Arxiu d'etiquetes: Darwin’s orchid

Evolution for beginners 2: coevolution

After the success of Evolution for beginners, today we’ll continue  knowing the basics of biological evolution. Why  exist insects that seem orchids and vice versa? Why gazelles and cheetahs are almost equally fast? Why your dog understands you? In other words, what is coevolution?

WHAT IS COEVOLUTION?

We know that it is inevitable that living beings establish symbiotic relationships between them. Some depend on others to survive, and at the same time, on elements of their environtment as water, light or air. These mutual pressures between species make that evolve together, and as one evolve as a species, in turn it forces the other to evolve. Let’s see some examples:

POLLINATION

The most known process of coevolution is pollination. It was actually the first co-evolutionary study (1859) by Darwin, although he didn’t use that term. The first to use the word coevolution were Ehrlich and Raven (1964).

Insects existed long before the appearance of flowering plants, but their success was due to the discovery that nectar is a good reserve of energy. In turn, the plants found in the insects another way more effectively to carry pollen to another flower. Pollination by the wind (anemophily) requires more production of pollen and a good dose of luck to at least fertilize some flowers of the same species. Many plants have developed flowers that trap insects until they are covered with pollen and then set them free. These insects have hairs in their body to enable this process. In turn some animals have developed long appendages (beaks of hummingbirds, butterflies’ proboscis…) to access the nectar.

Polilla de Darwin (Xantophan morganii praedicta). Foto de Minden Pictures/Superstock
Darwin’s moth (Xantophan morganii praedicta). Photo by Minden Pictures/Superstock

It is the famous case of the Darwin’s moth (Xanthopan morganii praedicta) of which we have already talked about. Charles Darwin, studying orchid Christmas (Angraecum sesquipedale) saw that the nectar was 29 cm inside the flower. He sensed that there should exist an animal with a proboscis of this size. Eleven years later, Alfred Russell Wallace reported him that the Morgan’s sphinxs had proboscis over 20 cm long, and a time later they were found in the same area where Darwin had studied that species of orchid (Madagascar). In honor of both it was added “praedicta” to the scientific name.

There are also bee orchids that mimic female insects to ensure their pollination. To learn more about these orchids and the Christmas one, do not miss this post by Adriel.

Anoura fistulata, murcielago, bat
The bat Anoura fistulata and its long tongue. Photo by Nathan Muchhala

But many plants not only depend on insects, also some birds (like humming birds) and mammals (such as bats) are essential to pollination. The record for the longest mammal tongue in the world is for a bat from Ecuador (Anoura fistulata); its tongue measures 8 cm (150% of the length of its body). It is the only who pollinates one plant called Centropogon nigricans, despite the existence of other species of bats in the same habitat of the plant. This raises the question of whether evolution is well defined, and occurs between pairs of species or it is diffuse due to the interaction of multiple species.

PREDATOR-PREY RELATIONSHIPS

The cheetah (Acinonyx jubatus) is the fastest vertebrate on land (up to 115 km/h). Thomson’s gazelle (Eudorcas thomsonii), the second (up to 80 km/h). Cheetahs have to be fast enough to catch a gazelle (but not all, at risk of disappearing themselves) and gazelles fast enough to escape almost once and reproduce. The fastest gaelles survive, so nature selects in turn faster cheetahs, which are who eat to survive. The pressure from predators is an important factor that determines the survival of a population and what strategies should follow the population to survive. Also, the predators will find solutions to possible new ways of life of their prey to succeed.

Guepardo persiguiendo una gacela. Foto de Federico Veronesi
Cheetah hunting a Thomson’s gazelle in Kenya. Photo by Federico Veronesi

The same applies to other predator-prey relationships, parasite-host relationships, plants-herbivores, improving their speed or other survival strategies like poison, spikes…

HUMAN AND DOGS … AND BACTERIA

Our relationship with dogs since prehistoric times, it is also a case of coevolution. This allows, for example, to create bonds with just looking at them. If you want more information, we invite you to read this post where we talk about the issue of the evolution of dogs and humans in depth.

