Arxiu d'etiquetes: colour

Colour change in chamaleons: an emotional rainbow

Many people consider chameleons to be the masters of camouflage. Their ability to change colour leads us to believe that these animals have evolved to blend in with their surroundings and to trick their predators. But, what would you think if I told you that camouflage isn’t the main reason for colour shifts in chameleons? In this new entry, apart from explaining how chameleons change their coloration, we’ll show you how these cryptic animals use colour change for a wide array of reasons.

MYTHS ABOUT CHAMELEONS

Chameleons (Chamaeleonidae family) are extremely cryptic lizards, as their coloration is usually very similar to that of their habitat’s. Also, many chameleon species present the ability to actively shift their colours, making their camouflage even more complex.

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Usambara soft-horned chameleon female (Kinyongia tenuis) displaying striking colouring. Photo by Keultjes.

There is much misunderstanding regarding chameleons’ colour changing abilities. Here you have some refuted myths about chameleons:

  • The different chameleon species can only change into a limited range of colours.
  • Chameleons do not change their coloration rapidly, as they do it subtly. If they did, they would be much easier to spot by their predators.
  • Chameleons don’t change their colours depending on what they are touching but, as we’ll see below, their reasons are much more complex.

Video from Viralweek which gives a wrong idea about how a veiled chameleon changes its colours (Chamaeleo calyptratus).

But, how do chameleons change their colours? Many other animals, like cephalopods and some fish and lizards, also have the capacity to shift colours. In most cases it is achieved using chromatophores, a type of pigmentary cell found on ectothermic animals. In colour-changing animals, chromatophores are distributed in multiple layers and have the ability to contract, expand, aggregate or disperse, causing different colour variations.

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Detail of a cuttlefish chromatophores, by Minette Layne. Depending on whether they contract or expand, different colours can be appreciated.

For a long time it was thought that chameleons changed their colours using only their chromatophores. But a recent study showed that chameleons bring colour change to the extreme. This study was being conducted by a team of biologists and physicists when they noticed something special: chameleons do not present any green pigment in their skin!

PIGMENTS AND CRYSTALS

In order to explain how chameleons change colours, first we must distinguish between two different kinds of coloration in animals: pigmentary and structural colour. Pigmentary colour is the commonest, as it’s the one that an organism presents due to pigments present in their tissues (such as melanin in human skin). Instead, as we explained in a former article, structural colour is generated by the refraction of light with some skin microstructures.

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Image of an upside down beetle in which various structural colours can be seen. Photo by David López.

And what happens with chameleons? Well, it’s a combination of both mechanisms. Chameleons present black, red and yellow chromatophores, which they can contract and expand voluntarily. Also, in a study conducted with panther chameleons (Furcifer pardalis), it’s been proved that they also present two layers of guanine nanocrystal-bearing cells, called iridiophores, which reflect light. Then a chameleon’s green coloration is acquired by the blue light reflected by the iridiophores that goes through the outer yellow chromatophores.

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Scheme of a chameleon’s skin section in which the iridiophores (blue) with nanocrystal layers and the different kinds of chromatophores can be seen; xanthophores (yellow), erythrophores (red) and melanophores (black). Image by David López.

Chameleons also present a series of neural circuits that allow them to control de composition and the distance between the iridiophores’ nanocrystals in different parts of their skin. This allows them to control the wavelength of the light reflected by the iridiophores and so, the colour. Combined with the chromatophores, the different chameleon species can cover most of the visible spectrum of colours.

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Differences in the colouring of a panther chameleon when it’s relaxed and excited, and its relation with the composition and distribution of the iridiophore nanocrystals. Image extracte from Teyssier & Saenko.

CHANGING COLOURS FOR WHAT?

Even if there are other squamosal species that can shift colours, this usually is because of a physiological response to thermoregulation, excitement or changes related to reproduction. Chameleons, also have an important part of their nervous system dedicated to changing colour rapidly, consciously and reversibly. They can even change different skin regions to different colours and, while one region becomes more orange or red, another one becomes more bluish or whitish, creating pretty striking colour effects and contrasts.

But then, why do chameleons change their colours? Well, the truth is that the kaleidoscopic abilities of these lizards have different functions, varying among the different species.

CAMOUFLAGE

The most obvious motive (even if not the most important) is camouflage. Even if the standard coloration of most chameleon species is cryptic enough, in case of necessity chameleons are able to blend in even more with their surroundings. This helps them not to be detected by their prey, but mainly to go unnoticed by their predators.

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Mediterranean chameleon (Chamaeleo chamaeleon) perfectly blending in with its surrounding. Photo by Javier Ábalos Álvarez.

