Rappels de Biologie Évolutive

Rappels de Biologie Évolutive

• Espèce: A group of organisms capable of interbreeding and producing viable, fertile offspring. Definitions vary among researchers.
• Grassé: A group of living beings descended from a common ancestor, sharing similar genotypes, and prevented from naturally hybridizing due to genetic, anatomical, or ecological reasons.
• Mayr: Natural populations that are reproductively isolated.
• Dobzhansky: A closed gene pool.
• De Quiroz: Metapopulations in the process of becoming distinct.
• Pool génique: The complete genetic information shared by a sexually compatible population.
• Phénotype: Measurable traits resulting from the interaction of genes and the environment.

Forces Évolutives

Mutation

• Random changes in DNA, the primary source of genetic variation.
• Typical rates: 10⁻⁹ to 10⁻¹⁰ per nucleotide per generation.
• Important for genetic variability and natural selection.

Dérive Génétique

• Random changes in allele frequencies in small populations.
• Example: Buri (1956) study on Drosophila melanogaster demonstrating divergence among populations over 19 generations
• Effects: Loss of genetic diversity, fixation of non-adaptive alleles.
• Influencing factors: Population bottlenecks, founder effect (colonization of new areas).

Migration

• Gene flow between populations through migration.
• Models: Island model (free gene flow between isolated populations), two-dimensional model (more frequent gene exchange between nearby populations), metapopulation model (populations are fragmented), stepping-stone model (gene flow is confined to adjacent populations).

Équilibre Hardy-Weinberg

• Ideal population where allele frequencies remain constant from one generation to the next.
• Conditions: Non-overlapping generations, large population size, random mating, no gene flow, no mutations.

Évolution et Adaptation

• Adaptation: Genetic and phenotypic changes that enhance an organism's fitness.
• Natural selection: Differential transmission of traits that offer an adaptive advantage.

Mécanismes de Spéciation

• 1. Pré-zygotiques*

• Isolement spatial (géographique): Populations separated by geographical barriers. (e.g., lions in Africa vs. tigers in Asia)

• Isolement temporel: Reproductive periods differ. (e.g., different breeding times in frogs)

• Isolement écologique: Different ecological niches. even if they occupy the same geographic region. (e.g., different feeding or nesting habitats)

• Isolement éthologique: Different courtship behaviors.

• Incompatibilité morphologique: Incompatible reproductive structures.

• 2. Post-zygotiques*

• Incompatibilité embryonnaire: Unsuccessful embryo development due to genetic incompatibility.

• Mortalité infantile: Death of hybrid offspring.

• Stérilité des hybrides: Inability of hybrids to reproduce.

• Dégénérescence des hybrides: Impaired health or fertility in subsequent hybrid generations.

Bases Biologiques du Comportement

• Animal behavior results from natural selection.
• Optimized for maximizing fitness.
• Concepts: Social behavior (altruism, cooperation), sexual selection (unequal investment in reproduction).

Écologie Comportementale

• Analyzing behavior in its ecological context.
• Aspects: Foraging strategies, predator/prey interactions, social group dynamics.

Applications Pratiques

• Conservation: Using evolutionary principles to manage endangered species.
• Agriculture: Applying understanding of gene flow and genetic diversity to improve domestic crop and animal breeding.

Cas des Hybrides

• Mules and hinnies: Artificial crosses, often infertile.
• Ligers and tigons: Problematic for conservation, with offspring often not viable.