Vomeronasal organ volume increases with body size and is dissociated with loss of a visual signal in Sceloporus lizards

Many organisms communicate using signals in different sensory modalities (multicomponent or multimodal). When one signal or component is lost over evolutionary time, it may be indicative of changes in other characteristics of the signaling system, including the sensory organs used to perceive and process signals. Sceloporus lizards predominantly use chemical and visual signals to communicate, yet some species have lost the ancestral ventral color patch used in male-male agonistic interactions and exhibit increased chemosensory behavior. Here, we asked whether evolutionary loss of this sexual signal is associated with larger vomeronasal organ (VNO) volumes (an organ that detects chemical scents) compared to species that have retained the color patch. We measured VNO coronal section areas of 7–8 adult males from each of 11 Sceloporus species (4 that lost and 7 that retained the color patch), estimated sensory and total epithelium volume, and compared volumes using phylogenetic ANCOVA, controlling for body size. Contrary to expectations, we found that species retaining the ventral patch had similar relative VNO volumes as did species that have lost the ancestral patch, and that body size explains VNO epithelium volume. Visual signal loss may be sufficiently compensated for by increased chemosensory behavior, and the allometric pattern may indicate sensory system trade-offs for large-bodied species.

Methods
All details regarding data collection and preprocessing can be found in the associated manuscript.