After more than a hundred Friday Fellows, there is still one group with no representatives here: the archaeans. But this is going to change today with the indroduction of our first Friday Fellow archaean, and it is a very interesting one for sure.
Scientifically known as Haloquadratum walsbyi, it is sometimes called Walsby’s Square Haloarchaeon and, as its name suggest, it has an unusual square shape.
A drawing showing a set of four cells of Walby’s square haloarchaeon.
This interesting archaean was discovered in 1980 by Anthony Edward Walsby in brine ponds of the Sinai Peninsula. It was later discovered in several other lakes with high concentrations of salt around the world and was first cultivated in the laboratory in 2004, but only in 2007 it was formally described and received a binomial name.
The square cells of the Walsby’s square haloarchaeon are very thin, about 0.2 µm thick, and measure about 2 µm on each side. They grow very slowly, forming a thin sheet over a surface, the largest recorded sheet measuring 40 × 40 µm. If the growing conditions are not ideal, the cells deteriorate to a ragged square or other shapeless flat form.
Photographs of cells of Haloquadrum walsbyi showing the crystal-shaped air vacuoles. Image extracted from Burns et al. (2007).
Inside the cells, the Walsby’s square haloarchaeon has small gas vesicles that look like small crystals. They help the cell remain at the surface of the very salty water they inhabit. In order to survive, this archaean needs water with a concentration of salt of at least 14%, but the conditions become ideal only above 23%.
Although we know some interesting things about this species, there is still much more to learn. Who knows what mysteries this small square-shaped creature is hiding from us?
European in origin, but currently cosmopolitan, today’s Friday Fellow is a very useful earthworm for humans. Scientifically known as Eisenia fetida, this species has many different popular names, including tiger worm, red californian earthworm, red wiggler worm, etc.
Two specimens of Eisenia fetida. Photo by iNaturalist.org user nzwormdoctor.*
The tiger worm rarely lives underground, prefering to live among decaying vegetable matter, such as in the leaf litter, therefore being considered an epigean species. Due to its adaptability to live among and feed on decaying organic material, it is widely used by humans for vermicomposting, i.e., producing humus to be used as a nutrient rich soil in cultivation of vegetables. As a result, it has been introduced worlwide.
When molested, the tiger worm secrets a yellow and pungent liquid from its celomic cavity that has been shown to be toxic to some vertebrates, thus probably being a defense mechanism against predators.
Due to its agriculatural importance, the tiger worms has been used in many studies regarding its response to different soil contaminants, including pesticides, and its presence on the amount of inorganic nutrients, such as carbon and nitrogen, in the soil.
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Albanell, E.; Plaixats, J.; Cabrero, T. (1988) Chemical changes during vermicomposting (Eisenia fetida) of sheep manure mixed with cotton industrial wastes. Biology and Fertility of Soils, 6(3): 266–269.
Spurgeon, D. J.; Hopkin, S. P. (1999) Comparisons of metal accumulation and excretion kinetics in earthworms (Eisenia fetida) exposed to contaminated field and laboratory soils. Applied Soil Ecology, 11(2–3): 227–243.
Zhang, B.-G.; Li, G.-T.; Shen, T.-S.; Wang, J.-K.; Sun, Z. (2000) Changes in microbial biomass C, N, and P and enzyme activities in soil incubated with the earthworms Metaphire guillelmi or Eisenia fetida. Soil Biology and Biochemistry, 32(14): 2055–2062.
For a long time, culture was considered a human trait, but nowadays we recognize the existence of culture in many other species, such as other primates, whales and some birds too. Now there are some evidences of culture being found in bats too.
A group of researchers from China studied the calls of the Chinese rufous horseshoe bat (Rhinolophus sinicus) across different populations and compared them to genetic and environmental variables to determine whether the differences where linked to genetic differences between the populations or to different environments that would force the bats to change their calls in order to use them more successfully.
The results indicate that none of those two factors were strongly linked to the acoustic differences in the calls. The most likely explanation is that the differences happen due to cultural drift. The bats are teaching a way to speak to their children that is slightly different from what their neighbors speak, even if the neighbors are genetically similar and live in a similar environment.
As an animal’s call is an important variable during mating, this may eventually lead to reproductive isolation even without genetic differences. Culture can also shape evolution!
The adjective “giant” can be quite relative. When regarding microorganisms, even something with a few milimeters can be considered a giant, and that is the case with the giant amoeba Chaos carolinense (sometimes wrongly written as Chaos carolinensis).
