The history of Systematics: Plants in Systema Naturae, 1758 (Part 6)

by Piter Kehoma Boll

Finally a new post in the History of Systematic series. This is the sixth part of Linnaeus’ classification of plants. See parts 1, 2, 3, 4 and 5. Here, I’ll present two more classes which are characterized by having the stamens arising from a common base in the flower.

16. Monadelphia (“single brothers”)

“Husbands, or brothers, arising from one base”, i.e., the filaments of the stamens are fused in a single body.

16.1 Monadelphia Pentandria (“single brothers, five males”), five stamens fused into a single structure: Waltheria (gray mallows), Hermannia (hermannias), Bombax (cotton trees), Melochia (melochias).

1758Linnaeus_monadelphia_pentandria

These 5 species belonged Linnaeus’ Monadelphia Pentandria (from left to right): sleepy morning (Waltheria indica), three-leaved hermannia (Hermannia trifoliata), chocolateweed (Melochia corchorifolia), red cotton tree (Bombax aculeatum, now Bombax ceiba). Credits to J. M. Garg (sleepy morning), C. E. Timothy Paine (hermannia), Jeevan Jose (chocolatewed), Dinesh Valke (cotton tree).

16.2 Monadelphia Decandria (“single brothers, ten males”), ten stamens fused into a single structure: Connarus (Indian zebrawood), Geranium (geraniums), Hugonia (a species of doubtful identity).

1758Linnaeus_monadelphia_decandria

The above species were put by Linnaeus in the order Monadelphia Decandria: Indian zebrawood (Connarus monocarpus, left) and bigroot geranium (Geranium macrorhizum, right). Credits to Dinesh Valke (zebrawood) and Wikipedia user Hardyplants (geranium).

16.3 Monadelphia Polyandria (“single brothers, many males”), many stamens fused into a single structure: Stewartia (silky camellia), Napaea (glade mallow), Sida (fanpetals), Adansonia (baobabs), Pentapetes (gojikas), Gossypium (cottons), Lavatera (tree mallows), Malva (mallows), Malope (mallow worts), Urena (caesarweeds), Alcea (hollyhocks), Hibiscus (hibiscuses), Althaea (marshmallows), Camellia (camélia).

1758Linnaeus_monadelphia_polyandria

Linnaeus classified the above species as Monadelphia Polyandria (from left to right, top to bottom): common baobab (Adansonia digitata), arrowleaf fanpetal (Sida rhombifolia), glade mallow (Napaea dioica), common marshmallow (Althaea officinalis), common hollyhock (Alcea rosea), common mallow (Malva sylvestris), garden tree mallow (Lavatera thuringiaca), common caesarweed (Urena lobata), Levant cotton (Gossypium herbaceum), Chinese hibiscus (Hibiscus rosa-sinensis), gojika (Pentapetes phoenicea), silky camellia (Stewartia malacodendron), common camellia (Camellia japonica). Credits to Jeevan Jose (fanpetal), Pablo Alberto Salguero Quiles (marshmallow), Stan Shebs (hollyhock), Joanna Voulgaraki (mallow), Bob Peterson (caesarweed), H. Zell (cotton), Andrew Fogg (hibiscus), Frank Vicentz (camellia), Wikimedia users Atamari (baobab), Botaurus stellaris (tree mallow), Melburnian (silky camellia), flickr users peganum (glade mallow), Lalithamba (gojika).

17. Diadelphia (“two brothers”)

“Husbands originating from a double base, as well as a double mother”, i.e., the filaments of the stamens are gathered in two bodies.

17.1 Diadelphia Pentandria (“two brothers, five males”), two structures formed of five fused stamens: Monnieria (monnieria).

17.2 Diadelphia Hexandria (“two brothers, six males”), two structures formed of six fused stamens: Fumaria (fumitories).

17.3 Diadelphia Octandria (“two brothers, eight males”), two structures formed of eight fused stamens: Polygala (milkworts), Securidaca (safeworts).

