Variability of jaw muscles in Tunisian street dogs and adaptation to skull shape

Abstract

The impact of artificial selection on the masticatory apparatus of dogs has been poorly studied, and comparative data with dogs subjected to more natural constraints are lacking. This study explores the jaw musculature of Tunisian street dogs, which are largely free from the influence of breed-specific selection. The masticatory muscles (digastric, masseter, temporalis, and pterygoid) of 27 adult dogs were dissected and muscle mass and physiological cross-sectional area (PCSA) were quantified, providing a baseline for comparisons between dogs from more natural versus more controlled environments. Our findings reveal that the morphology of the jaw adductor muscles is remarkably conserved among dogs, despite significant variation in skull shape. Additionally, all masticatory muscles scale isometrically with body mass. Notably, females exhibit functional adaptations that optimize muscle strength, particularly in the temporalis muscle, despite showing smaller overall muscle volumes compared to males. This could be linked to differences in predation, competition for food, or factors related to sexual behavior. Preliminary evidence suggests that captivity may limit the development of muscle mass and PCSA in the temporalis muscle, likely due to changes in lifestyle and diet. Significant relationships were also observed between skull shape and muscle data, particularly in the mandible, indicating that skull variability reflects jaw adductor muscle anatomy to some degree. This study enhances our understanding of jaw muscle morphology and function in feral dog populations and offers insights into the adaptation of the masticatory apparatus in dogs.