Data from: Repeated invasions into the twilight zone: evolutionary origins of a novel assemblage of fishes from deep Caribbean reefs

Mesophotic and deeper reefs of the tropics are poorly known and underexplored ecosystems worldwide. Collectively referred to as the ‘twilight zone’, depths below ~30–50 m are home to many species of reef fishes that are absent from shallower depths, including many undescribed and endemic species. We currently lack even a basic understanding of the diversity and evolutionary origins of fishes on tropical mesophotic reefs. Recent submersible collections in the Caribbean have provided new specimens that are enabling phylogenetic reconstructions that incorporate deep-reef representatives of tropical fish genera. Here, we investigate evolutionary depth transitions in the family Gobiidae (gobies), the most diverse group of tropical marine fishes. Using divergence-time estimation coupled with stochastic character mapping to infer the timing of shallow-to-deep habitat transitions in gobies, we demonstrate at least four transitions from shallow to mesophotic depths. Habitat transitions occurred in two broad time periods (Miocene, Pliocene–Pleistocene), and may have been linked to the availability of underutilized niches, as well as the evolution of morphological/behavioural adaptations for life on deep reefs. Further, our analysis shows that at least three evolutionary lineages that invaded deep habitats subsequently underwent speciation, reflecting another unique mode of radiation within the Gobiidae. Lastly, we synthesize depth distributions for 95 species of Caribbean gobies, which reveal major bathymetric faunal breaks at the boundary between euphotic and mesophotic reefs. Ultimately, our study is the first rigorous investigation into the origin of Caribbean deep-reef fishes and provides a framework for future studies that utilize rare, deep-reef specimens.

全球范围内，热带中光层珊瑚礁（mesophotic reefs）及更深海域的珊瑚礁仍是认知匮乏、探索不足的生态系统。约30~50米以下的海域被统称为“暮光带”，栖息着诸多浅海海域不存在的礁栖鱼类物种，其中包含大量未被描述的特有物种。目前我们甚至对热带中光层珊瑚礁鱼类的多样性与演化起源都缺乏基础认知。近期在加勒比海开展的载人潜水器采集工作获取了全新标本，使得我们得以开展包含热带鱼类属群深礁代表物种在内的系统发育重建研究。本研究聚焦于物种多样性最为丰富的热带海洋鱼类类群——鰕虎鱼科（Gobiidae，俗称鰕虎鱼）的深度演化过渡事件。通过分化时间估算结合随机性状映射法，推断鰕虎鱼从浅海向深海生境过渡的时间节点，本研究证实至少存在四次从浅海到中光层海域的生境过渡事件。生境过渡事件主要发生在两个宽泛的地质时期（中新世、上新世-更新世），其成因可能与未被充分利用的生态位可获得性，以及适配深礁生存的形态/行为适应性演化有关。此外，本研究分析显示，至少有三个入侵深海生境的演化支系后续发生了物种形成，这反映了鰕虎鱼科内另一种独特的辐射演化模式。最后，我们整合了加勒比海95种鰕虎鱼的深度分布数据，在真光层与中光层珊瑚礁的交界带发现了显著的水深区系分界现象。综上，本研究是首个针对加勒比海深礁鱼类起源开展的严谨调查，同时为后续利用珍稀深礁标本开展的研究提供了研究框架。