1758Linnaeus_diadelphia_hexandria_octandria

The plant to the left, the common fumitory (Fumaria officinalis) was in the order Diadelphia Hexandria, while the plant to the right, the common milkwort (Polygala vulgaris), was in the order Diadelphia Octandria. Credits to Isidre Blanc (fumitory) e Radio Tonreg (milkwort).

17.4 Diadelphia Decandria (“two brothers, ten males”), two structures formed of ten fused stamens: Amorpha (false indigo), Ebenus (ebonies), Erythrina (coral trees), Spartium (brooms), Genista (more brooms), Lupinus (lupins), Anthyllis (kidney vetches), Aeschynomene (jointvetches), Piscidia (), Borbonia (cape gorses), Aspalathus (more cape gorses), Ononis (restharrows), Crotalaria (rattlepods), Colutea (bladder sennas), Phaseolus (beans), Dolichos (longbeans, lablab bean), Orobus (vetchlings), Pisum (peas), Lathyrus (more vetchlings), Vicia (vetches), Astragalus (milkvetches), Biserrula (more milkvetches), Phaca (even more milkvetches), Psoralea (some trefoils), Trifolium (clovers or trefoils), Glycyrrhiza (licorices), Hedysarum (sweetvetches), Coronilla (more vetches), Ornithopus (bird’s-foot), Scorpiurus (scorpion’s-tails), Hippocrepis (horseshoe vetches), Medicago (alfalfas), Trigonella (fenugreek and allies), Glycine (soybeans), Clitoria (pigeonwings), Robinia (locusts, caraganes, riverhemps), Indigofera (indigos), Ulex (gorses), Cicer (chickpea), Ervum (lentils, vetches), Cytisus (laburnums and even more brooms), Galega (galegas), Lotus (bird’s-foot-trefoils), Arachis (peanut).

1758Linnaeus_diadelphia_decandria

These 36 plants were included in the order Diadelphia Decandria (from left to right, top to bottom): coral bean (Erythrina herbacea), fishfuddle (Piscidia erythrina, now Piscidia piscipula), heart-shaped capegorse (Borbonia cordata, now Aspalathus cordata), weaver’s broom (Spartium junceum), dyer’s broom (Genista tinctoria), desert false-indigo (Amorpha fruticosa), Indian jointvetch (Aeschynomeme indica), blue rattlepod (Crotalaria verrucosa), field restharrow (Ononis arvensis), common kidney vetch (Anthyllis vulneraria), white lupin (Lupinus albus), bladder senna (Colutea arborescens), common bean (Phaseolus vulgaris), lablab bean (Dolichos lablab, now Lablab purpureus), common pea (Pisum sativum), hairy vetchling (Orobus hirsutus, now Lathyrus hirsutus), grass vetchling (Lathyrus nissolia), common vetch (Vicia sativa), Chickpea (Cicer arietinum), lentil (Ervum lens, now Lens culinaris), common laburnum (Cytisus laburnum, now Laburnum anagyroides), common gorse (Ulex europaeus), peanut (Arachis hypogaea), licorice (Glycyrrhiza glabra), scorpion vetch (Coronilla glauca), little white bird’s-foot (Ornithopus perpusillus), horseshoe vetch (Hippocrepis comosa), prickly scorpion’s-tail (Scorpiurus muricatus), alpine sweetvetch (Hedysarum alpinum), indigo (Indigofera tinctoria), common galega (Galega officinalis), Asian pigeonwing (Clitoria ternatea), common soybean (Glycine max), alpine milkvetch (Astragalus alpinus), white clover (Trifolium repens), Cretan ebony (Ebenus cretica). Credits to Everglades NPS (coral bean), Jon Richfield (capegorse), Bernd Haynold (dyer’s broom), Dinesh Valke (jointvetch), J. M. Garg (rattlepod), Kristian Peters (restharrow, vetch, bird’s-foot), Massimiliano Marcelli (lupin), Mauricio Laurente (bean), Bogdan Giuşcă (hairy vetchling), Carl Davies-CSIRO (chickpea), Christian Kooyman (lentil), Jean François Gaffard (laburnum), H. Zell (peanut), Carsten Niehaus (scorpion vetch), Isidre Blanc (horseshoe vetch), Hans Hillewaert (scorpion’s-tail, clover), Nicola Cocchia (galega), Tusli Bhagat (pigeonwing), Jörg Hempel (milkvetch), Rüdiger Kratz (ebony), flickr users jayeshpatil912 (fishfuddle) and Eskimo Potato (sweetvetch), Wikimedia users Hectonichus (weaver’s broom), AnRo0002 (false indigo, kidney vetch, bladder senna), Dalgial (lablab), Rasbak (pea), Sannse (grass vetchling), Rosser1954 (gorse), Pharaoh han (liquorice), Pancrat (indigo), vegetalist (soybean).

