Friday Fellow: Salmon Fluke

by Piter Kehoma Boll

Leia em Português

Everybody knows salmons, especially the Atlantic salmon, Salmo salar, and many of us love to eat this fish species as well. However, I’m not here to talk about the Atlantic salmon itself, but to talk about one of its closes companions and antagonists, the salmon fluke.

Scientifically known as Gyrodactylus salaris, the salmon fluke is a flatworm of the clade Monogenea, a group of ectoparasites that infect mainly fish. As its name suggests, the salmon fluke infects salmons, such as the Atlantic salmon, and closely related species, such as the rainbow trout Onchorhynchus mykiss.

Several salmon flukes on a host. Photo by Tora Bardal. Extracted from https://www.drivaregionen.no/no/Gyrodactylus-salaris/

The salmon fluke was first discovered in 1952 in salmons from a Baltic population that were kept in a Swedish laboratory. Measuring about 0.5 mm in length, the salmon fluke attaches to the skin of the fish and is too small to be seen with the naked eye. The attachment happens using a specialized organ full of tiny hooks, called haptor, located at the posterior end of the body. When feeding, the salmon fluke attaches its mouth to the surface of the fish using special glands in its head and everts its pharynx through the mouth, releasing digestive enzymes on the fish, dissolving its skin, which is then ingested. The wounds caused by the parasite’s feeding activity can lead to secondary infections that can seriously affect the salmon’s health.

Artificially colored SEM micrograph of five specimens of Gyrodactylus salaris. Credits to Jannicke Wiik Nielsen. Extracted from https://www.vetinst.no/nyheter/kan-gyrodactylus-salaris-utryddes-i-drammensregionen

Different from most parasitic flatworms, monogeneans such as the salmon fluke have a single host. During reproduction, the hermanophrodite adults release a ciliated larva called oncomiracidium that infects new fish. A single fluke can originate an entire population because it is able to self fertilize.

During the 1970’s, a massive infection by the salmon fluke occurred in Norway following the introduction of infected salmon strains. This led to a catastrophic decrease in the salmon populations in the country, affecting many rivers. Due to this evident threat to such a commercially important species, several techniques have been developed to control and kill the parasite. The first developed methods included the use of pesticides in the rivers, but those ended up having a negative effect on many species, including the salmons themselves. Currently, newer and less aggressive methods have been used.

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References:

Jansen, P. A., & Bakke, T. A. (1991). Temperature-dependent reproduction and survival of Gyrodactylus salaris Malmberg, 1957 (Platyhelminthes: Monogenea) on Atlantic salmon (Salmo salar L.). Parasitology, 102(01), 105. doi:10.1017/s0031182000060406

Johnsen, B. O., & Jenser, A. J. (1991). The Gyrodactylus story in Norway. Aquaculture, 98(1-3), 289–302. doi:10.1016/0044-8486(91)90393-l

Meinilä, M., Kuusela, J., Ziętara, M. S., & Lumme, J. (2004). Initial steps of speciation by geographic isolation and host switch in salmonid pathogen Gyrodactylus salaris (Monogenea: Gyrodactylidae). International Journal for Parasitology, 34(4), 515–526. doi:10.1016/j.ijpara.2003.12.002

Wikipedia. Gyrodactylus salaris. Available at < https://en.wikipedia.org/wiki/Gyrodactylus_salaris >. Access on December 26, 2018.

Whose Wednesday: Adolf Schlagintweit

by Piter Kehoma Boll

Leia em Português

Today I am going to introduce you to a German explorer that had a tragic and early death.

Adolf von Schlagintweit was born on 9 January 1829 in Munich, the second son of Rosalie Seidl and Joseph Schlagintweit, an ophthalmologist. He had four brothers, Hermann, Eduard, Robert and Emil. Joseph taught science to his sons at home and raised in them the desire to become explorers, which all five did, becoming known as The Schlagintweit Brothers.

A portrait of Adolf von Schlagintweit by Julius Schlegel.

