Speciation

Speciation

A. Speciation: process by which one species splits into 2 or more species

  1. Biological species concept: species is a group of populations that can interbreed in nature and produce viable, fertile offspring

  2. Morphological species concept: characterizes species by body shape or other structural features

  3. Ecological species concept: characterizes species by how it interacts with the environment

  4. Phylogenetic species concept: characterizes species as the smallest group that shares a common ancestor

    1. one branch on the phylogenetic tree

    2. comparing molecular gene sequences


B. Reproductive Isolation: barriers that prevent gene flow between two species

  1. Prezygotic barriers: before the zygote

    1. Habitat isolation: live in different habitats

    2. Temporal isolation: breed at different time

    3. Behavioral isolation: different courtship rituals

    4. Mechanical isolation: incompatible reproductive anatomy 

    5. Gametic isolation: gametes cannot unite

  2. Postzygotic barriers: after the zygote

    1. Hybrids: offspring from interspecies mating

    2. Hybrid inviability: hybrid zygote fails to develop 

    3. Hybrid infertility: hybrid is born but sterile

      1. Chromosome from parents differ in numbers or structure

      2. Meiosis in hybrid cannot produce functional gametes

      3. Donkey (64) + Horse (62) = Mule (63)

    4. Hybrid breakdown: 

      1. First generation hybrids are viable/fertile

      2. Subsequent generations are feeble/ sterile

      3. Cultivated crops


C. Isolation prevents gene flow

  1. Allopatric speciation: “other homeland”

    1. Speciation that occurs when a population is geographically divided

  2. Sympatric speciation: “same homeland”

    1. Habitat differentiation 

    2. Sexual selection


D. Phylogeny: evolutionary history of a species or group of species

  1. Systematics: discipline of classifying organisms and determining evolutionary relationships

  2. Taxonomy: discipline of classifying organisms and naming organisms

  3. Binomial nomenclature: two-part scientific name

    1. 18th century by Carolus Linnacus

    2. Uses Latin

    3. Genus Species

E. Hierarchical classification: groups organisms into categories 

  1. Domain: Eukarya 

  2. Kingdom: Animatia

  3. Phylum: Chordata

  4. Class: Mammalia

  5. Order: Primata

  6. Family: Hominidae

  7. Genus: Homo

  8. species: sapiens

F. Phylogenetic tree: branching diagram showing evolutionary history 

  1. Cladistics: classifying organisms by inferring phylogeny from homologous characters

    1. Clade: related group

    2. Shared ancestral character: character that originates from ancestor

    3. Shared derived character: novel character unique to clade

  2. Branch points: divergence from common ancestor

  3. Taxon: group at end of branch

  4. Sister taxa: groups that share an immediate common ancestor 

  5. Monophyletic: “single tribe” ancestor species and all descendants 

  6. Paraphyletic: “beside the tribe” ancestor species and some but not all descendants 

  7. Polyphyletic: “many tribes” grouping w/many different ancestors


G. How to determine phylogeny

  1. Morphology

    1. Homology: phenotypic and genetic similarities due to shared common ancestry

    2. Analogy: convergent evolution producing similar adaptations that evolved independently 

    3. Plesiomorphy: ancestral homologous trait shared between taxa

    4. Apomorphy: derived homologous trait unique to later clade/taxon

    5. Homoplasy: analogous trait that evolved independently

  2. Genes

    1. DNA alignment

    2. can be homologous or analogous

  3. Biochemistry

    1. Test function of enzymes


H. Phylogenetic trees as hypotheses 

  1. Models of phylogeny are updated as new info is gathered 

  2. Maximum parsimony: simplest explanation is best

    1. choose the model with fewest evolutionary events


I. Three Domains/ Five Kingdom

  1. Domain Archaea

    1. Kingdom Monera- Prokaryote

  2. Domain Bacteria

    1. Kingdom Monera - Prokaryotes

  3. Domain Eukerya - Eukaryotes

    1. Kingdom: Protista 

    2. Kingdom: Fungi

    3. Kingdom: Plantae

    4. Kingdom: Animalia