Hypoxia inducible factors: Indicators of hypoxia in Lake Erie fauna

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Hypoxia inducible factors Indicators of hypoxia
in Lake Erie fauna

• Betsy Bodamer
• Aquatic Ecology
• December 7, 2007

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Outline

• Hypoxic Inducible Factors
• What are they anyway?
• How have they been used so far?
• Lake Erie Hypoxia and Fauna
• Lake Erie stratification/hypoxia
• Hexagenia burrowing mayfly
• Yellow Perch
• Research questions

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What is a Hypoxic Inducible Factor?

• a.k.a. HIF-1
• DNA binding protein
• heterodimeric transcription factor
• Two different subunits - a and ß
• a subunit unstable and degrades under normoxia
• HIF-1a activates transcription of a number of
  hypoxia-induced genes

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What is a Hypoxic Inducible Factor?

• VEGF enhances proliferation of blood vessels
  for increasing oxygen supply
• Glucose Transporters enhance glucose transport
• Enolase enhance glycolysis and glucose uptake
• Varity of glycolytic enzymes
• In mammals and fish EPO gene transcription
  enhances red blood cell production

• In summary During hypoxic conditions, HIF-1a
  increases
• Glycolysis (ATP production)
• Erythropoiesis (red blood cell production)
• Angiogenesis (blood vessel production)

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HIF -1a Applications

• HIF-1 has been identified in mammalian, fish, and
  insect species.
• Fish Mainly used as a measurement of hypoxic
  response in toxicology studies
• Effect of copper exposure in rainbow trout (Van
  Heerden et al. 2004)
• PCB exposure on killifish (Kraemer and Schulte
  2004)
• TCDD (dioxin) exposure on zebrafish (Prasch et
  al. 2004)
• Insects Identified in dipteran insects
• Drosophila melanogaster (Arquier et al. 2006)
• Gall Fly (Morin et al. 2005)
• Few ecological studies

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HIF -1a Applications

• Take Home Message
• These proteins accumulate in cells under hypoxic
  or anoxic conditions.
• HIFs respond quickly to hypoxic exposure
• Degrade under normoxia
• Quantifiable
• Therefore, HIFs are a useful tool in measuring
  physiological and/or behavioral responses to
  hypoxic conditions in ecological studies.

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Lake Erie Hypoxia Fauna

• Summer stratification
• Hypoxic hypolimnetic waters

Benthic Invertebrates Burrowing mayfly
Benthic Feeding Fish Yellow Perch
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Hexagenia vs Hypoxia
(Bridgeman et al. 2006)
Even brief periods of hypoxia can be detrimental
to mayfly nymph populations.
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Bobbing for benthos?
25 miles
12 Feet
(Bridgeman)
Yellow perch have been caught in nets in severely
hypoxic waters (Hasler 1945, Hubert and
Sandheinrich 1983, and Bodamer personal
observation)
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• Previous research has shown that fish
  (mudminnows) are capable of diving into hypoxic
  water in order to feed upon benthic invertebrates
• Ingested air bubbles?
• Gas bladder?
• Regardless of surface access
• Anaerobic metabolism
• Hypoxic waters may not always provide refuge from
  predation
• (Rahel and Nutzmann 1994)

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The main question...

• Can HIFs be used to measure...
• the duration of exposure to hypoxic conditions
  experienced by Lake Erie yellow perch and
  hexagenia mayfly nymphs?
• the physiological and behavioral responses to
  hypoxia by Lake Erie yellow perch and hexagenia
  mayfly nymphs?

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Physiological questions

• Can a relationship between HIF-1a and duration of
  exposure to hypoxia be constructed via lab
  experiments?
• Can this relationship be used to accurately
  estimate the amount of time spent foraging in
  hypoxic conditions within the hypolimnium (as
  opposed to normal conditions above the
  thermocline) by yellow perch?
• ...or the amount of time mayflies are exposed to
  hypoxia?

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Behavioral Questions

• If yellow perch are not diving to the benthos for
  food, how are they acquiring this resource?
• Feeding above
• Temporarily move out of the dead zone?

25 miles
(Bridgeman)
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Behavioral Questions

• Is there a threshold concentration of HIF at
  which mayfly nymphs abandon their benthic tunnels
  to move to more suitable conditions?
• And hence a threshold exposure to hypoxia?

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Any Questions?