Fig. 2: Colonization and demographic history of seahorses.
a Phylogenetic tree and divergence time estimates for 21 seahorse species. The branch line thickness corresponds to the population size estimates (Ne) and colors indicate different lineages. Symbols I–III indicate calibration points. b–d Predicted colonization routes (colored arrows) of seahorses based on divergence time, distribution, vicariance events, and ocean currents (white arrows). Maps modified from Ron Blakey © 2016 Colorado Plateau Geosystems Inc (License # 60519). b The Indo-Australian Archipelago was the center of origin (red marking) of the genus Hippocampus before seahorses diversified and dispersed globally 18–23 Ma. c Seahorses initially colonized the Atlantic Ocean through the opening Tethyan seaway, which, after its closure (Terminal Event during 7–13 Ma), separated this Tethyan lineage from its Indian Ocean sister lineage. The latter, subsequently rapidly diversified (yellow marking) in the Arabian Sea, establishing a second center of seahorse diversification. d A second seahorse colonization event of the Atlantic Ocean occurred from the Indian Ocean about 5 Ma by passing the South African tip, and finally arriving in the East Pacific Ocean through the still open Panama seaway approximately 3.6 Ma. Source data are available at Figshare (Datasets 4–6).
