MACROEVOLUTION

Macroevolution

large evolutionary changes that result from the accumulation of many small changes(microevolution) over time

Speciation

splitting event that creates two or more distinct species from a single ancestral species

First requirement for speciation

Genetic isolation: a barrier to gene flow that separates two populations

Second requirement for speciation

Genetic divergence: mutation, natural selection, and genetic drift act on the isolated populations, making them different

Biological species concept

a group that can interbreed and produce viable, fertile offspring, and is reproductively isolated from other groups

The major disadvantage of the Biological Species Concept

cannot be applied to asexual organisms, fossils, or populations that don’t overlap geographically

Morphospecies concept

defining a species based on being morphologically distinct Idifferentin shape and form)

Disadvantage of Morphospecies concept

misidentifies polymorphic species (same species different forms) and miss cryptic species (different species, same look)

Phylogenetic Species Concept

A species is the smallest monophyletic group (a clade) on a phylogenetic tree

Monophyletic group( a clade)

An ancestral population plus all of its descendants

Synapomorphy

A unique trait found in a common ancestor and all of its descendants, but not in more distant ancestors Iwhite fur in polar bears)

Disadvantage of the Phylogenetic Species Concept

Very few-well estimated phylogenies are available, so it can’t be used for most organisms yet

Phylogeny

The branching evolutionary history of a group of organisms

Tip

endpoint of a branch; represents a living or extinct species

Node

a point where a branch splits, represents the most recent common ancestor of the descendant grous (speciation event) 

Root

Most recent ancestral branch in the tree, representing the common ancestor of all groups in the tree

Polytomy

A node that splits into three or more branches. Shows uncertainty about relationships

Where are existing species always located on a phylogenetic tree?

Only on the branch tips, never within the tree.

Sister group

Two species that are each other’s closest relatives, sharing a recent common ancestor

are phylogenetic trees facts

No, they are hypotheses that are based on the best available data and can be tested

Prezygotic Isolation

Isolation that prevents mating or fertilization (a zygote is never formed)

Temporal isolation

Populations breed at different times

Ex. Bishop and Monterey pines release pollen at different times of the year

Habitat Isolation

Populations breed in different habitats (Mainland mice and beach mice)

Behavioral Isolation

Populations do not interbreed due to different courtship displays

Ex. Male songbirds sing species-specific songs

Mechanical Isolation

Mating fails because the male and female reproductive structures are incompatible

Ex. Inset genitalia fit together like a lock and key

Gametic Isolation

Mating fails because the eggs and sperm are incompatible

ex. Sea urchin sperm can’t penetrate a different species egg

Postzygotic isolation

Isolation that occurs after a zygote is formed; the hybrid offspring do notsurvive or are sterile

Hybrid Inviability

Hybrid offspring die at some point during early development

ex. Ring-necked dove and rock dove eggs rarley hatch

Hybrid Sterility

Hybrid offspring mature but are sterile as adults

Ex. A mule, the offspring of a horse and donkey, is sterile