Genome sequences reveal global dispersal routes and suggest convergent genetic adaptations in seahorse evolution

Seahorses have a circum-global distribution in tropical to temperate coastal waters. Yet, seahorses show many adaptations for a sedentary, cryptic lifestyle: they require specific habitats, such as seagrass, kelp or coral reefs, lack pelvic and caudal fins, and give birth to directly developed offspring without pronounced pelagic larval stage, rendering long-range dispersal by conventional means inefficient. Here we investigate seahorses' worldwide dispersal and biogeographic patterns based on a de novo genome assembly of Hippocampus erectus as well as 358 re-sequenced genomes from 21 species. Seahorses evolved in the late Oligocene and subsequent circum-global colonization routes are identified and linked to changing dynamics in ocean currents and paleo-temporal seaway openings. Furthermore, the genetic basis of the recurring bony spines adaptive phenotype is linked to independent substitutions in a key developmental gene. Analyses thus suggest that rafting via ocean currents compensates for poor dispersal and rapid adaptation facilitates colonizing new habitats. A new seahorse genome and the re-sequenced genomes of 21 other species shed new light on the evolutionary origin and global dispersal routes of seahorses, and show that bony spines-a key adaptation against predation-probably evolved multiple times via independent substitutions in the bmp3 gene.

Automated summary

Seahorses have a global distribution in tropical to temperate coastal waters and show many adaptations for a sedentary, cryptic lifestyle. New genome assembly and re-sequenced genomes of 21 other species shed light on the evolutionary origin and global dispersal routes of seahorses, revealing that rafting via ocean currents compensates for poor dispersal and bony spines likely evolved multiple times through independent substitutions in a key developmental gene.