Also, in a study conducted with Smith’s dwarf chameleons (Bradypodion taeniabronchum), is was proved that these were able to adjust the degree of their colour shifts to the visual capacities of their predators. Birds and snakes both feed on chameleons but, while the former have a great perception of shapes and colours, the latter doesn’t have such a sharp vision. It’s seen that Smith’s dwarf chameleons show more convincing colour changes when faced with a predator bird, than they do when faced with a snake.

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Photos of a Smith’s dwarf chameleon blending in when facing two decoy predators, a shrike and a mamba. Photo by Devi Stuart-Fox.

THERMOREGULATION

Chameleons are ectothermic and, like most reptiles, depend on external sources of heat. Apart from the more superficial iridiophores (called S-iridiophores), chameleons have a deeper layer of iridiophores called D-iridiophores, which (even if they present a much messier nanocrystal structure that cannot be modified) highly reflect infrared light, and it is thought that they must have some thermoregulation-related function. Many other lizards also present an iridiophore layer similar to D-iridiophores.

Apart from D-iridiophores, chameleons also shift to darker or lighter colours in order to regulate their body temperature. This becomes more apparent in species that live in habitats with more extreme climates. As we explained in an earlier entry, the Namaqua chameleon (Chamaeleo namaquensis), which inhabits deserts in south-western Africa, presents an almost black colour during the early morning hours, in order to absorb the maximum heat, while during the hottest hours it shows a whitish coloration, in order to reflect the maximum solar radiation.

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Two different coloration patterns in a Namaqua chameleon, a lighter one (photo by Hans Stieglitz) and a darker one (photo by Laika ac).

COMMUNICATION

The main function of chameleons colour change is intraspecific communication. Chameleons use different colour patterns known as liveries in some countries, which are changed in order to transmit information to other individuals of their same species like their stress degree, their reproductive or health status, etc… A chameleon’s standard coloration is usually similar to that of their habitat. So, this colour pattern usually indicates a healthy animal, while if they feel sick or have some physical problem, they usually present paler and duller colorations.

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Dominance and submission patterns on three dwarf chameleon species (Bradypodion sp.) Image from Adnan Moussalli & Devi Stuart-Fox.

In many species, females present more conspicuous and contrasted patterns when they are in heat, while they show a darker coloration after mating. When seeing these signals, males know which females are available and with which females they should better save their energy. Males also present more eye-catching patterns during the mating season, in order to indicate their intentions to females and to warn their rivals.

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Female carpet chameleon (Furcifer lateralis) with a pattern that indicates that it’s already pregnant and that it has no interest in mating. Photo by Bernard Dupont.

Finally, outside mating season, all chameleons use their boldest colours during their encounters with rivals of their same species. It’s in these situations when chameleons show the most contrasted patterns, apart from inflating and looking bigger and more aggressive, in order to scare off their rivals.

Video of a panther chameleon (Furcifer pardalis) acting aggressively when presented with a “rival”. Video from The White Mike Posner.

As we’ve just seen, the variety of colorations among the distinct chameleon species is huge. Yet, their incredible abilities haven’t saved chameleons from being on the endangered species list, as many of them are in danger of extinction, mainly because of the destruction of their habitat due to the logging industry and because of poaching for the illegal exotic animal trade. We hope that with a better awareness of these spectacular and colourful lizards, future generations can still delight with chameleon colour shifts for a long time.

REFERENCES

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

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Flowers wearing turban, the Tulip fever

The spring beginning has allowed some of you to enjoy the beautiful colours of those flowers that have already bloomed. This time I’m going to talk about one of the most colourful, simple, but wonderful flowers you probably already will have had the opportunity to observe in many gardens or in nature. It is the tulip. Besides introduce you this plant, in this article I will make a more detailed description of its morphological parts. I think it’s a good example to start learning vocabulary, because its structure is quite clear and simple. Therefore, if you are interested in learning some technical vocabulary, now it’s a perfect chance. But, do not think I’m just going to talk about the technical aspects, because reading this article you will also be able to learn the history behind the tulips. And as you will see, these flowers caused a good fever!

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Artistic image of several tulips (Photo taken by Adriel Acosta).

 INTRODUCTION

The tulips (Tulipa sp.) are flowers that when are closed seem a turban. This plants have been very popular and well-known for very long time, because of its high ornamental interest.

