Tag: Anatomy

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Redundant Ergot by Sarah Das Gupta

The equine ergot
is mysterious and odd
someone blundered

by Sarah Das Gupta

Having had many horses in a long life, I can’t see the importance of the ‘ergot’ in 2023. For those unaware, the ergot is a small callosity on the underside of the fetlock of a horse. In horses, ergots can range from pea-sized to 3.8 cm in diameter and can be found on all four legs or absent on some or all of them.

The ergot has long been felt to be a vestige of the multi-toed foot of ancestral horses, and some horse owners trim them down to near skin level. However, the ergot’s redundancy may only be skin deep, as recent research suggests that the internal structure of the ergot beneath the visible external callus continues to have a function in modern horses.

Lusi and Davies (2017) studied the subcutaneous ergot tissue and found that “its overall connectivity, and the presence of nerve fibers and Ruffini endings strongly suggest that the ergot and its derived ligaments contribute to joint support, movement, and tension distribution in the distal limb.”

Further reading:

‘The Observer’s Book of Horses and Ponies’, R S Summerhays, Frederick Warne & Co. Ltd.

‘The Connectivity and Histological Structure of the Equine Ergot—A Preliminary Study’, Carla M. Lusi and Helen M.S. Davies, 2017, https://doi.org/10.1016/j.jevs.2017.01.003

Author bio:

Sarah Das Gupta is a young 81 year old. Loves writing haiku and most forms of poetry. Is learning to walk after an accident. Main outside interests include equine sports. Lives near Cambridge, UK. Read other sciku by Sarah here: ‘Redundant Vets‘, ‘Dog’s Mercury’ , ‘Bird’s Foot Trefoil’, ‘Mistletoe’ and ‘The Glastonbury Thorn’.

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Darwin’s Finches

islands diverging
beaks for seeds and bugs and blood
letters rearranged

Darwin’s finches are a group of 18 species of passerine birds found across the Galápagos Islands (hence their other name of Galápagos finches). The group are a poster child for Darwin’s theory of evolution by means of natural selection. During his voyage on the HMS Beagle he collected specimens from what later turned out to be 12 of the 18 species, although Darwin himself didn’t realise the significance at the time, not realising they were all types of finch (ornithologist John Gould corrected him about the species) and not recording which islands they came from (he was later able to correctly assign them based on the notes of others on the voyage).

As the finches colonised the islands and began to adapt to the varied habitats and food resources available, the different groups diverged from each other, resulting in the separate species we see today. The finches themselves have a huge variety of forms (likely leading to Darwin’s confusion), most notably in their beak shapes and sizes. Their beaks are highly specialised to the food sources available on the different islands, with different species feeding on nuts, seeds, flowers, nectar, leaves, cacti, and invertebrates (including insects, parasites, larvae and spiders).

Perhaps the strangest of all is the Vampire Ground Finch (Geospiza septentrionalis) which feeds on the blood of other birds such as blue-footed boobies and Nazca boobies. It’s theorised that this behaviour evolved from mutualistic behaviours where the finch would clean parasites from the plumage of larger birds. These days their sharp beaks are used to peck their victim’s skin until it starts bleeding and the finches feed on the blood. Their unpleasant behaviours don’t stop there, however, as they steal eggs and roll them into rocks to break the shells, and they’ll also eat guano – excrement from seabirds. Since fresh water is scarce on their home islands (Wolf Island and Darwin Island), they also feed on nectar from Galápagos prickly pear flowers.

Molecular studies of Darwin’s finches suggests that the timing and spatial expression of at least four genes are responsible for the differences in beak structure, alphabetic changes that led to anatomical changes: BMP4 (which encodes Bone morphogenetic protein 4), CaM (which encodes Calmodulin), ALX1 (which encodes ALX homeobox protein 1), and HMGA2 (which regulates the expression of other genes).

A note about the sciku: this sciku has been written using a scale and focussing structure – narrowing in from the vast islands to the beaks to the individual letters of DNA. Have you ever tried writing sciku with a focussing structure? If so, how did you get on? Let us know in the comments below!

Interested instances of evolution in action? Check out this sciku by Prof Matthew J. James on the classic example of evolution, the Peppered Moth: Dark Moths.

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Aye-Aye!

The northern monkey.

Never in need of a lift

with its pseudothumb.

The aye-aye is a curious primate found in Madagascar that has possibly the most unusual hands in the animal kingdom. Their hands are so elongated that they account for around 41% of their total length of the forelimb. The aye-aye’s long, bony third finger is its calling card – unique in the animal kingdom, it’s a specialised tool for getting grubs out of deep holes and probing for food whilst foraging.

Yet such specialisation can have costs, including weakening the ability of aye-ayes to grip. Hartstone-Rose & Dickinson et al. (2019) suggest that the aye-aye’s pseudothumb may have evolved to combat this disadvantage. The researchers found the pseudothumb has bony, cartilaginous and muscular features, suggesting that it enhances the aye-aye’s grip of smaller items such as thin branches.

