Organisms have a limited amount of energy to spend so they much allocate it to competing demands.
How are resources divided among life history stages or functions?
Energy Budget
C = P - R - (U + F)
C = energy consumed
P = production (excess energy)
R = respiration
U = urea
F = feces
(U+F = W; waste)
Growth/Reproduction Tradeoff
The excess energy must be used either for growth or reproduction. It is a dynamic situation and it is not characteristic of an organism's entire life history.
Examples:
- Douglas fir width of growth rings vs. number of cones per tree
- Goldenrod increased biomass dedicated to reproduction when found in sunny areas.
Parent/Offspring Conflict
There is an optimum energy expenditure from the parents in order to ensure offspring fitness. Beyond that point there is decreased return of energy expenditure.
Size/Number Tradeoff
The optimal number and size of eggs to produce occurs at intermediate clutch sizes.
Observed in birds, mammals, lizards, amphibians
Mean fitness of offspring is inversely proportional to the total number of offspring produced.
Example: lizards fed to satiation still exhibited similar, albeit weaker, pattern.
An alternate hypothesis is that hatching mass is limited by maximum body capacity rather than by energy.
Effect of offspring survival as a function of size: Bryozoans; larger egg size, better survival
Size vs. Number in Varying Quality of Environment for Offspring
As environmental quality deteriorates, the organism should produce fewer and larger gametes.
Shell vs. Tissue Growth
Seen in Littorina snail preyed upon by crabs.
Allocation to defense vs. maintenance
Crab chemicals cues influenced shell growth
Clonal, Modular, and Unitary Organisms
Clonal organisms can respond quickly to environmental conditions to take advantage of resources to reproduce.
Unitary/Aclonal
- Germ line separate from somatic cell line. (Germ line - reproductive)
- Fixed cell fates
- Body form is highly determinative
Clonal
- Cell fates are not fixed. Great deal of plasticity.
- Body form is indeterminate. There is an ability to change body type or body plan.
Within clonal organisms, there can be modular an non-modular organisms.
Modular
- Grow by repeated iteration of parts
- Bryozoans, corals, ascidians
Non-modular
- Do not grow by repeated iterations of parts
- Lizards, plants, aphids, daphnia
Clone: assemblage of individuals genetically identical by descent.
Genet: whole organism of one genotype
Ramet: clonally produced part of genet
Being clonal can sometimes yield a competitive advantage.
Clonal organisms can reproduce asexually by fission, fragmentation, budding, parthenogenesis.
Consequences of cloning
Advantages:
- Enables fit genotypes to be inherited intact
- Enables rapid colonization, particularly over short distances
- Reproductive output doesn't necessarily decrease with age.
- Rapid utilization of food resources
- Polymorphism: specialization of modules for different functions
- Can survive partial mortality
- Reduce risk of genotype mortality by replicating parts of clone
Disadvantages
- Mutational meltdown: accumulation of deleterious mutations
- Inability to respond quickly to environmental change via natural selection due to loss of genetic variation
- May have poor long distance colonizing ability
- Fission may divide organism into smaller than optimal body size
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