Environment-modifying activities of dung beetle larvae shape their growth and life history traits

Organisms are not just passive recipients of environmental pressures but are able to shape the environment they experience. Yet, the mechanisms and the evolutionary implications of such niche construction remains poorly understood. Here, we study these effects in the gazelle dung beetle (Digitonthophagus gazella). Larvae of this species develop in an underground brood chamber (a so-called ‘brood ball’) consisting of cow dung which serves as a sole source of food for a single developing larva. Throughout its development, the larva extensively modifies its environment by constantly eating, regurgitating, and shaping particle sizes within the brood ball. At the end of juvenile development, what’s left of the once fibrous cow dung is a fine mixture of particles and previous research suggests that these larval manipulations increase environmental quality and nutrient availability. However, how larval modifications affect larval growth and how these modifications differ between species remain poorly understood. We studied the impact of larval environmental modifications on development in the dung beetle Digitonthophagus gazella. We did this by transplanting eggs into modified and unmodified environments, whilst excluding maternally derived microbes. Additionally, we included a heterospecific (Onthophagus binodis) modified environment to investigate species-specific differences of niche construction. Counter to expectations, we found larval modifications by conspecifics did not confer a fitness benefit to D. gazella. However, surprisingly, individuals from heterospecific treatments emerged significantly quicker. Our research adds to the growing literature on the complex interactions between organisms and their environment and how those interactions feedback on organismal development and performance.