A note about the sciku – Aye-ayes are lemurs and are not monkeys (they’re strepsirrhine primates). The sciku calls them northern monkeys because ‘aye’ is a common term in the north of England and in Scotland meaning ‘yes’, and ‘why-aye’ or ‘wey-aye’ are northern (mainly Geordie) terms for ‘well yes’ or ‘well, yes of course’. The term northern monkey is also a derogatory term in the UK for someone from the north of England (the counter of which is southern fairy).

Original research: https://doi.org/10.1002/ajpa.23936

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Tiny predator

Cambrian fossil,
your pincers – a coat of arms.
Ancient arachnid.

The Burgess Shale in the Canadian Rockies has some of the most complete and well preserved fossils found anywhere in the world, allowing researchers to gain huge insights into life millions of years ago during the middle Cambrian period.

Now a new species has been described that illuminates the early development of chelicerate – a group of over 115,000 species that contains spiders, scorpions and horseshoe crabs.

In their paper Aria & Caron (2019) describe the morphology of Mollisonia plenovenatrix, including robust but short chelicerae (pincers) that were located between the animal’s eyes, in front of its mouth. These are the predecessors of the pincers that spiders and scorpions use to kill, hold and cut their prey.

It’s likely that the species hunted close to the sea floor, using long walking legs and other sensory limbs to detect prey. The finding suggests that the origin of the chelicerate must be earlier in the Cambrian period and that the group must have rapidly expanded to fill an underutilised ecological niche.

A note about the sciku: For the sake of the poem I have simplified chelicerate to arachnids. Lead author Cédric Aria has described the pincers (chelicerae) as the ‘coat of arms’ of the chelicerate which felt suitably poetic.

Original research: http://dx.doi.org/10.1038/s41586-019-1525-4

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Shrimp molting by Prof Hortense Le Ferrand

Hiding, weak and soft,
Mantis Shrimp matures and grows,
Preparing attack.

by Prof Hortense Le Ferrand

The Mantis Shrimp is an extraordinary animal in many ways. One of its striking features is its dactyl club: this is a biomaterial that is so hard and tough that it uses it to dismantle crabs and break seashells. But the Mantis Shrimp also grows by molting: during this process, it discards its club, and builds a new one.

In the paper by Amini et al (2019), the club of the Mantis was dissected during its maturation, from day zero to one month. It was observed that a thin membrane, initially folded into a cavity at the centre of the “old” club got inflated, before slowly being converted into the hard deadly appendage. The Mantis remained hidden in its nest until the biomineralization completed and the extraordinary mechanical properties of the club got recovered.

Original research: https://doi.org/10.1073/pnas.1816835116

Dr Hortense Le Ferrand is an Assistant Professor at Nanyang Technical University, Singapore. Hortense’s interests are on the fabrication and design of novel materials and systems inspired by nature. Check out her earlier sciku ‘Closing the Trap’ here.

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Astonishing carrier

Angolan spider –

astonishing carrier.

What is your horn for?

A new species of horned baboon spider has been described that has a soft horn on its back, unlike any spider previously found in the world. The species was found in Angola and Midgley and Engelbrecht (2019) have named it Ceratogyrus attonitifer – its name being a combination of the Latin for astonishment (attonit-) and carrier (-fer). The purpose of the large and soft horn on the spider’s back is currently completely unknown.

Original research: http://dx.doi.org/10.3897/afrinvertebr.60.32141

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A body projects by Prof Tania Douglas

A body projects

to a model of others

and finds its own shape

by Tania Douglas

Reyneke et al (2018) review the state of the art in 3D reconstruction of bone from 2D images, based on deformable models. Such reconstructions are useful in a variety of clinical applications such as surgery planning and postoperative evaluation, and implant and prosthesis design.

Original research: https://doi.org/10.1109/RBME.2018.2876450

Prof Tania Douglas is the South African Research Chair in Biomedical Engineering & Innovation at the University of Cape Town, South Africa. You can follow her on Twitter under the handle @tania_douglas

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Underground sound

Listening for sound

whilst deep underground requires

middle ears to hear.

 

Animals living in different environments will face different auditory challenges. To investigate how environment shapes evolution Koyabu et al (2017) compared middle ear morphology across terrestrial, aquatic and subterranean species from the order eulipotyphla (including hedgehogs, moles and shrews).

They found that a subterranean lifestyle involved adaptations that allow for improved sound transmission at low frequencies and reduced transmission of bone-conducted vibrations. The adaptations observed included “a relatively shorter anterior process of the malleus, an enlarged incus, an enlarged staples footplate and a reduction of the orbicular apophysis”.

Original research: https://doi.org/10.1098/rsos.170608