18. Polyadelphia (“many brothers”)

Husbands originating from more than two mothers, i.e., stamens are gathered in three or many bodies.

18.1 Polyadelphia Pentandria (“many brothers, five males”), more than two structures of five fused stamens: Theobroma (cacao and bay cedar).

18.2 Polyadelphia Icosandria (“many brothers, twenty males”), more than two structures of twenty fused stamens: Citrus (citrus fruits trees).

18.3 Polyadelphia Polyandria (“many brothers, many males”), more than two structures of many fused stamens: Hypericum (St. Johnswort), Ascyrum (St. Andrew’s cross).

1758Linnaeus_polyadelphia

The cacao tree (Theobroma cacao, left) was one of the members of the order Polyadelphia Pentandria; the citron (Citrus medica, middle left) was a member of the order Polyadelphia Icosandria; and the Balearic St. Johnswort (Hypericum balearicum, middle right) and the St. Andrew’s cross (Ascyrum hypericoides, now Hypericum hypericoides) were members of the order Polyadelphia Polyandria. Credits to H. Zell (cacao tree), Christer T Johansson (citron), Wikimedia user Eric in SF (St. Johnswort), Bob Peterson (St. Andrew’s cross).

With a few exceptions, most of the plants in these classes currently belong to the families Malvaceae and Fabaceae (Leguminosae) of flowering plants. I guess we still need three more posts on the plants and then we are done! I hope the next part won’t take so long.

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References:

Linnaeus, C. (1758) Systema Naturae per Regna Tria Naturae…

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Friday Fellow: Brown spot of maize

by Piter Kehoma Boll

I’ll continue the parasite trend from last week, but this time shifting from human parasite to maize parasite, and from a prokaryotic to a eukaryotic parasite. So let’s talk about Physoderma maydis, commonly known as the brown spot of maize or brown spot of corn.

The Brown spot of maize is a fungus of the division Blastocladiomycota that infects corn (or maize) plants. Its common name comes from the fact that it causes a series of brown spots on the leaves of an infected plant.

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The brown spots seen on this corn leaf are due to an infection by Physoderma maydis. Credits of the photo to Clemson University – USDA Cooperative Extension Slide Series.*

The life cycle of the brown spot of maize is as complex as that of many fungi. The infection of the plants occur through spores that remain in the soil during winter and are carried to the host by the wind, germinating in the rainy season. The germinated spores produce zoospores, flagellated spores able to swim. Swiming through the maize leaf, the zoospores infect single cells and produce zoosporangia at the surface of the leaf. The zoosporangia release new zoospores that infect new cells. In late spring and summer, the zoospores produce a thallus growing deep inside the maize leaf that infects many cells and produces thick-walled sporangia. After the plants dies and the leaves become dry and broke, the sporangia are released and reach the soil, where they wait for the next spring to restart the cycle.

The brown spot of maize is a considerable problem for maize crops in countries with abundant rainfall. Heavy infections may kill the maize plant or severely reduce its fitness before the ears are ready to be harvested. Although fungicides may help in slowing down the infectio throughout the crops, one of the most efficient ways to reduce the damage is to destroy, usually by fire, the remains of the last harvest.

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References:

Olson, L. W.; Lange, L. (1978) The meiospore of Physoderma maydis. The causal agent of Physoderma disease of maize. Protoplasma 97: 275–290. https://dx.doi.org/10.1007/BF01276699

Plantwise Knowledge Bank. Brown spot of corn (Physoderma maydis). Available at: < http://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=40770&gt;. Access on Agust 7, 2017.

