BIOB32 Weeks 9-10 Notes
Week 9 - Factors Influencing the Cost of Locomotion
There is a negative allometric relationship between body mass and metabolic rate
possibly due to the cost of locomotion
smaller animals spend more energy moving around the environment
The Cost of Locomotion:
depends on:
metabolic rate (P) - power
body mass (W)
speed (V)
since time is eliminated, speed is not important: animals can move at “natural speeds”
P/(WxV)
Killer Whales:
cost of transport changes with speed
at slow speeds, their costs are very high
so on a regular, they probably choose to swim faster to be at low cost
Cost of transport can change within a species
so when comparing cost of transport, we tend to use minimum cost to compare
Horses:
evolve different ways of moving through the environment at different speeds
for overall low cost of locomotion
for example, at some point it is easier to run than to speed walk
running and walking is different ways of moving the leg muscle
at different speeds, walking really slowly is inefficient as it is very costly
as speed increases, O2 consumption decreases and then increases again at a speed to high, at which it is more efficient to trot than to speed walk
walking and trotting intersect at a certain time it is more expensive to walk at that speed than to trot
Knut Schmidt-Nielsen
first to bring up the idea that cost for locomotion was variable
father of comparative animal physiology
desert fox has large ears
its better to dissipate heat through their body
large surface area
efficient for the hot environment
opposite to arctic fox that must retain heat so it has small ears
Most cost of locomotion studies use a controlled environment
A study on goats put trackers on the organisms to test in natural environment
linear paths vs. curved paths
as speed increases, cost decreases
angular velocity is how much the organism is turning
as angular velocity increases, the cost also increases
turning is costly → more costly to cover distances if you have to turn
Swimming is the cheapest, flying is second cheapest and running/walking is the most expensive way to move around
Center of mass - where the body’s mass is most concentrated
ex. if the center of mass is in the human gut, you must use a lot of energy to prevent that part from falling to the ground due to gravity
walking/running animals spend energy to keep their center of mass off the ground, which is why the cost of locomotion is so high
if leg muscles cannot produce enough force and spend energy to keep your center of mass of the ground, you will end up on the ground
Runners must overcome gravity
Fliers
do not need to overcome gravity entirely through muscular action, can also rely on lift
flap wings down to produce lift, which requires energy
or passively (without energy) because the wing is structured in a way that air flows more rapidly above than below the wing
lifts the animal up without using energy
The faster moving air produces less pressure than the slower moving air, causing the wing to lift toward the area of low pressure.
Swimmers
gravity tries to pull them to the floor of the ocean
drag - there more resistance to movement in water than in air
it is easier to move your hands in air than in water
buoyancy is the upward force that acts on objects submerged in fluid
air offers a little buoyancy
water offers free upward force (water exerts a strong upward force)
yes drag is important but no way near as important as overcoming gravity
a fish that experiences more drag will have a higher cost, but no where as costly as a flier or runner of same size
counteracts the downward pull of gravity, allowing objects to float or appear lighter in a fluid
Movement:
powered by muscle contraction
Myosin ATPase uses ATP to contract
Ca-ATPase uses ATP to pump Ca back out of the cytosol to relax the muscle
Ca floods into the cytosol to bind to tryponin during contraction
both processes use energy
As animals get larger in size, their cost of transport decreases
the energy they need to spend to relax their muscle decreases
ARC running (cost of transport while running) decreases as body mass increases (negative allometric correlation)
AR cost (how much energy is used to relax a muscle that has been activated) closely resembles the ARC line suggesting that use of Ca2+ ATPase determines overall cost of transport
when you are larger, you contract and relax less often per distance (larger animal covers more ground than a smaller one)
taking steps, a larger animal covers more ground in one step than a smaller one
likely due to limb length, wing length, or fin length
cross-bridge cost (to bring actin and myosin together for contraction) also has a negative relationship with body mass but does not parallel the ARC line as closely as AR does
Nocturnal Lizards
99% of geckos are nocturnal, even though most lizards are dinural
ectothermic, poikelothermic (body temperature varies with the environment)
normally it gets colder at night so body temperature decreases → slows down metabolic rate → slows down ATPases which makes it harder to power muscle contractions and relaxations
impacts ability to move
within animals, geckos have a very low metabolic rate per body mass, and even lower with increasing mass
also within just lizards
hypothesis: they developed a cheaper cost of locomotion
lower cost of transport to move around at night
trade-offs: there must be a cost to travelling cheaply
ex. it is cheaper to take multiple TTC busses but it takes more time than an expensive GO bus (time is the cost to travelling cheaply)
some geckos re-evolve diurnal (secondarily), which is the more expensive cost of transport
perhaps nocturnal geckos evolved muscles with a slower velocity of shortening compared to diurnal with faster velocity of shortening