With his older brother Hermann, Adolf studied the geography of the Alps from 1846 to 1848, publishing a study about it in 1850 entitled Untersuchungen über die physikalische Geographie der Alpen. Later, the two brothers were joined by their younger brother Robert and together the three published new studies of the Alps in 1854 in a work entitled Neuer Untersuchungen über die physikalische Geographie und Geologie der Alpen. At this time, the famous botanist and explorer Alexander von Humboldt was interested in studying the geology of the Indian subcontinent, but was too old to do it himself, so he convinced the East India Company to hire the three Schlagintweit brothers to do it.

Traveling to India, the three brothers started exploring the Deccan Plateau in central India and from there moved to the north toward the Himalayas. They did not travel together and only reunited occasionally. Their last reunion happened in the fall of 1856 and, by the beginning of 1857, Hermann and Robert returned to Europe, but Adolf decided to stay and continue exploring.

After crossing the mountains of Tibet, Adolf ended up near Kashgar, a region that is currently part of China, near the borders with Kyrgyzstan and Pakistan. This region was at the time under conflict, with the East Turkestan Khojas claiming the territory and invading it constantly. The leader of the Khojas during this period was Wali Khan, who was notorious for his brutality and tyranny.

Despite all the warnings from members of his party, who started to desert, and from people fleeing from the region, Adolf was decided to reach Kashgar, and so he did. At the city border, he was met by the Khojas and brought before the Khan. Seeing no use for Europeans explorers wandering through his territory, Wali Khan accused Adolf of being a spy working for the Chinese and had him beheaded on 26 August 1857, at the early age of 28.

In 1859, the Kazakh ethnographer Shoqan Walikhanov, disguised as a merchant, visited Kashgar and found Adolf’s notebook in a tobacco shop, where it was being used to wrap tobacco leaves. He purchased the notebook and tracked down a skull that most likely was Adolf’s. He took the notebook and the skull with him to the Russian Empire, which allowed the information about the circumstances of Adolf’s death finally reach Europe and his family.

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References:

ExecutedToday.com. 1857: Adolf Schlagintweit, intrepid explorer. Available at < http://www.executedtoday.com/2009/08/26/1857-adolf-schlagintweit-wali-khan-kashgar/ >. Access on January 8, 2019.

Wikipedia. Adolf Schlagintweit. Available at < https://en.wikipedia.org/wiki/Adolf_Schlagintweit >. Access on January 8, 2019.

Wikipedia (in German).
Adolf Schlagintweit. Available at < https://de.wikipedia.org/wiki/Adolf_Schlagintweit >. Access on January 8, 2019.

High temperatures affect the judgement of zebra finches and of humans studying them

by Piter Kehoma Boll

Leia em Português

The zebra finch, Taeniopygia guttata, is an Australian bird that is often used as a model for behavioral studies focused on their vocalization.

Zebra finch (Taeniopygia guttata). Photo by Jim Bendon.*

Recently, a research team from Australia discovered a new call in this species and named it “incubation call”. This particular vocalization was identified as occurring during the last five days of incubation when one of the birds, either the male or the female, was alone with the eggs, and only when temperatures were above 26°C. This raised the hypothesis that this call is used by the parents to communicate to the embryos that the environmental temperature is high and that this information would be used by the nestlings to adapt their behavior and metabolism to higher temperatures.

An experimental study was conducted where eggs were kept in incubators under a constant temperature and exposed (test) or not (control) to recorded incubation calls. The results indicated that nestlings that were exposed to incubation calls grew faster in high temperatures than those that were not exposed to the calls. The mean difference in nestling mass between different temperatures and treatments was of about 2 g only, although the difference in mass between two randomly selected nestlings could be as much as 6 g. Additionally, the R² value of the analyses, which tells how much of the variation is explained by the measured variable, was only 0.1, i.e., temperature explained only 10% of the growth differences between different temperatures in both treatments.

Nestlings in a nest.