Robertson, A. E. (2015) Physoderma brown spot and stalk rot. Integrated Crop Management News: 679. http://lib.dr.iastate.edu/cropnews/679/

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Friday Fellow: H. pylori

by Piter Kehoma Boll

I already introduced three species of bacteria here, all of them free-living and/or friendly little ones. But we all know that many bacteria can be a real annoyance to us humans, and so it’s time to show some of those, right?

I decided to start with one that I thought to have living inside me some time ago (but it happened that I don’t), and this is the ill-tempered Helicobacter pylori, which as usual lacks a common name, but is commonly called H. pylori for short by doctors, so that’s how I’ll call it.

empylori

Electron micrograph of a specimen of H. pylori showing the flagella.

The most common place to find the H. pylori is in the stomach. It is estimated that more than half of the human population has this bacterium living in their gastrointestinal tract, but in most cases it does not affect your life at all. However, sometimes it can mess things up.

H. pylori is a 3-µm long bacterium with the shape of a twisted rod, hence the name Helicobacter, meaning “helix rod”. It also has a set of four to six flagella at one of its ends, which make it a very motile bacterium. The twisted shape, together with the flagella, is thought to be useful for H. pylori to penetrate the mucus lining the stomach. It does so to escape from the strongly acidic environment of the stomach, always penetrating towards a less acidic place, eventually reaching the stomach epithelium and sometimes even living inside the epithelial cells.

In order to avoid even more the acids, H. pylori produces large amounts of urease, an enzyme that digest the urea in the stomach, producing ammonia, which is toxic to humans. The presence of H. pylori in the stomach may lead to inflammation as an imune response of the host, which increases the chances of the mucous membranes of the stomach and the duodenum to be harmed by the strong acids, leading to gastritis and eventually ulcers.

The association between humans and H. pylori seem to be very old, possibly as old as the human species itself, as its origin was traced back to East Africa, the cradle of Homo sapiens. This bacterium is, therefore, an old friend and foe and it will likely continue with us for many many years in the future.

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References:

Linz, B.; Balloux, F.; Moodley, Y. et al. (2007) An African origin for the intimate association between humans and Helicobacter pyloriNature 445: 915–918. https://dx.doi.org/10.1038/nature0556

Wikipedia. Helicobacter pylori. Available at < https://en.wikipedia.org/wiki/Helicobacter_pylori >. Access on August 5, 2017.

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Darwin’s Planaria elegans: hidden, extinct or misidentified?

by Piter Kehoma Boll

During his epic voyage on the Beagle, Charles Darwin visited Rio de Janeiro, Brazil, and collected some amazing land planarians, a group that until then was very little known. One of the species he found was Geoplana vaginuloides, the type-species of the genus Geoplana, at that time named Planaria vaginuloides.

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Geoplana vaginuloides (Darwin, 1844), the first Brazilian land planarian species to be described. Photo by Fernando Carbayo.*

The second species described by Darwin was named Planaria elegans. Darwin’s description is as it follows:

“Position of the orifices as in P. vaginuloides. Anterior part of the body little elongated. Ocelli absent on the anterior extremity, and only a few round the margin of the foot. Colours beautiful; back snow-white, with two approximate lines of reddish brown; near the sides with several very fine parallel lines of the same tint; foot white, exteriorly clouded, together with the margin of the body, with pale blackish purple: body crossed by three colourless rings, in the two posterior of which the orifices are situated. Length 1 inch; breadth more uniform, and greater in proportion to length of the body, than in last species.
Hab. Same as in P. vaginuloides. [Rio de Janeiro]”

And this is all we know about this species. Darwin did not provide any drawing and later researchers did not report this species again, except when mentioning Darwin’s publication. As you can see by the description, it is not very accurate. He does not say what is the breadth of each line or band, neither how many of the “several fine parallel lines of the same tint” there are. Here is a quick drawing I did of how I imagine the creature would be:

image description

My idea of what Darwin’s Planaria elegans may have looked like. Head to the left. Credits to myself, Piter Kehoma Boll.**

In 1938, Albert Riester described a land planarian from Barreira, a district in the city of Teresópolis, Rio de Janeiro, naming it Geoplana barreirana. He described it as it follows (translated from the original in German):

“Land planarian found on a leaf after a rain; greatest lenght ca. 20 mm. Middle of the back white with two fine purple-red (atropurpureus light) parallel stripes. Outside of the white also limitted by pale red, then follows (on both sides) a black band and laterally a black-brown marmorate pattern over brown background. The middle stripe ends at the rear [end]. Head spotted, marked with transversal spotted bands (regenerate?). Underside gray, bordered by black-brown. Anterior end is arched backwards.”

