Friday, 3 January 2020

Understanding enrolment behaviour in Chitons.

The ability of armoured animals to roll into a defensive ball is known from many disparate groups. This ability, called conglobation or enrolment, is known from Mammals such as Pangolins, Manidae, and Hedgehogs, Tenrecinae, and Echidna, Tachyglossidae, Arthropods including some Isopods, Trilobites, Pill Millipedes and larvae of other groups, and, among Molluscs, the multi-shelled Chitons. These animals have the flexibility to curve their entire body and touch the anterior to the posterior end, such that the hard dorsal elements cover the whole outer surface and the softer, ventral parts are protected inside the ball. Species with this ability span a broad variety of ecological niches and both terrestrial and aquatic environments; while the ability to display protective armour in every direction is doubtless beneficial to defence, the ability to become more spherical may have additional and more relevant implications in terms of functional morphology. Chitons are unusual among ball-forming invertebrate animals in that they entirely lack mechanisms that lock the body in the enrolled position. By contrast, many Trilobites, Oniscoid Isopods and Millipedes have intricate locking (or coaptive) devices that are modifications of the exoskeleton. Many of these ball-forming taxa with coaptive devices protect legs, antennae and reproductive structures, and at least some develop spines that protrude outward when the animal is in the enrolled position. Spines provide an additional defence against gape-limited predators, and in aquatic contexts may affect hydrodynamic dispersal. Conglobation with coaptive devices is common among living terrestrial arthropods, but is essentially unknown in living adults in the sea, perhaps implying that passive defence in the form of coaptive rolling up into a ball is no longer as effective as it once was during the Paleozoic heyday of the Trilobites.

In a paper published in the journal Biology Letters on 2 October 2019, Julia Sigwart of the Marine Laboratory at Queen’s University Belfast, Geerat Vermeij of the Department of Earth and Planetary Science at the University of California, Davis, and Peter Hoyer, also of the Marine Laboratory at Queen’s University Belfast, present the results of a study in which they  applied an experimental approach to test the response of dislodged Chitons with and without exposure to the threat of potential predation.

A Chiton attached to the substratum by its soft foot is well defended by its dorsal scleritome and will respond to disturbance by holding fast to the surface. The Chiton scleritome and its overlapping plates have been analysed as an armour that optimizes a trade-off between defence and mobility. When rolled into a ball, the valves and girdle together provide a complete armour, although much of the ‘ball’ is muscular tissue covered only by a thin cuticle. The potential predators in modern shallow marine settings, including Fish, Seastars, Birds and Crabs, are likely to consume an unattached Chiton whole. Anecdotal speculation has suggested the primary advantage of curling into a ball could instead be mobility, to allow Chitons to roll to a better position. This implies that enrolment is not a passive defence against attack, but perhaps a strategy to improve circumstances. If the tendency of armoured marine animals to roll into a ball is a passive defensive behaviour, then Chitons could be expected to spend relatively more time curled up in the presence of a predator, but if it is not then Chitons should spend less time enroled when a predator is nearby.

A Chiton, Mopalia swanni, in (a) in normal position, and (b) rolled into a ball, anterior is at top in both images. This species was not used in this experiment but shown for illustrative purposes. Sigwart et al. (2019).

Live Chitons were collected from the intertidal at Pinnacle Gulch in Bodega Bay, California and held in aquaria on flowthrough seawater at the University of California, Davis' Bodega Marine Laboratory. Chitons used in these experiments included three species: Mopalia hindsii (17 seventeen specimens), Mopalia muscosa (4 specimens), and Lepidozona mertensii (3 specimens). These species co-occur in the rocky intertidal in Northern California and are broadly distributed on the Pacific coast of North America. The Purple Sea Star, Pisaster ochraceus was selected to produce the predator cue as it is a co-occurring predator known to consume Chitons.

In each trial, a single randomly selected Chiton was placed up-side-down in the centre of the experimental aquarium. Seawater was siphoned continuously from one of two sources, selected by a coin flip: the 40 litre holding aquarium with captive Chitons (control condition), or a separate 20 litre aquarium holding a single Purple Sea Star (predator treatment). These two source aquaria were fed continuously with flow-through seawater. 

Chitons left up-side-down on a flat surface were never able to right themselves, except by manoeuvring close enough to the wall to contact and attach to the vertical surface. This occurred four
times in 24 trials, three of which were in the presence of the predator cue; the control animal that made contact with the side did so only after 109 minutes of a 120-minute trial, while animals in the predator treatment that manoeuvred themselves to the side did so relatively much faster, after 43–87 minutes.

