飛蜥滑翔之形態適應

Abstract

雖然動力飛行的適應性演化已被廣泛研究，但與滑翔相關的形態適應仍有待釐清。飛蜥屬（Draco）是一個特別引人注目的例子，因為牠們是少數使用肋骨而非四肢來支撐翼膜的脊椎動物，有關於其全身性滑翔形態適應的綜合研究仍相當缺乏。本研究透過外部形態測量與微電腦斷層掃描（micro-CT），分析飛蜥亞科（Draconinae）共 30 種蜥蜴（包含 17 種會滑翔及 13 種不會滑翔的物種），以探討飛蜥在身體、骨骼與爪部形態上的滑翔適應特徵。結果顯示，飛蜥在多個身體系統中展現出協調的形態適應，以優化滑翔表現。例如身體的頭部、四肢及整體體型呈現一致性的縮小，可能有助於降低體重並使重心後移，以提升滑翔效率；同時，前肢與後肢之間的距離維持不變，以確保翼膜面積充足。在骨骼形態方面，飛蜥的非特殊肋骨較不滑翔物種薄，且肱骨與特殊肋骨的粗度增長均受到限制，呈現出長度延伸但重量增加受限的特徵，顯示牠們可能藉由拉長這些結構來最大化翼面積，同時避免增加過多重量而影響滑行。爪部形態方面則展現出一種獨特的適應組合：高曲率有助於提升攀爬抓握能力，而較短的爪長則可能降低著陸時結構失效的風險。這些發現顯示，飛蜥在演化滑翔能力的過程中，發展出跨系統的整合性形態變化，以達成減重、氣動性能與機械穩定性之平衡，進而揭示脊椎動物滑翔運動所面臨的演化限制與權衡。

While adaptive evolution in powered flight has been extensively studied, the morphological adaptations underlying gliding locomotion remain poorly understood. Flying lizards (Draco) represent a particularly intriguing case, as they are among the few vertebrate groups that utilize ribs rather than limbs to support their wing membranes. However, comprehensive studies of their whole-body morphological adaptations for gliding remain lacking. In this study, I investigated body, bone, and claw morphological adaptations for gliding in Draco lizards by analyzing 30 species in the subfamily Draconinae, including 17 gliding and 13 non-gliding species, using external morphological measurements and micro-computed tomography (micro-CT) scans. My results reveal that flying lizards exhibit coordinated morphological adaptations across multiple body systems to optimize gliding performance. Body morphology shows consistent size reduction in head, limbs, and overall body size, likely reducing mass and shifting the center of mass rearward to improve gliding efficiency, while the distance between forelimbs and hindlimbs is preserved to maintain adequate wing membrane area. Bone morphology demonstrates coordinated weight reduction patterns: non-specialized ribs are relatively thinner in flying lizards compared to non-gliding species, while both the humerus and specialized ribs exhibit constrained thickness growth relative to length, suggesting elongation to maximize wing area while minimizing weight gain. Claw morphology reveals a distinctive adaptation pattern, combining high curvature for enhanced arboreal grip with reduced length to minimize structural failure risk during landing. These findings demonstrate that gliding evolution in Draco lizards involves integrated morphological changes that appear to achieve an optimal balance between weight reduction, aerodynamic performance, and mechanical stability, providing insights into the evolutionary constraints and trade-offs that shape gliding locomotion in vertebrates.