Its genus is distributed in the central and western Asia, in the Mediterranean and in Europe. It is known that its origin belongs to the centre of Asia and, from there, their distribution has been expanded naturally and by human actions. And, although about 150 species are known in the nature, human intervention has greatly increased the species list. Caused both by hybridization (forcing the offspring of two interesting species) and by selective breeding (choosing the offspring which has more value).

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Tulip crop in Amsterdam (Photo taken by Rob Young). 

 THE TULIP FEVER

As already mentioned above, tulips are one of the most ornamental plants used, both in decoration as in landscaping. And while the tulip crop is rather old, the boom occurred in Europe during the seventeenth century. Giving rise to what is known as Tulip mania or the Tulip fever. In those moments, especially in Netherlands and France, a high interest in the cultivation of these plants awoke. The fever was so great that people were selling goods of all kinds to buy tulip bulbs, even reaching up to sell the most valued as the house or farm animals.

The cause of this was originated in the Netherlands, where the single-coloured tulip bulbs were being sold at that time. But afterwards, the Eastern bulbs that give rise to flowers with variegated colours appeared. And they were very attractive. Although the cause was uncertain in that moment, it was known that if a single-coloured bulb touched other marbled-coloured bulb, the first one would turned into a marbled-coloured bulb. This caused the tulip’s price began to increase and soon after occurred the first speculative bubble in history.

Nowadays, we know that the cause is due to a virus which is transmitted from some bulbs to others; this virus is known as Tulip breaking virus.

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Anonymous gouache on paper drawing, 17th century, of the “Semper Augustus”. A representation of one of the most popular tulips which was sold at record price in Netherlands (Public Domain).

MORPHOLOGICAL CHARACTERS

 The plant

 Tulips are geophytes, that is, they have resistance bodies underground to survive during unfavourable seasons, the winter. These organs are bulbs, which have been used on crops to preserve these plants.

Its leaves are linear or linear-lanceolate, i.e., they are long, narrow and acute. Parallel venation can be observed on its leaves, so a nerve is by side other and with the same direction. Their arrangement is usually in rosette: this means that the leaves are born agglomerated in the bottom of the plant above the bulb, and at the same level. Even so, you can sometimes see some leaves along the stem, cauline ones. These are sessile, without petiole, and wrap a little the stem.

To cultivate tulips, we can use their bulbs or fruits. These seconds are capsules, a dried fruits, opened due the action of some valves. At first, the seeds are hooked inside these capsules and then are released and distributed on the environment.

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Tulip (Photo taken by Adriel Acosta).

The flowers

Tulips appear in early spring, due they are plants adapted to very dry Mediterranean climate or cold areas.

As you have seen, the flowers are solitary or appear to 3 gathered in one stem. They are usually large and showy, hermaphrodite, therefore, they have both male and female reproductive organs, and are actinomorphous, that is, they can be divided symmetrically for more than two planes of symmetry.

These flowers have 3 inner tepals and 3 external that are free among them, without being bound or fused. We talk about tepals when the sepals (calyx pieces) and petals (corolla parts) are similar between them. In this case, the tepals are petaloid, because they adopt typical colours and shapes of the petals.

In the inner part of the flower, we can see 6 stamens divided equally into 2 whorls; being these two closely spaced between them, so they seem to arise from the same point. And right in the centre, surrounded by these stamens, there is the gynoecium, female part of the flower. This gynoecium consists of the ovary and 3 stigmas attached to this directly. The stigmas are this part of female reproductive organs where it should arrive pollen to fertilize the ovaries.

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Parts of tulip flower: 1. Sepal, 2. Petal, 3. Stamen, 4. Female reproductive organ (ovary and 3 stigmas) (Photo taken by Adriel Acosta).

 As you have seen in this article, some flowers have caused curious stories and a great impact on our society. Also, you have had the opportunity to observe in detail the tulip’s structure. One more time, I wish you liked it.

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REFERENCES

  • A. Aguilella & F. Puche. 2004. Diccionari de botànica. Colleció Educació. Material. Universitat de València: pp. 500.
  • Bolòs, J. Vigo, R. M. Masalles & J. M. Ninot. 2005. Flora manual dels Països catalans. 3ed. Pòrtic Natura, Barcelona: pp. 1310.
  • Notes of Phanerogamae and Applied Plant Physiology, Degree of Environmental Biology, Ambiental, UAB
  • F. Schiappacasse. Cultivo del tulipan. http://www2.inia.cl/medios/biblioteca/seriesinia/NR21768.pdf
  • Fundación para la Innovación Agraria; Ministerio de Agricultura. 2008. Resultados y Lecciones en Tulipán. Proyecto de Innovación en XII Región de Magallanes. Flores y FOllajes/ Flores de corte (11).