Left in a prone orientation, Chitons adopted the enrolment position around 30% of the time overall; however, there was a strong association between the predator cue and time spent arching. The odds of an individual spending time in a ball are 2.85 times higher without a predator cue. In the presence of a predator cue, the odds of an individual Chiton spending time arching are 2.93 times higher. 

The sample sizes for Lepidozona mertensii (3 specimens) and Mopalia muscosa (4 specimens) were too small to allow robust comparison among species, although the trends were apparently broadly consistent in all three species used. Lepidozona mertensii spent more time overall curled into a ball, compared to the total group, and spent considerably more time rolled in the control condition  than in the presence of a predator cue.

In the presence of the chemical cue of a distant predator, the urgent pressure to reattach to the substratum prompted more exposed positions in Chitons, but that would (and in a few cases did) enable the animal to reattach to the substratum and regain normal posture. Chitons are not able to right themselves on an isolated, flat surface such as the bottom of an experimental aquarium. But extended flat surfaces and still water are unusual in the context of rocky marine benthos. The articulating armour of Chitons is flexible and the inability of chitons to right themselves is generally limited to environments with flat surfaces and no current. In normal circumstances, on a rugose surface in a dynamic environment with moving water, a rolled-up chiton can expect to be transported to a new position very rapidly, and an arching Chiton might also be buffeted more rapidly toward a potential safe haven. Although Chitons are often considered ‘primitive’, there is mounting evidence for neurological complexity and this behaviour suggests a certain level of strategic response.

The behaviour associated with conglobation has been studied most closely in Arthropods, especially the terrestrial Pill Bug, Armadillidium sp., which can roll into a completely sealed ball. In experimental exposure, Isopods were marginally more likely to be attacked when extended rather than when rolled into a ball, and the animals do use conglobation as an active response to attack by potential predators. Likewise, a dislodged Chiton, if physically prodded, would also roll up rather than arch and leave the foot exposed. Conglobation in Isopods has secondary advantages in that it may help prevent desiccation as well as predation, which would only be relevant for Chitons in the rare event of dislodgement when exposed to air at a low tide. There are certainly protective benefits to curling into a ball, but the ball configuration in Chitons and other animals is entirely incompatible with normal feeding and locomotion.

Some arthropods lack coaptive devices that lock the ball configuration, including a few terrestrial Caterpillars and Spiders. These animals roll into a wheel-like configuration and use powerful appendages to propel themselves away from danger. This situation, and the observation that the ability to roll into a ball is associated with rolling away from a disadvantageous situation rather than with direct or even indirect contact with a predator, is mirrored in Sigwart et al.'s observations of chitons. Whether energy-intensive as in these terrestrial Arthropods, or more passive, as in Chitons, rolling away evidently does not require coaptive devices and is more a temporary measure.

In Chitons, the action of enrolment is controlled by the diagonal dorsoventral muscles that connect the eight shell valves to the ventral foot. All Chitons are able to use anterior–posterior flexing, including species with reduced or internal shells (such as Cryptochiton stelleri). This muscular arrangement and additional longitudinal muscles also cause the typical curled posture in Aplacophoran Molluscs, which are anatomically and phylogenetically related to Chitons. This is in contrast to the coaptive interlocking exoskeletal elements involved in the conglobation postures of Arthropods. Although the shell-less condition in Aplacophorans is derived, curling does not require an exoskeleton and does not require physical coaptive devices.

The ability of animals to transform into a defended sphere is a solid defence with multiple benefits; however, the results here suggest that anti-predatory defence is not the principal merit for Chitons. Chitons demonstrate behavioural decision-making when faced with the threat of a potential predator, to enable it to right itself and regain a safe foothold. By contrast, some other species with coaptive mechanisms resist attack by a predator through special morphological features that strengthen the exoskeleton and make it difficult to manipulate for a gape-limited or skeleton-breaking predator. The rolled-up configuration in Chitons and other animals without coaptive devices is superficially convergent, but the similarity in these different forms of rolling up may hide fundamentally different approaches to defence.

See also...

https://sciencythoughts.blogspot.com/2020/01/shellfish-use-at-oakhurst-period-at.htmlhttps://sciencythoughts.blogspot.com/2019/12/unloved-paraphyletic-or-misplaced.html
https://sciencythoughts.blogspot.com/2019/10/eromangateuthis-soniae-large-fossil.htmlhttps://sciencythoughts.blogspot.com/2019/10/modiolus-cimbricus-new-species-of.html
https://sciencythoughts.blogspot.com/2019/08/washington-woman-hospitalised-by.htmlhttps://sciencythoughts.blogspot.com/2019/07/royal-canadian-mounted-police.html
Follow Sciency Thoughts on Facebook.