A chaotic mess as any good amoeba. Photo by Tsukii Yuuji.
Measuring up to 5 mm in length, the giant amoeba is a freshwater organism and is easily seen with the naked eye and, since it is also easily cultivated in the laboratory, it became widely used in laboratory studies.
As with amoebas in general, the giant amoeba has an irregular cell with several pseudopods that can contract and expand. The cell has hundreds of nuclei, as it is common with species of the genus Chaos, this being the main difference between them and the closely related genus Amoeba.
The diet of the giant amoeba is variable and includes bacteria, algae, protozoan and even some small animals. In the lab, they are usually fed with ciliates of the genus Paramecium.
A specimen of Chaos carolinense feeding on several individuals of Paramecium. Photo by Carolina Biological Supply Company.*
Wouldn’t the giant amoeba make a nice unicelular pet?
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Tan, O. L. L.; Almsherqi, Z. A. M.; Deng, Y. (2005) A simple mass culture of the amoeba Chaos carolinense: revisit. Protistology, 4(2): 185–190.
As the second species of today, I’m bringing a terrible but beautiful predator of the Portuguese man o’ war, the sea swallow Glaucus atlanticus, which is, in my opinion, one of the most beautiful sea creatures.
Also known as blue dragon, blue glaucus and many other names, the sea swallow is a small sea slug that measures up to 3 cm in length as an adult. This species is pelagic, meaning that it lives in the open ocean, neither close to the bottom nor close to the shore. Although it is found in all three oceans, genetic evidences indicate that the populations from the Atlantic, the Pacific and the Indian oceans have diverged more than 1 million years ago.
The sea swallow has a gas-filled sac in the stomach that makes it float upside down in the water, meaning that its ventral side is directed upward. The wide blue-bordered band running along the body, as seen in the picture above, is the slug’s foot. It’s dorsal side, which is directed downward, is completely white or light gray.
Being a carnivorous species, the sea swallows feeds on several cnidarian species, especially the Portuguese man o’ war. It usually collects the cnidocytes (the sting cells) of its prey and put them on its own body, so that it becomes as stingy as or even stingier than its prey. If you find one lying on the beach, be careful.
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Churchull, C. K. C.; Valdés, Á.; Foighil, D. Ó (2014) Afro-Eurasia and the Americas present barriers to gene flow for the cosmopolitan neustonic nudibranch Glaucus atlanticus. Marine Biology, 161(4): 899-910.
Wikipedia. Glaucus atlanticus. Available at < https://en.wikipedia.org/wiki/Glaucus_atlanticus >. Access on June 18, 2017.
And so we finally reached the 100th Friday Fellow! In order to commemorate, we will have two Friday Fellows today, just as we had during the 50th one. And to start I chose a cnidarian that always caught me attention.
Living in the Atlantic Ocean and known popularly as Portuguese man o’ war, its binomial name is Physalia physalis, both words derived from the Greek word for bubble, physalis. And the Portuguese man o’ war is, in fact, like a floating bubble with some stuff attached, or at least it looks like that.
A Portuguese man o’ war lying on the beach. Photo by Anna Hesser.*
Most people may think that the Portuguese man o’ war is a jellyfish due to its looks, but it is actually part of another group of cnidarians, the siphonophores. Their body is not a single individual, but rather a colony of several smaller animals, called zooids, which are speciallized to have different functions within the colony and cannot live separately. They are all derived from the same embryo, thus being clones from each other.
The upper portion of the Portuguese man o’ war has a gas-filled sack, which is called the pneumatophore and is the original organism derived directly from the embryo. Below the pneumatophore there are several different kinds of organisms, such as nectophores for swimming, dactylozooids for defense and capture of prey, gonozooid for reproduction and gastrozooids for feeding. The long tentacles, which reach more than 10 m in length, are composed by dactylozooids and fish for prey throughout the water.
As other cnidarians, the Portuguese man o’ war has nettle-like cells which sting and inject venom. In humans, the venom usually cause pain and let whip-like marks on the skin where the tentacles touched. Sometimes more severe complications will results and in rare cases it may result in death.
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Stein, M. R.; Marraccini, J. V.; Rothschild, N. E.; Burnett, J. W. (1989) Fatal portuguese man-o’-war (Physalia physalis) envenomation. Annals of Emergency Medicine 18(3): 312–315.
