Reproductive Energetics Flashcards
What is all the energy acquired by animals is ultimately allocated to?
Basic categories
- Metabolic processes
- New body tissue (growth or reproduction)
- Loss as waste products
Energy budgets are used to describe the partitioning of ingested energy
Ein = Eout + P
What formulation do the energy budgets for marine organisms use?
Most energy budgets published for marine organisms use the formulation suggested for the International Biological Programme (IBP) in the 1970s
C = P + R + U + F
What do the letters of C = P + R + U + F stand for?
C = P + R + U + F
- C = consumption (Ein); - energy in
- P = production (somatic & reproductive); - synthesising new tissue for both tasks
- R = respiration; - is something we can measure
- U = excretion (urine); - also mucous in some organisms. Urine are bi-products of production processe.
- F = faeces
All components of any energy budget expressed in the same unit (J or KJ)
The major difficulty is the R term. Essentially we are dealing with losses to metabolism (work is done and energy lost as heat)
Subdivide into things we can tease apart and measure;
- Basal metabolism (bare minimum processes to keep the organisms going.
- Active metabolism
- Energy for digestion, absorption and processing of food
Give an example of one part of R that you can identify.
We may also add to R the Specific Dynamic Action (SDA)
SDA is the metabolic cost associated with processing food – leads to a raised metabolic rate – Post-Prandial Thermogenesis (after meal creation of heat)
What does this paper show? (SDA)
SDA, as measured by O2 uptake after feeding of 3 different energy content meals, in Pleuronectes platessa
Jobling & Davies (1980)
Looks at variability in SDA as recorded by oxygen consumption. Fed foods of varying energetic content, as recorded oxygen consumption.
Take away message - as the energetic content of the meal in terms of KJ’s increases we see greater postprandial response.
What are the problems with measuring R in the energy budget?
Respiration is a measure of demand for ATP. Yet ATP is used for a variety of separate metabolic activities which will compete for the demand for ATP. This means there are lots of external impacts on energy budgets such as temperature, activity, age and health.
To break this down, you can get a good measure of the activity and standard resting respiration.
How do you redefine R to take into account the competing demands for oxygen
∑R = Rb + Rs + Rg + Ra
- Rb = basal (maintenance) metabolism
- Rs and Rg = costs for synthesis of somatic and gonad tissue
- Ra = locomotor activity
Therefore Rstd = Rb + Rs + Rg
Apply this refinement to the original model (C = P + R + U +F) (picture)
Production can be allocated into two differetn sinks dependant on whether you are growing or reproducing.
Divisions of the energy budget grouped into physiological sinks
Ps + Rs = total cost of producing somatic tissue
What is the most difficult term in the energy budget to calculate?
Most difficult term to measure is Ra
- Still, only a few published energy budgets for marine invertebrates consider this term – must be significant for pelagic species
- Measure O2 consumption of animal at rest and determine the relationship between locomotor activity and O2 demand – used extensively with adult and larval fishes in the lab
- Also need data from activity patterns in the wild – very rarely available
What is the difference between the energy budget terms for outputs?
- the F term represents energy content of material that is ingested but not assimilated
- the U term represents material assimilated but later excreted as nitrogenous waste products (also mucus!)
What is the dichotomy in the definition of assimilation?
A has been termed absorption (all energy that is taken in) and A1 assimilation (truer measure of assimilation - only energy that is being taken in and allocated to creating ATP)
- A - a measure of assimilation being - how much energy is assimilated over how much went in.
- A1 - not thinking about nitrogenous waste. Just thinking about material allocated to ‘real work real jobs’
Accounting for seasonal variability
give an example
- We see huge evidence out there in the literature that seasonal variability has a large influence over patterns of respiration.
- A nice example is the Antarctic calm Laternula elliptica (Brockington, 2001) –Seasonal variations in growth rate and/or gametogenesis may explain most of the observed seasonal patterns of respiration.
