Evolutionary history of Otophysi
Posted: 24 Jun 2011, 01:30
Evolutionary history of Otophysi (Teleostei), a major clade of the modern freshwater fishes: Pangaean origin and Mesozoic radiation.
Masanori Nakatani, Masaki Miya, Kohji Mabuchi, Kenji Saitoh and Mutsumi Nishida.
BMC Evolutionary Biology 2011, 11:177.
Abstract:
Freshwater harbors approximately 12,000 fish species that correspond to 43% of all modern fish diversity. Surprisingly, a single ancestral lineage evolved into about two thirds of this enormous biodiversity ([almost equal to] 7900 spp. placed in four orders, 64 families and 1068 genera), and is currently distributed throughout the world's continents except Antarctica. Despite such remarkable species diversity and ubiquity, the evolutionary history of this major freshwater fish clade -- Otophysi -- remains largely unexplored. To provide an overview of the history of otophysan diversification, we constructed a timetree based on whole mitogenome sequences across 110 species representing 55 of the 64 families.
Partitioned maximum likelihood analysis based on unambiguously aligned sequences (9923 bp excluding quickly saturated third codon positions) confidently recovered monophyly of Otophysi and the two constituent subgroups (Cypriniformes and Characiphysi). Within the latter clade that comprises three orders (Gymnotiformes, Characiformes, Siluriformes), Gymnotiformes was placed as the most basal clade. One of the two suborders in Characiformes (Characoidei) was reproduced as more closely related to Siluriformes than to its own suborder (Citharinoidei), rendering the characiforms paraphyletic. This novel relationship, however, was confidently supported by the analysis of independent nuclear markers. A relaxed molecular-clock Bayesian analysis of the divergence times and reconstruction of ancestral habitats on the timetree suggest that a common ancestor of the Otophysi entered freshwater around the end-Permian (251 Ma) when mass extinction events dramatically altered the ecological structure of marine communities under super anoxic conditions. Subsequent basal divergences during the Triassic (251-200 Ma) on the supercontinent Pangaea successively produced five major lineages (common ancestors of the present-day orders or suborders) that survived the end-Triassic mass extinction around 200 Ma. The five major ancestral lineages underwent remarkable radiations during the Jurassic through early Cretaceous (200-100 Ma), providing a framework for the modern otophysan diversity when the Pangaean breakup produced humid tropical climates over the formerly arid interiors of the supercontinents.
The present timetree demonstrates that survival of the ancestral lineages through the two consecutive mass extinctions on Pangaea and subsequent radiations during the Jurassic through early Cretaceous shaped the modern familial diversity of otophysans. Pangaean origin and Mesozoic radiations of the modern otophysans are consistent with recent arguments based on biogeographic inferences and molecular divergence time estimates. No fossil otophysan, however, has been recorded before the Albian, the early Cretaceous 100-112 Ma, creating a >100 million year time span without fossil evidence. This formidable ghost range partially reflects a genuine difference between estimated ages of stem-group origin (molecular divergence time) and crown group morphological diversification (fossil divergence time); the ghost range, however, would be filled with discoveries of older fossils that can be used as more reasonable time constratints as well as with developments of more realistic models that capture rates of molecular sequences accurately.
Full paper here.
Masanori Nakatani, Masaki Miya, Kohji Mabuchi, Kenji Saitoh and Mutsumi Nishida.
BMC Evolutionary Biology 2011, 11:177.
Abstract:
Freshwater harbors approximately 12,000 fish species that correspond to 43% of all modern fish diversity. Surprisingly, a single ancestral lineage evolved into about two thirds of this enormous biodiversity ([almost equal to] 7900 spp. placed in four orders, 64 families and 1068 genera), and is currently distributed throughout the world's continents except Antarctica. Despite such remarkable species diversity and ubiquity, the evolutionary history of this major freshwater fish clade -- Otophysi -- remains largely unexplored. To provide an overview of the history of otophysan diversification, we constructed a timetree based on whole mitogenome sequences across 110 species representing 55 of the 64 families.
Partitioned maximum likelihood analysis based on unambiguously aligned sequences (9923 bp excluding quickly saturated third codon positions) confidently recovered monophyly of Otophysi and the two constituent subgroups (Cypriniformes and Characiphysi). Within the latter clade that comprises three orders (Gymnotiformes, Characiformes, Siluriformes), Gymnotiformes was placed as the most basal clade. One of the two suborders in Characiformes (Characoidei) was reproduced as more closely related to Siluriformes than to its own suborder (Citharinoidei), rendering the characiforms paraphyletic. This novel relationship, however, was confidently supported by the analysis of independent nuclear markers. A relaxed molecular-clock Bayesian analysis of the divergence times and reconstruction of ancestral habitats on the timetree suggest that a common ancestor of the Otophysi entered freshwater around the end-Permian (251 Ma) when mass extinction events dramatically altered the ecological structure of marine communities under super anoxic conditions. Subsequent basal divergences during the Triassic (251-200 Ma) on the supercontinent Pangaea successively produced five major lineages (common ancestors of the present-day orders or suborders) that survived the end-Triassic mass extinction around 200 Ma. The five major ancestral lineages underwent remarkable radiations during the Jurassic through early Cretaceous (200-100 Ma), providing a framework for the modern otophysan diversity when the Pangaean breakup produced humid tropical climates over the formerly arid interiors of the supercontinents.
The present timetree demonstrates that survival of the ancestral lineages through the two consecutive mass extinctions on Pangaea and subsequent radiations during the Jurassic through early Cretaceous shaped the modern familial diversity of otophysans. Pangaean origin and Mesozoic radiations of the modern otophysans are consistent with recent arguments based on biogeographic inferences and molecular divergence time estimates. No fossil otophysan, however, has been recorded before the Albian, the early Cretaceous 100-112 Ma, creating a >100 million year time span without fossil evidence. This formidable ghost range partially reflects a genuine difference between estimated ages of stem-group origin (molecular divergence time) and crown group morphological diversification (fossil divergence time); the ghost range, however, would be filled with discoveries of older fossils that can be used as more reasonable time constratints as well as with developments of more realistic models that capture rates of molecular sequences accurately.
Full paper here.
