Plants and animals can also live in marriage

When we think about the life of plants it is difficult to imagine without interaction with the animals, as they establish different symbiotic relationships day after day. These symbiotic relationships include all the herbivores, or in the contradictory way, all the carnivorous plants. But there are many other super important interactions between plants and animals, such as the relationships that allow them to help each other and to live together. So, this time I want to present mutualism between plants and animals.

And, what is mutualism? it is the relationship established between two organisms in which both benefit from living together, i.e., the two get a reward when they live with the other. This relationship increase their biological effectiveness (fitness), so there is a tendency to live always together.

According to this definition, both pollination and seed dispersal by animals are cases of mutualism. Let’s see.

POLLINATION BY ANIMALS

Many plants are visited by animals seeking to feed on nectar, pollen or other sugars they produce in their flowers and, during this process, the animals carry pollen from one flower to others, allowing it reaches the stigma in a very effective way. Thus, the plant gets the benefit of fertilization with a lower cost of pollen production, which would be higher if it was dispersed through the air. And the animals, in exchange, obtain food. Therefore, a true relationship of mutualism is stablished between the two organisms.

 “Video:The Beauty of Pollination” – Super Soul Sunday – Oprah Winfrey Network (www.youtube.com)

The extreme mutualism occurs when the species evolve depending on the other organism, i.e., when there is coevolution. We define the coevolution such as these evolutionary adaptations that allow two or more organisms to establish a deep relationship of symbiosis, due that the evolutionary adaptations of one specie influence the evolutionary adaptations of another organism. For example, this occurs between various orchids and their pollinators, as is the well- known case of Darwin’s orchid. But there are many other plants that also have co-evolved with their pollinators, as a fig tree or cassava.

In no way, this should be confused with the trickery produced by some plants to their pollinators, that is, when they do not obtain any direct benefit. For example, some orchids can attract their pollinators through odours (pheromones) and their curious forms that resemble female pollinator, stimulating them to visit their flowers. The pollinators will be impregnated with pollen, which will be transported to other flowers due to the same trickery.

Bee orchid (Ophrys apifera) (Autnor: Bernard DUPONT, flickr).

SEED DISPERSAL BY ANIMALS

The origin of seed dispersal by animals probably had occurred thanks to a co-evolutionary process between animals and mechanisms of seed dispersal in which both plants and animals obtain a profit. The most probably is that this process began in the Carboniferous (~ 300MA), as it is believed that some plants like cycads developed a false fleshy fruits that could be consumed by primitive reptiles that would act as seed dispersers. This process could have intensified the diversification of flowering plants (angiosperms), small mammals and birds during the Cretaceous (65-12MA).

The mutualism can occur in two ways within the seed dispersal by animals.

The first case is carried out by animals that eat seeds or fruits. These seeds or some parts of the fruits (diaspores) are expelled without being damaged, by defecation or regurgitation, allowing the seed germination. In this case, diaspores are carriers of rewards or lures that result very attractive to animals. That is the reason why fruits are usually fleshy, sweet and often have bright colours or emit scents to attract them.

For example, the red-eyed wattle (Acacia cyclops) produces seeds with elaiosomes (a very nutritive substance usually made of lipids) that are bigger than the own seed. This suppose an elevated energy cost to the plant, because it doesn’t only have to produce seeds, as it has to generate the award too. But in return, the rose-breasted or galah cockatoo (Eolophus roseicapillus) transports their seeds in long distances. Because when the galah cockatoo eats elaiosomes, it also ingest seeds which will be transported by its flight until they are expelled elsewhere.

On the left,  Galah  cockatoo (Eolophus roseicapillus) (Autnor: Richard Fisher, flickr) ; On the right, red-eyed wattle’s seeds (black) with the elaiosome (pink) ( Acacia cyclops) (Autnor: Sydney Oats, flickr).

And the other type of seed dispersal by animals that establishes a mutualistic relationship occurs when the seeds or fruits are collected by the animal in times of abundance and then are buried as a food storage to be used when needed. As long as not all seed will be eaten, some will be able to germinate.