Fortunately, Riester provided a drawing, which you can see below:

Barreirana_barreirana_Riester

Geoplana barreirana drawn by Riester (1938).

They look a bit alike, right? Fortunately Geoplana barreirana (currently named Barreirana barreirana) was found by later researchers and we have photographs! See one specimen below:

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A specimen of Barreirana barreirana found in the Tijuca National Park, Rio de Janeiro. Photo by Fernando Carbayo.*

Riester did not describe any transversal marks on his specimens, but he may have mistaken them for color loss in preserved specimens or something like that. Otherwise the specimen looks very similar to Riester’s drawing, and the internal anatomy, which Riester provided as well, is also compatible.

Now let’s try to fit Darwin’s description of Planaria elegans in this photograph. White background, two reddish brown stripes and several fine parallel stripes of the same tint. He likely described the animals from preserved specimens, even though he have seen them alive and collected them. Perhaps the colors had already faded a little and the black stripes, which internally touch two of the reddish stripes, may have been considered a single purple-red stripe? It is not clear, in his description, whether there is white between the “reddish brown” stripes and the “pale blackish-purple” sides, as I did in my drawing, or not, as in Barreirana barreiranabut certainly the dark gray sides of B. barreirana could be the same as the pale blackish purple sides of Planaria elegans, don’t you think? And B. barreirana HAS three white “rings” crossing the body. You can see the first and the second very clearly on the specimen above. The third one is not very well marked, but you can see a third white mark interrupting the gray sides. And the second and almost third marks seem to be quite where one would expect the two orifices (mouth and gonopore) of the planarian to be!

And what about the ventral side? Darwin described P. elegan‘s as being white with a pale blackish purple border as the sides of the dorsum. Riester described G. barreirana‘s as being gray bordered by black-brown. Here is Barreirana barreirana‘s ventral side:

Barreirana barreirana from below

Ventral side of Barreirana barreirana from the Tijuca National Park, Rio de Janeiro. Photo by Fernando Carbayo.*

It is white, or pale gray perhaps, and the borders are of the same color as the sides of the dorsum!

I think it is very, very likely that Darwin’s Planaria elegans and Riester’s Geoplana barreirana are the same species. The fact that no one but Darwin has ever seen a specimen of Planaria elegans makes it even more likely.

What do you think?

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See also:

How are little flatworms colored? A Geoplana vaginuloides analysis.

The fabulous taxonomic adventure of the genus Geoplana.

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References:

Darwin, C. (1844) Brief Description of several Terrestrial Planariae, and of some remarkable Marine Species, with an Account of their Habits. Annals and Magazine of Natural History 14, 241–251.

Riester, A. (1938) Beiträge zur Geoplaniden-Fauna Brasiliens. Abhandlungen der senkenbergischen naturforschenden Gesellschaft 441, 1–88.

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Friday Fellow: Common Water Bear

by Piter Kehoma Boll

Tiny and tough, our newest Friday Fellow can be found hidden among the moss throughout most of the planet, and perhaps even beyond it, for if there is a species to which space is a piece of cake, that species is the common water bear Milnesium tardigradum.

783px-sem_image_of_milnesium_tardigradum_in_active_state_-_journal-pone-0045682-g001-2

A Scaning Electron Microscope (SEM) image of a specimen of the common water bear in its active state. Photo extracted from Schokraie et al. (2012).*

You may have already heard of tardigrades or water bears, tiny chubby animals that are able to withstand the harsher conditions, such as intense desiccation, radiation and even the vacuum of outer space. Most of the data regarding the toughness of these organisms comes from the common water bear, the most widespread species of the phylum Tardigrada.