5 comments:

  1. I was diagnosed of herpes virus, I have tried all possible means to get cure but all my effort proved abortive, until a friend of mine introduced me to a herbal doctor called Chief Dr Lucky, who prepare herbal medicine to cure all kind of diseases including herpes virus (Herpes), when i contacted this herbal doctor via his email, he sent me herpes virus herbal medicine via courier service, when i received the herbal medicine he gave me step by step instructions on how to apply it, when i applied it as instructed i was totally cured from the virus within 3 weeks of usage. Contact this great herbal doctor today to get your cure. 
    Via Email : chiefdrlucky@gmail.com
    Whats App : +2348132777335
    website : http://chiefdrluckysolutionhome.website2.me/    

    ReplyDelete
  2. Hello viewers around the Globe, I was despondent because i had a very small penis, about 2.5 inches soft and 4 inches hard not nice enough to satisfy a woman, i have been in so many relationship, but cut off because of my situation, i have used so many product which doctors prescribe for me, but none could offer me the help i searched for. i saw some few comments on the internet about this specialist called Dr, OLHIA and i decided to contact him on his {oliha.miraclemedicine@gmail.com} so I decided to give his herbal product a try. i emailed him and he got back to me, he gave me some comforting words with his herbal pills for Penis Enlargement, Within 3 week of it, i began to feel the enlargement of my penis, " and now it just 4 weeks of using his products my penis is about 9 inches longer, and i had to settle out with my Ex girlfriend Ella, i was surprised when she said that she is satisfied with my sex and i have got a large penis. Am so happy, thanks to Dr OLIHA I also learn that Dr OLIHA also help with Breast Enlargement Hips and Bums Enlargement etc.. If you are in any situation with a little Penis, weak ejaculation, small breast_hips_bums do get to Dr OLIHA now for help on his email {oliha.miraclemedicine@gmail.com} or whats app him number: +2349038382931

    ReplyDelete
  3. Hello everyone out there, I'm here to give my testimony about a herbalist doctor who helped me. I was infected with HERPES SIMPLEX VIRUS in 2011, I went to many hospitals to heal myself but there was no solution, so I was thinking how I can get a solution so that my body can be well. One day I was in the river thinking about where I can go to get a solution. so a lady walked towards me telling me why I'm so sad and I open everything by telling her my problem, she told me she could help me, she introduced me to a doctor who uses herbal medicines to cure the SIMPLEX HERPES VIRUS and gave me your email, so I sent you an email. He told me everything I had to do and also gave me instructions to take, which I followed correctly. Before I knew what was happening after two weeks, the SIMPLEX HERPES VIRUS that was in my body disappeared. therefore, if you also have a broken heart and need help, you can also send an email to {oliha.miraclemedicine@gmail.com}or whatsapp him number: +2349038382931 or Facebook page https://www.facebook.com/drolihamiraclemedicine/Contact him today and he will have a testimony ... Good luck!
    Dr. OLIHA also cures:1. HIV / AIDS2. HERPES 1/23. CANCER4. ALS (Lou Gehrig's disease)5. Hepatitis B6. chronic pancreatic7. emphysema8. COPD (chronic obstructive pulmonary disease)

    ReplyDelete
  4. Please share as you read okay you may save a soul today,natural herbs
    are really great, I was cured from HIV positive by a doctor
    called DR ONUWA from West Africa, now I believe that natural
    herbs and roots has their own way of working, based on medical report
    I was told that HIV positive has no cure even when I saw a post
    about Dr ONUWA how he cured many people with his herbal medicine I
    doubted it at first but just decided to give it a try because I was so desperately trying to get rid of my problems not knowing it was going to be the end of this deadly virus in my body, please if you have anyone with this same virus or diseases like this contact Dr ONUWA on EMAIL DRONUWA2@GMAIL.COM I'm a living testimony of his
    herbal medicine and don't forget to share as you read okay,
    please save a soul today

    ReplyDelete
  5. Dr Moses Herbal medicine is a good remedy for herpes simplex virus cure. i want to inform the public how i was cured from (HERPES SIMPLEX VIRUS) by DR Moses, i visited different hospital but they gave me list of drugs like Familiar, Zovirax, and Valtrex which is very expensive to treat the symptoms and never cured me. I was browsing through the Internet searching for remedy on HERPES and i saw comment of people talking about how DR Moses cured them, when i contacted him he gave me hope and send a Herbal medicine via UPS ( Delivery service ) to me and i drank it, seriously it worked for me, am a free person now without any problem, my HERPES result came out negative... Contact him if you need his assistance email him ehichioyaspelltemple@gmail.com or whatsapp him on +2348057508654 

    ReplyDelete