Diversification of the turtle's shell comprises remarkable phenotypic transformations. For instance, two divergent species convergently evolved shell‐closing systems with shoulder blade (scapula) segments that enable coordinated movements with the shell. We expected these unusual structures to originate via similar changes in underlying gene networks, as skeletal segment formation is an evolutionarily conserved developmental process. We tested this hypothesis by comparing transcriptomes of scapula tissue across three stages of embryonic development in three emydid turtles from natural populations. We found that alternative strategies for skeletal segmentation were associated with interspecific differences in gene co‐expression networks. Notably, mesenchyme homeobox 2 (MEOX2) and HOXA3‐5 were central hubs driving the activity of 2,806 genes in a candidate network for scapula segmentation, albeit in only one species. Even so, scapula muscle overgrowth corresponded to the activity of similar myogenic networks in both species. This and other derived developmental processes were not observed in the third species, which displayed the ancestral (unsegmented) scapula condition. Differential gene expression tests against this reference lineage supported histological and network analyses. Our findings illustrate that molecular underpinnings of convergent evolution, including during the diversification of the atypical turtle “body plan,” are influenced by variation in underlying developmental processes.

中文翻译：

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基因网络变异和海龟收敛进化的替代途径。

龟壳的多样化包括显着的表型转化。例如，两个不同的物种会聚在一起进化成具有肩blade骨（肩cap骨）段的壳关闭系统，从而能够与壳协调运动。我们预期这些不寻常的结构会通过基础基因网络中的类似变化而起源，因为骨骼片段的形成是进化上保守的发育过程。我们通过比较来自自然种群的三只em龟的胚胎发育三个阶段的肩cap骨组织的转录组，来检验这一假设。我们发现骨骼分割的替代策略与基因共表达网络中的种间差异有关。值得注意的是，间充质同源盒2（MEOX2）和HOXA3-5是驱动2的活动的中心枢纽，肩one骨分割候选网络中的806个基因，尽管只有一种。即使这样，肩species骨肌肉的过度生长也对应于两个物种中类似的成肌网络的活动。在第三个物种中没有观察到这种和其他衍生的发育过程，该物种表现出祖先（未分段）的肩cap骨状况。针对该参考谱系的差异基因表达测试支持了组织学和网络分析。我们的发现表明，包括非典型海龟“身体计划”多样化在内的趋同进化的分子基础受基础发育过程变化的影响。在第三个物种中没有观察到这种和其他衍生的发育过程，该物种表现出祖先（未分段）的肩cap骨状况。针对该参考谱系的差异基因表达测试支持了组织学和网络分析。我们的发现表明，包括非典型海龟“身体计划”多样化在内的趋同进化的分子基础受基础发育过程变化的影响。在第三个物种中没有观察到这种和其他衍生的发育过程，该物种表现出祖先（未分段）的肩cap骨状况。针对该参考谱系的差异基因表达测试支持了组织学和网络分析。我们的发现表明，聚合进化的分子基础，包括在非典型海龟“身体计划”多样化期间，都受到潜在发育过程变化的影响。