Environmental modifications of dung beetle larvae shape their growth and life history

Organisms are not just passive recipients of environmental pressures but can shape the environment they experience. Yet, the mechanisms and evolutionary implications of such niche construction remain poorly understood. Here, we studied these effects in the gazelle dung beetle (Digitonthophagus gazella). Larvae of this species develop in an underground brood chamber (a 'brood ball') composed of dung, which serves as the sole source of food for a single larva. Throughout its development, the larva extensively modifies its environment by constantly eating, regurgitating and shaping particle sizes within the brood ball. 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 by transplanting eggs into previously modified or unmodified environments, whilst controlling for the confounding effect of maternally derived microbes. Additionally, we also studied how D. gazella larvae grow in an environment that was modified by a different species (Onthophagus binodis) to investigate species-specific differences of niche construction. Counter to expectations, we found that larval modifications by conspecifics did not confer a fitness benefit to D. gazella. However, surprisingly, individuals developing in a brood ball modified by a heterospecific individual emerged significantly quicker. These findings provide mixed support that environmental modifications by a larva enhance its growth. Our research adds to the growing literature on the complex interactions between organisms and their environment and how those interactions feed back on organismal development and performance.