Department of Biology, Howard University, 415 College Street NW, Washington, DC 20059, USA.
Department of Biology, University of Hawaii, Hilo, 200 West Kawili Street, Hilo, HI 96720, USA.
Integr Comp Biol. 2019 Aug 1;59(2):394-409. doi: 10.1093/icb/icz022.
Suction feeding and gill ventilation in teleosts are functionally coupled, meaning that there is an overlap in the structures involved with both functions. Functional coupling is one type of morphological integration, a term that broadly refers to any covariation, correlation, or coordination among structures. Suction feeding and gill ventilation exhibit other types of morphological integration, including functional coordination (a tendency of structures to work together to perform a function) and evolutionary integration (a tendency of structures to covary in size or shape across evolutionary history). Functional coupling, functional coordination, and evolutionary integration have each been proposed to limit morphological diversification to some extent. Yet teleosts show extraordinary cranial diversity, suggesting that there are mechanisms within some teleost clades that promote morphological diversification, even within the highly integrated suction feeding and gill ventilatory systems. To investigate this, we quantified evolutionary integration among four mechanical units associated with suction feeding and gill ventilation in a diverse clade of benthic, primarily suction-feeding fishes (Cottoidei; sculpins and relatives). We reconstructed cottoid phylogeny using molecular data from 108 species, and obtained 24 linear measurements of four mechanical units (jaws, hyoid, opercular bones, and branchiostegal rays) from micro-CT reconstructions of 44 cottoids and 1 outgroup taxon. We tested for evolutionary correlation and covariation among the four mechanical units using phylogenetically corrected principal component analysis to reduce the dimensionality of measurements for each unit, followed by correlating phylogenetically independent contrasts and computing phylogenetic generalized least squares models from the first principle component axis of each of the four mechanical units. The jaws, opercular bones, and branchiostegal rays show evolutionary integration, but the hyoid is not positively integrated with these units. To examine these results in an ecomorphological context, we used published ecological data in phylogenetic ANOVA models to demonstrate that the jaw is larger in fishes that eat elusive or grasping prey (e.g., prey that can easily escape or cling to the substrate) and that the hyoid is smaller in intertidal and hypoxia-tolerant sculpins. Within Cottoidei, the relatively independent evolution of the hyoid likely has reduced limitations on morphological evolution within the highly morphologically integrated suction feeding and gill ventilatory systems.
硬骨鱼类的抽吸式摄食和鳃呼吸在功能上是耦合的，这意味着两者所涉及的结构有重叠。功能耦合是形态整合的一种类型，广义上是指结构之间的任何协变、相关或协调。抽吸式摄食和鳃呼吸还表现出其他类型的形态整合，包括功能协调（结构协同工作以执行功能的趋势）和进化整合（结构在进化历史中大小或形状协同变化的趋势）。功能耦合、功能协调和进化整合都在一定程度上被提出限制形态多样化。然而，硬骨鱼类表现出非凡的颅部多样性，这表明在某些硬骨鱼类类群中存在促进形态多样化的机制，即使在高度整合的抽吸式摄食和鳃呼吸系统中也是如此。为了研究这一点，我们量化了与抽吸式摄食和鳃呼吸相关的四个机械单元在一个多样化的底栖、主要是抽吸式摄食鱼类（Cottoidei；棘鳍鱼和相关鱼类）类群中的进化整合。我们使用来自 108 个物种的分子数据重建了棘鳍鱼的系统发育，并从 44 个棘鳍鱼和 1 个外群分类单元的微 CT 重建中获得了四个机械单元（颌骨、舌骨、鳃盖骨和鳃弓）的 24 个线性测量值。我们使用系统发育校正的主成分分析来减少每个单元的测量维度，然后对四个机械单元中的每一个的第一主成分轴进行相关和计算系统发育广义最小二乘模型，以检验四个机械单元之间的进化相关性和协变。颌骨、鳃盖骨和鳃弓显示出进化整合，但舌骨与这些单元没有正整合。为了在生态形态学背景下检验这些结果，我们在系统发育方差分析模型中使用了已发表的生态数据，证明了在捕食难以捉摸或抓握的猎物（例如，容易逃脱或粘在基质上的猎物）的鱼类中，颌骨更大，并且在潮间带和耐缺氧的棘鳍鱼中，舌骨更小。在 Cottoidei 中，舌骨相对独立的进化可能降低了高度形态整合的抽吸式摄食和鳃呼吸系统中形态进化的限制。
