An extensive summary of the lecture notes of Life History of Aquatic Organisms (AFI-31306). This summary can be used for multiple studies at Wageningen University.
Life History of Aquatic Organisms
Summary lecture notes AFI-31306
2018
1. Introduction to life history theory
1.1. Introduction
Life histories = events related to survival and reproduction that happen between birth and death. Survival and
reproduction are the most important for fitness and have a big role in natural selection. Boundary conditions
(both external and internal) have influence on this.
1.2. Genotype and phenotype
For natural selection, you need both phenotype and genotype. Heritable variability determines whether there is
a reaction on selection (genotype) and for this, individuals need to differ in fitness (fenotype). Analysis of
evolution and fitness components = life history evolution.
1.3. Life history traits
Life history traits have a direct influence on reproduction and survival (example: Pattern of growth, size at birth,
size at maturity etc.)
1.4. An explanatory framework
Stearns life history framework, elements:
- Demography: Euler Lotka equation for growth speed. R0 = ∑lxmxdx.
- Quantitative genetics and reaction norms: Most of the times a lot of genes with a small effect.
Phenotypic plasticity = the possibility of a genotype to produce different phenotypes in different
environments. Reaction norm = The curve that relates to the phenotypes a genotype can produce in
different environments. Plasticity is important:
o It influences the genetic reaction on selection in environments
o In this way, selection can produce the optimal reaction norm to create maximal fitness.
o It can serve as buffer for changes in the environment.
Life history traits have a high plasticity. GxE interactions = genotypes have different reactions in
different environments.
- Trade-offs: There is an evolutionary constraint = not everything can be maximized and resources are
limited. Improvement of one results in decrease of the other. Sometimes, they are genetically linked. In
a physiological terms, trade-offs are caused by allocationof resources. Important trade-offs: survival vs.
Reproduction, Size vs. Amount of offspring.
- Lineage specific effects: Some traits are in a taxon for a long time. By this we can determine the
amount of microevolution.
Genotype influences the phenotype and the other way around (by natural selection).
1.5. Natural selection and fitness
Genes carry the memory of selection using generations of sexual populations. Fitness = temporal measurement
of numerical dominance. Fitness is also determined by environmental factors and other phenotypes in the
population. There is no clear definition of fitness.
1.6. Adaptation and contraint
Definitions of adaptation:
- Functional approach: Adaptation is the change in phenotype which is a reaction on a specific
environmental signal and has a clear functional relationship to the signal. This results in an
improvement of growth, survival or reproduction.
- Phylogenetic approach: Homologous traits that are unique for a species and are functional associated
with the change in habitat and selection pressure that is also unique for that species.
Nienke Klerks Summary AFI-31306 1
, - Microevolutional approach: Adaptation is the status of a trait which was predicted in that state by an
optimality model.
Definitions of constraint:
- Causal phylogenetic: every pattern or state can contribute to the phylogeny in contrast to the recent
microevolution within the current population
- Biomechanical: Organisms are constraint to obey the laws of physics and chemistry.
- Systems: Need that every state of development needs to continue where the last one ended.
There is a lot of debate about the definitions of constraint and adaptation.
1.7. Predictions for the evolution of life history traits
Genotypic reproductive success is determined by growth speed and the consequences for the age and size at
maturation. Advantages of early maturity and being small:
- Higher chance to reach age at maturity
- Shorter generation time
Advantages of late maturity and being big:
- Bigger when mature so higher fertility
- Lower adult mortality
- Higher quality of offspring
Lack clutch = maximal clutch size with surviving offspring. So most of the times mean clutch size. Reproductive
effort model = reproduction has both costs and benefits. It needs to be investigated what the optimal
investment is. Advantages of longer life span:
- Higher amount of reproductive cycles
- Enough compensation time for mortality off offspring
- Lower insecurity about reproduction
Longer life span iteroparity, shorter life span semelparity. In risky places: reproduce early and have more
offspring. In constant environment: late maturity and lower amount of offspring.
2. Life histories of marine mammals and relevance for population ecology
2.1. General Marine Mammal Life History
Life history strategy is defined by how animals allocate their energy in growth, reproduction and survival
throughout their lifetime. Natural selection tries to maximize reproductive fitness. Marine mammals have a
high range of strategies. Allocation first in growth, then in reproduction.
