Speciation

Morphological Data: Practical tool for identifying species.
- Members of one species appear more similar to each other than to members of other species.
Molecular Data: May not always align with morphological data.
Phenotypes: results from genotype.
- Different genotypes may lead to similar or identical phenotypes.

Morphological/Biochemical Changes: Affect an organism’s fitness; essential for survival and reproduction.
Adaptations: Modifications enhancing fitness.
Variation: Without it, adaptation cannot occur!

Population: A group of individuals of the same species living in proximity and reproducing with one another.

Definition: A species is a group of interbreeding individuals or populations, reproductively isolated from others.
- Within Species: Interbreeding leads to viable, fertile offspring.
- Between Species: Presence of reproductive isolation.
Example: Platanus species (P. orientalis vs. P. occidentalis) demonstrate interbreed capability despite morphological distinctions.
Reproductive Isolation: Some organisms reproduce asexually, complicating species classification (e.g., Rubus species).

Evolutionary Species Concept: A lineage maintaining a unique identity over time.
Phenetic Species Concept: Defines species via clusters of phenotypically similar individuals.
Biological Species Concept: Based on actual/potential interbreeding individuals, emphasizing reproductive isolation.
Ecological Species Concept: Species defined by occupying the same ecological niche.
Phylogenetic Species Concept: Smallest monophyletic group distinguished by unique character.

Definition: Two populations become geographically isolated due to a physical barrier, preventing gene flow.
- Both populations experience local adaptations, evolving into distinct lineages.

Definition: Small populations at geographical range edges experiencing different environmental conditions.
- Small population subject to genetic drift leading to speciation.

Definition: Speciation occurs without geographical barriers.
- New lineages arise within existing populations, requiring mechanisms to prevent gene flow.
- Can occur rapidly due to:
  - Simple mutations causing drastic phenotypic changes.
  - Chromosomal rearrangements causing gamete variation.
Polyploidy: Involves multiple sets of chromosomes, prevalent in plants (haploid to tetraploid).

Allopatric Speciation: Involves geographical barriers leading to reproductive isolation and divergence.
Parapatric Speciation: Occurs across environmental gradients and involves dispersed populations.
Sympatric Speciation: Happens within populations with no geographical separation, leading to reproductive isolation and divergence.

Reproductive Isolating Barriers:
- Prezygotic Barriers: Prevent zygote formation; includes premating and postmating mechanisms.
- Postmating, Prezygotic Barriers: Gamete transfer occurs but does not result in fertilization.
- Postmating, Postzygotic Barriers: Hybrid zygotes form with reduced fitness.

Resource Efficiency: Gametes, especially eggs, are costly to produce; prezygotic barriers account for over 95% of isolation.

Temporal Isolation: Mating occurs at different times (e.g., flowering plants at different times).
Habitat Isolation: Species occupy different habitats preventing encounters.
Floral Isolation: Floral adaptations influence pollinator interactions and reduce gene flow.

Agamospermy: Asexual reproduction leading to genetically identical offspring.
Autogamy: Self-pollination within a flower.
Xenogamy: Outcrossing between individuals of different plants.
Geitonogamy: Pollination between flowers on the same plant; genetically identical to autogamy.

Incompatibility: Prevents effective pollen germination; competition among pollen tubes.
- Gametic Isolation: Egg and sperm failure to unite effectively.

Hybrid Inviability: Reduced survival of hybrids, with intrinsic (development failure) and extrinsic (competition failure) factors.
Floral Isolation & Hybrid Sterility: Ineffective pollination leads to few hybrid occurrences and reduced fertility among hybrids.