Measuring up to 0.7 mm in length, the common water bear has eight legs with claws on their end and is considered a predator, feeding on a variety of other small organisms, including algae, rotifers and nematodes. It has a worldwide distribution and is commonly found living on moss, such as the cosmopolitan silvergreen moss already presented here.

As members of the supergroup Ecdysozoa (which also includes arthropods and roundworms), tardigrades undergo ecdysis, also commonly known as molting, a process through which they shed their exoskeleton. In the common water bear, females always lay eggs around the time of molting. Before leaving the old exoskeleton, the females lay the clutch of eggs, which may vary from 1 to 12 eggs, between the old and the new exoskeleton and usually remain inside the old exoskeleton several hours after laying the eggs. When they finally leave, the eggs remain inside the shed skin, which perhaps helps them to be more protected from danger.

Milnesium_tardigradum

A clutch of seven eggs is left in the empty exoskeleton while the female leaves. Photo by Carolina Biological Supply Company.**

When the habitat of the common water bear gets dry, it enters in a state called cryptobiosis, in which the body shrinks and the metabolism stops. Under this state, known as tun, it can withstand high doses of radiation and both high and zero air pressure, surviving even in the environment of outer space. It is not invincible, however. Radiation in doses above 1000 Gy may not always kill them, but always let them sterile, which is, evolutionary, basically the same thing.

615px-sem_image_of_milnesium_tardigradum_in_tun_state_-_journal-pone-0045682-g001-3

SEM image of the common water bear in the tun state. Photo extracted from Schokraie et al. (2012).*

Nevertheless, the American cockroach is just an amateur regarding survival when compared to the common water bear.

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References:

Horikawa, D. D.; Sakashita, T.; Katagiri, C.; et al. (2009) Radiation tolerance in the tardigrade Milnesium tardigradumInternatonal Journal of Radiation Biology, 86(12): 843–848. http://dx.doi.org/10.1080/09553000600972956

Schokraie E, Warnken U, Hotz-Wagenblatt A, Grohme MA, Hengherr S, et al. (2012) Comparative proteome analysis of Milnesium tardigradum in early embryonic state versus adults in active and anhydrobiotic state. PLoS ONE 7(9): e45682. https://dx.doi.org/10.1371/journal.pone.0045682

Suzuki, A. C. (2003) Life history of Milnesium tardigradum Doyère (Tardigrada) under a rearing environment. Zoological Science 20(1): 49–57. https://doi.org/10.2108/zsj.20.49

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They only care if you are cute: how charisma harms biodiversity

by Piter Kehoma Boll

Which of the two species shown below is more charismatic?

Tangara_chilensis

Tangara chilensis (Paradise Tanager). Photo by flickr user ucumari.*

854px-apocrypta_guineensis2c_volw-wyfie_op_f_sur2c_manie_vd_schijff_bt2c_f

Apocrypta guineensis (a fig wasp). Photo by Wikimedia user JMK.**

You probably would pick the first one. And if I’d ask you which one deserves more attention and efforts to be preserved, you would likely choose the bird as well, or at least most people would. But what is the problem with that? That’s what I am going to show you now.

As we all know, the protection of biological diversity is an important subject in the current world. Fortunately, there is an increase in campaigns promoting the preservation of biodiversity, but unfortunately they are almost always directed to a small subset of species. You may find organizations seeking to protect sea turtles, tigers, eagles or giant pandas, but can you think of anyone wanting to protect beetles? Most preservation programs target large and charismatic creatures, such as mammals, birds and flowering plants, while smaller and not-so-cute organisms remain neglected. And this is not only true in environments that included non-biologist people, but in all fields of research. And more than only leading to a bias in the protection of ecosystems, this preference leads to thousands of understudied species that could bring biotechnological revolutions to humandkind.

