IB 150 U3: Speciation & Cladistics

Microevolution

the small evolutionary changes within a pouulation over time

Macroevolution

The formation of new spececies over a generation.

Biological species

populations of interbreeding organisms that are reproductively isolated from other groups

Why does the biological species concept not apply to all organisms?

Some species reproduce asexually and do not adhere to the interbreeding criteria.

Also, ring species that can interbreed with some but not all surrounding species.

3 steps of speciation (from one species → many different)

Step 1:reduced gene flow. The allele frequencies have to be different between populations

Step 2: Genetic divergence. two populations need to become genetically different

Step 3: reproductive isolation. The two species cannot interbreed.

Prezygotic reproductive isolation (types)

The gametes never get the chance to fuse.

Habitat: wrong place.

Temporal: wrong time.

Behavioral: don’t like each other.

Mechanical: doesn’t fit

Gametic Barrier: surface molecules dont like each other

Postzygotic reproductive isolation mechanisms (types)

gametes fuse but offspring cannot reproduce

Hybrid inviability: the hybrid dies during development

Hybrid infertility: the hybrid lives, but cannot reproduce (cannot make gametes)

Reduced hybrid fitness: the hybrid cannot find a mate

Allopatry speciation

Why does it cause reduced gene flow?

a species is seperated geographically (in two differnt locations) and cannot physically mate.

Parapatry speciation

Why does it cause reduced gene flow?

The populations are adjacent, but very distinct.

this leads to differnt selectionp pressures, and prevents going into tother habitat, and thus reduced gene flow

Sympatric speciation

Why does it cause reduced gene flow?

The species live in the same area but do not mate.

this can be because of behavioral things(sexual selection/ niche patternspr habitats) , or chromosomal differences

what are the differnt types of barriers in allopatric speciation

Dispersal: barrier was already there, and organisms somehow get across it.

Vicariance: a new barrier appears, actively splitting the species.

Monophyletic grouping

Groups all the decendants of a common ancestor in one group (a accurate clade)

Polyphyletic grouping

groups distantly related species into a group (inaccurate)(one is not as related as the others)

paraphyletic groupings

it misses some of the species that belong to the clade (missing a descendant)

What do clades do?

Reconstruct an evolutionary history to find the evolutionary relationships and commonalities between species.

Shared derived trait

A trait that evolved in the most recent evolution (a species is singled out because of it)

THEY DEFINE THE “SUB-CLADES”

Shared ancestral

A trait started in an ancestor and is shared by the “newer” species

SHARED WITH SPECIES IN ALL “SUB-CLADES”

Analogous/convergent traits

traits that species share, but are not due to a common ancestor (phenotypically similar, genotypically dissimilar). They evolved independently

why does analogous/ convergent evolution occur?

Organisms share a similar niche, and thus develop similar traits that are helpful in that niche.

Homologous

a trait that IS shared because of a common ancestor, but has evolved to have a different purpose. They are genotypically similar, but phenotypically disimilar).

Maximum parsimony

requires the LEAST amount of evolutionary steps. it is simplicity.