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Amazing Symbioses

May 29, 2012

This photo site compiles remarkable cases of symbiosis between pairs of unrelated animals. The boxer crab is one of the most bizarre things I’ve ever seen. Each of the crab’s claws carries a small stinging sea anemone–for the crab to defend itself. In turn, presumably the anemone receives transport and food.

Then there is the goby shrimp relationship. In this video, the goby fish acts as a sentry at the burrow of the shrimp. The fish gets a home, and the shrimp gets warned of predators.

Here is a three-way symbiosis of ant, caterpillar, and acacia tree. The ant feeds on nectar from the caterpillar, which feeds on the acacia tree, while the ants protect the acacia from more severe predation.

And this dugong gets parasites cleaned off by two kinds of associated fishes.

It’s enough to remind us that all life, indeed, cooperates as much as we compete. Could we rewrite all of Darwin as The Survival of the Most Cooperative?

  1. May 29, 2012 11:05 pm

    Two things came to mind immediately during/after reading your post:

    1. Human/Dog symbiosis in combat and a recently submitted bill to change the status of military dogs – ‘reclassifies military dogs as “canine members of the armed forces” instead of equipment’:

    2. Cooperation and evolution reminded me of a series of recent talks by Sarah Coakley:

    • May 30, 2012 8:38 am

      That’s certainly interesting. Are we defining “canine rights” now?

  2. heteromeles permalink
    May 30, 2012 12:14 pm

    Cool, more symbiotes!

    Actually, I’ve had a lot of fun arguing whether canines are mutualistic symbiotics or social parasites. The point isn’t to annoy dog lovers, but to point out how complicated symbioses can be, especially when you start doing cost-benefit analyses and using the analysis to talk about fitness effects.

    Here’s the deal: if you analyze current human-canine relationships strictly in terms of energy and nutrient flows, it is clear that dogs are parasites: there’s clearly a one-way flow of energy and resources towards them, and they don’t provide much in the way of energy and nutrients to humans. It’s also clear that they used to be part of a more balanced symbiosis where dogs helped hunters and hunters, were eaten as food, and so forth. It’s also probable that, before the more balanced symbiosis, ancient dogs were apparent commensals, useful primarily for cleaning up garbage and providing warning of threats, but not directly benefitting humans (see dingos and pariah dogs).

    However, if you look at the social benefits dogs provide, it’s less clear. Do dogs help people live longer? Do they provide necessary services? Do they take the place of children, and is this good or bad? Is an animal bred as a fashion accessory a parasite, a symbiont, or a mutualist? Does our practice of sterilizing many pets complicate an analysis of fitness based on lifestyle? Is our mania for creating new breeds a type of speciaition (perhaps as social parasites?) or something else entirely?

    There’s not a simple answer to any of these questions, and this can be an interesting classroom discussion. The point is that symbioses look very different depending on the framework within which you analyze them. A relationship can look like parasitism in one analytic framework, and a mutualism in another. I don’t think there’s one correct answer here, and that’s what makes it so fun.

    • May 30, 2012 7:39 pm

      You basically covered a whole chapter on symbiosis there. The textbook view of symbiosis is that it includes parasitism. Like fungi in lichens, it can go either way. Human parasites and viruses are now thought to contribute to our fitness–in most cases. We’re simply unaware of the ones that cause no harm, but vastly outnumber those that do.

    • heteromeles permalink
      May 30, 2012 11:43 pm

      Thanks Joan! I guess that’s kind of the point. Since most people are pretty sophisticated about relationships in general, I figure that talking about dogs can be a good way to get people thinking about symbioses. Of course, if students are simply looking for the right answers to the next test, as opposed to understanding, this approach can certainly annoy them too.

      My favorite comparison is between symbiosis and romance. Ideally, romance is a mutually supporting relationship. In practice, it’s a lot messier than that, and I’m sure every partner has considered his or her significant other to be a parasite at least once…. Since a majority of college students have either been in a relationship or have been close witnesses to their parents’ relationships, they get the complexity pretty fast.

  3. SFreader permalink
    May 30, 2012 2:06 pm

    It’d be interesting to map an ecosystem based on the variety and number of different species and their relationships with other species to see/find out which species tend to thrive (and revive) better. For example, if more than x% of species have a particular form of interdependency, does this mean that that species is a greater or lesser risk of vanishing? (Perhaps having ‘learned’/acquired one species-interdependency primed that species to be able to form another – albeit less beneficial – interdependency.)

    Is it coincidence or a known data point that the parasite/helper species referenced in your post appear to be ‘less evolved’ than their host species?

    • May 30, 2012 7:41 pm

      Not sure about that. Which is which? The acacia tree and ant are both at the highest level of multicellular complexity, if we can define such a thing. The goby is vertebrate, shrimp invertebrate.

  4. May 30, 2012 2:24 pm

    I enjoyed the tour of strange bed-fellows (sea-beds, that is). Thanks for sharing this, Joan.

    Survival of the most cooperative? Hard to say–many human body features were once separate organisms (or so I’m told–you’d know better than I). Does this mean those species survived?

    If these under-sea duos and tree-top trios are co-dependent, does that mean that a lack of partner(s) results in death? And if so, are they truly separate species still? Or should we consider symbiotic groupings as sub-species of their non-symbiotic forebears?

    • May 31, 2012 5:49 pm

      These are open questions.
      A “true” symbiosis means one or both partners require the association to survive. True symbiotic partnerships would have species different from their closest free-living relatives.

      For microbes, “true” symbioses tend to evolve into a single organism, like mitochondria within cells. For macro-scale organisms it’s different; like the orchid pollinated by a particular species of wasp. They remain distinct organisms but completely depend upon each other.

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