The sex of organ geometry

Abstract

Organs have a distinctive spatial arrangement within the body; this is commonly overlooked in the context of how organs function or communicate. We hypothesise that there is a logic to the shape of an organ and its proximity to its neighbours. Using volumetric scans of large numbers of Drosophila melanogaster flies, we develop methods to quantify 3D features of organ shape, position and inter-individual variability. We find that both the shape of organs and their relative arrangement are stereotypical yet sexually dimorphic, and reveal unexpected inter-organ adjacencies and left-right organ asymmetries. Focusing on the intestine, which traverses nearly the entire body, we investigate how sex differences in 3D organ geometry arise. The configuration of the adult intestine is only partially determined by physical constraints from adjacent organs; its sexually dimorphic shape is actively maintained by the vascular-like tracheal system. Indeed, a new and bidirectional mechanism of sex differentiation first renders trachea sexually dimorphic. Then, tracheal branches hold the gut loops together into a male or female shape. This previously unrecognised level of biological complexity is physiologically significant and could enable or confine communication across organs, helping explain signalling paradoxes and sex differences in organ function.