Zebrafish Study on Hibernation

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According to recent research by Queen’s University Belfast in the United Kingdom, zebrafish’s hibernating habits may prove helpful for humans in Mars missions.

Zebrafish

  • Scientific Name: Danio rerio
  • It is a tropical freshwater fish belonging to the minnow family (Cyprinidae) of the order Cypriniformes.
  • Habitat/Range: Native to rivers and streams of South Asia.
  • Features
    • It is a popular aquarium fish.
    • It is about 4 cm long and has dark-blue and silvery longitudinal stripes.
  • IUCN Red List Status: Least concerned.
  • Significance
    • It is a good research stand-in for humans because of similarities in brain, heart, liver, kidneys.
    • Genome sequencing has shown that 84 per cent of the genes that cause disease in humans are also found in zebrafish.
    • Zebrafish embryos are transparent and develop outside the mother’s body, so scientists can manipulate genes to model human diseases and directly observe disease changes in live animals.
    • Also, these embryos absorb drugs added to the water they are in so they have been used successfully to discover possible new drugs.
    • So far, zebrafish studies have yielded insights into cancer, diabetes, muscle diseases, and more.
    • Also, their induced hibernation habits may prove helpful in space journeys and reduce their bad effects on human bodies.

(Image Courtesy: BBC)

About the Study

  • Researchers exposed zebrafish to radiations similar to that of a six-month journey to Mars.
  • The radiation caused signatures of oxidative stress, stress hormone signaling and halting of the cell cycle within the zebrafish.
  • Then they induced torpor (a form of hibernation with a state of reduced metabolic activity) in a second group of zebrafish exposed to the same kind of radiation.
  • They analysed their gene expression patterns to assess the protective effects during this induced state of physical or mental inactivity.

Findings of the Research

  • The results showed that torpor lowered the metabolic rate within the zebrafish and created a radioprotective effect, protecting against the harmful effects of radiation.
  • Replicating hibernation may therefore protect astronauts against the harsh conditions of space flights.
    • Long-term space travel is incredibly detrimental to human health and includes challenges such as radiation exposure, bone and muscle wastage, advanced ageing and vascular problems.
  • Significance: The research gives insights into how a reduction in metabolic rate could offer protection from radiation exposure and could help humans achieve hibernation, counter measuring the damage they currently face during spaceflight.
  • Effects of Hibernation 
    • Humans hibernating on space flights would lead to reduced brain function which would cut down on psychological stress.
    • The change to their metabolism would stop them requiring food, oxygen or water.
    • There was also a possibility it would protect their muscles from wasting due to the effects caused by radiation and microgravity.

Hibernation

  • It is a physiological condition or a state of greatly reduced metabolic activity and lowered body temperature adopted by certain mammals as an adaptation to adverse winter conditions.
  • It is a means of energy conservation and protects against harsh conditions, such as food scarcity and low environmental temperatures.
  • While hibernation is most often seen as a seasonal behavior, it is not exclusive to cold-weather as there are tropical hibernators as well, who go in Aestivation.
  • Factors Responsible
    • Temperature
    • Food Shortages
    • Protection (Hibernating animals do not make any noise or movements, hence are hard to detect for predators).
  • Variety of amphibians, reptiles, insects and mammals hibernate. There are cases noticed even in birds and fish as well.
  • The hibernator relies on a combination of reserve body fat, stored food supplies (in rodents only) and a protected den.
    • At intervals of several weeks the animal elevates its body temperature, awakens, moves about, feeds, and then returns to its state of torpor.
  • Such animals which do not undergo much lowering of body temperature and are rather easily awakened, are not considered true hibernators.
  • True Hibernators
    • They spend most of the winter in a state close to death.
    • Body temperature is close to 0° C (32° F)., the respiration is only a few breaths per minute and the heartbeat is so slow and gradual as to be barely perceptible.
    • Among mammals, true hibernators are found only in the orders Chiroptera (bats), Insectivora (hedgehogs and allies) and Rodentia (ground squirrels, marmots, etc).
  • Exposed to moderate warmth, the animal slowly awakens, requiring an hour or more to reach an alert state.
  • Threats: Animals may die during hibernation from lack of fat, severe weather or premature awakening.

Related Practises

  • Aestivation
    • This is the equivalent process to hibernation, but for animals in hot climates that are trying to escape extreme heat or drought.
    • Many terrestrial and aquatic animals aestivate including lungfish, earthworms, snails, amphibians and reptiles, including Nile crocodiles.
    • They bury themselves in the ground, which protects them from the heat and they wait for the wet season or cooler temperatures.
      • Some land snails climb trees to escape the heat of the ground, sealing themselves into their shells using dried mucus.
    • However, there is a danger of large numbers of aestivating animals perishing in periods of prolonged drought.
  • Torpor
    • It is a brief period of suspended animation, usually lasting less than a day, when an animal’s breathing, heartbeat, body temperature and metabolism are reduced.
    • It conserves energy in the short term and often helps the animal survive a brief time of poor conditions, such as cold nights.
    • Birds such as hummingbirds and frogmouths, or small mammals such as bats, can go into torpor every day.
    • One of the problems with torpor is that the animals are too sluggish to react to predators and if the cold is unusually long, the animal may die if its body temperature drops too low.
  • Denning
    • It is a light form of dormancy typical of bears, where the animal is groggy, but easily roused.
    • A bear’s body temperature only drops a few degrees, but it loses up to 40 per cent of its body weight, which is more than true hibernators.
      • Amazingly, many female bears give birth and suckle young while denning.
    • Bears can be woken easily during a mild spell of weather, but may not have enough energy to survive the rest of the winter.

Source: DTE