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The Dosidicus gigas, commonly known as the jumbo squid, has adapted amazing to extremely low oxygen levels in the Eastern Pacific Ocean. This apex predator exhibits the extraordinary ability to function with very low levels of oxygen via metabolic suppression.
Suppression of metabolic activity increasingly becomes a necessity in the Eastern Pacific Ocean as pollution continues to deoxygenate its waters. Without proper oxygen supply, most organisms become sluggish and sick. This state called hypoxia frequently hospitalized people. For example, people dealing with COVID respiratory issues often end up hospitalized because proper oxygen is not supplied to their muscles. Yet, the jumbo squid lives in perpetually hypoxic conditions and functions well.
In a study titled Metabolic suppression during protracted exposure to hypoxia in the jumbo squid, Dosidicus gigas, living in an oxygen minimum zone, a team of biologists investigated the metabolic levels and oxygen consumption rate of these deep sea creatures. In their experiment, Dosidicus gigas organisms were exposed to normal and subcritical oxygen levels. Factors like total metabolic rate, oxygen consumption, metabolite number, and gene expression were taken into consideration.
Metabolism is defined as the sum of total chemical reactions in an organism's body. Adult jumbo squid were discovered to function at nearly half (52%) metabolic functions while still actively swimming and hunting. ATP acts as the key player of all metabolic reactions, known also as the body’s energy currency. Jumbo squids can fully function at 30% of its normal ATP levels. This animal is able conserve energy by suppressing energy expensive reactions like protein synthesis.
By shutting down energy expensive cellular activities like biosynthetic pathways and ion pumping hypoxic environments become tolerable. This squid primarily adapts via post-translational modifications to histones as well as an array of transcription factors.
Jumbo squids displayed specific cellular changes allowing metabolic suppression. Chromatin condensation occurs during hypoxic conditions. Condensed chromatin is harder to duplicate, therefore, the rate of transcriptions is significantly lower. Histones condensate DNA, making it less accessible to initiating transcription factors. Lysine acetylation neutralizes DNA’s histone tails which lowers is affinity. Post transcriptional effects like phosphorylation and acetylation of histone tails enhance the rate of transcription. This experiment found a 74% decrease is phosphorylation and acetylation on histone H3. All these factors lower translational activity and therefore lower ATP demand.
Other animals show metabolic suppression, but the jumbo squid is a rare species that is not sluggish during metabolic suppression. For example, goldfish can be exposed to deoxygenated waters if its owner forgets to change the fishbowl water. The goldfish’s behaviour becomes slow, drifty, and inactive. Dosidicus gigas behaviour remains relatively just as active as under normoxic conditions.
The jumbo squid’s ability to thrive with very little oxygen enhances its survival. Their hunting range can reach deeper levels than other predators, meaning they have the advantage to reach more prey. Jumbo squids can even stay extended periods in the ocean’s Oxygen Minimum Zone (OMZ). The depth pattern this species shows closely matches its key food source, the myctophid fish.
Survival in the increasingly deoxygenating Eastern Pacific Ocean demands the ability to metabolically suppress while functioning successfully. If pollution does not reverse, then the ocean will become even more acidic and continue deoxygenating. As a result, the jumbo squid might need to reach deeper oceanic levels as its food source becomes depleted.
Source:
Seibel, B. A., Trübenbach, K., Häfker, N., Zhang, J., Tessier, S. N., Rosa, R., & Storey, K. B. (2014). Metabolic suppression during protracted exposure to hypoxia in the jumbo squid, Dosidicus gigas, living in an oxygen minimum zone. Retrieved March 20, 2021, from https://jeb.biologists.org/content/jexbio/217/14/2555.full.pdf
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