Download LOSER: Antarctic Notothenioid Fishes

LOSER: Antarctic Notothenioid
Fishes
by: Priscilla Watson-Wynn
Antarctica
•
•
•
•
•
•
•
•
•
Fifth largest continent
The world’s most southern
continent
Surrounded by Southern
Ocean
98% covered in ice sheet & 2%
barren rock
Highest average elevation
Water temperatures between
-1.9° - 2°C
Ice temperatures between -28°
- 3°C
Desert environment
Cold adapted organisms - cold
yet thermally stable
environment
- highly stenothermal
Antarctic Circumpolar Current
• Ocean current that flows clockwise isolating Antarctica from
warmer ocean temperatures
• Allowed ice to form on land and surrounding sea
• This current created the Antarctic Polar Front that reinforces the
extremely cold waters that surround continent
• Has allowed 30 millions years of evolutionary adaptions for cold,
arid climate
Climate Change and Antarctic Peninsula
- Warming 5.4 times the
global average
- Waters surrounding the
West Antarctic Peninsula
are warming faster than
the worlds other oceans.
- have risen ~ 1°C in the
past 50 years
- predicted to rise
another 2°C in the coming
century
- Changes in marine
environment becoming
evident
- such as species
distribution and abundance
which result in community
and food web shifts
Ozone hole
• Largest on record
• Average
thickness is
about 300
Dobson units
• Increased
ultraviolet light
can damage DNA
of Antarctic
organisms
especially
Antarctic ice
fishes
Notothenioid= Antarctic ice fishes
•
Belongs to
perciform suborder
Notothenioidei
• Channichthyidae
family with no
hemoglobin
• Dominant fish fauna
in terms of species
and biomass
• Unique in that they
are the only known
vertebrate that
have no circulating
hemoglobin, oxygen
binding protein, as
adults
- many species
within family also don’t
express myoglobin
Notothenioid fishes and evolution
• Their success in Antarctic
environment due to special
blood-borne antifreeze
glycoproteins
- prevents freezing of body fluids
by absorbing small ice crystals and
inhibiting their growth
• This novel ice binding protein
found to be evolved from
pancreatic trypsinogen
• There is a small sequence
divergence in the two genes
which tells us that transformation
of the gene happened 4-15 mya
which correlates to the estimated
time Antarctica started freezing
Protein evolution and
organismal adaptations
to environmental conditions!
Chen et al., 1997
Nototheniod fishes adaptations to
colder climate
• Larger and more extensive
vasculatures, greater blood
volumes, larger hearts, and more
numerous cardiac mitochondria
compared with similar sized red
blooded notothenioids
• Combination of high- throughput
circulatory systems, low absolute
metabolic rates, and the well
oxygenated waters of Southern
Ocean allow these fish to get
enough oxygen
… downside
• Loss of hemoglobin has
resulted in higher energetic
expense to the circulatory
system
• Loss of myoglobin (in some
species) has resulted in
decrease in cardiac
performance
• Oxygen carrying capacity of
ice fishes is 10% less than
that of red blooded fishes
• Lost genes to cope with
higher temperatures like
turn on heat shock proteins
As temperatures rise…
• Warmer water holds less dissolved oxygen,
thus there will be less oxygen available to ice
fish with no hemoglobin
• This will result in metabolism increase creating
a mismatch between oxygen supply and
demand
- aka hypoxia
Thermal Tolerance of Antarctic
Notothenioid Fishes Correlates with
Level of Circulating Hemoglobin
( Beers,J.,Sidell,B., 2011)
• Evaluate whether thermal tolerance limits
correlate with readily accessible metrics of blood
oxygen- carrying capacity (e.g., hematocrit) of
both white and red-blooded species
• Assess the capacity of a notothenioid species
(Notothenia coriiceps) to adjust thermal limits in
response to 1 week exposure at a modestly
increased environmental temperature of 4°C
Methods
• Five species of Antarctic notothenioid fishes from Antarctic peninsula,
April-May 2007 and 2009
- Chaenocephalus aceratus, Chionodraco rastrospinosus, Notothenia
coriiceps, Gobionotothen gibberisfrons, Lepidonotothen squamifrons
• Thermal tolerance experiments
-Temperature was elevated acutely from ambient temperatures at a
constant rate of 3.6°C h-1
- CTmax defined as the temperature where animals lost righting response
(LRR)
-exposed a group of N. coriiceps at 4°C for 1 week
• Drew blood from fishes to determine plasma lactate concentration
• Total RNA was extracted from brain, heart, and pectoral muscle tissue of
C. rastrospinosus and N. coriiceps
- measure the mRNA levels for two hypoxia-inducible genes, HIF-1α and
PHD2
Results: Thermal tolerance is directly
correlated with hematocrit
-N. coriiceps one week
exposure to 4°C had no
effect on Ctmax
indicating and inability
to compensate for
rising temperatures, at
least under
experimental
conditions
Figure 1
• In previous research
found that
hematocrit is closely
correlated to the
expression of
hemoglobin in these
species
Results: Effect of acute temperature
elevation on hematocrit and plasma
lactate
Figure 2
Figure 3
Results: Effect of acute temperature
elevation on mRNA levels of hypoxiaFigure 4: red- blooded
Figure 5: white- blooded
inducible genes C. rastrospinosus
N. coriiceps
Are Antarctic ice fishes “losers” of
climate change?
• Results suggest that ice fishes are
sensitive to temperature changes
because of their lack of
hemoglobin making them very
stenothermal
• Insufficient supply of oxygen to
tissues that results in increase in
temperature may lead to
limitations in cardiovascular
physiology
• Will be vulnerable to effects of
global warming which may have
consequences in physiological
performance, geographic
distribution and species survival
• will act as a canary in a coal mine
for climate change