A squirrel that is recollecting som nuts (Author: William Murphy, flickr)

But this has not finished yet, since there are other curious and less well-known examples that have somehow made that both animals and plants can live together in a perfect “marriage.” Let’s see examples:

Azteca and Cecropia

Plants of the genus Cecropia live in tropical rain forests of Central and South America and they are very big fighters. The strategy that allow them to grow quickly and capture sunlight, avoiding competition with other plants, resides in the strong relationship they have with Azteca ants. Plants provide nests to the ants, since their stems are normally hollow and with separations, allowing ants to inhabit inside. Furthermore, these plants also produce Müllerian bodies, which are small but very nutritive substances rich in glycogen that ants can eat. In return, the ants protect Cecropia from vines and lianas, allowing them to success as a pioneer plants.

Ant Plants: Cecropia – Azteca Symbiosis (www.youtube.com)

Marcgravia and Bats

Few years ago, an interesting plant has been discovered in Cuba. This plant is pollinated by bats, and it has evolved giving rise to modified leaves that act as satellite dish for echolocation performed by these animals. That is, their shape allow bats to locate them quickly, so they can collect nectar more efficiently. And at the same time, bats also pollinate plants more efficiently, as these animals move very quickly each night to visit hundreds of flowers to feed.

Marcgravia (Author: Alex Popovkin, Bahia, Brazil, Flickr)

In general, we see that the life of plants depends largely on the life of animals, since they are connected in one way or another. All the interactions we have presented are part of an even larger set that make life a more complex and peculiar one, in which one’s life cannot be explained without the other’s life. For this reason, we can say that life of some animals and some plants resembles a marriage.

REFERENCES

• Notes from the Environmental Biology degree (Universitat Autònoma de Barcelona) and the Master’s degree in Biodiversity (Universitat de Barcelona).
• Bascompte, J. & Jordano, P. (2013) Mutualistic Networks (Chapter 1. Biodiversity and Plant-Animal Coevolution). Princeton University Press, pp 224.
• Dansereau, P. (1957): Biogeography: an Ecological Perspective. The Ronald Press, New York., pp. 394.
• Fenner M. & Thompson K. (2005). The Ecology of seeds. Cambridge: Cambridge University Press, 2005. pp. 250.
• Font Quer, P. (1953): Diccionario de Botánica. Editorial Labor, Barcelona.
• Izco, J., Barreno, E., Brugués, M., Costa, M., Devesa, J. A., Fernández, F., Gallardo, T., Llimona, X., Parada, C., Talavera, S. & Valdés, B. (2004) Botánica ªEdición. McGraw-Hill, pp. 906.
• Murray D. R. (2012). Seed dispersal. Academy Press. 322 pp.
• Tiffney B. (2004). Vertebrate dispersal of seed plants through time. Annual Review of Ecology, Evolution and Systematics. 35:1-29.
• Willis, K.J. & McElwain, J.C. (2014) The Evolution of Plants (second edition). Oxford University Press, pp. 424.
• National Geographic (2011). Bats Drawn to Plant via “Echo Beacon”. http://news.nationalgeographic.com/news/2011/07/110728-plants-bats-sonar-pollination-animals-environment/

Socratea exorrhiza: plants also learn to walk!

This time I am going to present the plant that is becoming famous worldwide, the walking palm (Socratea exorrhiza). It has always been said that plants do not move from their place, but the nature surprises us once again with an example like this. Then, you can view more of this extraordinary plant.

INTRODUCTION

The walking plant, Socratea exorrhiza, is a palm tree (Arecaceae) that lives in the rainforest of Centre and South America. It can reach to 25 meters of height and 16 centimetres of diameter, but it is usually around 15-20 meters of height.

The walking palm at los Puentes Colgantes near Arenal Volcano, Costa Rica (Photo taken by Hans Hillewaert).

Along with the orchids and other herbs, palm trees are the most abundant plants in tropical forests. But the palms are very curious as they have arboreal morphology: tree height and measures. But, no truly secondary growth is developed, i.e., they haven’t tissues for the increase in thickness of the roots, stems and branches. This means that, if the plant grows in height, it has to be a mechanism that can support its own weight. And we know that is not due to the thickness of the stem, which is pretty slim. So, what is the mechanism? And how does it work?