In an interesting study published this week in Nature’s Scientific Reports (see reference below), Troudet et al. analyzed the taxonomic bias in biodiversity data by comparing the occurrence of data on several taxonomic groups to those groups’ diversity. The conclusions are astonishing, although not that much surprising. The most charismatic groups, such as birds, are, one could say, overstudied, with an excess of records, while other, such as insects, are highly understudied. While birds have about 200 million occurences above the ideal record, insects have about 200 million below the ideal number. And the situation does not seem to have improved very much along the years.

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The bias in interest is clear. The vertical line indicates the “ideal” number of occurrences of each group. A green bar indicates an excess of occurrences, while a red bar indicates a lack of occurrences. Birds and Insects are on the opposite extremes, but certainly the insect bias is much worse. Figure extracted from Troudet et al. (2017).***

Aditionally, the study concluded that the main reason for such disparity is simply societal preference, i.e., the most studied groups are the most loved ones by people in general. The issue is really a simple matter of charisma and has little to do with scientific or viability reasons.

The only way to change this scenario is if we find a way to raise awareness and interest of the general public on the less charismatic groups. We must make them interesting to the lay audience in order to receive their support and increase the number of future biologists that will choose to work with these neglected but very important creatures.

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See also:

Once found and then forgotten: the not so bright side of taxonomy

The lack of taxonomists and its consequences on ecology

Unknown whereabouts: the lack of biogeographic references of species

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Reference:

Troudet, J.; Grandcolas, P.; Blin, A,; Vignes-Lebbe, R.; Legendre, F. (2017) Taxonomic bias in biodiversity data and societal preferences. Scientific Report 7: 9132. https://dx.doi.org/10.1038/s41598-017-09084-6

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Friday Fellow: Pink Cellular Slime Mold

by Piter Kehoma Boll

Protists have always been problematic organisms, and today’s Friday Fellow is not different. In fact, it has probably been one of the most problematic ones. Known scientifically as Acrasis rosea, it has no common name, as you may have guessed already, so I will call him the pink cellular slime mold, as I saw him being called once.

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Isolated (or not so much) cells of Acrasis rosea. Photo by Shirley Chio.*

The pink cellular slime mold is a single-celled organism with an amoeboid shape. It feeds on a variety of bacteria and yeasts and is commonly found in decaying plant matter. When the food supply is completely consumed and the cells start to starve, they gather and form a colony that act as a single organism that moves like a plasmodium similar to that of slime molds. For this reason they were originally called cellular slime molds and considered related to other organisms showing a similar behavior, such as those of the genus Dictyostelium.

This plasmodium moves through the formation of “pseudopods”. Eventually the cells start to form a pile reaching up into the air that produce fruiting bodies in the form of branched chains of spores. There is a slight division of labor between stalk and spore, but both groups of cells are viable to produce a new generation.

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The chains of spores are visible in this image of the pink cellular slime mold during its plasmodium phase. Photo by Shirley Chio.*

The whole process is similar to what is seen in species of Dictyostelium, but the division of labor and the morphology of the plasmodium and the fruiting bodies are a bit more complex. However, with the advancement of molecular phylogenetics, all the slime mold and cellular slime mold classification fell apart.

While Acrasis was revealed to be an excavate, being closely related to organisms such as the euglenas and parasitic flagellates, Dictyostelium is closely related to the true slime molds, such as the already presented here many-headed slime.

But the excavates are still a problematic group among the protists, and so the real position of the pink cellular slime mold may not be settled yet.

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References:

Bonner, J. T. (2003) Evolution of development in the cellular slime molds. Evolution and Development 5(3): 305–313. http://dx.doi.org/10.1046/j.1525-142X.2003.03037.x

Olive, L. S.; Dutta, S. K.; Stoianovitch, C. (1961) Variation in the cellular slime mold Acrasis rosea*. Journal of Protozoology 8(4): 467–472. https://dx.doi.org/10.1111/j.1550-7408.1961.tb01243.x

Page, F. C. (1978) Acrasis rosea and the possible relationship between Acrasida and Schizopyrenida. Archiv für Protistenkunde 120(1–2): 169–181. https://doi.org/10.1016/S0003-9365(78)80020-7

Weitzman, I. (1962) Studies on the nutrition of Acrasis roseaMycologia 54(1): 113–115.

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