Commensalism, Mutualism, or Somewhere on the Borderline: A Relationship between a Frog and a Spider

By Angela Tsang

There are many different types of relationships species can participate in which can be fatal or profitable. Commensalism is when two species are in a relationship and one of the species benefits from the relationship while the other species is unaffected; so it is not beneficial or detrimental to the other species. Mutualism is very similar to commensalism but differs slightly. Mutualism is when two species are in a relationship and both the species receive benefits. Sometimes predators and prey find themselves in these intricate relationships.

For example, some microhylid (narrow mouthed) frogs and theraphosid spiders have been observed to share the same burrow (Cocroft and Hambler 1989, Csakany 2002). This is an interesting relationship because in this case the amphibian is the smaller of the two species and shares the tarantula’s humble abode. Both the frog and tarantula seem to become active at night and rest during the day (Cocroft and Hambler 1989). It is believed the microhylid becomes active at night because there is less chance of desiccation. In very dry weather, some species of microhylid can only be found in the spider’s burrows, a specific microhabitat (Cocroft and Hambler 1989). When the two species rest during the day, they reside in the same burrow in very close proximity to each other.

Spiders have been shown to be important predators of some juvenile frog species so it seems very peculiar that the predator (spider) would share its home Cocroft and Hamblerwith potential prey because the tarantula regularly eats frogs similar in size to the microhylids (Cocroft and Hambler 1989, Csakany 2002). One hypothesis suggests the frog secretes, through their skin, some sort of compounds that could be detrimental to the spider if it preys upon its “neighboor”. A study done by Garton and Mushinsky (1979) showed that the narrow mouthed frog uses ample amounts of skin secretions. These secretions come from poison glands which cover the little amphibian’s body, even the limbs and all the way down to the palms of the hand and feet (Garton and Mushinsky 1979). This experiment also tested the toxicity of the secretions on mice, and the skin extracts were able to kill all six of the test mice within 14 minutes (Garton and Mushinsky 1979). They further tested to see if the secretions reduced predation. This was confirmed when the predators would bite and release the frog immediately after (Garton and Mushinsky 1979). This paper supports the hypothesis that the microhylid frog is not worth eating for the tarantula. But why would the microhylid place itself in so much danger? The effect was confirmed by Csakany (2002) in a preliminary experiment.

A female tarantula, Pamphobeteus sp, with a juvenile and a microhylid frog, Chiasmocleis ventrimaculata. Photo by Biggi/Tomasinelli, source Biggi and Tomasinelli 2014, used with permission.

The adult female spider will aggressively defend its burrow against larger predators (Cocroft and Hambler 1989, Csakany 2002). This was proven in an experiment. Hunt (1980) added garter snakes which prey on the microhylids, near the tarantula’s burrow and the snake ate all the frogs outside of the burrow. But the female spider was able to defend to burrow from the snake thus keeping the little frogs inside safe as well (Hunt 1980). This shows how aggressive the female spider will become while protecting her territory. So the little frogs get bonus protection from the Sun and from various predators, all thanks to his spider burrow-mate.

But what does the tarantula gain by sharing its home? Some researchers believe the spider does not receive any benefits from the frog which would classify the relationship between and amphibian and spider as a commensal one. However, Rödel et al. (2013) stated the amphibians prey on ant species, and these ants happen to enjoy tasty snacks such as the tarantula’s eggs. Now the little frog becomes the hero while it protects the developing or baby spiders. This relationship has yet to be proven experimentally or observationally but in theory if the little frog acted as a baby sitter, then the relationship would be a mutual one.

The theraphosid spider and the microhylid frog have a very interesting relationship. The frog receives protection on various levels and the spider may or not be benefitting from living with the little frog. Depending on which information seems more firm the two species could be in a commensal or mutual relationship but for now they are somewhere on the borderline.

REFERENCES

Cocroft, R.B. and K. Hambler. 1989. Observations of a commensal relationship of the microhylid frog Chiasmocleis ventrimaculata and the burrowing theraphosid spider Xenesthis immanis in southeastern Peru. Biotropica 21(1):2-8.

Csakany, J. (2002). Study on the Chemical Communication between the Microhylid frog, Chiasmocleis ventrimaculatata, and a Theraphosid Spider involved in a commensal relationship. Unpublished report, State University of New York. 13pp.

Garton, J.D. and H.R. Mushinsky. 1979. Integumetary toxicity as an antipredator mechanism in the narrow mouthed frog, Gastrophryne carolinensis. Canadian Journal of Zoology 57:1965-1973.

Hunt, R.H. 1980. Frog sanctuary in a tarantula burrow. Natural History 89(3): 48-53

Rödel, M.O., Brede, C., Hirschfeld, M., Schmitt, T., Favreau, P., Stöcklin, R., Wunder, C. and D. Mebs. 2013. Chemical camouflage – a frog’s strategy to co-exist with aggressive ants. PLoS ONE 8(12): e81950.