Lucy's lectures Flashcards
Control + integration
Physiological functions under endocrine and nervous control. Endocrine systems use hormones as chemical messengers. Hormones are normally seen as the slower part of the control system, vs rapid nervous control.
Endocrine system
Increasing complexity with biological, organisation, and evolutionary origin. Most studied in arthropods.
Beginnings of crustacean endocrinology
-1920s = colour change in shrimp caused by a blood borne factor, originating from eyestalks.
-1940s = eyestalk removal and replacement type experiments to see effects on blood glucose level.
We now know eye stalks have many hormones including CHH (crustacean hyperglycaemic hormone), which are used in reproduction, osmoregulation and energy metabolism. There is also MIH (moult inhibiting hormone) which regards the carapace.
Energy metabolism in response to stress
-During emersion (can’t get back in the water), there is an increase in CHH which drives an increase in blood glucose, which means more ATP is needed to increase metabolism.
During migration in Christmas Island red crabs
They have to journey to the ocean to breed, they have a marine larval stage. They have many physiological adaptions to cope with the energetic demands of migration. For example, they can deal with high lactate build-up very well, and can walk continuously for 45 minutes. Timing of the monsoon rains actually dictates when they begin their migration.
Red crabs
During experiment; Crabs exercised for 10 minutes and then recovered for 10 minutes. CHH increases rapidly during exercise, lactate increased rapidly and remained high even 1 hour into recovery. Glucose increased significantly 1 hour into recovery.
Seasonally dependant negative feedback loops regulate energy supply
Crabs were injected with glucose or saline control every 8hr for 3d previous to exercise experiment. During wet seasons there is more glucose in migrating crabs, but less CHH. And in dry seasons when crabs aren’t migrating, there is high CHH. Glycogen also tends to decrease during migration since they use a lot of energy by moving and digging, that’s why CHH is most important when they are returning tired.
CHH + osmoregulation during the migration of Christmas Island blue crab
-They don’t migrate until monsoon season is in full swing
-They then return during dry season
-So they try to stay close to freshwater the whole time
Blue crabs were shipped to the UK, CHH was injected into crabs and haemolymph sampled were taken. Both increase glucose conc in crabs. Salinity also has a significant effect on circulating CHH, a lot more CHH was released when saline.
Effect of CHH on seasonal branchial uptake
It does have an effect, sodium uptake increased in both pre-wet and wet seasons, and also happened in red crabs but to a lesser extent. CHH on the other hand, has no effect on sodium uptake during season. Shows sodium uptake changed depending on the time of year. CHH has a significant effect on antennal gland filtration in blue crabs, but not in red.
Moulting cycle
hHw crabs grow, the exoskeleton in a container, so unless it is shed, they can’t get bigger throughout their life cycle. Once they shed it, their shell underneath is very soft, so they need to be hidden, and as soon as its shed, they eat the exoskeleton to reclaim minerals and strength. They even have a new set of gills or gill area during the shed. This is hormonally controlled, so at any time they are somewhere in their cycle (like a period). When the inhibiting hormone falls, the process of moulting can begin.
They also have to lose mass on their claws first to even get out, they also then need enough energy to harden the shell and regrown the claws. Aquatic crabs will immediately take up water to make sure there is enough capacity to grow into, and in case they meet an opponent. They use it to swell the exoskeleton. Land crabs do this using air. As they grow into the shell, they expel the water or air.
Hormonal control of embryonic development and hatching: MIH and CHH are important for both hatching and moulting.
Why migrate?
For reproduction to maximise reproductive success, or to avoid sub-optimal seasonal conditions. There are different food requirements for different age classes, they avoid competition for the same food sources or move somewhere else to exploit them.
-Migration requires complex interplay between behaviour and physiology.
Diurnal vertical migration (DVM)
Many planktonic organisms undergo diurnal vertical migrations, moving towards surface during the night, descend during the day.
-Challenger expedition = only found copepods in surface at night
-DVM is the largest synchronised movement of biomass on the planet, important for marine ecosystem function and carbon cycling
-Copepods swim 400-800m per day, passive sinking can be as important as downward swimming during the day. Swim up actively at night.
-DVM is considered to reflect trade-off between the need to feed versus predator avoidance.
How do they know where to migrate?
-Must be able to navigate using both sun and moon and compensate for variation of where each one is
-When antennae were painted in amphipod, they were unable to orientate correctly to the moon, but could still follow their daily activity rhythms.
-Clock genes are rhythmically expressed in both tissues, suggests they have anatomically discrete lunar and solar orientation. Sun compass is likely in brain, moon compass in antennae.
