An interaction between cancer progression and social environment in Drosophila

The ecological benefits of sociality in gregarious species are widely acknowledged. However, only limited data is available on how the social environment influences non-communicable disease outcomes. For instance, despite extensive research over the past decades, the role of the social environment on cancer progression remains unclear and controversial. This is mainly because epidemiological studies suffer from the complexity of inter-correlated factors and it is still unknown whether distinct social group composition can also differentially affect tumor growth. Here, we exposed adult Drosophila with colorectal-like tumors to different social environments. We show that both cancerous flies bred in complete isolation, or in a group with non-cancerous individuals, exhibit increased tumor progression compared to those bred with other cancerous conspecifics. Based on video-tracking and social interaction analyses, we propose that this dramatic effect may be a consequence of perceived social isolation due to differential social interaction rates. We found that flies can discriminate between individuals at different stages of tumor growth; control flies actively avoid flies with cancer but only at the later stages of tumor development, whereas cancerous flies display strong social interactions with cancerous flies in the early stages of tumor growth. Our study demonstrates the reciprocal links between cancer and social interactions, as well as highlighting how sociality impacts health and fitness in animals and its potential implications for disease ecology and ecosystem functioning.