Another example is the relationship we have established with the bacteria in our digestive system, essential for our survival. Or with pathogens: they have co-evolved with our antibiotics, so using them indiscriminately has favored these species of bacteria to develop resistance to antibiotics.

THE IMPORTANCE OF COEVOLUTION

Coevolution is one of the main processes responsible for the great biodiversity of the Earth. According to Thompson, is responsible for the millions of species that exist instead of thousands.

The interactions that have been developed with coevolution are important for the conservation of species. In cases where evolution has been very close between two species, if one become extint will lead to the extinction of the other almost certainly. Humans constantly alter ecosystems and therefore biodiversity and evolution of species. Just declining one species, we are affecting many more. This is the case of the sea otter (Enhydra lutris), which feeds on sea urchins.

Nutria marina (Enhydra lutris) comiendo erizos. Foto de Vancouver Aquarium
Sea otter (Enhydra lutris) eating sea urchins. Photo by Vancouver Aquarium

Being hunted for their fur, urchins increased number, devastated entire populations of algae (consumer of CO2, one of the responsible of global warming), seals who found refuge in the algae nonexistent now were more hunted by killer whales… the sea otter is therefore a key species for the balance of this ecosystem and the planet, as it has evolved along with urchins and algae.

Coevolutive relations between flowers and animals depend on the pollination of thousands of species, including many of agricultural interest, so we must not lose sight of the seriousness of the issue of the disappearance of a large number of bees and other insects in recent years. A complex case of coevolution that directly affects us is the reproduction of fig.

TO SUMMARIZE

As we have seen, coevolution is the evolutionary change through natural selection between two or more species that interact reciprocally.

It is needed:

  • Specificity: the evolution of each feature of a species is due  to selective pressures of the feature of the other species.
  • Reciprocity: features evolve together.
  • Simultaneity: features evolve simultaneously.

REFERENCES

MIREIA QUEROL ALL YOU NEED IS BIOLOGY

Orchids: different colours and shapes for everyone

The orchid family is composed of a big number of species, about 20.000. Even they are almost around all world, the most live in tropical places and they are epiphytes, that is, they live over other plants. Nowadays, the number of the species is boosted by the commercial interest. Trying to find new characters and colours, many gardeners and hobbyists have created new varieties from the breeding of two distinct species of orchids, that is, they have made artificial hybridization. Even so, it can also happen in nature as usual.

MORPHOLOGICAL CHARACTERISTICS

The orchid flower owns a single structure. The most representative part is the column or gynostemium, which is the result of masculine and feminine reproductive parts combined. The perianth, consisting of the calyx (the outermost whorl of parts that form a flower. Its pieces are the sepals) and the corolla (composed of all of the petals), has free pieces and is zygomorphic (single symmetry plane). A much differentiated petal can be seen, it’s the lip. It adopts a different attractive shape and it can own macules (attractive spots for the pollinators). The lip is also adapted to capture the pollinators’ attention and can possess a long prolongation called spur and it has nectar. The flowers may be accompanied by a bract, a modified or specialized leaf.

parts orchidStructure of orchid flowers (Photo taken by Gisela Acosta).

The flower development is very singular in some orchids. Some flowers are born backwards and when they are maturing the ovary twist 180º to help flower stay in proper position, being the own ovary who acts as a peduncle, linking flower and stem. This kind of flower development is called resupinate. The flowers can be solitary or grouped in inflorescences.

orchis masculaResupinate development of flowers (Orchis mascula) (Photo taken by Jonathan Billinger).

The orchids are entomophilous, that is, are pollinated by insects. Depending of the specie, the orchid will be pollinated by a type of insect or other. Even so, this relation or form of pollination (the position in which bees, bumblebees and other hymenoptera get to copulate) cannot be used to describe how evolution happened in orchids; this pollination mechanism was used in the past to classify species, but molecular analyses have denied its worth.