2.2 Characteristics of Catacean Life Histories
All Catacean species (whales, dolphins and porpoises) have a long lifespan and most of them migrate. There is
little known about the species, most information is about whales. Common characteristics to be able to live in
the water:
- 1 large precocial young
- Gestation time ≈ 1 year
- Long living
Longitudinal and cross sectional studies have been performed to obtain data. Life history reflects the
adaptations for a certain niche and by this you can understand demography. Density dependence = responding
to changes in the availability of resources through time. Age-specific reproduction rates and survival rates are
critical to quantify a species demography, but these data are mostly not known for cetacean species. There are
new technologies to contribute to the knowledge about the species (for example: molecular genetic
techniques, VHF and satellite tracing).
2.3. Characteristics of Pinniped life history
Features of pinnipeds (seals):
- High annual survival rate: longevity of 2-4 decades
- Age at maturity delayed by 2-6 years
- Maximum of 1 offspring per female per reproductive cycle
They have a semi-aquatic existence which led to a narrow range of life histories. They rely for reproduction on
ice or land. They have by mammalian standards, a high body size. They have precocial young. Life histories are
represented by demographic models based on survival and fecundity rates. There are only a few species with
complete information (and most of the times only information about the females). Constraint of pinnipeds:
Nienke Klerks Summary AFI-31306 2
, - Being homeothermic
- High spatial and temporal variability in distribution of resources
- Phylogeny (for example: reproduction of land)
Due to reproduction of land, the reproduction area and forage area are separated. Seasonality of food
availability leads to seasonality of reproduction now polygynous mating systems with an annual cycle of
reproduction. Fitness = number of offspring across lifetime. How pinniped make investment decision to
optimize fitness is unknown. Age of first reproduction is not constant, is a reflection of mean growth rate (so
density dependent) and can be determined by natural selection.
2.4. Sirenian Life History
Unique feature of serenian species (sea cows) is that they are herbivorous. Fossil records of 50 million years old
(as old as catacean). Study of life histories both in field and laboratory time consuming and expensive. Species
are long living and large. Estimating age due to GLG (growth layer groups) in bones. Low amount of information
about the species (most of manatee and dugong). Gestation length approximately 12-14 months and have
seasonal reproduction. The group of species is threatened.
3. Niche adaptation
3.1. Natural selection is the only known explanation for adaptation
Organisms are well adjusted to living in their environment. Adaptation is a crucial concept in natural theology
which explain the properties of nature theologically (by action of god).
3.2. Natural selection is not the only explanation of evolution
We should accept a pluralism of evolutionary processes and not only rely on natural selection. We need drift as
well as selection in a full theory of evolution.
3.3. Natural selection can in principle explain all known adaptation
Darwin called evolution gradual: complex adaptation evolve in small steps. Types were natural selection could
not account for:
- Coadaptation = complex adaptation with evolution have required mutually adjusted changes in more
than one of their parts (group of species, genes or traits which undergo the same adaptation)
- Functionless or disadvantageous rudimentary stages
3.4. New adaptations evolve in continuous stages from pre-existing adaptations, but the continuity takes
various forms
New adaptation evolve in small stages from pre-existing organs, behaviour etc. There is continuity. Probably,
many organs evolved by gradual transformation of a structure with a constant function. Sometimes they can
change function with small change in structure = preadaptation (example: feathers first function was probably
thermoregulation and not flying). Not use the term exaptation. Third possibility for new adaptation:
combination of 2 pre-existing parts.
3.5. Genetics of adaptation
Approaches of genetic steps of adaptations:
- Goldschmidtian: adaptation and new species evolve by macromutations = mutation with large
phenotypic effect
- Fischer: adaptive evolution mainly proceeds in many small steps. Assumption: organisms is near the
adaptive optimum and adaptation has a single peak
- Wright: adaptive evolution is facilitated by random drift in small, subdivided populations
Factors of mutations: Chance that mutations are substituded = chance that mutations arise x chance that
mutations are advantageous x selective advantage of mutations. Depending on ecological conditions, there are
small and large mutations.
3.6. The study of adaptiveness in three stages
Stages of study of adaptiveness:
1. identify what kinds of genetic variant the character could have
2. develop a hypothesis which predicts the features of the organ exactly and makes testable predictions
3. Test your predictions. Methods:
Nienke Klerks Summary AFI-31306 3
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