when muscles contract, they shorten
isometric contraction is the maximal force when not shortening
Vmax is contracting so fast that there is no force produced
force is highest at no shortening, as shortening increases, force decreases
efficiency is work done (FxD)/ energy used
most efficient at low velocity
not during isometric because no distance is made, so D=0
greater when more work is done with less energy required
power is force x velocity of shortening
rate of energy utilization is speed
powerful muscles → faster locomotion
diurnal has more predators during the day so speed is valued, but for nocturnal geckos don’t have many predators at night so they trade-off between power or efficiency
diurnal muscles are more powerful with a high velocity of shortening
Week 9 - Lab
Changes in environmental conditions (temperature, salinity, dissolved oxygen, and pH) can be stressful to an animal as it threatens homeostasis - maintenance of a relatively constant internal state
also infections, starvation, pollutant exposure
elevate metabolic rate during stress, which means the rate of nutrient utilization increases
Vertebrates
stress stimulates the release of epinephrine and cortisol from the adrenal glands
hormone that cause an increase in blood glucose and fatty acids
Crustacean (invertebrates)
crustacean hyperglycemic hormone (CHH) produced by the eyestalk plays a similar role
when eyestalks are removed, crustaceans do not exhibit hyperglycemia or hyperlipidemia in response to stress
This lab aims to determine whether hyperglycemia is a component of stress response in Dungeness crabs
Glucose can be metabolized via oxidative phosphorylation and lactate fermentation to produce ATP
oxidative phosphorylation yields more while lactate fermentation is faster but for a shorter period of time
lactate fermentation causes hemolymph acidification which cannot be tolerasted for a long period of time because the bacteria can die in low pH environments
The lab also aims to determine if short-term stress exposure in Dungenous crabs is supported via oxidative phosphorylation or lactate fermentation
assuming that glucose mobilization takes place
Week 10 - The Origins and Consequences of Specific Dynamic Action
Max Rubner:
coined the term specific dynamic action which refers to the summed cost of ingestion, digestion, absorption, assimilation, and elimination of a meal
other terms exist, including:
diet-induced thermogenesis
heat increment of feeding
postprandial metabolic response
energy cost of digestion
how much energy an animal spends to process a meal
Prior to ingesting a meal, the frog is at its RNR (resting metabolic rate)
which is slightly above (oxygen consumption if more than) its standard metabolic rate
After ingesting the meal, the oxygen uptake increases until it reaches SDA peak
After the peak, it begins to come back down.
SDA duration is how long after a meal it took to return to RMR
Pre-absorptive processes:
prey handling
swallowing/chewing
secretion of gastric acid
enzyme secretion
Absorptive processes:
hormone secretion (ex. insulin)
intestinal absorption
glucose absorption requires Na+ to go with it, creating a sodium gradient requires ATP
transport of nutrients
Post-absorptive processes:
amino acid deamination
glycogen production
urea production
excretion
protein synthesis
Gastric processing (pre-absorptive processes)
Westerm Diamondback Rattlesnake
used these snakes because they have the more proteolytic venom → venom contains the most proteases which break down mice
3 hypotheses for why snakes adapted to venom:
defense: to deter predator from eating it
predatory: to reduce the cost to get food
digestive: to digest prey before consumption
venom gland is derived from parotid gland
one of the salivary glands that have a role in digestion
so the venom might be connected to the digestive function
researchers collected venom and infected mice with it and fed them to snakes
expectation: the SDA cost will be less because the venom would’ve pre-digested it a bit
but studies found that it wasn’t the case, the SDA response was the same for pre-injected and not injected
therefore, suggests that mechanical digestion, not chemical digestion is a significant contributor to SDA
Energy Costs:
on average, 10% of the meal energy is used to power digestive processes
a 100kJ meal takes 10kJ to process
universal for every animal group
independent of body mass
‘Specific’ in SDA
the value of SDA was specific to the kind of meal
all together the SDA coefficient (%) average will be around 10%, but individually, but type of meal it differs
SDA coefficient is the % of total energy content in meal put towards SDA
proteins are generally above 10% and have the highest SDA coefficient
gelatin has 0 because it is an incomplete protein
does not contain all of the essential amino acids
most proteins have high SDA because you need to digest them into amino acids, absorb them, build them into functional proteins
incomplete proteins are absorbed as amino acids but do not build into functional proteins because some are missing
indigestible carbohydrates (starch and cellulose) have SDA of 0
cannot digest so no glucose is absorbed when these are eaten
digestible carbohydrates (glucose, sucrose) have a high SDA because they are absorbed and built into glycogen which is an expensive process
lipids have an SDA of 0 because we are able to digest them and build lipids but building fats is not as expensive, it is very cheap
Consequences:
when an animal is digesting a meal, its metabolic rate rises above SMR/BMR, and reduces the available aerobic scope
cost paying for digestion reduces the energy available for locomotion, reproduction, thermogenesis, etc.
