One of the most enigmatic patterns in biodiversity is the increasing number of unique species as we move from the poles to the equator. Might this also mean that interactions between species become stronger with decreasing latitude? Nathan et al., in collaboration with Dr. Vinita Gowda from the TREE Lab in the Department of Biological Sciences at IISER Bhopal set out to test this for a mutualism between a widely distributed plant species (Ricinus communis, commonly known as the castor oil plant) and ants. In this interaction, the plants provide sugary nectar on glands called extrafloral nectaries (EFNs) to ants, which protect the plants from being eaten by herbivores. The researchers traversed a 20° latitudinal gradient in India, from Ramnagar in Uttarakhand to Kanyakumari in Tamilnadu sampling ten populations of R. communis, measuring EFN traits and interactions with ant species. They found that plants in southern sites produced more and larger nectaries and attracted more ants, as they predicted. However, counter to their predictions, plants in northern sites suffered higher herbivory, perhaps due to poorer ant defense or interbreeding with agricultural varieties. This is one of the first studies to test for latitudinal trends in an ant-plant mutualism. For more details, kindly visit https://link.springer.com/article/10.1007/s00442-025-05772-7
