Data from: Many paths to a common destination: morphological differentiation of a functionally convergent visual signal

Understanding the interacting outcomes of selection and historical contingency in shaping adaptive evolution remains a challenge in evolutionary biology. While selection can produce convergent outcomes when species occupy similar environments, the unique history of each species can also influence evolutionary trajectories and result in different phenotypic endpoints. The question is to what extent historical contingency places species on different adaptive pathways and, in turn, the extent to which we can predict evolutionary outcomes. Among lizards there are several distantly related genera that have independently evolved an elaborate extendible dewlap for territorial communication. We conducted a detailed morphological study and employed new phylogenetic comparative methods to investigate the evolution of the underlying hyoid that powers the extension of the dewlap. This analysis showed that there appear to have been multiple phenotypic pathways for evolving a functionally convergent dewlap. The biomechanical complexity that underlies this morphological structure implies that adaptation should have been constrained to a narrow phenotypic pathway. However, multiple adaptive solutions have been possible in apparent response to a common selection pressure. Thus, the phenotypic outcome that subsequently evolved in different genera seems to have been contingent on the history of the group in question. This blurs the distinction between convergent and historically contingent adaptation and suggests that adaptive phenotypic diversity can evolve without the need for divergent natural selection.

解析选择作用与历史偶然性在适应性演化塑造过程中的交互效应，仍是进化生物学领域的一项核心挑战。尽管当物种栖息于相似环境时，选择作用可催生趋同演化结果，但每个物种独特的演化历史同样会影响其演化轨迹，最终产生各异的表型终点。当前亟待解答的核心问题是：历史偶然性在多大程度上会将物种导向不同的适应性演化路径，进而影响我们对演化结果的预测能力？在蜥蜴类群中，多个远缘属物种已独立演化出结构复杂的可伸缩喉扇（dewlap）用于领地通讯。本研究开展了详尽的形态学分析，并采用新型系统发育比较方法（phylogenetic comparative methods），探究驱动喉扇伸缩的舌骨（hyoid）的演化历程。分析结果显示，演化出功能趋同的喉扇，实则存在多条不同的表型演化路径。该形态结构背后的生物力学复杂性，本应意味着适应性演化被限定在狭窄的表型路径范围内。然而，面对共同的选择压力，不同类群实则演化出了多种适应性解决方案。因此，不同属类后续演化出的表型结果，似乎取决于该类群自身的演化历史。这一发现模糊了趋同适应与历史偶然性适应之间的界限，同时表明适应性表型多样性的演化，未必需要依赖趋异的自然选择作用。