Spare Ribs, Anyone? – The Iberian Ribbed Newt

Throughout the natural world both animals and plants have developed an immeasurable variety of techniques to deter predators from making them their next meal. Plants grow thorns, jellyfish drag stinging tentacles and snakes rattle their tails and bare poisonous fangs, and amphibians are no exception. However, none are as masochistically defensive as the Iberian (or Spanish) Ribbed Newt (Pleurodeles waltl).

As the name suggests, this largely aquatic-dwelling amphibian is found throughout the Iberian Peninsula (Portugal, Spain, Andorra and Gibraltar) and Morocco. They can grow to up to 30 centimetres (12”) in length and feed mainly on small insects, worms and tadpoles. The ribbed newt was relatively common and, preferring calm, stagnant water could be frequently found inhabiting ponds and old village wells. However, recently the IUCN (International Union for Conservation of Nature) designated the species as being ‘Near Threatened’ in 2006 due to an apparent dwindling in population caused by damage to their aquatic habitat from such things as drainage, chemical pollution and development caused by demands in tourism, making the species now largely extinct in coastal areas and around large cities.

Being small, soft and numerous (frogs eggs can number in the thousands), and lacking in claws, teeth, and strength, amphibians form an important part of the food chain and are hunted by mammals, birds, reptiles and even some arthropods such as spiders. Despite this, many amphibians have developed powerful toxins in order to deter attackers, such as the ‘Poison Dart Frog’ – named due to the Amazonian Indians’ habit of tipping the ends of their hunting darts with the frog’s poison. The poison is produced from a gland (the parotoid gland) and secreted through pores in the skin as a milky alkaloid (a chemical bond formed by base nitrogen atoms with an alkaline pH). The downside of this defensive tactic is that in order for the poison to be administered to the attacker the amphibian must first be bitten, which could result in serious injury or even death for our froggy friend. It is for this reason that many frogs, toads, newts and salamanders have evolved bright colours and patters (an evolutionary mechanism known as aposematism) to warn predators of their toxins without the need of being bitten first! However, being dull gray in colour it seems that the Iberian ribbed newt didn’t get the memo and instead of following this rather sensible pattern, devised its own way of dealing with its predatory problems. Although it secretes poison through its skin like other amphibians, it has a unique and grim way of administering the dose: It punctures its own skin with its sharp ribcage, which, after tipping themselves with poison upon exiting the body, are left protruding to stab or graze any unlucky attacker. The combination of poison and spikes makes a very effective form of defence (especially if the newt is picked up in the mouth of its predator) and this is how she does it:

Imagine looking down at the skeleton of a newt from above with the backbone running vertically from north to south in front of you. In its relaxed state the sharp, spear-shaped ribs of the newt gently flow back at an angle (averaging around 50°) from the spine toward the tail like waves streaming behind a slow moving ship.  However, when agitated, the newt, whilst keeping the rest of its body still, rotates its entire ribcage anteriorly forward so that the ribs angle perpendicularly to the spine at an angle close to 90°. This massive forward movement of the ribcage causes the body to expand so that the sharp tips of the ribs lacerate the body wall and project freely from the sides of the trunk forming a row of –now poisonous– barbs.  Light microscopy illuminates the complex anatomy of the animal, and shows that each spear-like rib is connected to its corresponding vertebra (individual columns that make up the spine) by a well-developed, flexible, two-headed joint.

This incredible (albeit rather gruesome) form of defence was first noted by a natural historian 1879 and it was previously thought that the newt must possess some permanent openings or pores through which the ribs could pierce. Indeed the newt does have a row of tubercles (wart-like nodules) running down either side of its trunk and it is through these that the ribs seem to project. However research has shown that although these tubercles exist, the skin in the penetration areas are completely firm and lack any permanent pores through which the ribs could be projected. The newt has to therefore pierce its own skin de novo with every time it adopts a defensive posture.

Despite this masochistic action, the laceration seems to do very little (if any) harm to the newt and the animal has been observed to resume such normal activities as eating and mating almost immediately afterward. Amphibians’ poison is usually contained to the glands, though despite the poison-tipped ribs being contracted back into the body leaving the substance to seep into the body tissues, the chemical seems to have no effect on the newt at all, leading scientists to conclude that its system has developed a complete tolerance to the poison. The self-inflicted wounds also cause very little harm due to the noted rapid healing processes of amphibians, which are known not only to have an extraordinary ability to repair their skin but can also regenerate limbs, eyes, spinal cords, hearts, intestines, and even their upper and lower jaws.

*This is due to a biological process known as cell dedifferentiation. In biology cell differentiation is the process by which a less specialized cell (i.e. a stem cell) transforms itself into a more specialized cell type (a cell that serves a specific purpose e.g. a blood cell/bone cell etc) in order to carry out a specific job within the body. Dedifferentiation is a similar process but it works in reverse; where differentiated cells (cells that already serve a specific purpose) revert to their earlier developmental stem-cell stage, often as part of a regenerative process. The cells at the site of the newt’s (or other amphibians’) injury have the ability to de-differentiate, reproduce rapidly, and differentiate again to create new skin, a new limb or even a new organ and provide rapid rehabilitation.

The Iberian Ribbed Newt is a wonderful example of how if any kind of genetic variation (no matter how bizarre) proves to be at all beneficial to the survival of a species, natural selection will see it thrive and multiply.

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2 Comments on “Spare Ribs, Anyone? – The Iberian Ribbed Newt”

  1. Marta M. Says:

    remember me not to try to catch any of them when I go back to Spain… hahaha

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