Guest Lecture 1

Discrete Traits:
- Inherited in a Mendelian fashion if controlled by a single gene.
- Can be understood through controlled crosses or pedigrees.
Continuous Traits:
- Most traits show a continuous range of variation, governed by multiple genes, each exerting small effects under Mendelian inheritance rules.
- Quantitative traits are measured numerically.
- Studying genetic variation for quantitative traits is complicated due to multiple contributing genes.

Influencing Factors:
- Expression of many genes.
- Additive gene effects.
- Variability in gene effects across loci.
- Dominance and epistatic interactions among alleles.
- Environmental variation affects traits.
- Visual Representation:
- The distribution of additive effects is represented by a bell curve.

Population Description:
- Populations analyzed through trait means, variances, and covariances among traits and relatives.
Variance Concepts:
- Variance: Dispersion around the mean, calculated as average squared deviations from the mean.
- Co-variance: The product of deviations from the mean for two measures taken simultaneously.

Phenotype (P): Influenced by genetics (G) and environment (E).
Phenotypic Variance (VP): Can be separated into genetic (VG) and environmental (VE) components.
Heritability in Broad Sense (H2):
- Defined as the fraction of phenotypic variance that is genetic.
- Formula: $VP = VG + VE$
- Heritability: $H^2 = \frac{VG}{VP}$

Additive Genetic Variation (VA):
- Measures phenotypic variance due to directly inherited genetic effects.
- Non-additive sources of genetic variance are due to dominance (VD) and epistasis (VI).
Heritability in Narrow Sense (h2):
- Represents the additive genetic variance as a fraction of the phenotypic variance:
- Formula: $h^2 = \frac{VA}{VP} = \frac{VG}{VP} = VA + VD + VI$
- Indicates parental resemblance and predicts the response to selection.

Methods:
- Slope estimation of offspring values on average parental values.
- Heritability can be estimated in natural populations with known parentage and traits measured in large samples (typically hundreds of families).
- Example: Human height has an estimated heritability of 0.57 derived from Galton’s data (1889).

The slope of the best-fit line from average parent-offspring height comparisons directly measures heritability (h2).
Diagram: Slope indicating varying heritability:
- Flat / little heritability: suggest low genetic impact.
- Steep slope / high heritability: suggest stronger genetic influence.

Heritability (h2) forecasts variance inheritance available for selection.
Selection Differential (S):
- Difference between the population mean and selected parents.
Response to Selection (R):
- Difference between offspring of selected parents and the population mean.
- Breeder’s Equation: $R = h^2 S$
- Importance for improving artificial selection.

Indicates resemblance due to inherited genes.
The potential for evolutionary change.
Predictability of traits based on genetics.
A measure of genetic variation in a population at a specific time and environment.
Not a fixed species property, not equivalent to inheritance or heredity - heritability is a statistical measure.

Require large sample sizes compared to other genetic diversity measures (e.g., heterozygosity).
Necessity for precise pedigree information, behavioral data, or genetic markers for relatedness.
Accurate phenotype measurement is challenging.
Parameters (variances and heritability) are trait and population-specific.
Difficulty in isolating environmental and maternal effects from genetic ones.

Mousseau and Roff (1987) conducted studies comparing heritability of different traits.
Findings:
- Morphometric traits more heritable than physiological and behavioral traits.
- This trend supports the idea of selection limiting genetic variation in fitness traits (Fisher's Fundamental Theorem).

Mutation: Source of all genetic variation.
Migration: Transfers genetic variation between populations.
Genetic Drift: Reduces genetic variation over time.
Selection: Can both erode genetic variation (stabilizing or directional) and maintain variation (disruptive or balancing).

Study by Stirling et al. (2002): Confirmed earlier trends, showing mean heritability of behavior at approximately 0.3.
Dokcherman et al. (2019): Discussed limitations in applying heritability findings across different populations.

Behavior	Definition
Activity	Movement rate and patterns of individuals.
Aggression	Antagonistic behavior toward others.
Boldness	Measures of predator avoidance and inspection (e.g. escape response).
Communication	Transfer of information between individuals or groups.
Exploratory Behavior	Investigation of novel environments.
Foraging	Behaviors related to searching, handling, and consuming food.
Mating	Courtship and copulation behaviors.
Migration/Dispersal	Movement among areas during organism's life (repeatedly or singular).
Parental Effort	Expenditure that benefits offspring.
Social Behavior	Affiliative and grouping behaviors (e.g. allogrooming).
Other	Additional behaviors not captured in previous categories.

Sample Sizes:
- Ectothermic (n = 187)
- Endothermic (n = 289)
- Invertebrates (n = 87)
- Vertebrates (n = 389)
- Designated sample sizes for each behavior included in analysis.

Detailed evaluation of heritability across various species using a phylogenetic tree representation and forest plots showing mean effect sizes.

Measurements:
- Boldness: How frequently a ram comes to the trap.
- Docility: Handling difficulty measures during trapping.
Heritability Estimates:
- Boldness: $h^2 = 0.39$
- Docility: $h^2 = 0.65$
Concepts:
- Breeding value represents the additive effects of genes for traits against the population mean.
- Genetic correlation reflects how two traits may be co-inherited due to shared genetic architecture.

Objectives reiterated for emphasis, reinforcing key concepts around quantitative traits, variance, and heritability.

A wide variety of references provided to explore topics in greater depth and context around heritability and behavior studies.