Data from: Ontogenetic development of intestinal length and relationships to diet in an Australasian fish family (Terapontidae)

Background: One of the most widely accepted ecomorphological relationships in vertebrates is the negative correlation between intestinal length and proportion of animal prey in diet. While many fish groups exhibit this general pattern, other clades demonstrate minimal, and in some cases contrasting, associations between diet and intestinal length. Moreover, this relationship and its evolutionary derivation have received little attention from a phylogenetic perspective. This study documents the phylogenetic development of intestinal length variability, and resultant correlation with dietary habits, within a molecular phylogeny of 28 species of terapontid fishes. The Terapontidae (grunters), an ancestrally euryhaline-marine group, is the most trophically diverse of Australia's freshwater fish families, with widespread shifts away from animal-prey-dominated diets occurring since their invasion of fresh waters. Results: Description of ontogenetic development of intestinal complexity of terapontid fishes, in combination with ancestral character state reconstruction, demonstrated that complex intestinal looping (convolution) has evolved independently on multiple occasions within the family. This modification of ontogenetic development drives much of the associated interspecific variability in intestinal length evident in terapontids. Phylogenetically informed comparative analyses (phylogenetic independent contrasts) showed that the interspecific differences in intestinal length resulting from these ontogenetic developmental mechanisms explained ~65% of the variability in the proportion of animal material in terapontid diets. Conclusions: The ontogenetic development of intestinal complexity appears to represent an important functional innovation underlying the extensive trophic differentiation seen in Australia's freshwater terapontids, specifically facilitating the pronounced shifts away from carnivorous (including invertebrates and vertebrates) diets evident across the family. The capacity to modify intestinal morphology and physiology may also be an important facilitator of trophic diversification during other phyletic radiations.研究背景：脊椎动物中最被广泛认可的生态形态学关联（ecomorphological relationship）之一，为肠道长度（intestinal length）与日粮动物性饵料（animal prey）占比呈负相关。尽管多数鱼类类群呈现这一通用模式，但其他演化支仅表现出极微弱的相关性，部分类群甚至呈现相反趋势。此外，这一关联及其演化起源极少从系统发育视角（phylogenetic perspective）得到关注。本研究基于28种棘臀鱼科（Terapontidae，俗称吹砂鱼grunters）鱼类的分子系统发育树（molecular phylogeny），记录了该类群肠道长度变异的系统发育演化历程，及其与食性的相关性。棘臀鱼科为起源于广盐性海洋的类群（euryhaline-marine group），是澳大利亚淡水鱼类科中营养生态位多样性最高（trophically diverse）的类群，自其入侵淡水生境以来，已广泛发生脱离动物性饵料主导食谱的食性转变。 研究结果：对棘臀鱼科鱼类肠道复杂度的个体发育（ontogenetic development）过程进行描述，并结合祖先性状状态重建（ancestral character state reconstruction）分析，结果显示复杂的肠环（intestinal looping/convolution）在该科内已独立演化多次。这种个体发育模式的改变，是造成棘臀鱼科鱼类肠道长度出现显著种间变异（interspecific variability）的核心驱动因素。基于系统发育的比较分析（系统发育独立对比，phylogenetic independent contrasts）表明，由上述个体发育机制产生的肠道长度种间差异，可解释棘臀鱼科日粮中动物性物质占比约65%的变异量。 研究结论：肠道复杂度的个体发育过程，似乎是澳大利亚淡水棘臀鱼科鱼类出现广泛营养分化（trophic differentiation）的重要功能创新，该创新尤其推动了该科类群脱离肉食性（包括捕食无脊椎动物和脊椎动物）食谱的显著转变。此外，改造肠道形态与生理机能的能力，或许也是其他类群辐射演化（phyletic radiations）过程中，推动营养生态位分化的重要助力。