Sunday, 10 December 2017

Pleistacantha kannu: A new species of Spider Crab from the Bay of Bengal.

Spider Crabs, Majidae, are a distinctive group of Crabs with carapaces that are longer than they are wide and come to a point at the front. They have extremely elongate legs for Crabs, and tend to be covered in bristles, which are often covered in Algae, providing a form of camouflage.

In a paper published in the journal ZooKeys on 29 November 2017, Peter Ng of the Lee Kong Chian Natural History Museum at the National University of Singapore, Raveendhiran Ravinesh of the Department of Aquatic Biology & Fisheries at the University of Kerala, and  Samuthirapandian Ravichandran of the Center of Advanced Study in Marine Biology at the Annamalai University, describe a new species of Spider Crab from the Bay of Bengal.

The new species is placed in the genus Pleistacantha, and given the specific name kannu, in honour of the late T. Kannupandi of the Center of Advanced Study in Marine Biology at the Annamalai University,for his work on Crustaceans. This species has longer legs than other members of the genus, and these are free of spines. They are orange-brown in colour.

Pleistacantha kannu, colour in life. (A) Male (length 106.2 mm, width 87.0 mm), (B) ovigerous female (length 84.4 mm, width 71.5 mm). Ng (2017).

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Understanding the dispersal of Rockwood and Spoonwood seeds in the South African Fynbos.

The Fynbos of the Western Cape, South Africa, is a dry shrubland ecosystem, prone to frequent fires, which play an important ecosystem function, clearing old growth and stimulating growth of the seeds of fire adapted trees and shrubs such as Mountain Cypress, Widdringtonia nodiflora, and various Protea species. Within this ecosystem there are patches of rocky habitat, such as cliffs, rock outcrops and scree slopes, where non-fire tolerant species such as Rockwood, Heeria argentea, and Spoonwood, Hartogiella schinoides, dominate. Unlike Cypresses and Proteas, these species produce large, fleshy fruits, which are not fire tollerant, and which appear to only survive fires by nestling deep within rock crevices, a location which they are unlikely to reach on their own, suggesting an animal vector is placing them there. It has been suggested that the Rock Hyrax, Procavia capensis, may be responsible for dispersal of the large fleshy seeds of the Rockwood, while the smaller, as redder, seeds of the Spoonwood are probably dispersed by a Bird (the colour red is often associated with dispersal of seeds or pollination by Birds, since few Mammals or Insects have receptors for this colour in their eyes).

In a paper published in the South African Journal of Science on 27 November 2017, Joseph White and Jeremy Midgley of the Department of Biological Sciences at the University of Cape Town, describe the results of a series of tests intended to determine the animals responsible for the dispersal of the seeds of the Rockwood and Spoonwood trees.

 Intact and cross-sectioned fruits of (a), (b) Heeria argentea and (c), (d) Hartogiella schinoides, showing the thin, fleshy pericarps and chlorophyllous endosperm/embryo. White & Midgley (2017).

White and Midgley placed Rockwood seeds in front of camera traps in both Fynbos shrublands and rocky areas within theses shrublands. 

The seeds placed in the rocky areas were ignored by Rock Hyrax, suggesting that this animal is not responsible for the dispersal of these seeds, while 66% of the seeds were removed by the smaller Namaqua Rock Rat, Micaelamys namaquensis. The Cape Genet, Genetta tigrina, and Cape Grey Mongoose, Galerella pulverulenta, were also seen near seeds in these rocky areas, but took no notice of them, which is unsurprising as neither species usually consumes seeds.

A Namaqua Rock Rat, Micaelamys namaquensis. Andrew Deacon/iSpot.

Four species of seed-eating Mammals were seen around the seeds placed in the Fynbos shrublands, the Four-striped Grass Mouse, Rhadbomys pumilio, the Vlei Rat, Otomys irroratus, the Cape Spiny Mouse, Acomys subspinosus, and the Cape Porcupine, Hystrix africaeaustralis. Of these only the Four-striped Grass Mouse paid any attention to the seeds, and this species removed only a very small number.

