Sociobiology on the fly; understanding social interactions in multispecies groups

The effects of social environments on individuals are widespread, even in species not classically thought of as social (Bailey and Moore 2018). These can range from reproductive decisions (Bretman et al 2009) to ageing (Leech et al 2017; Fricke and Bretman 2019), stress and immune responses (Leech et al 2019), and even differences in host microbiomes (Tung et al 2015; Leech, McDowall et al in prep). The picture is complicated because often these effects are sex-specific and depend on the age of the interacting partners. For example, in terms of lifespan and decline in physical functions, males are more sensitive to contact with other males, but females are highly sensitive to contact with males (Leech et al 2017, Fricke and Bretman 2019).
However, whilst we think of social environments as interactions between conspecifics, species are rarely found in single species groups. Clearly this can alter competition for resources such as food, but effects are likely to influence individuals in multiple ways even beyond this direct competition, for example by acting as a source of pathogenic or mutualistic bacteria. For example, males respond to the presence of other males, which signals mating competition, and we have shown that males will produce some responses to males of some but not all heterospecifics (Bretman et al 2017). Others have shown that aggression between males depends on the species identity of the males involved, with more closely related species being subjected to as much aggression as conspecifics (Gupta et al 2019). In recent experiments we have found that conspecific contact is important for male cognitive abilities (increases learning and memory), but heterospecifics do not have any effect, yet for females the opposite is true (Rouse et al in prep). Moreover, these behavioural differences go hand in hand with gene expression changes, suggesting that conspecific/ heterospecific social environments have differential effects at the molecular level. Therefore species recognition seems more or less important depending on which behaviours or traits are being studied, and it has been suggested that this is one reason why complex sensory cue systems have evolved in the ability to produce socially-plastic responses (Dore et al 2018).
Our aim is to explore the multifaceted social effects in a wider community ecology framework. We will use fruit flies as a model, as in much of the work referenced above. In the wild, flies live in multispecies groups (Atkinson 1979), so interact with conspecifics and heterospecifics regularly. Different fly species can be easily cultured together and are highly amenable to experimental manipulation. This means we can investigate the influence of multispecies groups on a range of individual traits whilst controlling for resource availability. We will test interspecies social effects on fundamental life history traits such as lifespan and reproductive output, whether interactions are symmetrical or unidirectional, and investigate potential mechanisms such as sensory cues and the role of the microbiome. This will advance our understanding of sociobiology beyond single species interactions.