Notes on symbiosis

spider frog

Photo courtesy of Francesco Tomasinellni

Symbiotic relationships exist throughout the natural world. From bacteria living in human digestive systems, to bees pollinating flowers and dogs living with humans to fish hanging out underneath sharks; many species have a mutual relationship with another in some form. With the recent focus on a story about tarantulas and frogs doing the rounds, I would like to document a few symbiotic relationships which naturally occur in nature.

So what is this frog-tarantula relationship? The headline to the article which has come into focus states that ‘Tarantulas are keeping frogs as pets’. This isn’t actually the case. What they are in fact doing is working together; a mutual dependency where both parties benefit from the outcome. This is what we know as mutual symbiosis.  There are several different types of symbiotic relationship:

Mutulistic symbiosis: Both parties are working together to receive benefits.
Commensalistic symbiosis: One species will benefit from another but the second party will be neither helped nor harmed
Parasitic symbiosis: Where one party reaps benefits from another, causing harm, detriment or death.

The story about the tarantula-frog relationship isn’t a new one, it was actually first documented nearly 25 years ago by Crocraft & Hambler. It refers to  Xenesthis immanis, a large burrowing tarantula that comes from Peru and Chiasmocleis ventrimaculata, a tiny, narrow mouthed frog also known as the Dotted Humming frog. The frogs and spiders live with each other, despite the fact that the frog would probably make a fairly decent meal for the tarantula. So how can prey and predator feel so comfortable around each other? Well, it is believed that the tiny frogs are used to guard the spiders eggs. Ants are the main source of food for the Dotted Humming frogs, however they are also one of the biggest threats to the tarantula’s eggs. The frogs guard the spider’s eggs and in return, the tarantula protects the tiny amphibian from other predators, such as other arthropod species. Since the first sighting in 1989, there has been further documentation of these frogs and tarantulas living and working together leading us to believe they have well sealed their mutual symbiotic relationship.

The fact that two such creatures can form a mutually beneficial relationship seems almost sweet to us, if not a little unbelievable, however it is going on all over the animal kingdom.

If you head into any fish shop or aquarium today, they will tell you (and try to sell you) about the brilliance of shrimps. Shrimps are excellent for cleaning up. They remove lots of debris from water and plants and consume it, leading to a reduction of rubbish in the water column. And it isn’t just us humans who have picked up on this. Cleaner shrimp (Palaemonidae sp., Hippolytidae sp., Stenopodidae sp.) get their name because that is exactly what they do: clean. Like tiny dentists, they spend their time cleaning up the insides of the mouth’s of other , eating the parasites living in there. The shrimps congregate in mass numbers at ‘cleaning stations’, waiting for interested fish to come along, queue up and when it is their turn, open their mouths for the shrimp to head in and get to work. The shrimps get a good meal and the fish get a decent oral clean. These shrimps aren’t fussy either, there have even been cases of human divers heading down and opening their mouths and getting their teeth cleaned!

Another example of symbiosis involving mouths is the supposed relationship between Crocodiles and Egyptian Plovers. There are written accounts of Plovers flying in to remove food from crocodiles open mouths which date back as far as 480 BC and the National Geographic ran the same story back in 1986, however there is still no hard evidence that this relationship actually exists or that the crocodiles do entertain the birds in this fashion. No photographic or video material has been produced and there are some who do not believe this actually happens.

Another famous relationship is that of the Oxpecker and a variety of large mammals. It was believed for a long time that Oxpeckers were doing good for many mammals, however ongoing research by Paul Weeks et al. has suggested that this is not correct and this actually may be a case of Parasitic symbiosis. Oxpeckers eat a variety of small parasites such as ticks, lice, fleas etc. The birds can often be seen sitting atop Rhinos, Hippos, Elephants, Wildebeest or cattle, feeding from the insects on their skin. It used to be common thought that the Oxpeckers were doing the mammals a favour; removing all those nasty parasites they didn’t want. However, there is a new school of thought that suggests the Oxpeckers are doing more harm than good. Often, when they consume a tick or flea, the ecto-parasite has already had its fill, meaning it will have already bitten the mammal and spread any disease that it may be carrying. The Oxpecker may remove the parasite, but there is no evidence that they are causing a reduction in infestations. The birds have also been observed creating or opening wounds on their host and drinking their blood. In fact some mammals, such as Elephants, will work to remove these birds from their backs suggesting the relationship is not enjoyed by both parties.

Symbiosis doesn’t just happen in the animal kingdom however, it is also apparent in the plant world. The final relationship I want to mention here (which is absolutely my favourite) is Lichen. Lichen is often described as an entity all of its own, but is actually just an example of symbiosis working perfectly. Lichens are a hybrid of a fungus and algae or cyanobacteria. The algae part which forms lichen is called a photobiont and the fungi part is a mycobiont. For the fungus, having the algae around is important because it can perform photosynthesis, enabling the normally heterotrophic fungi to harvest this and create its own food. In return, the algae uses the fungus to help it expand its habitat range. Fungus is fantastic at adapting to different habitats, so by teaming up, the algae can reach further afield. There are many different types of lichen, made up by different types of fungus and different algae or cyanobacteria. Some people argue that the relationship is not mutual and is in fact a form of parasitic symbiosis on the part of the fungi as it uses up so much of the sugars the algae develop through photosynthesis, however there is substantial evidence for both arguments and a concrete conclusion has not yet been reached.

These are only a few examples of symbiosis. There are hundred of different types of relationships out there, all just as fascinating as the next. It will be interesting to know whether more symbiotic relationships will form as we continue to evolve and which species will rely on which?



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