Developmental perturbations and the robustness of limb modularity: Insights from anuran anatomical networks

Developmental anomalies provide a powerful window into the rules and constraints shaping morphological evolution. Here, we use anatomical network analysis to investigate how congenital perturbations affect the structural organization of anuran limbs. We analyzed a specimen of Leptodactylus bufonius exhibiting bilateral brachydactyly in both fore- and hindlimbs and unilateral polyphalangy, and compared its limb networks to those of a typical conspecific. Developmental perturbations resulted in structural reorganization, including reduced node and link number and increased graph density. At the node level, betweenness centrality markedly declined in stylopodial and zeugopodial elements, disrupting the characteristic proximodistal hub-periphery organization of the limb. This shift reflects a loss of proximodistal polarization associated with distal reduction. Modular organization was robust to these perturbations: module number remained unchanged in the forelimbs and in the left hindlimb, and decreased in the right hindlimb, which exhibited the most extensive morphological reduction. Although module membership showed subtle changes, the overall number and composition of modules remained broadly conserved across reference and anomalous limbs. Thus, despite substantial anatomical perturbation, modular organization was largely maintained, with marked reorganization occurring only in the most severely affected limb. The anomalous morphology studied here demonstrates that developmental systems can accommodate profound modifications while maintaining organismal viability. Our study engages with the broader community discussion on modularity and the methodological frameworks used to investigate it. More broadly, this study highlights how anatomical network approaches can contribute to evo-devo research by quantifying how developmental disruptions reshape the organization of complex morphological systems.