Molecular and circadian clocks
-Molecular clock; a molecular system able to maintain a given biological rhythm even under free-running conditions (when cue is removed).
-Circadian clocks increase zooplankton fitness by optimising the temporal trade-off between feeding and predator avoidance.
Diurnal variation in light = major driver
Proven by latitude, season and eclipses.
But still occurs in deep water habitats and at high latitudes during winter where light is limited, suggesting other ways of controlling it.
Energetic costs during DVM
(hormonal control, metabolic energy)
-Copepods adjust metabolic capacity during DVM demonstrating they are energetically adapted to cope with DVM temperature changes
Energy usage during migration in green turtles
-Only come onto land once a year to deposit their eggs, males almost never go onto land
-They are large ectotherms with a low metabolic rate, allows them to use energy sparingly
-Metabolic rate and energy expenditure was low in foraging turtles, compared to migratory turtles. They build-up substantial energy reserves at the foraging site which is required to sustain the energy-demanding breeding migration
-Tend not to forage in their nesting sites, seagrass beds along the coast of the tropical Atlantic are popular foraging spots
Green turtle migration
During migration; deal with strong counter currents by staying close to shore, they perform deeper and shorter dives whilst crossing the mouth of the amazon to help avoid the most turbulent surface layers of the plume. Show the plasticity of the green turtle population when reducing energy costs induced by migration.
Post-migration + pre-breeding energy usage in migrating birds
- Reproduction and migration are the two most energy demanding processes, transitioning from one to another requires many physiological adjustments
- When arriving at breeding grounds they need to recover and prepare for breeding which is a body condition critical to reproductive success
- When migrating they fast so when they arrive, they have to deposit fat and degrade muscular mass from flying. They remodel their body composition to have more space for lipid reserves. Females start fat deposition earlier than males, to cope better with the lipid demands of egg formation.
energy budget
How we can measure energy flow. Seen as a balance sheet of all sources of useful energy gain, storage and loss. Feeding -> digestion -> nutrition. Measurement of all components enables documentation of the complete energy budget.
C = P + U + F + M + W out
C - Consumption (sources of energy e.g. food and drink)
P - Production e.g. tissue growth (stored energy)
U - Urine (energy loss)
F - Faeces (energy loss)
M – Metabolism (energy loss)
W - Work (energy loss e.g. energy usage)
Dynamic energy budget theory (DEB)
-An extension of the energy budget model that also takes into account the laws of thermodynamics.
-The uptake and allocation of energy/nutrients as well as the consequences for physiological organisation throughout an organisms life cycle. E.g., the relationship of energetics with aging and effects of toxicants.
-Theory recognises 3 main stages: embryo (doesn’t feed or reproduce), juvenile (feeds but doesn’t reproduce), adult (both feeds and allocates energy to reproduction).
What do we use the information from energy budget calculations for?
-Ecological contexts = e.g., to calculate the energy flow through the fiddler crabs and the marsh periwinkle. Converting dry weight, faeces, respiration and egestion rates to find the net production.
-Metabolic contexts = resting metabolic rates calculated to inform energy budget calculations. Metabolic rate influenced by temperature, and if crabs were carrying eggs, also if cut capacity was full.
-Estimate maximum growth rates and age at maturity = theory can be used to estimate these for species where we can’t take measurements, like the hagfish.
Estimating growth rates in hagfish
The only data available is the length and mass at birth, at puberty and oxygen consumption. Estimated growth rate for the Atlantic hagfish is much less than for the pacific hagfish. Estimated age at maturity is lower in pacific, which could have implications for fisheries.
Energy budgets; why gull-billed terns feed on fiddler crabs
Fiddlers have low energy content and low digestible flesh to exoskeleton. Food intake limited by gut capacity? Poor quality of fiddlers is offset by high capture rates, daily energy expenditure could easily be met by feeding on fiddler crabs.
Scope for growth: bivalves
-Can be measured directly or indirectly by the scope for growth (SFG, how much energy do they have left for growth after everything else).
-SFG measured by clearance rate (CR), absorption efficiency and respiration rate
-All of this can directly affect the energy available for growth, maintenance and reproduction.
How to calculate SFG
C - total energy consumed,A - total absorbed energy
C = CR x particle concentration x energy of food
A = C x absorption efficiency
SFG = A x respiration rate
Can be used to quantify the direct and indirect effects of climate change.
-Direct = what is the effect of exposure to high pCO2 on the energy budget of bivalve species. SFG decreases with increases in pCO2.
-Indirect = what is the effect of exposure to toxic dinoflagellates on the energy budget of bivalves. There was a decline in SFG with increasing toxic algae concentration. Driven by decreases in absorption efficiency. CR only declines in clams dosed with highest concentration.