One of the most intriguing aspects, however, was the fact that the incubation call was produced at temperatures as low as 26°C, which is not particularly hot in the natural environment of the zebra finch. Thus, another team conducted new studies to understand better how and when the “incubation call” was produced. They decided to rename this call as the “v-call” because their shape is an inverted V in spectrograms. They discovered that the v-call is related to panting, when the birds breathes quickly with its bill open to help reduce body temperature and is likely a side effect of panting and not a deliberate directed call. It is also not produced only during the last 5 days of incubation, but during the whole incubation period and the chick rearing, and some birds are more likely to v-call than others. The results suggest that the v-call is unlikely to have evolved as an incubation call and is more likely a side effect of panting. There is, however, the possibility that embryos can use this information to modulate their growth, although more studies are needed.

Other recent studies with the zebra finch indicate that elevated temperatures can have negative effects on the bird’s reproductive fitness. Temperatures around 40°C reduce sperm quality in male zebra finches and reduce the ability of females to discriminate between songs produced by males of the same species and males of different, distantly related species. A combination of these two effects can lead to a severe decrease in reproductive success by reducing the mating events and reducing sperm ability to fertilize eggs.

A physiological modulation in embryos to deal with the adverse effects of higher temperatures, as suggested by the use of the v-calls, would be certainly benefitial. Maybe this is a behavior still under selection? Let’s see what further studies tell us.

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References:

Coomes CM, Danner RM, Derryberry EP (2019) Elevated temperatures reduce discrimination between conspecific and heterospecific sexual signals. Animal Behavior 147: 9–15. https://doi.org/10.1016/j.anbehav.2018.10.024

Hurley LL, McDiarmid CS, Friesen CR, Griffih SC, Rowe M (2018) Experimental heatwaves negatively impact sperm quality in the zebra finch. Proceedings of the Royal Society B: Biological Sciences 285(1871): 20172547. https://doi.org/10.1098/rspb.2017.2547

Mariette MM, Buchanan KL (2016) Prenatal acoustic communication programs offspring for high posthatching temperatures in a songbird. Science 353(6301): 812–814. https://doi.org/10.1126/science.aaf7049

McDiarmid CS, Naguib M, Griffith SC (2018) Calling in the heat: the zebra finch “incubation call” depends on heat but not reproductive stage. Behavioral Ecology 29(6): 1245–1254. https://doi.org/10.1093/beheco/ary123

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* This work is licensed under a Creative Commons Attribution-Share Alike 2.0 Generic License.

The history of Systematics: Brisson’s system

by Piter Kehoma Boll

Previously, we saw that Linnaeus classified animals into 6 classes: Mammalia, Aves, Amphibia, Pisces, Insecta and Vermes and retained that system in future editions of Systema Naturae. At the same time that Linnaeus was publishing the 10th edition of Systema Naturae, which is the first work to use binomial nomenclature for animals, Brisson, a French zoologist, was creating his own system of classification.

Brisson decided to classify animals into 9 classes: Quadrupeda, Cetacea, Aves, Reptilia, Pisces cartilaginosi, Pisces proprie dicti, Insecta, Crustacea and Vermes. He describes the characters of animals in each class in his work “Regnum animale in classes IX. Distributum sive synopsis methodica”.

Class 1. Quadrupeda: hairy body, at least in some areas, and four feet.

Class 2. Cetacea: naked and elongate body, fleshy fins, horizontally flat tail.

Class 3. Aves: body covered by feathers, corneous bill, two wings, two feet.

Class 4. Reptilia: either naked body and four feet or scaly body and either four or no feet, and breathing through lungs.

Class 5. Pisces cartilaginei: cartilaginous fins and breathing through openings to naked gills.

Class 6. Pisces proprie dicti: fins consisted of little bones and breathing with gills covered by a movable and partially ossified cover.

Class 7. Crustacea: head equipped with antennae, and eight or more feet.

Class 8. Insecta: before last metamorphosis, with several stigmata or breathing organs; after last metamorphisis, head equipped with antennae, and six feet.

Class 9. Vermes: the body, or at least part of it, retractile, without antennae, feet or stigmata.

