Molecular adaptation in a deep-sea alien…*ahem* amphipod

Space: the final frontier…or is it? I was inspired Jeremy’s post yesterday to talk about that deep dark abyss that takes up the vast majority of our mostly blue planet. For the record, I’m in agreement with the assessments for the marine (micro)biologists. After perusing images of the critters down there, you might wonder if it’s not more interesting (or at least equally interesting) to dive deep under the ocean to see what might be the closest to aliens we can currently get (discussed recently here). One glimpse of a goblin shark (maybe kinda scary for some kids) or anglerfish, should convince you.

Image from The Conversation: Inspiring aliens since 1979

In fact, some of the amazing creatures that call the ocean depths “home”, were likely the inspiration for the design of the original creatures in Alien (see here, here, or even here). These articles suggest, organisms of the genus Phronima, a group of deep sea hyperiid amphipods (a suborder of amphipods only found in the marine environment) were the first Alien. As you can see from these images, they have amazing eyes, and they also might remind you of their distant shrimp cousins.
One of the craziest things about the organisms that inhabit the deep sea is that they can survive there at all. On average, the ocean is about 3.6 kilometers deep (2.3 miles, for those non-kilometer inclined) with the Mariana Trench the deepest location in any ocean, the max depth of 10,994 meters is found in a valley of the trench is known as the Challenger Deep, discovered in 1875. To survive at high hydrostatic pressure, low temperature, completely in the dark, and not to mention with limited food, any life at such a nutty location likely must have distinct adaptations. One of these unique organisms is Hirondella gigas, an amphipod that apparently loves all of those hardships, as it’s endemic to multiple hadal (term for the zone anywhere from 6,000 to ~11,000 meters deep) trenches in the Pacific Ocean including Challenger Deep.
“Overall, our results indicate that genetic adaptation to the hadal environment by H. gigas may be mediated by both gene family expansion and amino acid substitutions of specific proteins.”
In a study recently published by Lan and colleagues in Molecular Ecology, they explore the transcriptome of H. gigas collected from 10,929 meters in the Challenger Deep. By closely analyzing these data, and comparing them to transcriptomes of shallow-water amphipod species, the authors found evidence for how H. gigas has genetically adapted to live in the deepest place in the ocean.
“In conclusion, our work identifying positive selection and gene family expansion within H. gigas has provided new insights into molecular adaptation to the hadal trench environment.”
In particular, the authors observed positive selection in the gene encoding replication factor A1 (RFA1) which is known to assist in DNA replication and repair, and so might be helpful for dealing with life at high hydrostatic pressure. They also identified other unique characteristics in the transcriptome which suggest that H. gigas is adapted to deal with freezing cold temperatures, since various cold shock proteins were found to be under positive selection.
It’s constantly more apparent how helpful molecular tools are in unraveling evolution. Studying unique model organisms that inhabit the extreme environments on this planet provide an interesting window into the molecular side of adaptation. This study was able to explore the transcriptome of an amphipod that inhabits the Challenger Deep. Not bad, for humans.
Lan, Y., Sun, J., Tian, R., Bartlett, D.H., Li, R., Wong, Y.H., Zhang, W., Qiu, J.W., Xu, T., He, L.S. and Tabata, H.G., 2017. Molecular adaptation in the world’s deepest‐living animal: Insights from transcriptome sequencing of the hadal amphipod Hirondellea gigas. Molecular Ecology.

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