STILT ROOTS

Many arborescent palms, i.e., that are not trees but similar, develop a set of aerial roots. These are characterized by being located above ground level. This is the case of the Walking palm (Socratea exorrhiza) and other palms (such Iriartea deltoidea). Stilt roots are generally very numerous and high.

Stilt roots (Photo taken by Ruestz).

STILT ROOTS’ FUNCTIONS

The functions performed by these roots have been and are still a debate. Still, it has been proposed that they can provide different benefits.

First, their presence allows greater stability and support of the stem, which can grow faster. This is very interesting, because in tropical forests light is a very powerful limiting factor. And the fact that the plant can reach higher heights, spending less energy in developing a thick trunk or underground roots that stabilize, makes this specie more competitive. But, while providing stability, it has not been shown to result in an advantage to grow in slope.

On the other hand, it is also thought that roots let colonize (expand to) new places that contain many large organic wastes, generally branches or dead trunks of other trees. This is because the roots can avoid them by moving over them.

In addition, it has been found that the stilt roots increase the plants’ survival when tropical storms are violent (as explained in the next section) and also facilitate their own aeration when floods occur. Still, it has not been confirmed that they allow the palm to grow in marshy places.

Although it has been begun to possess an extensive knowledge, all functions of these very singular roots of palm trees are still unknown. Even so, it should be mentioned another function discovered on the Walking palm, which is precisely what allows the plant to “walk”.

HOW DOES THE WALKING PALM WALK?

Socratea exorrhiza is known as the Walking palm and this is because it can change its position for two reasons. Although the second, presented below, is what gives rise to its common name.

The first, known since more time ago, it is quite common due to strong tropical storms. It’s caused when the palm is in normal position (phase 1 of the image) and then is knocked down by another tree or branch and it’s flattened (phase 2 of the image). Once above the soil, the palm has the ability to regrow and recover, thanks to the development of new stilt roots on the old stem; while the old stilt roots die (phase 3 of the image). Finally, the organism grows again, but having changed its place (phase 4 of the image). Therefore, the palm can survive even when it’s lying over the ground and still can recover itself.

Smartse – Bodley, John; Foley C. Benson (March 1980). Stilt-Root Walking by an Iriateoid Palm in the Peruvian Amazon. Biotropica (jstor: The Association for Tropical Biology and Conservation) 12 (1): 67-71

The second case has been discovered more recently and it is the reason why this plant has become popular nowadays. It is believed that its roots grow towards areas where there is more light; while on the other side, the roots die. So, the stem changes its place very slowly, but each year the displacement can reach up to 1 meter.

Simon Hart’s explicative video (Youtube Channel: Harold Eduarte).

As you have seen, plants never cease to amaze. Reaching as curious cases like this. Remember, if you liked it, please don’t forget to share in different social networks. Thank you.

REFERENCES

• Notes of Forest Ecology, Degree of Environmental Biology, UAB.
• Avalos, Gerardo; Salazar, Diego; and Araya, Ana (2005). Stilt root structure in the neotropical palmsIrlartea deltoidea and Socratea exorrhiza. Biotropica 37 (1): 44–53.
• Avalos, Gerardo and Fernández Otárola, Mauricio (2010). Allometry and stilt root structure of the neotropical palm Euterpe precatoria (Arecaceae) acroos sites and successional stages. Ametican Joranl of Botany 97 (3): 388-394.
• Goldsmith, Gregory; and Zahawi, Rakan (September–December 2007).The function of stilt roots in the growth strategy of Socratea exorrhiza (Arecaceae) at two neotropical sites. Revista de Biologia Tropical 55 (3–4): 787–793.
• Zotz, G.; Vollrath, B. (2003).The epiphyte vegetation of the palm Socratea exorrhiza – correlations with tree size, tree age and bryophyte cover. Journal of Tropical Ecology 19

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