Symbiosis - What's in it for me?
As anyone who’s ever spent time in an office will testify, team work can sometimes be something of an acquired taste. There are many types of relationship in the work place but whether it’s a debate about desks or an argument over annual leave, it’s fair to say there can be the odd tiff. However, you don’t have to go far into the natural world before you find a more harmonious example of cooperation, all without a jammed printer in sight.
Let me introduce the Goby, a family of small, demersal (bottom dwelling) fish and the Pistol Shrimp, a family of shrimp characterised by their one large claw. Each animal is in something of a pickle. The Goby is small, typically less than 10 centimetres (4 inches) long and has no defence against the larger predatory fish on the coral reefs many gobies call home. It needs a burrow to shelter in and also to spawn its young, but excavating such a burrow with only a tiny mouth is hard work. The Pistol Shrimp, on the other hand, has no problem digging; its claws are specifically adapted for this job. However, the shrimp suffers from being virtually blind. This makes it a very easy meal for passing predators (Z. Jaafar 2012). Each animal has something the other wants - the Goby needs a burrow and the Pistol Shrimp needs protection from predators.
This has caused an amazing relationship to evolve between the two. The shrimp excavates a burrow as normal but this time it rests one of its sensitive antennae on the tail of the Goby. The Goby then uses its much better eyesight to keep an eye out for threats, when it spots impending danger it flicks its tail warning the shrimp that it’s time to scarper back into the burrow! In return for its skills as a lookout the Shrimp digs a larger burrow and allows the Goby to share it at night. The Goby also uses it as a safe place to spawn. This relationship is so successful that some species of Pistol Shrimp rarely leave their burrow without a Goby, says Annemarie Kramer from the University of Salzburg. (1)
In Biology we call a relationship between two creatures symbiosis .More specifically in this case we call it Mutualism because both the Goby and the Pistol Shrimp are benefiting from working together. For us humans with our desk jobs this is the best kind of team to be in, everyone working together and benefiting from each other’s skills. To continue our office-themed odyssey through symbiosis I want to show you the other two types of symbiotic relationship starting off with Commensalism.
Commensalism is all about one party gaining something from the other without having a significant effect on its partner. Perhaps you’ve given a colleague advice recently or maybe you were the one looking for some guidance? If so that was a great example of Commensalism - one of you benefited from the consultation and the other didn’t particularly gain or lose out. The natural world has many fascinating examples of this but my favourite is the relationship between some of the world’s largest ocean dwellers and the humble barnacle.
Every year, Humpback Whales migrate thousands of miles between the Arctic Ocean and the waters around Columbia and Panama. Unnoticed by the majority of whale watchers that flock to see this natural wonder are the tens of thousands of remarkable barnacle hitch-hikers each whale is carrying. Whilst it might seem an unlikely partnership, the secret of its success is that the barnacle and the Humpback both feed on plankton that they filter from the water. As you can imagine a whale weighing in the region of 35 tonnes needs to consume a lot of plankton, as a result it is constantly searching for the water that is richest in the tiny invertebrates that its diet consists of. The barnacle takes advantage of the whale’s mobility to carry it through waters where the most food can be found. As I mentioned earlier, whilst the barnacle gains from this relationship it seems the host whale neither benefits nor loses out.
However there is a mystery to how the barnacle larvae ever become attached to a host as John Zardus, a marine biologist at The Citadel military college in Charleston, South Carolina explains - “We don’t really know how they’re doing it, these microscopic larvae that are swimming around in this huge ocean — how do they find a whale? … It just seems preposterous, actually.” One theory says that the barnacle larvae reach the whales during the breeding season when they congregate in warm shallow water, but this has never been confirmed.
To add to the intrigue Yasuyuki Nogata and Kiyotaka Matsumura from the Environmental Research Laboratory have published a paper (2) that strongly indicates the whales use a chemical signal to actively attract barnacle larvae to settle on them. This doesn’t support the idea of the relationship being commensal. In the pair’s paper they describe placing two samples of larvae in separate petri dishes and attempting to incubate them; one dish also contained a small sample of skin from a humpback whale (taken from a whale that died whilst stranded on a beach). In the presence of the piece of skin the larvae reached the adult stage (what we would recognize as a barnacle) and settled, but those without it died.
It seems we still have much to learn about the intricacies of this relationship and indeed barnacles themselves have been frustrating scientists far back into the past. Even Charles Darwin, one of the greatest ever biologists, declared after nearly a decade of intense barnacle study “I hate a Barnacle as no man ever did before!”
Our final type of symbiotic relationship is one you will have heard of though for all the wrong reasons, because Parasitism is the final infamous member of our trio of symbiotic relationships. A parasitic relationship is one in which one organism (the Parasite) benefits whilst the other (the host) loses out. At this point I feel it best to let your imagination take care of finding a work place analogy to a parasitic relationship!
I do however have an example from the natural world that is well worth exploring and that is Brood Parasitism. Brood Parasites are organisms that manipulate a host into raising their young for them as if they were their own. You’ll probably be familiar with the common cuckoo laying an egg in another birds nest and the young cuckoo being raised by the host. The cuckoo gains by reducing the effort needed to raise its young whilst the host bird loses out due to the excess effort required to feed a young cuckoo (Cuckoo chicks often grow much larger than the host bird). Whilst this may be a familiar case study what is not understood fully is why the host bird doesn’t simply reject the invading Cuckoo chick. Two theories are offering solutions to this question.
One is named "the nest-site hypothesis" which says that the Cuckoo mother chooses from a selection of nests to find the nest her egg will most likely go unnoticed in. An interesting side note at this point is that different individuals within the species of the Common Cuckoo lay eggs that mimic the pattern of a specific species of host bird common in the areas they nest in. Whilst one female might specialise in imitating the egg of a reed warbler, another might copy the colouring of a dunnock. These are called mimetic eggs. Evidence for this theory is that mimetic eggs are nearly always found in the correct corresponding host nest.
Our other hypothesis (one of the best named in biology in my opinion!) is the Mafia hypothesis. In it, the parasitic species manipulates the host using intimidation to prevent the imposter being ejected from the nest. The parasite (in this case a great spotted cuckoo) regularly checks the host nest for signs of its egg being rejected, if this happens the nest is ‘depredated’ upon –the nest is destroyed and the nestlings killed or injured . The threat of violence keeps the host from rejecting the imposter egg; the cuckoo literally blackmails the host into caring for its young!
We’ve now seen each of the three types of symbiosis; Mutualism, Commensalism and Parasitism and it seems that whilst nature has some examples of amazing teamwork it also has its fair share of less harmonious relationships. Perhaps we’re not so far removed from the animal kingdom after all? I’ll leave you with a piece of advice - next time a colleague asks you to work together symbiotically be sure to find out which type of symbiosis they are looking for.