Speciation

What is a species? Species == “kind” or “type” in Latin Typological (morphological) species == a group of organisms that share certain characteristics which are different than other groups—usually differences in anatomy. Each kind of organism is fixed and immutable and can be represented by an ideal individual, the type specimen (Linnaean Nomenclature)

What is a species? 2. Biological species concept== Reproductively isolated group of actually interbreeding natural populations that produce fertile offspring This definition is hard to apply because most organisms don’t live together and never have a chance to interbreed.

A B B A Easy Hard How do we know if 2 species interbreed? Sympatric species = ranges overlap Allopatric species = ranges don’t overlap A B B A Easy Hard How can we test if two populations are 2 species? Biological species definition used 10% of the time Morphological & chem. differences used 90% of the time.

Problems in identifying species: 1. Polymorphic species = species with many different types of individuals

Problems in identifying species: 2. Sibling species = virtually identical species

Problems in identifying species: 3. Sibling species = virtually identical species Madagascar’s Supportive Lemur Lepilemur mustelinus One species 7 species

Problems in identifying species: 4. Ring Species = continuous gradual shift in phenotype over a large range. The end populations can’t interbreed.

Problems in identifying species: 5. Asexual species = can’t use biological species definition 6. Fossil species = can’t use biological species definition

What Keeps Species From Interbreeding ? Reproductive Isolating Mechanisms

Reproductive isolating mechanisms Pre-zygotic Barriers before zygote formation Ecological (Habitat) Isolation Share territory, but occupy different regions Behavioral Isolation e.g. frogs only respond to calls of the same species

Pre-zygotic Barriers cont’ 3. Mechanical Isolation == Distinct reproductive parts Gametic Isolation Mating occurs but egg and sperm are incompatible due to lack of interaction of receptors on the cell membranes

Post-zygotic Barriers= after zygote Hybrid inviability fertilization occurs but zygote, embryo or larva dies Hybrid Sterility. Healthy hybrid unable to reproduce due abnormal gametes; e.g. mules. Populations do not strive to become species

How are Species Formed?? Microevolution Mechanisms of Speciation Allopatric speciation (=geographic speciation) Two steps: 1. Geographic separation of a once continuous population 2. Reproductive isolation produced during genetic drift or natural selection

How Does Geographical Isolation Occur? Dispersal 2. Barriers 3.Continental Drift

Allopatric Speciation

Allopatric Speciation

Allopatric Speciation Kaibab Squirrel Albert’s Squirrel

Sympatric Speciation Ecological speciation = speciation within a population occurring in a single habitat. Mechanism?

Sympatric Speciation Instantaneous speciation= new species formed in one generation Mutation Not probable Polyploidy. Common in plants Autopolyploidy—diploid gametes form zygote producing new species e.g. bananas Allopolyloidy—two different species hybridize and double their chromosomes

Hybrid Speciation Spartina alterniflora x Spartina maritina e.g. Marsh grasses Spartina alterniflora x Spartina maritina American British Spartina townsendii

SYMPATRIC SPECIATION 2. Gradual Speciation E.g.. Tephritid fly specializing on different host trees (hawthorn vs. apple)

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