BIO LESSON 2

Phenotypic Variation in Birds

  • Observed average beak depth: 9.5 mm

  • Beak size categories: Size 6 and Size 12

  • Significance of beak depth: 1 or 2 mm difference can impact survival and reproduction drastically.

Heritability of Traits

  • Key point: If a trait is not heritable, it cannot undergo natural selection.

  • Example: Flamingos turning pink due to carotenoid food, showing environmental influence on a trait that's not genetic.

  • Heritability measures how much of the phenotype variation is attributed to the genotype.

  • Definition of phenotype: Includes environmental and genetic factors influencing traits.

Heritability Calculation

  • Heritability formula: H^2 = Vg / Vp

    • Vg = variance due to genotype

    • Vp = total variance in phenotype

  • Decomposition of Vp into Vg and Ve helps understand phenotype variance.

Broad vs. Narrow Sense Heritability

  • Broad sense heritability includes all genetic variance; narrow is more specific.

  • Highly heritable traits (closer to 1) can change rapidly in populations while low heritable traits (closer to 0) evolve more slowly.

  • Importance of heritability in understanding trait transmission across generations.

Regression Analysis Method

  • Uses line of best fit to analyze phenotype data between parent and offspring.

  • Example: Average beak depth of parents versus their offspring plotted to show correlation.

  • Closer clustering of data points to the line indicates more genetic influence.

Influence of Environment on Traits

  • Dots above or below the line reflect environmental impacts on phenotype.

  • More spread indicates higher environmental influence.

  • The correlation between phenotype and environmental factors is a critical part of understanding natural selection.

Longitudinal Study Findings

  • 52 years of bird data on Daphne Major Island showed populations fluctuated significantly (from 1400 to 200 during drought).

  • Bird population survival directly linked to seed availability affected by environmental conditions.

Non-Random Survival and Selection

  • Larger beaks tended to benefit survival at times, while smaller beaks benefitted at other times.

  • Selection pressures are not static; they change with environmental factors.

  • Example: Average beak size increased from 9.5 mm to 10.2 mm post-drought.

Adaptive Evolution Insights

  • Natural selection does not aim for perfection but rather adapts traits based on fluctuating environments.

  • Trade-offs observed: larger beak size may enhance survival but impact other traits negatively (like speed).

Kin Selection and Altruistic Behaviors

  • Individuals may engage in altruistic behaviors (e.g., alarm calling) to benefit their relatives, enhancing shared gene transmission.

  • Kin selection emphasizes survival of shared genes over individual risk.

Importance of Genetic Variation

  • Genetic variation is crucial for adaptability in changing environments.

  • New adaptations can emerge from persistent selection pressures over generations.

Natural Selection Principles

  • Natural selection acts on individuals, not populations, assessing fitness relative to environmental contexts.

  • Examples of artificial versus natural selection illustrate the underlying principles of heritability and adaptive change.

  • Key takeaway: Natural selection does not lead to perfection; it produces a multitude of traits optimized for survival in specific environments.