Searching for the removed seeds revealed a number of seeds with their pericarps (outer fleshy parts) removed, having apparently been gnawed off by a Rodent or similar animal. Experimentation with seeds revealed that 60% of those with the percarp removed germinated, while none of those with it left intact did so, suggesting that this is a natural part of the plant's life cycle, providing a free meal to the Rock Rats, which probably retreat into rock crevices with the seeds to enjoy a meal out of sight of predators such as the Genet and Mongoose.

A Heeria argentea seedling emerges from a dark, rocky crevice at Limietberg Nature Reserve. White & Midgley (2017).

The same procedure was repeated for the seeds of the Spoonwood tree, though without the camera trap. As predicted, some of these seeds were observed being removed by Red-wing Starlings, confirming that these smaller seeds are available to Birds, but a search for the seeds in crevices again found most of the removed seeds, which again showed signs of having the pericarps removed by a Rodent, suggesting that Rats are likely to be the most important distributors of this species as well.

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Magnitude 4.0 Earthquake in San Diego County, California.

The United States Geological Survey recorded a Magnitude 4.0 Earthquake at a depth of about 11.1 km roughly 14 km to the northeast of the town of Julian in San Diego County, California, slightly after 4.30 pm local time on Wednesday 6 December 2017 (slightly after 0.30 am on Thursday 7 December GMT). There are no reports of any damage or injuries relating to this quake, but people have reported feeling it across much of southern California and parts of northeastern Baja California, Mexico.
The approximate location of the 6 December 2017  San Diego County Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

 The extent of and movement on the San Andreas Fault. Geology.

Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.

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Observing the Elias 2-24 Protoplanetary Disk with the Atacama Large Millimeter/Submillimeter Array.

The Ophiuchus Molecular Cloud is a dense molecular cloud roughly 125 parsecs (408 light years) from Earth in the constellation of Ophiuchus, that forms one of the closest areas of star-formation to the Earth. This region contains over 200 known T Tauri stars (very young stars which have not yet begun to generate heat by hydrogen fusion, but which produce considerable energy through gravitational heating) and at least 16 protostars (stars which are still gaining mass by accretion from a surrounding disk, the accretion disk, and are emitting ionised material in jets from their poles). Elias 2-24 is a T Tauri star within the Ophiuchus Molecular Cloud with an estimated age of 400 000 years and mass roughly equal to that of the Sun. This star is surrounded by a protoplanetary disk (a dense structure from which planets are thought to form) from which matter is still actively accreting onto the star, and which is roughly edge on when seen from Earth, making it a good candidate for observation by astronomers trying to understand these structures.

In a paper published on the arXiv database at Cornell University Library on 18 November 2017, and accepted for publication in the Astrophysical Journal Letters, a team of scientists led by Lucas Cieza of the Facultad de Ingenier a y Ciencias, N ucleo de Astronom a at the Universidad Diego Portales, and the Millennium Nucleus Center of Protoplanetary Disks in ALMA Early Science, describe the results of a study of the Elias 2-24 Protoplanetary Disk made with the Atacama Large Millimeter/Submillimeter Array (ALMA) on 13 and 14 July 2017.

Cieza et al. immaged the Elias 2-24 Protoplanetary Disk at a range of wavelengths, intended to detect the densities of different molecules. Molecules will absorb light as energy across a broad part of the spectrum, but can only absorb a finite amount of light before being forced to re-emit some of this energy. However this energy is not released in random bursts, but radiated at specific frequencies determined by the atoms present in the molecule, which atoms are bound to which other atoms, and even which isotopes of each element are present. This gives each molecule its own unique spectrographic signature, which can be used by astronomers to detect different molecules in distant objects such as protoplanetary disks.

Using this method Cieza et al. were able to detect three distinct gaps in the protoplanetary disk around Elias 2-24, at distances of 20, 52, and 87 AU from the star (i.e. 20, 52 and 87 times as far from the star as Earth is from the Sun), and have widths of 6, 28 and 11 AU, respectively. Such gaps in protoplanetaty disks are thought to be caused by the formation of planets, as matter from the disk accretes onto the forming protoplanetary body. Calculating the amount of matter that would be missing from the disks in this gap, Cieza et al. suggest that enough material has been used to form planets with masses of 4, 20 and 10 times that of Jupiter, though they do not believe that all of the missing material would have been used up by planetary formation; much of it is likely to have been ejected from these gaps by tidal forces generated by the forming protoplanets.

