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Kingdoms in the canopy

Bromeliads, bugs, and bacteria

The Amazon rainforest is full of life. Rivers cut their way down from the Andes in the west of South America to the Atlantic in the east, trees laden with other plants tower above a rich undergrowth crawling with critters, and the forest breathes to the rhythm of crickets and frog calls. During my PhD at the Manchester Metropolitan University (UK), I had the privilege to work in a tiny part of the northwest of this extensive forest, where the Andes slide away into Amazonia.


For my research, I was interested in studying bromeliad communities. Bromeliads are amongst the plants which adorn the trees of Neotropical rainforests. There are some 3000+ species of bromeliads across the tropical and subtropical Americas, many of which present a rosette-like morphology with a space in the middle of their leaves. This tank is a phytotelm and accumulates water, which is then colonised by an array of microorganisms, including plankton and a wealth of bacteria. Frogs take advantage of these hanging gardens to safely deposit their tadpoles away from the more dangerous streams and ponds on the forest floor. Around these tiny aquatic ecosystems revolves a rich community of invertebrates, from ants and beetle larvae to cockroaches and tarantulas.

Many factors have been found to explain the richness and complexity of these microcosms, a big one is size. Bigger bromeliads can sustain larger and more diverse communities, as one might expect. However, I wondered whether the genetic identity of a bromeliad of a given species could influence the composition of the community living within it. It is not such a far-fetched idea as it may seem on the surface – there is a whole field of research into the genetics of species interactions, largely known as community genetics. What is more, one study found that bromeliad genotype explained 1% of the variation in the aquatic invertebrate community within bromeliads on trees in Belize. Could this be the case in an even more diverse tropical forest? Could an effect on bacteria mediate this connexion between bromeliad genotype and the aquatic invertebrate community?


So off I went to the Amazon to climb trees. Dangling from ropes and harnesses, I measured and collected plants strapped to trunks and branches. All the invertebrates where collected and identified to morphospecies and the phytotelm was sampled for bacteria. Back in the lab, I got busy extracting bromeliad and bacterial DNA for sequencing.


As often happens in science, the results of the analyses came back "negative": there was no relationship between the bromeliad genotype. I must admit, I was a little disappointed, it would have been an exciting finding. However, on the flipside, there are positives to genetic diversity of the bromeliads not affecting community structure of the animals. It may imply that a scenario of loss of genetic diversity in the bromeliad community shouldn't have big implications for the diversity of the communities they can sustain. Of course, a loss of genetic diversity would have implications for the bromeliads themselves, such as reduced adaptive potential, but that's another story.


Xaali O'Reilly Berkeley, Postdoctoral researcher


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