Lecture 7: Populations: Natural selection & evolution Flashcards
Define population
A group of individuals of the same species living in the same location
define species
A group of individuals that naturally interbreed with each other and produce fertile offspring
define natural selection
-Differential survival and reproduction of individual organisms dictated by the interactions between phenotype and the environment
-leads to evolution in the next generation— the process that is unique to populations.
-primary non-random mechanism of evolution
-is an ecological process
define evolution
Change in a population’s gene pool over time
Three key steps in adaptive evolution by natural selection
- Heritable variation
- Differences in reproductive success among individuals
- Heritable phenotype of more reproductively successful individuals is more prevalent in the following generation.
Mutation
-Any change in the DNA that codes for a gene or the expression of a gene
-Some changes can cause fatal phenotypic changes, some are neutral or “silent”, some can result in beneficial changes - the raw material of adaptive evolution
Pleiotropy
Single genetic change that results multiple phenotypic effects.
Epistasis
Hierarchical control of the expression of one gene by another gene.
Polygenic traits
Complex interactions among many genes, resulting in continuously varying phenotypic traits
Epigenetic changes
Heritable phenotype changes that do not involve alterations in a DNA sequence
3 major types of natural selection
- Stabilizing selection.
- Directional selection.
- Disruptive selection
Stabilizing selection
-When ecological interactions increase survival and fitness of the most common phenotype in the population
-parent population starts of broader then progeny population
-progeny population gets thinner with the mean phenotype being higher than the parent phenotype
-the phenotype on the ends of the parent distribution are lost in the next generation
Directional selection
-When ecological interactions increase survival and fitness of a rare phenotype in the population
-all of the phenotypes on one end of the parental distribution are favored become the mean in the next generation
-individuals in the other end are doing poorly and in the next generation, they are entirely gone
-the environment changes, and it pushes the population to fit that particular environment
Disruptive selection
-When ecological interactions increase survival and fitness of two or more rare phenotypes in the population.
-the two ends of the parent distribution become the mean in the progeny population, results in the parent population’s mean lowering
When does selection act?
Environment can “select” (create differential survival) at any stage before and during reproduction.
Evolution through random processes
- genetic drift
- bottleneck effect
- founder effect
define genetic drift
any random loss of genetic variation followed by reinforcement
define the bottleneck effect
random loss of genetic variation due to severe reduction in population size
define the founder effect
random subset of original genetic variation in small populations that occupy a new area.
How do phenotype and genotype interact?
-Selection acts on the genotype via the phenotype.
-Genotype of an individual is fixed, BUT a phenotype might have the capacity to vary with environment in ways that are adaptive.
Phenotypic plasticity
The capacity of an individual’s phenotype to respond developmentally to environmental change within its lifetime.
Adaptive phenotypic plasticity
The capacity of an individual’s phenotype to respond developmentally to environmental change in a way that increases its survival and reproduction
Reaction norms
-The observed relationship between individual phenotype and the environment
-the observable pattern of phenotypic plasticity within a population
define acclimatization
-Dynamic phenotypic plasticity in response to repeated (especially seasonal) environmental shifts
-reversible
define developmental phenotypic plasticity
-Permanent phenotypic plasticity that tracks persistent environmental characteristics during development
-irreversible
-shows up during juvenile development and stays through adulthood
Reciprocal transplant experiments
-take 2 organisms that have adapted to their respective environments and swap them and observe the results
-help address why populations from different environments show different phenotypes
results of Reciprocal transplant experiments - genetic factors
phenotypes in each population are insensitive to environmental change
results of Reciprocal transplant experiments - environmental factors (phenotypic plasticity)
individuals in each environment has similar reaction norms
results of Reciprocal transplant experiments - differenced responses to environment (both genetic and phenotype)
reaction norms in each population have evolved in response to different prevalent environments