In this same work, he describes in detail the first two classes. The class Aves is described in a separate work, “Ornithologia, sive, synopsis methodica sistens avium divisionem in ordines, sectiones, genera, species, ipsarumque varietates”, but the remaining classes are never presented, so I will have to deal with those three only.

Class 1. Quadrupeda

This class is composed by all mammals known at the time, except for the cetaceans, which were in the following class, Cetacea. Brisson divided quadrupeds into 18 orders, but did not gave them names, only described them based on the number of teeth and types of nails. Linnaeus used dentition as the main character to classify mammals, but did it using different criteria.

Class 2. Cetacea

This class was composed by the cetaceans and was divided into 4 orders, each with a single genus. The orders were based on the (apparent) distribution of teeth.

In the following image you can see the classification of both Quadrupeda and Cetacea and their comparison to Linnaeus’ 1767 system.

Comparison of Linnaeus’ and Brisson’s systems for mammals. Asterisks indicate genera that are still valid today and were created by the respective authors. A † indicate a genus that is no longer valid.

Some curiosities when we compare mammals in both systems:

1. Linnaeus’ genus Trichechus included manatees and walruses. Brisson classified walruses into a separate genus, Odobenus, but included manatees in the genus Phoca, together with seals and sea lions!

2. Linnaeus included weasels and otters in the genus Mustela and civets in the genus Viverra. Brisson, on the other hand, put civets in the genus  Mustela, together with weasels, but put otters in a separate genus, Lutra.

3. While Linnaeus put hyaenas with dogs in the genus Canis and badgers with bears in the genus Ursus, Brisson had separate genera for hyaenas and badgers, named Hyaena and Meles.

4. Brisson put mice and rats in the genus Mus, dormice in the genus Glis and South-American short-tailed rodents, such as cavies and pacas, in the genus Cuniculus. Linnaeus had them all in Mus.

5. Brisson separated giraffes in their own genus, Giraffa, while Linnaeus classified them in the genus Cervus with deer.

Class 3. Aves

Brisson’s classification of birds was very different from that of Linnaeus. There were many more orders and genera. In fact, some genera used by Linnaeus in 1767 were created by Brisson. See below how complex the relationship of one system to the other is:

Comparison of Linnaeus’ and Brisson’s classification of birds. See the huge difference between both systems. Asterisks indicate genera that are still valid today and were created by the respective authors. A † indicate a genus that is no longer valid.

Unfortunately, Brisson never published his classification of other animals, so we must move on to the next authors in the following posts.

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References:

Brisson M-J (1762). Regnum animale in classes IX. Distributum, sive, Synopsis methodica. Lugduni Batavorum apud Theodorum, Haak. 316 pp.

Brisson M-J (1763a). Ornithologia, sive, synopsis methodica sistens avium divisionem in ordines, sectiones, genera, species, ipsarumque varietates. Apud Theodorum Haak, Lugduni Batavorum : 534 pp.

Brisson M-J (1763b). Ornithologia, sive, Synopsis methodica sistens avium divisionem in ordines, sectiones, genera, species, ipsarumque varietates. Apud Theodorum Haak, Lugduni Batavorum : 542 pp.

Friday Fellow: Toothed Micrasterias

by Piter Kehoma Boll

Leia em Português

A new year is beginning with Friday Fellow, and we are going to start small with a lovely tiny alga named Micrasterias denticulata, or the toothed micrasterias as I decided to call it. Found in freshwater habitats, especially peat bogs with acid water, all around the world, this species belongs to the order Desmidiales, which is characterized by its peculiar cell anatomy.

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  One individual of Micrasterias denticulata collected in Spain, Credits to Proyecto Agua.*

As most desmids, the toothed micrasterias is a single-celled organism and its cell is divided into two halfs, called semi-cells, which are united by a narrow isthmus. Each semi-cell contains a large chloroplast, and the nucleus lies within the isthmus. Due to its symmetrical cell with a well-defined shape, including a series of lobes, the toothed micrasterias and other species of its genus are ideal organisms for the study of cell morphogenesis.

