close-up of tiger tail seahorse

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The genes that make seahorses so weird

Seahorses are bizarre little ocean anomalies, from their tube-shaped snouts to their prehensile tails. Perhaps their most unusual trait: It’s the males that give birth. Now, for the first time, a research team has begun to investigate the genetic basis for these evolutionary oddities, by sequencing and analyzing the genome of a male tiger tail seahorse (Hippocampus comes) and comparing it with the DNA of other bony fish species. The seahorse species, the team reports today in Nature, evolved at a faster rate than its ancestors, leading to key genetic changes. For example, the tiger tail lacks most of the genes that influence enamel development; instead of teeth, its jaws have fused into a tubular snout and tiny mouth, suitable for slurping up food from the sea floor. And although most fish depend on their sense of smell for survival, H. comes has relatively few smell-related genes. The tiger tail and related seahorses also lack the genes for pelvic fins—which might explain their elongated tails and bony body armor. But H. comes does have an abundance of one gene: Dubbed Pastrisacin, the gene is associated with male pregnancy, and the seahorse genome contains six copies of it