Energetics
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Metabolic scaling relationships
Behavioral thermoregulation
Torpor and hibernation
Fat storage
Migration
Biological clocks
Discussion Readings
• Kortner, G. and F. Geiser 2000 The temporal
organization of daily torpor and hibernation: circadian and
circannual rhythms. Chronobiology International 17:103128.
• Geiser, F. and R.M. Brigham 2000 Torpor, thermal
biology and energetics in Australian long-eared bats
(Nyctophilus) J. Comp. Phyiol. B 170:153-162.
• Park, K. J., G. Jones, and R. D. Ransome. 2000. Torpor,
arousal and activity of hibernating Greater Horseshoe Bats
(Rhinolophus ferrumequinum). Functional Ecology
14:580-588.
Aerobic respiration
• Occurs in mitochondria of all aerobic organisms
• Glucose + oxygen + water =>
carbon dioxide + water + energy
• C6H12O6 + 6O2 + 6H2O => 6CO2 + 12H2O + energy
• Energy is stored by converting ADP -> ATP
• 1 mole of glucose contains 670 kcal
• Consequently, oxygen consumption can be used to
measure energy production
Energetics of homeothermy
Homeothermy: maintain constant
warm body temperature. Most
mammals are at 35-39oC
Heterothermic: allow body temp
to fall with ambient temperature
Animals must spend energy to
keep warm or cool off when the
ambient temperature is out of
their thermal neutral zone
Energy expenditure in the western
pipistrelle (Pipistrellus hesperus)
Thermal conductance
Heat conduction occurs when
there is a temperature difference
between body and air.
Depends on surface area of animal.
Measured as the amount of energy
needed to maintain that difference.
Note that small mammals have
high conductance due to high
surface area to volume ratios.
Bats have higher conductance than
other mammals due to large lungs
and large wing membranes
Log-log plot
Metabolic rate scales with body mass.75
Note: if y = aMb then
log y = log a + b*logM
If b < 1, then y increases
slower than M
If b > 1, then y increases
faster than M
Therefore, mass specific metabolic rate
declines with body size in birds and mammals
Nonflying eutherian mammals
Diet influences metabolic rate
Reasons for energy budget fluctuations
Availability - e.g.
seasonality
Demand - e.g.
pregnancy
Both - e.g.
winter, night
Lactation is costly
Roost selection
Behavioral thermoregulation
Nycticeius humeralis
Evening bats
Phyllostomus hastatus
Greater spear-nosed bats
Torpor is a reduction in body temperature
Torpor saves energy
Energy use increases
linearly as ambient
temperature decreases for
an active animal that
maintains a constant body
temperature
Arousal from torpor can be expensive
Hibernation = long torpor
Ground squirrel maintained at 4oC
Hibernation
has evolved
twice in bats
and has
allowed some
species to
occupy cold
climates
Vespertilionidae
Rhinolophidae
Hibernacula temperature preferences
During hibernation bats
maintain body
temperature about 1oC
above ambient, but
rarely below 6oC
Some bats move north to hibernate
Gray bat (Myotis sodalis)
Bats rarely roost deep in caves
because the temperature is too
warm. Consequently, they
have to move when it gets cold
or warm outside. This makes
them vulnerable to disturbance
during hibernation.
Body weight during hibernation
Bats can arouse faster than other hibernators
a =ventral temperature, b = rectal temperature
Due to nonshivering thermogenesis
Myotis myotis
Brown adipose tissue (BAT)
contains fat cells with many
blood vessels and mitochondria
which gives the tissue a brown color.
When BAT is oxidized, the blood
is heated quickly.
BAT seasonal accumulation
Myotis californicus
Migration
permits other
species to
occupy
temperate
regions
Molossidae
Phyllostomatidae
Temperate migration patterns
Nyctalus noctula
Noctule
Lasiurus cinereus
Hoary bat
Migration routes of lesser longnosed bats (Leptonycteris curasoae)
Feed on cactus going north, agave going south
Biological clocks
• Clock periods
– Circannual
– Circalunidian
– Circadian
• Clock Entrainment
Hibernation follows annual rhythm in
golden-mantled ground squirrels
Five animals were isolated at birth and kept in darkness at 3oC
Circannual clocks in bats
Testes growth and
feather molt in
stonechats follows
annual cycles
Qu ickT ime™ an d a T IFF ( Unco mpr esse d) de com press or a re ne eded to s ee th is pi cture .
Nestlings were removed from Kenya
and reared in Germany with constant
temperature and photoperiod and yet
retain annual molt and testes cycles.
Notice that the clock period drifted.
Kangaroo rat
feeding shows
lunar cycles
K-rat activity at a
feeder is confined to
dark periods
Quic kT ime™ and a T IFF (Unc ompres sed) dec ompres sor are needed to see this pic ture.
occurred during period
of seed shortages
Vampire bats also avoid
moonlight
Entrainment by environmental cycles
• Environmental cues set cycle period
– Species specific
• Types of cues
– Photoperiod
– Light pulse
– Food availability
Mouse activity entrains to light
12h light:12h dark
24 h dark
10 min light
10 mins of light per day are sufficient to reset the clock
Frequency of flights
within a cave by
Myotis
Note that bats show strong
circadian rhythm before and
after winter
Distribution of
circadian clocks in
tissues and taxa
Mammalian
clock
pathways
Clock summary
• per/tim/tau(dbt) genes control pacemaker
• Pacemaker occurs in SCN (suprachiasmatic nucleus) in
vertebrates, but is distributed in brain cells in some
insects
• SCN signals pineal gland to release melatonin
• Short pulses of light entrain SCN and pineal cells
• Drosophila, honey bees, hamsters and humans share same
genes - likely common ancestor was a flatworm that lived
about 600 MYA