Recently, Micrasterias denticulata has been used to study the effect of several environmental variables, especially pollutants and nutrients, on cell shape. Such studies are important to understand the effects of environmental changes caused by human activities, such as agriculture and waste production, on freshwater ecosystems. Living in an environment that changes constantly regarding pH, salinity and temperature, the toothed micrasterias is a tough organism and has developed mechanisms to avoid intoxication, such as crystalization of heavy metals to make them innactive inside the cell.

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References:

Affenzeller MJ, Darehshouri A, Andosch A, Lütz C, Lütz-Meindl U (2009) Salt stress-induced cell death in the unicellular alga Micrasterias denticulata. Journal of Experimental Botany 60(3): 939–954.
https://doi.org/10.1093/jxb/ern348

Niedermeier M, Gierlinger N, Lütz-Meindl U (2018) Biomineralization of strontium and barium contributes to detoxification in the freshwater alga Micrasterias. Journal of Plant Physiology 230: 80–91.
https://doi.org/10.1016/j.jplph.2018.08.008

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* This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Generic License.

Playful Womb: Baby sharks swim inside their moms

by Piter Kehoma Boll

Leia em português

Most female mammals are characterized by carrying their embryos in the uterus. As the embryos grow and develop, the space inside the uterus gets tight, which makes their ability to move very limited. In addition, mammal embryos are attached to the uterus by the placenta, so that moving too much may be harmful.

Things are different for sharks, which also tend to carry their embryos in the uterus. Lacking a placenta, shark embryos can move freely inside the uterus, and some recent observations revealed that they move a lot.

A specimen of Nebrius ferrugineus at the Great Barrier Reef. Photo by Anne Hoggett.*

Using an ultrasound device adapted to be used underwater, a group of Japanese scientists found out that the embryos of the tawny nurse shark Nebrius ferrugineus are very active inside the uterus. Female sharks in fact have two uteri, which are connected by a narrow passage just above the cervix (the “exit” from the uterus). The embryos were observed swimming constanly from one uterus to the other and in one occasion one of them even put its head through the cervix to “take a look” on things outside its mom.

Ultrasound images and schematic illustrations of a shark embryo swimming from one uterus into the other. Image from the original paper.

The reason for such an active life inside the uterus is not yet clear, but one hypothesis is that the embryos swim around looking for eggs and smaller embryos to eat. It may sound horrible, but baby sharks eating their siblings inside the uterus seems to be a common occurrence.

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Reference:

Tomita T, Murakumo K, Ueda K, Ashida H, Furuyama R (2018) Locomotion is not a privilege after birth: Ultrasound images of viviparous shark embryos swimming from one uterus to the other. Ethology. https://doi.org/10.1111/eth.12828

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* This work is licensed under a Creative Commons Attribution 4.0 International License.

Whose Wednesday: Ludwig von Graff

by Piter Kehoma Boll

Leia em português

Today we celebrate the birthday of a zoologist that is very special to me because he is one of the greatest names in the history of turbellarian research.

Ludwig Bartholomäus Graff de Pancsova, known as Ludwig von Graff, was born on January 2, 1851 in the city of Pancsova (Pančevo), currently part of Serbia, but at the time part of the Austrian Empire. He was the son of Willhelm Hermann Graff de Pancsova, a pharmacist, and Elisabeth de Sold.

He studied Medicine in Vienna, receiving his medical degree in 1871. Afterward, from 1871 to 1873, he studied zoology in Graz with the German zoologist Oskar Schmidt. In the summer of 1872, Schmidt was appointed to Strasbourg and Graff followed him, becoming an assistant at the zoological institute of that city. Due to a treatise he wrote on the anatomy of rhabdocoel flatworms while there, he received, in 1973, a doctoral degree.

Later in the same year, he moved to Munich and became an assistant of Karl Theodor Ernst von Siebold. While there, Graff became an expert on turbellarians and gained his habilitation in 1874 with a work entitled “Zur Kenntnis der Turbellarien” (“On the knowledge of turbellarians”).