One singular characteristic of tropical species is the velamen radicum: a multi-layered coating on the roots that acts as a sponge. In drought periods this coating protects from the drying and doesn’t allow the losing of water. And in rainy periods, this coating is swollen of water, which will be available to roots. Also, as these orchids are epiphytes, are adapted to drought places.

Pleione_limprichtii_Epiphytic orchid on a tree (Pleione limprichtii) (Photo taken by Adarsh Thakuri)

Orchids live in mutualism with fungus, that is, they establish a relationship in which both organisms are benefited when live together. The orchid seeds need the fungus’ aid to germinate. Many several fungus can stimulate their germination, but  Rhizoctonia (Basidiomycota) is predominant. The fungus degrades the seed coat and releases of dormancy period. Then, the seed begins to germinate and emits filaments, underground organs, and establishes an orchid mycorrhizae. The seed dormancy can last 20-30 years without germinating, but it will not be possible without the fungus action.

DIVERSITY

Within the great diversity of orchids, some flowers of diferent species create such original shapes that they seem animals, such as monkey orchid (Orchis simia), or insects, such as genus Phalaenopsis; their flowers supposedly resemble moths in flight, and that’s why they are known as the moth orchids.

Orchis simia & Phalaenopsis schillerianaOn the left, monkey orchid (Orchis simia) (Photo taken by Ian Capper); On the right, orchids that resemble moths in flight (Phalaenopsis schilleriana) (Photo taken by Amos Oliver Doyle).

The bee orchids (Ophrys), for example, have a specialized lip that can really attract the hymenopterans. It’s because it reminds female shape and colours and it also emits smells which are similar to female pheromones, doing the pollination more effective.

Ophrys apiferaBee orchid (Ophrys apifera) (Photo taken by Hans Hillewaert).

On the other hand, there are also many curious cases like the Darwin’s orchid (Anagraecum sesquipedale). It’s characterized by its long spur between 25 and 35 cm in length. Darwin guessed it should exist a butterfly that could take the nectar located in the spur and pollinates the flower at the same time. Xanthopan morgani is able and it’s the only one, so it’s one coevolution case.

Angraecum_sesquipedale & XanthopaOn the left, Darwin's orchid (Anagraecum sesquipedale)(Photo taken by Michael Wolf); On the right, Xanthopan morgani (Photo taken by Esculapio).

We can also see species with a high ornamental value, being the most of them from Asia and America. For example, the Cattleya genus has one of the highest floral value and it was used extensively for create new varieties. So, Cattleya has become very popular until today.  A good example is the easter orchid (Cattleya mossiae), which is also the national flower of Venezuela.

Cattleya mossiaeEaster orchid (Cattleya mossiae) (Photo taken by KENPEI).

When we speak of floral value, we can’t forget Rothschild’s slipper orchid (Paphiopedilum rothschildianum). It’s the most expensive orchid in world and it’s considered one of the most expensive flowers, too. Rothschild’s slipper orchid only lives in Mt. Kinabalu, on the island of Borneo, and it’s also one of the rarest orchids in nature of all of the species of Asian Slipper orchids.

Paphiopedilum_rothschildianum_Orchi_108Rothschild's Slipper Orchid (Paphiopedilum rothschildianum) (Photo taken by Orchi).

Furthermore, orchids are important in alimentation, being surely Vanilla planifolia the most relevant. It’s native to Mexico and vanilla is obtained of its fruits.

Vanilla planifoliaVanilla (Vanilla planifolia) (Photo taken by Michael Doss).

REFERENCES

The following sources have been consulted in the elaboration of this entry:

In conclusion, orchids are important in different aspects and that’s why a biggest knowledge of their diversity and biology is necessary. If you liked this article, wouldn’t forget to share it. Thanks for your interest.

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