aerobic scope is the difference between SMR/BMR and the maximum metabolic rate
measured the energy utilization rate available to an animal to do activities above what its doing under standard conditions
ex. energy available for locomotion, reproduction, thermogenesis
Hypoxia tolerance: the ability for animals to tolerate low oxygen levels in their environment
Atlantic cod:
at time = 0, cods are fed a meal (5% of its body mass)
under normoxic conditions, the oxygen consumption spiked up quickly and went back down (small SDA)
under hypoxic conditions, no high value was found and the SDA duration was longer
Dungeness crab:
food consumption and time spent eating differs when crab is placed in different oxygen levels
as oxygen levels decreased, the crab spent less time eating
because eating a meal causes a rise in oxygen consumption to process the meal
they avoid processing meals to pay the SDA cost
Return of appetite: while the SDA response is occurring, animals don’t want another meal → don’t eat much → appetite is low
appetite increases when they are no longer paying the cost of processing the first meal
Prussian carp:
even though the total amount of food given is the same, when they portions and times a food is given is more, the growth of the animal is better
regular feeding increases willingness to invest in body growth and maintenance (at the expense of reproductive output)
if the animal is only fed once, they prioritize putting energy towards reproduction to pass on their genes as soon as possible because they are not sure when the next meal will be
Locomotion:
European Sea Bass:
under normoxic conditions, the SDA difference between fed bass and not fed bass is relatively the same under each speed of swimming
there is always a relatively same difference in SDA
fed bass have a higher SDA because it is processing a meal while swimming
under hypoxic conditions, at faster speeds the difference disappears
the SDA is the same for fed and non fed bass
reduced aerobic scope for digesting
low available oxygen so the bass stops processing the meal to put all available oxygen towards locomotion
Rainbow trout:
U crit - critical swimming speed
how fast the trout swims sustainably
there is a slower speed when fed because they are still digesting
swimming speed depends on aerobic scope
the aerobic scope for swimming is larger when fasted than when satiated
Week 10 - Lab
Amylase digests starch
Vertebrates secrete amylase in the oral cavity (from salivary glands) and in the small intestine (from the pancreas)
Invertebrates (earthworms) secrete amylate into the digestive tract from their pharyngeal glands
pharyngeal glands are analogous to our salivary glands
amylase activity is much higher in the anterior gut compared to the posterior gut
Amylase permits dietary starch to be broken down into maltose and further into glucose
glucose gets absorbed by the blood to be circulated throughout the body and serve as an energy source for cells or stored as glycogen or fat
Proteases digest proteins
into small peptides and amino acids
Vertebrates secrete proteases including pepsin (from the stomach) and trypsin and chymotrypsin (from the pancreas)
Invertebrates (earthworms) secrete proteases in their digestive tract
Amino acids are absorbed by the blood and used to build proteins
proteins are structural components of animals but amino acids can also be converted into glucose or fat
Lipases digest triglycerols
major dietary fats
Vertebrate lipases are secreted via the pancreas
In earthworms, they are secreted by the pharyngeal glands
Triglycerol is hydrophobic (so ideally can be absorbed through the lipid bilayer of a cell) but it is too big, so it must be digested first
lipases cleave fatty acids from their glycerol backbone
free fatty acids can be absorbed into the body without transporters, but transporters can be used to speed up the process
glycerol is water soluble so specific transporters absorb it
because triglycerols are hydrophobic they accumulate into large globules which limits their digestion
lipase is a protein so it is water soluble, so it can only act on the surfaces of the globules but not within
so bile salts are secreted to emulsify fat globules (break them down into smaller pieces)
Many plant-based foods inhibit amylase, protease, and or lipase activity
as a deterrent against herbivory
inhibition would compromise the digestive and absorptive capacity of nutrient for those animals that consume the plants
but it can also be used to prevent the incidence of type 2 diabetes