On August 5, 1874, Graff married, in Lundenburg, Eugénie Pauline Karoline Emilie Schorisch.

A portrait of Ludwig von Graff. Credits to Alfred von Filz Reiterdank.*

In 1876, Graff was assigned Professor at the Academy of Forestry in Aschaffenburg, where he teached zoology until 1884. In 1884 he was also elected a member of the Academy of Sciences Leopoldina, the national academy of Germany, and accepted an invitation to become a professor of zoology at the University of Graz, where he remained until 1920. There, he greatly expanded the institute of zoology and its library, including many books he received from his father and from Karl Theodor von Siebold.

In order to expand the knowledge of the thousands of unknown turbellarian species, he embarked on several trips, going to Ceylon (Sri Lanka) and Java in 1893–1894, to Norway in 1902 and to North America in 1907. From 1896 to 1897, he was rector of the University of Graz.

Graff died on February 6, 1924, aged 73, after a long mental illness. He and Eugénie had 4 children, two daughters and two sons, including the gynecologist and radiologist Erwin von Graff.

Graff published several important works on turbellarians, including his Monographie der Turbellarien (Monography of the turbellarians), which includes a volume on land planarians that is still one of the most important references for land planarian researchers.

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References:

Books Received (1982) Bibliothek des Professors der Zoologie und vergl Anatomie, Dr Ludwig von Graff, in Graz. Nature 46: 54.
https://doi.org/10.1038/046054c0

Wikipedia (in German). Ludwig Graff de Pancsova. Available at < https://de.wikipedia.org/wiki/Ludwig_Graff_de_Pancsova>. Access on January 1, 2019.

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* This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Think of the worms, not only of the whales, or: how a planarian saved an ecosystem

by Piter Kehoma Boll

Leia em português

Due to the massive interference of human practices on natural habitats during the past decades, ecosystem restoration has become a trend in order to try to save what is still savable. Unfortunately, the effort of ecologists and other experts alone is not enough to achieve that, and a larger section of the society needs to be engaged in helping reach the goals. In order to do so, it is common to appeal to the beauty and cuteness of endangered species, which usually include mammals and birds, since they are more likely to caught the public’s attention. However, most of the endangered species are invertebrates or other less charismatic beings, and they are often ignored even by biologists.

Hopefully, things are able to change on this matter. Recently the first ecosystem restoration directed to save an invertebrate was successful, and I am here to tell you about it.

The invertebrate in question is a freshwater planarian named Dendrocoelum italicum. It was discovered in 1936 in a cave in northern Italy named Bus del Budrio. Inside the cave, there was a small freshwater pool, about 5 × 5 m or little more, caused by a waterfall from a small stream coming through a narrow elevated corridor. The species is apparently found only in this pool and nowhere else.

There are no available photos of Dendrocoelum italicum, but it should look similar to the widespread Dendrocoelum lacteum seen here, but D. italicum lacks the eyes. Photo by Eduard Solà.*

During the 1980’s, a pipe was installed to divert the water from the stream to a nearby farm. The waterfall ceased to exist and the pool dried up permanently. The planarian survived in a very narrow rivulet that formed inside the cave and some small isolated ponds resulting from water drips. This critical condition of the population was discovered in 2016 by a research group from the University of Milan. They informed the administrators of the cave about the situation and, together, the team started to raise awareness about the situation of the cave among the citizens that benefitted from the reservoir formed by the diverted water, which made the farmer responsible for diverting the water agree to remove the artificial structure.

Image of the inside of the cave. Photo by Livio Mola. Extracted from https://www.naturamediterraneo.com/forum/topic.asp?TOPIC_ID=57050

The removal happened on December 3, 2016 after all the planarians occurring in the rivulet were collected and stored in plastic tanks inside the cave. When the waterfall was restored, it quickly started to fill the old pool again and, one day later, the planarians were released into the pool.

