The world around us is full of fascinating interactions between organisms of different species. Some of these are predatory in nature, some parasitic, but many of them are mutually beneficial to both organisms. This is called mutualism, in which organisms from different species are in a relationship in which each organism benefits from the activity of the other. But most of these relationships haven't yet been studied in depth. In particular, the sensory biology of the interactions between species is yet to be understood; that is, the study of the sensory signals that are exchanged between interacting species--signals of vision, colour, scent, or chemicals.
Dr Renee M. Borges, Professor at the Centre for Ecological Sciences at IISc, and the researchers at her lab are working to understand just that.
One aspect of the research going on in Dr Borges' lab is related to the mutualism between ants and plants. There is one such ant-plant, Humboldtia brunonis, a legume that is endemic to the Western Ghats. These plants have nesting places for ants. The ants feed on the nectar from the extrafloral buds present on their leaves. (Extrafloral buds are those that are different from the nectaries that are in flowers.) In return, ants patrol and protect the leaves from caterpillars. Also, the waste from the ants provide nitrogen to the plant. The plant also harbours earthworms in their stems. Researchers study the multi-way interactions between the earthworms, ants and plants, and the resulting competition between them.
One of the most unique examples of mutualism in nature is the relationship between the fig plant and the fig wasp. Every fig species has its own fig-wasp. The flowers of the fig are contained in an enclosed structure called the syconium. The fig-wasp enters the syconium and lays its eggs inside the flowers. After the eggs hatch, the newly-hatched male and female fig-wasps mate, and the females leave the syconium with pollen. They then fly to find another fig tree of the same species, enter a syconium of that tree, and they lay their eggs and pollinate the flowers.
The fig, and the processes associated with it, form an extremely complex system. Since most of it is not completely understood yet, there is immense potential for study. Dr Borges says she wants to, in a sense, deconstruct the fig. Right now, research is going on about the flight capabilities of a fig wasp, which has to travel tens of kilometers to find a fig tree, within the 24 hours of life that it has. Its flight patterns are studied using turbulence and wind speed in a scaled-down model of a wind tunnel. Fig wasps are attracted by the scent of the fig tree, and so, studies are on about what chemicals attract the fig. There are parasitic fig wasps also in the picture--these lay eggs in the syconium, taking over the space and nutrition meant for the legitimate fig wasps. Researchers are studying how these parasitic fig-wasps know in which syconium to lay their eggs, and whether they obtain sensory information which enables them to make the decision.
A further line of study looks into how fig wasps create nurseries inside the flowers in the syconium. Do they hijack the biochemical mechanisms of plants, or do they just mimic plant hormones? The fig also has nematodes, which are small worms that hitchhike on pollinator fig-wasps to move from one fruit to another. These feed on fig-tissue. A study is on about what effect these nematodes have on fig-wasps. Initial studies show that they adversely affect the life span of the figs.
Another example of mutualism that is being studied in Dr.Borges' lab is that of fungi-farming termites. Termites actively farm, nurture and protect certain species of fungi. In return, the fungi provide nutrition to the termite by breaking down the lignin in wood, something that termites can't do on their own. Research is going on about how the presence of termites is necessary to control pest fungi, and why. Researchers are also studying the role of secretions in making termite mounds, which is known as Biocementation.
Another researcher is working in the forests of Maharashtra, with 110 species of plants and a network of visitors, birds, insects, bees. The study is about how chemical, visual and olfactory signals are understood--what signals do flowers end out, and how do they send, and who responds?
In previous work done in the past, the lab has also discovered the first nocturnal bee that can both fly under starlight and has colour vision at night.
What is the hardest part about working on sensory biology? Dr Renee Borges says, "It is like making a recording of an entirely new language. We know it means something, but we don't know what. Something like trying to decipher the Egyptian heiroglyphics without the Rosetta stone. We need to conduct experiments to try and understand what each "phrase" means. An insider viewpoint is necessary for that."
She says that the better the experiment is designed, the more accurate the results are. She urges her PhD students to "think like a fig-wasp/termite/nematode" because it is essential to set aside the senses that we have as humans, and to approach the subject like a wasp or a termite would.
Dr Borges also says that there is a lot of work to be done, that there is enough scope of study for ten more PhDs, if necessary.
Renee Borges http://ces.iisc.ernet.in/renee/