 Composite ALMA image of the Elias 2-24 Protoplanetary Disk, assembled from averaged images at different wavelengths. Cieza et al. (2017).

Cieza et al. further note that the temperatures at the inner two gaps, 23 and 15 K corresponds closely to those predicted for the snow-lines of Carbon Monoxide (23-28 K) and Nitrogen (12-15 K), i.e. the temperatures at which these molecules with cease to be disassociated gases and start to accrete into snow, suggesting that such snow-formation plays a role in the early stages of planetary formation.

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Saturday, 9 December 2017

Neotrygon vali: A new species of Maskray from Guadalcanal Island, in the Solomon Archipelago.

Maskrays, Neotrygon spp., are a group of Stingrays, Dasyatidae, found in the Indian Ocean and west Pacific. They get their name from a distinctive coloured marking around the eyes, which resembles a mask, but have a number of other distinctive features, including short tails with well developed dorsal fins, small mouths with enlarged cuspid teeth, and large pectoral fins with a single row of thorns along their dorsal midline.

In a paper published on the bioRxiv beta database on 25 July 2017, Philippe Borsa of Ecologie marine tropicale des océans Pacifique et Indien at the Institut de recherche pour le développement, describes a new species of Masked Ray from Guadalcanal Island, in the Solomon Archipelago.

The new species is named Neotrygon vali, where 'vali' means 'Stingray' in Gela, one of the languages spoken on Guadalcanal. The new species is described from a female specimen 295 mm in length obtained from the Plaza fish market in Honiara om Guadalcanal Island. It is distinguished from other Maskrays by the darkness of its eye marking and the pattern of blue spots on its dorsal surface, and confirmed as a new species by DNA analysis.

Guadalcanal Maskray Neotrygon vali showing the pigmentation patterns that differentiate it from Neotrygon kuhlii from Vanikoro. Borsa (2017).

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Acutogordius taiwanensis: A new species of Horsehair Worm from Taiwan.

Horsehair Worms, Nematomorpha, are parasitiod Worms related to Nematodes, but with a rather more complex life-cycle. The adult worms are extremely long, sometimes exceeding two meters in length, but seldom more than a millimetre in width, and are found in marine and freshwater ecosystems. The larval stages of these Worms are parasites, growing inside the bodies of other animals, and typically have a two-host life-cycle, with the young Worms infecting a secondary host shortly after hatching, then modifying the behaviour of this host so that it is more easily consumed by the primary host, inside which the Worm reaches maturity, emerging as an adult, typically with fatal consequences for the host. In freshwater Horsehair worms this primary host is typically a terrestrial invertebrate such as an Insect, enabling the Worms to reach new bodies of water and avoid seasonal drying of habitats.

In a paper published in the journal ZooKeys on 6 July 2017, Ming-Chung Chiu of the Department of Entomology at the National Taiwan University, Chin-Gi Huang of the Department of Earth and Life Science at the University of Taipei, and Wen-Jer Wu and Shiuh-Feng Shiao, also of the Department of Entomology at the National Taiwan University, describe a new species of Horsehair Worm from Taiwan.

The new species is placed in the genus Acutogordius, and given the specific name taiwanensis, meaning 'from Taiwan'. These Worms were found at a number of locations in Taiwan, with the primary hosts being a range of Crickets and Katydids and the secondary hosts being aquatic Snails. Adult male Worms reach 428 mm in length and 1.079 mm in width, though most are somewhat smaller, while females reach a maximum of 432 mm in length and 1.120 mm in width. Both are light brown in colour and covered in mucus.

Anterior end of Acutogordius taiwanensis. (A)–(C) Images of the anterior end showing the (A) white cap and dark-brown collar and (B)–(C) white spots scattered on the brown collar (D)–(F) SEM images of the anterior end surface that is (D) smooth (E) smooth but wrinkled on the tip with holes scattered on the dark-brown collar, and (F) wrinkled (A)–(F) are images from the same individual, respectively. Scale bars 500 μm (A)–(C), and 200 μm (D)–(F). Chiu et al. (2017).

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The Gemenid Meteors.