The ecosystem was monitored during the following two years until January 2018. The number of planarians varied greatly during the survey, but was not significantly larger after the restoration from what it was before. However, there was a significant increase in the population of a bivalve species, Pisidium personatum, and a small increase in the population of a crustaceon of the genus Niphargus. Additionally, annelids of the family Haplotaxidae, that were absent in the cave, appeared after restoration. Thus, it is clear that the ecosystem benefited from the reappearance of the pool.

Thanks to the efforts of those researchers, Dendrocoelum italicum now has a better chance to avoid extinction. However, this is not an isolated case. There are many cave-dwelling planarian species all around the world living under similar conditions, usually restricted to a single small pool inside a single cave. Many of those occur, or occurred, as D. italicum, in Italy, but the help came to late for some of them. For example, a closely related species, Dendrocoelum beauchampi, was discovered in 1950 in a cave in northwestern Italy named Grotta di Cavassola, but a recent survey found no planarians inside the cave, which seems to have suffered great alteration due to human activities. Similarly, the species Dendrocoelum benazzi was discovered in 1971 in central Italy in a cave named Grotta di Stiffe, but nowadays, with the cave open to turists and its water polluted, the planarians disappeared. It is very likely that both D. beauchampi and D. benazzi are now extinct. The situation is the same for other Italian species.

Out of Italy, a recently described species living a similar small environment is the Brazilian cave planarian Girardia multidiverticulata, which is known to occur in a small pool about 10 m² inside a cave named Buraco do Bicho in the Cerrado Biome.

Girardia multidiverticulata is a planarian species restricted a small 10 m² pool inside a cave in Brazilian cerrado. Credits to Souza et al. (2015)**

The case of Dendrocoelum italicum shows us it is possible to save small endemic populations of threatened habitats, but we need the help of the public. Let’s hope other ecosystems have a similar happy ending.

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References:

Manenti R, Barzaghi B, Lana E, Stocchino GA, Manconi R, & Lunghi E 2018. The stenoendemic cave-dwelling planarians (Platyhelminthes, Tricladida) of the Italian Alps and Apennines: conservation issues. Journal for Nature Conservation.

Manenti R, Barzaghi B, Tonni G, Ficetola GF, & Melotto A 2018. Even worms matter: cave habitat restoration for a planarian species increased environmental suitability but not abundance. Oryx: 1–6.

Souza ST, Morais ALN, Cordeiro LM, & Leal-Zanchet AM 2015. The first troglobitic species of freshwater flatworm of the suborder Continenticola (Platyhelminthes) from South America. Zookeys 470: 1–16.

Vialli PM 1937. Una nuova specie di Dendrocoelum delle Grotte Bresciane. Bollettino di zoologia 8: 179–187.

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* This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

** This work is licensed under a Creative Commons Attribution 4.0 International License.

Friday Fellow: Giant Clam

by Piter Kehoma Boll

One more giant is coming to our team, again from the sea, but this time from the bilvavian molluscs. Its name is Tridacna gigas, commonly known as the giant clam.

Found in shallow coral reefs of the Indian and Pacific Oceans, especially around Indonesia, the giant clam can grow up to about 1.2 m, weigh more than 200 kg and live more than 100 years, being the largest living bivalve mollusk.

The giant clam is seen in coral reefs as a giant lump of molluscan material. Watch out, Dory! Photo by flickr user incidencematrix.*

One interesting aspect of the giant clam and its close relatives is that they live in a symbiotic association with some dinoflagellates (the so-called zoxanthellae, also found in corals), having even a special structure, the zooxanthellal tubular system, to house them. During the day, the giant clam exposes its mantle to the light in order to allow the algae to photosynthesize. Part of the nutrients produced by the algae are given to the clam. This allows the giant clam to survive in otherwise nutrient-poor environments, where its standard bivalvian feeding stile, by filtering partiles from the water, would not be enought to allow it to grow properly.

A half-closed shell. Photo by The Central Intelligence Agency.