A long, long time ago, I wrote two posts here about the definition of species, explaining briefly the most important horizontal and vertical species concepts. So we all agree that species exists, but how they emerge? How one species become two, or how one species become another?
The phenomenon by which it occurs is called speciation. Well, sort of… It all depends on how you define a species, actually (so be certain to have read the posts I mentioned above).
Speciation is usually defined as the evolution of reproductive isolation, therefore it deals more with the concept of biological species, but also with the ecological concept and certainly needs some insights on the vertical concepts. If two populations are reproductively isolated, it means that the individuals of one of them are unable or unwilling to breed with those of the other. This usually arrives through genetic and ecological differences that lead to differences in behavior, morphology, physiology. And considering that, we can classify reproductive isolation into two groups: pre-zygotic and post-zygotic isolation.
In pre-zygotic isolation, the two species are reproductively isolated because they do not want or cannot mate and produce a zygote. This may happen simply because of different behaviors in which the two species occupy different places in the environment, mate at different times of the year or even because they are not sexually attracted to each other. There are several experiments using fruitflies that demonstrate how this may evolve pretty fast.
In the late 1980s, William R. Rice and George W. Salt separated individuals of Drosophila melanogaster depending on their preference for dark × light and wet × dry environments, allowing them to mate only with other specimens showing the same preferences. After several generations, the individuals of one group were unable to mate with those of other groups because of their strong habitat preferences, making them unlikely to interact. A similar experiment was performed by Diane Dodd using the species Drosophila pseudoobscura, in which one population was raised with starch as food and other with maltose as food. In this case, after several generations the flies showed a strong preference to mate with individuals of the same group and to reject those of the other group.
Such speciation events are called ecological speciation and are also well-documented in the wild, especially regarding fish preferring different habitats, such as shallow × deep water or still × running water. Eventually the individuals will diverge into two groups that are ecologically isolated in the same environment and consequently become reproductively isolated as well.
Post-zygotic isolation is generally a more advanced form of isolation that indicates deep genetic divergences. This is more commonly associated with the notion of biological species and is based on the inability of the individuals of the two species to produce viable offspring. They may mate with each other and even produce a zygote, but this will be unable to developed into an embryo or the offspring will be sterile or otherwise unable to survive enough to breed. A classical example is the mule, the hybrid of a mare and a donkey that is usully sterile.
In both forms of speciation mentioned above, reproductive isolation usually arises from the accumulation of small differences due to natural selection. This may be enhanced by two phenomena, pleiotropy and genetic hitchhiking.
Pleiotropy is the phenomen by which a single gene have influence over more than one phenotypic trait. For example, a gene that influences the shape of a bird’s bill may also make it change its diet and its song. Several human genetic diseases, such as phenylketonuria (PKU), are examples of pleiotropy.
Genetic hitchhiking, on the other hand, is the phenomenon by which a gene that is naturally selected carries neighbours genes that are in the same DNA chain with it. In fruitflies, for example, a gene that is linked to courtship behavior may be drawn with the gene linked to a digestive enzyme, so that flies that specialize in one kind of sugar have a different courtship behavior than others specialized in another sugar.
That’s all for now. In a future post, I’ll talk about the geographic and genetic variables in species formation.
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References and further reading:
Bolnick, D. I., Snowberg, L. K., Patenia, C., Stutz, W. E., Ingram, T. & Lau, O. L. 2009. Phenotype-dependent native habitat preference
facilitates divergence between parapatric lake and stream stickleback. Evolution, 63(8): 2004-2016.
Hendry, A. P.2009. Ecological speciation! Or the lack thereof? Canadian Journal of Fisheries and Aquatic Sciences, 66: 1383-1398.
Hoskin, C. J. & Higgie, M. 2010. Speciation via species interactions: the divergence of mating traits within species. Ecology Letters, 13: 409-420.
Maan, M. E., Hofker, K. D., van Alphen, J. J. M. & Seehausen, O. 2006. Sensory drive in cichlid speciation. The American Naturalist, 167(6):
Nosil, P. 2008. A century of evolution: Ernst Mayr (1904-2005). Ernst Mayr and the integration of geographic and ecological factors in
speciation. Biological Journal of the Linnean Society, 95: 26-46.
Turelli, M., Barton, N. H. & Coyne, J. A. 2001. Theory and speciation. TRENDS in Ecology and Evolution, 16(7): 330-343.