Study Shows Seahorse Ancestors Stood Upright
A new study indicates that the ancestors of seahorses likely stood upright some 20 to 25 million years ago, when the expanse of ocean between Australia and Indonesia was much shallower and full of sea grass.
In the most recent edition of Royal Society Biology Letters, researchers explain that upright posture ““ an exceedingly rare occurrence in the animal kingdom ““ was adopted some time during the Miocene epoch and allowed seahorses inhabit what was essentially a shallow underwater lawn.
The researchers noted that the atavistic behavior of modern seahorses ““ which still tend to reside in sheltered areas, such as beds of sea weed and coral reefs ““ corroborates their theory.
“Not only can an upright fish maneuver much better in such an environment than a horizontally-swimming one, but the upright sea grass blades would have improved their camouflage,” explained co-author of the research project Peter Teske, a postdoctoral researcher at Macquarie University’s Molecular Ecology Lab.
“Camouflage is of great importance to seahorses, which are poor swimmers,” he added. “It affords them both protection from predators and allows them to sneak up on their prey ““ including small crustaceans and tiny fish ““ without being noticed.”
Teske and his colleague Lucian Beheregaray’s research began when they started to question the origins of a small “non-upright proto-seahorse” known as the pygmy pipehorse. They wanted to find out when these small bony fishes diverged from their seahorse cousins and how this split fit into the bigger evolutionary picture of the Syngnathidae, the family of fish that includes seahorse, pygmy pipehorses and sea dragons.
Comparing genetic information between the genera Hippocampus and Idiotropiscis, which includes all seahorses and pipehorses respectively, they began to construct a phylogenetic family tree.
Molecular dating techniques point to a divergence of the pygmy pipehorses somewhere during the Late Oligocene period, just as shifting tectonic plates in the Indo-West Pacific oceans was creating vast expanses of shallow-water sea grass beds. From the data, researchers hypothesize that seahorses limited themselves to this new habitat and as a result were developed a number of peculiar characteristics.
“Seahorses are often considered to be highly unusual bony fishes because of their upright posture, their hard exoskeleton, their long suction-snout, their prehensile tail and the fact that it’s the males that give birth,” said Teske.
Male bony fishes in general tend to be exceptionally attentive fathers when compared to other members of the animal kingdom. None, however, comes close to comparing with amount of paternal attention that seahorse fathers lavish on their young.
“The most advanced form of male parental care is found in the seahorses, where a brood pouch has evolved that resembles a placenta, and male seahorses even go into labor!” explained Teske.
Both male and female seahorses have evolved tails that allow them to grip vegetation, while of number of them have also developed bizarre anatomical extensions that resemble plants and make for highly effective camouflage.
The beauty and oddity of seahorses have, unfortunately, made them a favorite collector’s item for divers, and eight of the 34 known sub-species have made their way onto the International Union for Conservation of Nature’s “Red List” of threatened species.
“So little is known about seahorses that we are at risk of losing these animals before we even know them,” said Ava Ferguson, senior developer for “The Secret Lives of Seahorses” exhibit in Monterey Bay Aquarium in California. “Until recently, we had no idea that seahorses were being caught and collected at a rate that threatens their survival.”
Ferguson is confident, however, that conservation efforts to protect rare aquatic environments will prove successful in revitalizing dwindling seahorse populations.
“When you save a seahorse, you also save some of Earth’s most precious marine habitats.”
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