities, see the world very differently from us. For example, most Hymenoptera 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 by the petals of a total of 110 purple, yellow flowers , red, pink and white of C. longiscapa. This allowed them to produce composite images of these variants seen by their many pollinator species.
Diversity hidden from human eyes
The results show that even within this single plant species, the diversity perceptible by pollinators was greater than by us. For example, Hymenoptera, just like us, can easily distinguish between red, purple, white, and yellow variants. But they can also distinguish flowers with high or low UV reflectance among yellow and purple flowers. A UV “bulls-eye pattern” at the heart of some flowers, which guides pollinators to nectar and pollen, is invisible to us.
An exception is the UV-reflecting pink and reddish C. longiscopa, which is quite distinct to human eyes, but likely appears similar to Hymenoptera. This visual diversity of C. longiscapa flowers is probably mainly due to differences between betalains – yellow, orange and purple pigments that are a typical trait of the plant order Caryophyllales to which cattails belong. Betalains don’t just color flowers: they also protect against drought, salt stress, and damage from reactive oxygen radicals under environmental stress – traits highly beneficial in deserts.
Pollinators guide the selection of new variants
The authors proposed that the upright diversity seen in C. longiscopa flowers is caused by variations in pollinator sensitivity and preference for various colors and patterns – a current evolutionary experiment that goes largely unnoticed by humans.
“The wide variation in flower color in C. longiscapa may be explained if different species of pollinating insects, through their preference for particular flower colors and patterns, could result in the reproductive isolation of these variants from other individuals. of the same plant species process could ultimately lead to the origin of new races or species,” Martinez-Harms said.
“In our next studies, we will further investigate the chemical identity and biological synthesis pathways of betalains and other floral pigments, as well as their relationship to traits such as fragrances produced by flowers. This should help us to understand their role in shaping interactions between plants and their pollinators, and in plant tolerance to biotic and abiotic stressors under fluctuating climatic conditions,” Martinez-Harms said.
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