2025-09-09 1

Gene flow
Genetic Drift
Mutation

Related to Evolution - Intro

Correlation between a trait in parent and offspring - is there a nongenetic reason for this correlation?

• Maternal effect - if a mother has less resources, their offspring may not preform as well
• Therefore this is not a heritable trait but an environmental factor
• Ideally you could rear them for a few generations in the lab to remove this effect

Gene flow is driven by dispersal

• emigration and immigration

Genetic Rescue of inbred wolf population

• Remnant wolf population of central Sweden that was geographically isolated from other wolves
• Founded by two individuals in the 1980s
• Outbred individuals preformed much better
• Is there a mechanism for inbreeding avoidance? Unsure

Genetic drift

• Change in allele frequency from chance events
• More of an effect on small populations, where genetic drift generally causes a reduction in overall variation since certain alleles will go extinct

Three Core Modes of Selection

Stabilizing

Reduction of variation, moving towards the mean

Directional

Moving towards one side of the distribution

• Example given of the Medium Ground Fish on Isla Daphne Major (Galapagos), where after a 1970s dought the larger beak sizes were selected for

Disruptive

Moving away from the mean in both directions

Example - Antibiotic Resistance

• Bacteria have a fast evolution rate and antibiotic resistance is heritable

Life History Trade-offs

• Examples are:
  • Number vs quality of offspring
  • Development time cs body size

Detecting Adaptation

Local adaptation studies

Example given with Trinidad pond guppies

• Able to study selective factors in a small localized natural area

Altitudinal/Latitudinal clines

• studying variation across latitude or altitude
• Can measure correlation with these values
• Drosophila melanogaster variation in wing size across latitudinal cline in Australia and USA.
• Latitude of course effects temperature, day length, UV intensity, seasonality
• since Drosophila reproduce quickly and are easy to keep large populations it is feasible to study evolution in the lab. You can take populations from the wild and isolate certain variables to study the effect of certain species

Phenotypic Variation

In this example, the three colored lines represent three different genotypes. In the first example, the phenotype is affected by the environment irrespective of the genotype

• So, for example, in the first one, the phenotype responds to the environment irrespective of genetics. Environment 1 is colder and environment 2 is warmer. So in this case, the phenotype changes in response to this regardless of their genetics.
• The second one, there is no change due to environment, only related to genes
• In the third one, there is an effect of both - genetic effect and environment effect but their responses are different. Meaning certain phenotypes are more effective in certain environments
  !Lecture 4 - Evolutionary Ecology_2025, p.30

Common Garden experiment

Three spined stickleback

• Convergent evolution in freshwater vs marine forms in Japanese and Canadian individuals
• Testing in a common garden environment shows that freshwater individuals with fewer plates have more flexibility allowing for greater escape in more confined conditions

Reciprocal Transplant

• Transplanting a plant from its northern edge to its southern edge of the natural range
  • Arabidopsis thaliana
• Estimate the fitness based on number of seeds per seed/seedling planted
• Fitness of local population is significantly higher than non-local population

Rescue of natural populations from extinction following environmental change

• Genetic Rescue and Demographic Rescue
• Heterozygosity (a measure of genetic diversity) accounted for greater survival rate. Patches with low diversity were more likely to go extinct if they didn't have enough mobility to mix with other populations

Evolutionary genetic rescue

• Demographic time series (abundance of population over time) showing an environmental stress and associated decline
• Stochastic threshold - threshold of being able to maintain intself
• Genetic rescue event where new genes are added - in theory this results in saving the population from going extinct