Tears to quench a thirst

21 May 2014
Comments: 0
21 May 2014, Comments: 0

The natural world that is all around us never ceases to surprise. Mother Nature weaves all manner of ties and bonds, many of them unknown to us, others hard to imagine until we come face to face with them. Species can interact in all sorts of ways. In previous entries, we have seen how pollination and seed dispersal provide mutual benefit (mutualism) for both the animal that transports the pollen or the seeds after they have fed on the nectar in the flowers or the pulp of fleshy fruit, and for the plant that manages to reproduce itself or to move to new areas, thanks to the movement of its host animal. On other occasions, interactions take place that benefit only one of the two parties, while the other species neither is harmed by nor gains anything from it (commensalism). A fascinating example of this type of interaction is what is known as tear feeding.

Sodium is an essential nutrient for life. However, while there is an abundance of this element in the oceans, it is less easily to find on land. This is why many species of insects travel to humid areas or seek out excrement or carcasses to thereby obtain the dissolved nutrients they contain. Some of these insects have become veritable specialists in obtaining the sodium they need from the tears of animals such as deer or crocodiles that can’t easily chase them away. One surprising case has been documented recently in the Yasuní National Park in Ecuador, right in the middle of the Amazon basin. There, the solitary bee Centris sp. “drinks” the tears of the Yellow-spotted “Terecay” River Turtle (Podocnemis unifilis), a species of Galapagos water turtle that lives in the great rivers and lakes of the Amazon.

This recently discovered interaction poses questions that have yet to be answered. To what extent do these bees depend on the turtles for their survival? Might they be able to find another species whose tears they could “drink” if the turtle were to disappear? Although we have no answers as yet, this little story encourages us to observe nature with eyes filled with curiosity, because we are surrounded by marvellous goings-on that we have yet to discover. All we need to do is keep our eyes open, and we’ll see all sorts of surprises.

Recommended reading:
Dangles, O., and J. Casas. 2012. “The bee and the turtle: a fable from Yasuní National Park.” Frontiers in Ecology and the Environment 10:446-447.

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