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How Did the Seahorse Get its Shape?


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This is a Guest Post by Stephanie Yin, a graduate of Brown University with a degree in environmental science. Yin is interested in using all forms of multimedia storytelling to convey contemporary science.

Seahorses are distinct fish, not least because they swim vertically rather than horizontally. This video examines how seahorses might have evolved this unusual upright stance. Much of our detective work on seahorse evolution comes from studying living pipehorses and pipefishes, with which seahorses share a common ancestor. When scientists Peter Teske and Luciano Beheregaray compared the genes of seahorses with those of pygmy pipehorses, they found that the two groups diverged during the Late Oligocene. This led them to connect tectonic events of that time with evolutionary benefits that an upright posture might have conferred onto primitive seahorses. Most notably, the collision of Indo-Australia with Eurasia led to the expansion of shallow seagrass beds — in which fish that could swim “standing up” would have been better suited to camouflage among vertical seagrass blades.

Scientist Sam Van Wassenbergh wondered if this upright orientation might also have contributed to the seahorses’ adoption of ambush hunting. While pipefishes actively pursue their prey, seahorses employ a very different method – they grip onto a blade of seagrass and passively wait for their prey to approach them. Turns out, this strategy is actually extremely effective, and seahorses are among the fastest feeders of aquatic vertebrates. To learn more, Van Wassenbergh and his colleagues explored the biomechanics of seahorse and pipefish feeding, and found some striking results.

These experiments tell an elegant story of evolution that connects morphology, environment and survival strategies. We see how the broad movement of tectonic plates can influence the morphology and behavior of a specific group of creatures. They also shed light on how, in the absence of a fossil record, we can still study recent evolution events by comparing extant species that share common ancestors. Put all together, the unique characteristics of the seahorse’s shape hold important lessons on how and why creatures evolve the way they do.

References:

How the Seahorse Got its Shape. Nature Video, 2011. Web. .

Teske, Peter R., and Luciano B. Beheregaray. “Evolution of seahorses’ upright posture was linked to Oligocene expansion of seagrass habitats.” Biology letters 5.4 (2009): 521-523.
Van Wassenbergh, Sam, Gert Roos, and Lara Ferry. “An adaptive explanation for the horse-like shape of seahorses.” Nature Communications 2 (2011): 164.

Carin Bondar About the Author: Carin Bondar is a biologist, writer and film-maker with a PhD in population ecology from the University of British Columbia. Find Dr. Bondar online at www.carinbondar.com, on twitter @drbondar or on her facebook page: Dr. Carin Bondar – Biologist With a Twist. Follow on Twitter @drbondar.

The views expressed are those of the author and are not necessarily those of Scientific American.





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