Institute of Oceanography, National Taiwan University, Taipei, Taiwan.
PLoS One. 2013;8(2):e56485. doi: 10.1371/journal.pone.0056485. Epub 2013 Feb 19.
The clupeoid fishes are distributed worldwide, with marine, freshwater and euryhaline species living in either tropical or temperate environments. Regional endemism is important at the species and genus levels, and the highest species diversity is found in the tropical marine Indo-West Pacific region. The clupeoid distribution follows two general pattern of species richness, the longitudinal and latitudinal gradients. To test historical hypotheses explaining the formation of these two gradients, we have examined the early biogeography of the Clupeoidei in reconstructing the evolution of their habitat preferences along with their ancestral range distributions on a time-calibrated mitogenomic phylogeny. The phylogenetic results support the distinction of nine main lineages within the Clupeoidei, five of them new. We infer several independent transitions from a marine to freshwater environment and from a tropical to temperate environment that occurred after the initial diversification period of the Clupeoidei. These results combined with our ancestral range reconstruction hypothesis suggest that the probable region of origin and diversification of the Clupeoidei during the Cretaceous period was the tropical marine precursor to the present Indo-West Pacific region. Thus, our study favors the hypotheses of "Region of origin" and "Tropical conservatism" to explain the origins of the longitudinal and latitudinal gradients of clupeoid species richness, respectively. Additional geological and paleontological evidence further define the tropical marine paleo-region of origin as the eastern Tethys Sea region. The Cretaceous fossil record of the Clupeoidei is partially incongruent with the results here as it contains taxa found outside this region. We discuss three possible causes of conflict between our biogeographical hypothesis and the distributions of the Cretaceous clupeoid fossils: regional extinction, incomplete taxonomic sampling and incorrect timescale estimation.
鲱形目鱼类分布于世界各地，包括海洋、淡水和广盐性物种，生活在热带或温带环境中。种和属水平的区域特有性很重要，热带海洋的印-西太平洋地区物种多样性最高。鲱形目鱼类的分布遵循两种物种丰富度的一般模式，即经度和纬度梯度。为了检验解释这两个梯度形成的历史假说，我们在重建其栖息地偏好的进化以及基于时间校准的线粒体基因组系统发育上重建其祖先范围分布的过程中，检验了鲱形目鱼类的早期生物地理学。系统发育结果支持在鲱形目中区分出九个主要支系，其中五个是新的。我们推断出，在鲱形目鱼类最初多样化之后，发生了从海洋到淡水环境以及从热带到温带环境的几次独立的转变。这些结果与我们的祖先范围重建假说相结合表明，在白垩纪期间，鲱形目鱼类的可能起源和多样化区域是现今印-西太平洋地区的热带海洋前身。因此，我们的研究支持“起源区域”和“热带保守主义”假说，分别解释了鲱形目鱼类物种丰富度的经度和纬度梯度的起源。更多的地质和古生物学证据进一步将热带海洋古起源区域定义为东特提斯海地区。鲱形目的白垩纪化石记录与这里的结果不完全一致，因为其中包含了该地区以外的分类群。我们讨论了我们的生物地理学假说与白垩纪鲱形目鱼类化石分布之间冲突的三个可能原因：区域灭绝、不完全的分类采样和不正确的时间尺度估计。