- Seasonal pulses of material coming in the spring in the Antarctic, causing pulses in biotic energy and productivity.
What factors may be at play, alongside seasonal variability in effecting respiration?
- In cold-water species, where Rb is low (and in particular sessile species where Ra is also low) the correlation will be very strong.
- Warm water species, correlation is much weaker as the temperature is having a much bigger effect.
- In discontinuous feeders, growth tends to occur in a pulse immediately following a meal and therefore Rs may explain much of the post-prandial SDA.
How can you work out Reproductive Effort (RE)?
- Reproductive effort - the reproductive cost
- Reproductive output - ‘what you realise and see’ how many gametes you produce
The reproductive effort will be a sum of activities such as producing gonadal tissue, locomotory costs such as guarding a mate,
RE = (Pg + Rg + Rab)/A
All components need to be summed over the entire year, but this means you lose the point specific measurement of what and animal is doing as a specific time.
But how can we measure Pg , Rg and Rab?
- Fecundity – number of gametes per parent (or per brood)
- Biomass of gametes – measured in units of energy (J)
- Biomass of gametes/Biomass of parents – ‘size-specific reproductive output’ or Gonad Index. This is very instantaneous and size-specific. Would be better to know the change in time of the gonads over time. (at any point in time would give the Pg value.
WG/(WG + WS)
How do you work out the reproductive effort, separate from the energy going into all other processes?
- Estimating the thermodynamic efficiency of synthesis allows Rg to be calculated based on measures of biomass produced (Pg). How efficient is it at turning ATP energy into proteins.
- Because this is going on, the true RE will be influenced by changes in energetic parameters that influence neither Pg or biomass (WS) leaving RO unaffected.
- temperature can have a big effect on this
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- temperature can have a big effect on this
Latitude and metabolism
- Polar, temperate and tropical regions all contain both active and sedentary species
- No persuasive argument for latitudinal cline in overall metabolism
- Lipid storage in pelagic invertebrates - speculative idea that greater lipid stored in copepods at higher latitudes show more energy is being stored, and not spent metabolically.
- Temperature compensation in growth is hard to establish
- Many polar organisms are very slow-growing –is that related to the low water temperatures?
- Some species can grow rapidly when sufficient food is available
- Slow growth rates may not reflect direct temperature limitation but are a consequence of a severe seasonal pattern in food availability (Clarke, 1983)
What relationships can reproductive effort and temperature predict?
Assuming output is constant.
Can use these relationships to examine the predicted variation in reproductive effort (RE), size-specific reproductive output (RO) and growth efficiencies (K).
Variation in annual RE when RO is constant and Rb varies with temperature and vice-versa.
Assuming that RO (Pg, Rg, Ps, Rs and WS) remains constant and there is no variation in Ra a theoretical annual reproductive effort (RE) can be calculated for all temperatures.
What relationships can reproductive effort and temperature predict?
Assuming RE is constant.
Now annual RE is constant and resultant variation in annual RO with temperature (latitude) can be calculated.
RO is lowest for a hypothetical polar population of marine invertebrates and highest for tropical population
These 2 examples are modelled extremes
Selection acting on natural populations, evolving to cope with environmental conditions, will affect both true RE and RO
Data for female caridean shrimp does indicate that RO for polar species is 60-70% that of temperate species (Clarke, 1979) – similar to model. So annual RE may be more similar than RO would suggest.
RE, RO and growth efficiency vary with temperature.
Annual vs Lifetime RE
If Rb is assumed to be the same for all populations then there will be a strong positive correlation between lifetime RE and temperature
BUT…..if Rb varies with temperature then lifetime RE becomes independent of temperature (latitude)
Across the range of P. borealis there is a balance between lifespan and basal metabolism resulting in more or less constant RE
What data would we need to test this further?
- Rb of Pandalus from populations at different latitudes
- RO of populations at different latitudes
- Energetic costs of brooding eggs
(Reproductive effort across species tends to be fairly constant across habitats
Good reading on pandalaus)