The giant clam is used as food in many Asian countries, especially Japan and countries from Southeast Asia and Pacific Islands. Additionally, the giant shell is considered a valuable decorative item and can be sold for large amounts of money. Due to such exploitations, the giant clam populations are starting to decline and the species is considered vulnerable by the IUCN.

An empty shell exposed in Aquarium Finisterrae, Galicia, Spain. Photo by Wikimedia user Drow male.**

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References:

Klumpp, D. W., Bayne, B. L., & Hawkins, A. J. S. (1992). Nutrition of the giant clam Tridacna gigas (L.) I. Contribution of filter feeding and photosynthates to respiration and growth. Journal of Experimental Marine Biology and Ecology, 155(1), 105–122. doi:10.1016/0022-0981(92)90030-e

Norton, J. H., Shepherd, M. A., Long, H. M., & Fitt, W. K. (1992). The Zooxanthellal Tubular System in the Giant Clam. The Biological Bulletin, 183(3), 503–506. doi:10.2307/1542028

Wells, S. (1996). Tridacna gigas. The IUCN Red List of Threatened Species doi:10.2305/IUCN.UK.1996.RLTS.T22137A9362283.en. Access on September 1, 2018.

Wikipedia. Giant clam. Available at < https://en.wikipedia.org/wiki/Giant_clam >. Access on September 1, 2018.

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Friday Fellow: Ehux

by Piter Kehoma Boll

We’ll continue among the unicellular marvels of the sea this week. This time our fellow is another member of a poorly known but hugely important group of protists, the coccolithophores.

The coccolithophores are a group of unicellular algae of the marine phytoplankton that is characterized by a series of calcium carbonate plates, called coccoliths, that cover their body, making them look like cells covered by scales.

Today we’ll know the most widespread and abundant species of this group, Emiliania huxleyi, usually simply called Ehux, which I will use here as its common name.

Scanning elctron micrograph cell of Emiliania huxleyi covered by coccoliths. Credits to Alison R. Taylor.*

Ehux is found in the oceans all around the world, being absent only close to the poles. According to the fossil record, this species appeared about 270 thousand years ago, but became the dominant coccolithophore only anout 70 thousand years ago. Due to its abundance, Ehux is an important species controling global climate. As a photosynthetic organism, it helps to increase atmospheric oxygen and decrease carbon dioxide. Additionally, the fact that its cell is covered by calcium carbonate plates increases even more its importance in removing CO2 from the atmosphere. By capturing CO2 as calcium carbonate, Ehux send it directly to the ocean floor when it dies and the shell sinks.

The life cycle of Ehux is not yet completely understood, but includes at least two different cell forms. The C form is spherical, nonmotile and covered by coccoliths (hence the name C) and can reproduce asexually by fission. Another form, called S (scaly) lacks coccoliths but is covered by a group of organic scales. This form is motile, swimming using two flagella, and also reproduces asexually by fission. How one form turns into the other is unclear, but there are some evidences that the C form is diploid and the S form is haploid, so C cells could turn into S cells by meiosis and two S cells could act as gametes and fuse to produce a new C cell. A third form, called N (naked) cell is similar to a C cell but is unable to produce the coccoliths. It is assumed that they appear by a mutation of C cells that makes them lose the ability to produce coccoliths, as N cells never change back to the C form.

A bloom of Ehux south of Great Britain as seen from a sattelite photo. Credits to NASA.

During some special conditions, such as high irradiance, ideal temperatures and nitrogen-rich waters, Ehux populations can cause blooms which extend over large portions of the ocean. This species is known as a producer of Dimethyl Sulphide (DMS), a flammable liquid that boils at 37°C and has a characteristic smell usually called “sea smell” or “cabbage smell”. The release of DMS in the atmosphere interferes in cloud formation, so that this is one more way by which Ehux influences global climate.

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References:

Paasche E (2002) Paasche, E. (2001). A review of the coccolithophorid Emiliania huxleyi (Prymnesiophyceae), with particular reference to growth, coccolith formation, and calcification-photosynthesis interactions. Phycologia 40(6), 503–529. doi:10.2216/i0031-8884-40-6-503.1

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