Herself's Houseplants

ladyslipper orchid

Scientists have discovered why orchids are one of the most successful groups of flowering plants – it is all down to their relationships with the bees that pollinate them and the fungi that nourish them.

The orchid family is one of the largest groups of flowering plants, with over 22,000 species worldwide. Today’s research suggests that there is such a huge range of species because orchids are highly adaptable and individual species can interact with bees, and other pollinators, in different ways.

For example, when orchids Pterygodium pentherianum and Pterygodium schelpei live side by side, Pterygodium pentherianum puts its pollen on the bee’s front legs, whereas Pterygodium schelpei puts it on the bee’s abdomen. This means that one bee can carry pollen from two distinct species without mixing it.

The study also shows how orchids are able to live harmoniously together, with different species working in partnership with different microscopic fungi in the soil, ensuring they do not compete with each other.

Prior to today’s study, it was known that orchids have strong interactions with bees, which pollinate the flowers in return for food such as nectar or oils, and also with fungi, which supply minerals to the roots in return for sugars. These relationships are amongst the best examples of nature’s system of ‘mutual benefit’ and are believed to have been important for enabling orchids to evolve into so many different species. However, the mechanisms by which these relationships affect the number of plant species, and these species’ ability to coexist, had remained obscure.

The group studied 52 orchid species in a small region of South Africa, which all secrete oil inside their flowers that female bees collect to feed to their larvae. In order to investigate which pollinating bees were visiting the different species, they collected orchid pollen from the bees for DNA sequencing and analysis. They found strong evidence that when an orchid moved to a new geographical area it adapted to a different pollinating bee species, and interestingly, some competing orchid species were able to adapt by placing pollen on different body parts of the same bee.

“What is remarkable in these orchids is that diversity is generated not only through switches between bees, but also by switches between different body parts of the same bee, so two closely related orchids might place pollen on different segments of one bee’s front leg,” added Professor Barraclough. “It’s given us a fundamental insight into how so many new species can originate, and once they originate how they are able to coexist without exchanging genes.”

The researchers also studied the microscopic fungi living on the roots of the orchid, to see how this relationship was affecting plant diversity. Most flowering plants host microscopic fungi in their roots that help the plant take up nutrients from the soil. Until now it has been difficult to investigate this interaction, as most of the fungi belong to species that are difficult to culture. The researchers overcame this challenge by combining a molecular technique known as DNA barcoding with field experiments. In contrast to the bees, where co-occurring orchid species normally share the same insect pollinator, the plants needed to use different fungal partners in order to coexist in the same region.

“By tapping into different kinds of fungi, different plant species access different pools of nutrients and so the problem of living together without competing for the same resources is solved,” said Professor Barraclough. However, the same fungal partners are found in different geographical areas and so orchid species that originate in different areas, by adapting to different pollinators, tend still to use the same fungi.

The team’s fieldwork shows that shifts in pollination traits were important for bringing about new species and allowing coexistence in a diverse group of orchids, whereas shifts in fungal partner were important for coexistence but not for speciation. Many other groups of flowering plants enter into similar relationships with pollinators and fungi, and both the origins and the future survival of that diversity could depend critically on understanding these relationships.

source

The Effects of Above- and Belowground Mutualism on Orchid Speciation and Coexistence

original photo

Scientists from the Max Planck Institute for Chemical Ecology in Jena, Germany, have solved a case of fraud that has been pending for 40 million years. Arum palaestinum, also called the Solomon’s lily, attracts drosophilids (vinegar flies) as pollinators by emitting odor molecules that resemble those produced during alcoholic fermentation of rotting fruit initiated by yeast. The plant accomplishes the illusion of yeast simply by producing six chemicals that – together in a specific mix – create the impression of fermentation in the fly brain. The produced volatiles include two chemicals which are very rarely encountered in plants but are typical of wine and vinegar – actually byproducts of yeast activity. The scientists showed that the lily’s fragrance targets a deeply conserved neuronal pathway specifically tuned to yeast odors. Thus, the Solomon’s Lily is exploiting a million-year-old instinct in flies for its own purposes.

The genus Drosophila – vinegar flies – consists of many species that feed on a variety of sources ranging from fruit to bacterial layers on certain tropical land crab species. For most drosophilids, yeast is the main food. Their antennae and antennal lobes, the
first brain region that receives input from the olfactory sensory neurons, are accordingly specialized in perceiving odor molecules typically emitted by growing yeast. The smallest concentrations are sufficient to lead vinegar flies to their food source.

Many flowering plants depend on insect pollinators; they ensure that offspring are produced and guarantee genetic variability. Flowers use colorful petals and odor bouquets to attract them. Although often pollination service is rewarded with sweet nectar, Arum palaestinum tricks its pollinators. The plant, also called the Solomon’s Lily, produces an odor in its violet-black flowers that to a human nose is most similar to a fruity wine. It was obvious that the plant attracts pollinators with this odor, namely vinegar flies. But unlike other flowers, Arum palaestinum does not give a reward in form of nectar; in fact, flies are trapped in the flower overnight and not released until the next day.

source (pdf)