Friday, October 22, 2010

Lethal Ribs!

Many amphibians, as small to moderately sized soft-skinned organisms, exhibit different defensive strategies for protecting themselves from larger predators. A few of these defensive behaviors include cryptic coloration, toxicity, and defensive displays. In the case of the Spanish ribbed newt, Pleurodeles waltl, an entirely different defensive concept has been employed. This particular salamandrid is capable of projecting its ribs through its skin when faced by a predator that they are unable to escape from.

A study was conducted at the University of Vienna to determine details of this particular salamandrid's defensive capabilities. When the Spanish ribbed newt was first picked up, it began to squirm in attempt to escape from its handler. After it was unable to escape, a milky substance was secreted from glands in its neck, dorsal and lateral trunk, and tail (arrows in figure a). This secretion caused irritation to human mucous membranes but was lethal to mice in small doses, suggesting it is toxic. When these two defensive strategies did not work, the newt projected its ten pairs of ribs through its body wall as a final defensive maneuver (figure b)

In order to project its spines, the newt sat very still, straightened its vertebral column, and then shifted the ribs forward. These ribs have a two-headed costo-vertebral joint that allows for a maximum 65 degree shift forward. The final third of the distal portion of the ribs were found to be surrounded by a connective tissue sheath that was determined to be a protection layer between external pathogens and the internal body cavity. Furthermore, this newt has 10 pairs of orange spots which correspond to each rib that is projected through the body wall. These orange spots are thought to add an aposematic signal that is helpful in highlighting the rib projections to predators. After close examination, it was determined that pores were absent from these orange spots. This proved that the ribs were indeed piercing the body wall and not just projecting through an existing pore.

The researchers suggested that the newt was immune to its own toxins and used the general ability of amphibians to both produce anti-microbial agents from specialized glands and to heal quickly. These features allow for the Spanish ribbed newt to project its ribs from its body in order to defend itself.

Self injury for the benefit of self preservation is also found in Echinotriton, a member of a sister clade to Pleurodeles.

Brought to you by: Karie Charlton


  1. Wow that is a really cool defense mechanism. I wonder how far out of the body the ribs can be projected? They also must be pretty sharp if this is an effective strategy.

  2. I wonder if other newts or salamanders mimic the orange spots of the Spanish ribbed newt to make predators think they also are capable of projecting their ribs with toxin and therefore will not eat them, like the Viceroy butterfly who mimics the color pattern of the Monarch butterfly who does contain toxins that taste foul to predators.

  3. Bobby-
    The paper said that the spots served to highlight the rib projections. With the bright orange spots, the spines were can be seen much easier by predators!

  4. Yowch, I can only imagine how much pain I would be in if I were a predator trying to eat one of these! This looks like a very effective defense.
    And I agree with Bobby. It would be very beneficial if a non-lethal species evolved similar-colored spots as a defense to ward off potential predators.

  5. I wonder if they have looked at the tissue healing that must take place after the ribs pierce the skin, especially if the ribs are tearing through the body cavity. That is very interesting that the ribs are covered in a layer that keeps pathogens out of the body cavity.

    It makes since that the newt uses this as a last defense.

  6. The defense mechanisms used by different organisms have always been of interest to me. This is a very cool mechanism that I have never heard of before. I wonder if there are other types of organisms that can do this same sort of thing.