Week 12 Flashcards
Explain how physiology and/or genetics can lead to life history trade-offs.
Physiological constraints:
Competition between reproduction and survival for energy allocation
*Selection should favour the optimal life history in a given environment
Negative genetic correlations:
such as antagonistic pleiotropy, can result in adaptations being in competition with one another.
However, physiological constraints and negative genetic correlations are not mutually exclusive!!
Ex) the phenotypic effect of allele A1 is increased energy allocation to early life reproduction. Due to physiological constraints, this results in decreased allocation to survival; this will result in a negative genetic correlation (due to pleiotropy) of reproduction and survival.
Explain how hermaphroditism can be an adaptation
In the case male to female ratios become drastically disproportionate (or there is less females and therefore, less reproduction), this can lead to extinction in dioecious species.
This is not an issue for hermaphroditic species
Define outcrossing.
Mating with another, genetically distinct individual
Define Self-fertilization (selfing).
Union of female and male gametes produced by the same genetic individual.
Define anisogamy.
Distinct male and female sexes, defined by gamete size (male gametes are smaller than female gametes)
Define Isogamy.
Uniting gamete cells are the same size
Define dioecious.
Distinct male and female individuals within a species
Define hermaphroditic.
What is sequential hermaphroditism?
Hermaphroditic: Performance of both male and female sexual functions by a single individual (earthworms, other plants/trees like roses)
Sequential hermaphroditism:
Some organisms (some fish, annelid worms, plants) change sex over the course of their lifespan. Note this is predictable using life history theory.
Define vegetative propagation.
Production of offspring from somatic tissue (e.g buds, ‘runners’)
Define parthenogenesis.
What is apoximis?
Parthenogenesis:
Development from an egg to which there has been no parental contribution of genes (virgin birth)
Apomixis:
Meiosis is suppressed. individual develops from one or more mitotically produced cells. Offspring is genetically identical to its mother (except for any mutations that occur in the cell line leading to the egg)
Provide (evolutionary appropriate) explanations for the benefits of sexual reproduction.
Despite its numerous costs, phylogenetic evidence suggests there is a long-term advantage of sexual reproduction.
Most asexual lineages of eukaryotes have arisen recently from sexual ancestors. Therefore, earlier arising asexual lineages must gave gone extinct.
(1) Sexual reproduction also combines new mutations/rare alleles to create new (potentially advantageous) genotypes
(2) Adaptation to varying environments (including parasite pressure). Recombination breaks down linkage disequilibrium and can result in rare genotypes.
(3) Separating beneficials from harmful mutations.
Muller’s ratchet: Mutations accumulate, ultimately leading to ‘mutation meltdown’ (accelerated loss of fitness) and the eradication of those genes from the breeding population. In asexual populations, these genotypes are maintained and more fit genotypes can even be lost to chance.
Hill-Robertson effect:
Without recombination, beneficial alleles can be lost, due to LD with deleterious alleles
List all the costs and benefits for asexual reproduction.
Pros:
- Quick
- does not require mate
- more reliable and less complicated
- less energy required
Cons:
- Halving the reproductive output of reproduction
- Lack of genetic diversity in the population
- More likely to go extinct
List all the costs and benefits for sexual reproduction.
Pros:
- Higher genetic diversity
- Increased genetic variation in the population (decreased probability of extinction.
Cons:
- Time, suitable conditions, and mate required
- Requires more energy
- Slower
- Others: STIs, aggressive males, mating attracts attention of predators and increases predation risk
