Wednesday, March 30, 2011

The Emperor and its Dancer


Hexabranchus sanguineus, more commonly known as the Spanish dancer, is a carnivorous slug found mostly in the waters surrounding Hawaii. It is called a Spanish dancer because of how its bright colors and movement through the water resembles a Flamenco dancer [1]. Some species of the slug are toxic, obtaining their toxicity by ingesting other toxic organisms, like the Portuguese man-of-war and many are most active at night [2]. In the daytime, they are pink with white patches, and at night, they are pinkish red and blotchy. Its mutualistic partner, Periclimenes imperator, is an emperor shrimp found in all areas of the Pacific Ocean, from Hawaii to Indonesia [4]. These organisms look like mini-lobsters with a duck-bill like head [5]. They also have the pink-red with white spots coloration, similar to that of the Spanish dancer and other organisms it inhabits.

Description of Relationship

The relationship between Hexabranchus sanguineus and Periclimenes imperator has long been established as mutualistic [1]. Although both can survive without the other, there are advantages to a shared interaction. The relationship is established simply through encounter. If these organisms meet, and both do not mind creating a relationship with the other, then interaction is formed. The shrimp can be found within the gills of the slug [2] and cleaning off any kind of growth and even parasites. Usually the shrimp is not alone, cleaning and travelling with a partner. The slugs receive a thorough cleaning while the shrimp receive a great food supply. A unique characteristic of this relationship is that once it is established, it usually remains for the life of the organisms [3].

Cost/Benefit Analysis

The benefits have been discussed above; however, there are some possible risks to each organism as well. Sometimes, when predators of the shrimp try to attack, the slug gets damaged or killed in the process. This emphasizes the importance of the shrimp’s ability to blend in with the slug [5]. Also, because the slug has to carry around the shrimp, extra energy has to be expended. The costs for the shrimp are minimal as well. There could be a chance that the slug accidentally eats the shrimp or if the shrimp accidentally ingests part of a toxic slug. This, however, probably does not occur frequently since the shrimp stay by the gills of the slug.



  1. According to the Red Queen Hypothesis as one species evolves so does the other so that they stay in the "same" place. Since the two organisms can live alone as well as together, is it possible that the Red Queen Hypothesis can fail and that one of the two organisms could out evolve the other? If this happen how do you think it would change the relationship that they currently share? Who would benefit most from evolving?

  2. “The Art of Being a Parasite” described a mutualistic circumstance called ‘reciprocal altruism’, in which two individual organisms benefit each other. One example provided was of vampire bats feeding members of the colony who had not hunted successfully on a particular night, with the “understanding” that the favor was to be returned at a future time. Is this relationship an example of reciprocal altruism, since it doesn’t necessarily happen on a species-wide level?

    Another concept brought up in the text was that of reciprocal pressures, which occur when two species in a mutualist relationship evolve not with the goal of outpacing each other (as in the Red Queen Hypothesis) but with the goal of forcing each other to work more towards their own benefit – as when orchids evolved the trait of deep nectar reservoirs, which forced moths to expose themselves (and subsequently visited orchids) to the first orchid’s pollen, ensuring that this first orchid could spread its DNA. Is it likely that something similar will occur in the Emperor shrimp/Spanish Dancer slug relationship? If so, what evolutionary pressures might be brought to bear on each participating species?

  3. I think that it is entirely possible for the two species to evolve out of accordance with the Red Queen Hypothesis because of the fact that they can live independently of one another. Even so, I do not think that their relationship would change dramatically. The slug still needs to be cleaned and the shrimp still needs to eat. Having this relationship just makes it easier for the both of them, and no matter how much they evolve, they still have the same needs.
    If, however, they were to evolve drastically, I think that the shrimp would benefit most. The slug can find other organisms to clean its body (like those talked about in class), so there is not a significant change there. The shrimp on the other hand could evolve to be able to live and form a relationship with a broader range of organisms.

  4. I do not think that this would be a good example of reciprocal altruism just because if either party wanted to end the relationship,it would happen. In the example with the bats, it seems what they do is an act of comraderie for a fellow community member; it is an action that has long been established. Because the relationship between the slug and shrimp is more or less created by random chance, I do not think it would be right to say that they feel the same kind of obligation to one another.
    I also do not think that it is likely for a relationship like that of the orchid and moth to develop between these two species. This is because this relationship is not formed on the basis of survival or for the passing of genes, but rather through convenience.