The Geminid Meteor Shower is expected to peak on Wednesday 13 December this year (2017) with potentially up to 120 meteors per hour being visible in areas of the Northern Hemisphere with a clear sky. This year peak activity for the shower coincides with a waning Crescent Moon, with the New Moon falling on Sunday 17 December, so viewing should be fairly good. The meteors appear to radiate from a point in the constellation of Gemini, hence their name.

The relative positions of the radiant point of the Gemenid Meteors (i.e. the point from which the meteors radiate) at 9.00 pm on 13 December 2017. Sky & Telescope.

Oddly for a meteor shower, the Geminids do not appear to be related to a comet, but instead are associated with an object called 3200 Phaethon, which is classed as an Apollo Asteroid (an asteroid with an orbit that crosses that of the Earth). 3200 Phaethon has a highly elliptical orbit, which takes it in as close as 0.14 Au (14% of the distance between the Earth and the Sun, more than twice as close as Mercury) and out as far as 2.4 AU (2.4 times as far from the Sun as the Earth or 1.6 times as far as Mars). 3200 Phaethon does not appear to produce any sort of halo (a cloud of material produced by the evaporation of gas ice from the surface of a comet, thought to be the source of most meteor showers); rather it appears dark in colour an is classed as a B-type Carbonaceous Asteroid, thought to have a surface covering of  anhydrous silicates, hydrated clay minerals, organic polymers, magnetite, and sulphides.

Asteroid 3200 Phaethon is a 5 km body with a highly eccentric orbit similar to that of a comet, which takes it closer to the Sun than any other named Asteroid. It appears to be the parent body of the Geminid Meteors, which share essentially the same orbit as it, as well as a group of larger bodies known as the Phaethon-Geminid Complex. Such meteor showers typically form from the tail of a comet; as the comet approaches its perihelion (the closest point in its orbit to the Sun), ice at the surface sublimates away (turns directly from a solid to a gas - liquids do not form in a vacuum), releasing particles of silica trapped in the ice, which continue to follow essentially the same path as the comet, creating a meteor shower every time the Earth passes through this stream. However, 3200 Phaethon, which has a 1.43 year orbital period in which it reaches 0.14 AU from the Sun (14% of the distance between the Earth and the Sun, or less than half the distance at which Mercury orbits) is thought to regularly suffer surface temperatures in excess of 1000K, making it highly unlikely that it has ice on its surface, which calls its potential role as the parent body to the Geminid Meteors into question.

Image of 3200 Phaethon taken on 20 November 2017 with the Pearl Telescope at the Tenagra Observatory in Arizona The asteroid is the point in the centre of the picture, indicated by the two red lines. The longer lines are stars, their elongation being caused by the telescope tracking the asteroid over the length of the exposure, in this case five exposures, each of 180 seconds. Gianluca Masi/Virtual Telescope/Michael Schwartz/Tenagra Observatory.
In a paper published on the arXiv online database at Cornell University Library on 17 June 2013, David Jewitt of the Department of Earth and Space Sciences and Department of Physics and Astronomy at the University of California Los AngelesJing Li of the Department of Earth and Space Sciences at the University of California Los Angeles, and Jessica Agarwal of the Max Planck Institute for Solar System Research, describe the results of a study of 3200 Phaeton using the NASA STEREO Spacecraft.

Jewitt et al. observed two successive perihelions of 3200 Phaeton, in June 2009 and May 2012. On both occasions they were able to observe a faint comet-like dust tail emerging from the body, even though it was apparently reaching temperatures that would rapidly destroy an icy comet. This tail grew rapidly, reaching a length of over 250 000 km within a day of first appearing, and appeared to represent material being lost from the parent body at a rate of about 3 kg per second.

Composite images of 3200 Phaethon in 2009 (top row) and 2012 (bottom row) compared with the projected sun- comet line (white). The Sun is to the upper right in each panel. Insets are 49000 square and show eld stars near to Phaethon to demonstrate the point spread function of the data. Each panel has North to the top, East to the left and shows the median of 30 images taken over a 1 day period. Jewitt et al. (2013).

Jewitt et al. suggest that at it's perihelion 3200 Phaethon is being heated to such a degree that hydrated minerals at its surface could be thermally fractured and desiccated, leading to the ejection of dust particles.

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