Morphospace analysis leads to an evo-devo model of digit patterning

Exploring the Influence of Neomorphic Gekkotan Paraphalanges on Limb Modularity and Integration

Digital specializations of geckos are widely associated with their climbing abilities. A recurring feature that has independently emerged within the sister families Gekkonidae and Phyllodactylidae is the presence of neomorphic paraphalanges (PPEs), usually paired, paraxial skeletal structures lying adjacent to interphalangeal and metapodial-phalangeal joints. The incorporation of PPEs into gekkotan autopodia has the potential to modify the modularity and integration of the ancestral limb pattern by affecting information flow among skeletal limb parts. Here we explore the influence of PPEs on limb organization using anatomical networks. We modeled the fore- and hindlimbs in species ancestrally devoid of PPEs (Iguana iguana and Gekko gecko) and paraphalanx-bearing species (Hemidactylus mabouia and Uroplatus fimbriatus). To further clarify the impact of PPEs we also expunged PPEs from paraphalanx-bearing network models. We found that PPEs significantly increase modularity, giving rise to tightly integrated sub-modules along the digits, suggesting functional specialization. Species-specific singularities also emerged, such as the trade-off between the presence of PPEs favoring modularity (along the proximodistal axis) and the interdigital webbing favoring integration (across the lateromedial axis) in the limbs of U. fimbriatus. The PPEs are characterized by low connectivity compared with other skeletal elements; nevertheless, this varies based on their specific location and seemingly reflects developmental constraints. Our results also highlight the importance of the fifth metatarsal in generating a shift in lepidosaurian hindlimb polarity that contrasts with the more symmetrical bauplan of tetrapods. Our findings support extensive modification of the autopodial system in association with the addition of the neomorphic and intriguing PPEs.

Musculoskeletal and tendinous details of selected anomalies in the locomotor system of anurans

Previous studies on anuran anomalies predominantly examine isolated cases or focus on external and skeletal features. Our study analyzes a comprehensive sample collected from 1991 to 2017, examining the muscle-tendon system in 24 anuran species across adult, juvenile, and metamorphic stages. This extensive sample size allows us to investigate consistent anomaly patterns across different developmental stages and anuran families, exploring potential common developmental or genetic factors. Our detailed anatomical examination, encompassing musculature, tendons, and skeletal structures, revealed that 21% of the specimens displayed anomalies, a noteworthy finding considering the extensive sample size and duration of the studied sample. Of these anomalies, 17% affected the locomotor system, predominantly in the upper limbs. Key anomalies included, forelimbs and hindlimbs brachydactyly, rotation in forelimbs, partial kyphotic lordosis, and scoliosis. Notably, the digit 4 in the forelimbs and digits 4 and 5 in the hindlimbs were particularly susceptible to teratogenic effects, indicating possible prolonged exposure during development. Our study also uncovered combinations of anomalies and identified a phenotype similar to Poland syndrome. The findings validate the "Logic of Monsters" (LoMo theory) by Alberch, although the name itself may not be deemed appropriate, showing that developmental disruptions in tetrapods are not random but follow distinct sequences and patterns. The name, while unfortunate, accurately reflects the unusual nature of these developmental anomalies. This contributes to the evolving "Evo-Devo-Path" framework, highlighting the study's importance in understanding developmental disruptions in tetrapods.