Gilbert Michelle C, Conith Andrew J, Lerose Catherine S, Moyer Joshua K, Huskey Steve H, Albertson R Craig
Organismic and Evolutionary Biology Graduate Program, University of Massachusetts, Amherst, MA 01003, USA.
Biology Department, Morrill Science Center, University of Massachusetts, 611 North Pleasant Street, Amherst, MA 01003, USA.
Integr Org Biol. 2021 Feb 16;3(1):obab003. doi: 10.1093/iob/obab003. eCollection 2021.
When novel or extreme morphologies arise, they are oft met with the burden of functional trade-offs in other aspects of anatomy, which may limit phenotypic diversification and make particular adaptive peaks inaccessible. Bramids (Perciformes: Bramidae) comprise a small family of 20 extant species of fishes, which are distributed throughout pelagic waters worldwide. Within the Bramidae, the fanfishes ( and ) differ morphologically from the generally stout, laterally compressed species that typify the family. Instead, and exhibit extreme anterior positioning of the dorsal fin onto the craniofacial skeleton. Consequently, they possess fin and skull anatomies that are radically different from other bramid species. Here, we investigate the anatomy, development, and evolution of the Bramidae to test the hypothesis that morphological innovations come at functional (proximate) and evolutionary (ultimate) costs. Addressing proximate effects, we find that the development of an exaggerated dorsal fin is associated with neurocrania modified to accommodate an anterior expansion of the dorsal fin. This occurs via reduced development of the supraoccipital crest (SOC), providing a broad surface area on the skull for insertion of the dorsal fin musculature. While these anatomical shifts are presumably associated with enhanced maneuverability in fanfishes, they are also predicted to result in compromised suction feeding, possibly limiting the mechanisms of feeding in this group. Phylogenetic analyses suggest craniofacial and fin morphologies of fanfishes evolved rapidly and are evolutionarily correlated across bramids. Furthermore, fanfishes exhibit a similar rate of lineage diversification as the rest of the Bramidae, lending little support for the prediction that exaggerated medial fins are associated with phylogenetic constraint. Our phylogeny places fanfishes at the base of the Bramidae and suggests that nonfanfish bramids have reduced medial fins and re-evolved SOCs. These observations suggest that the evolution of novel fin morphologies in basal species has led to the phylogenetic coupling of head and fin shape, possibly predisposing the entire family to a limited range of feeding. Thus, the evolution of extreme morphologies may have carryover effects, even after the morphology is lost, limiting ecological diversification of lineages.
当新的或极端的形态出现时，它们往往会在解剖学的其他方面面临功能权衡的负担，这可能会限制表型的多样化，并使某些特定的适应峰值无法达到。棘鲷科（鲈形目：棘鲷科）由20种现存鱼类组成，是一个小家族，分布于全球的中上层水域。在棘鲷科中，扇棘鲷属（ 和 ）在形态上与该科典型的通常粗壮、侧扁的物种不同。相反， 和 的背鳍在颅面骨骼上的位置极其靠前。因此，它们的鳍和头骨解剖结构与其他棘鲷科物种截然不同。在这里，我们研究了棘鲷科的解剖结构、发育和进化，以检验形态创新会带来功能（近因）和进化（终极）成本这一假设。在探讨近因效应时，我们发现背鳍过度发育与经过改造以适应背鳍向前扩展的神经颅有关。这是通过上枕嵴（SOC）发育减少来实现的，从而在头骨上提供了一个宽阔的表面区域用于背鳍肌肉组织的附着。虽然这些解剖结构的变化可能与扇棘鲷属鱼类机动性增强有关，但预计它们也会导致吸食式摄食能力受损，这可能会限制该类群的摄食机制。系统发育分析表明，扇棘鲷属鱼类的颅面和鳍的形态进化迅速，并且在棘鲷科中在进化上具有相关性。此外，扇棘鲷属鱼类的谱系多样化速率与棘鲷科的其他成员相似，这几乎不支持过度发育的内侧鳍与系统发育限制相关的预测。我们的系统发育树将扇棘鲷属鱼类置于棘鲷科的基部，并表明非扇棘鲷属的棘鲷科鱼类内侧鳍有所减少且上枕嵴重新进化。这些观察结果表明，基部物种中新型鳍形态的进化导致了头部和鳍形状的系统发育耦合，这可能使整个科的摄食范围受到限制。因此，极端形态的进化可能会产生遗留效应，即使在形态消失后，也会限制谱系的生态多样化。
