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

Reproductive 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

Why does the Biological species concept fail for fossils and asexual organisms?

Reproductive isolation can’t be evaluated

Ex. We can’t test if T.Rex could mate with other dinosaurs. It also doesn’t work for bacteria that reproduce by splitting

What is the problem with applying the Biological Species Concept to geographically separated populations?

It is difficult to assess if they would interbreed if they came into contact 

Ex. Polar bears and grizzly bears live in different areas. The concept can’t easily decide if they are separate species without an unnatural experiment

Morphospecies concept

defining species based on differences in morphology(size, shape, or other physical features). Assume distinct forms arise from lack of gene flow

The biggest advantage of the Morphospecies concept

Widely applicable to sexual, asexual, and fossil species when gene flow data is missing

How can the Morphospecies concept mistakenly classify one species as many

By misidentifying a polymorphic species (one species with multiple forms) as multiple species

Ex. A single species of butterfly with different wing patterns might be classified as three separate species based on looks alone

How can the Morphospecies Concept mistakenly classify many species as one

It can miss cryptic species that look identical but are genetically different are reproductively isolated

Ex. Two frog species may look the same but have different mating calls and can’t interbreed. 

What is a synapomorphy, and how is it used?

A unique, shared trait found in a common ancestor and all its descendants, but not in more distant groups. It defines a clade

White fur is a synapomorphy that identifies polar bears as a distinct monophyletic group within bears

What is the main drawback of the Phylogenetic species concept?

Relatively few feel-estimated phylogenies are available, so they can’t be used for most organisms yet

What is the difference between Systematics and Taxonomy

Systematics: The science of characterizing and classifying organisms and determining their evolutionary relationships

Taxonomy: The practice and science of naming and classifying individual species

Applying the Biological Species concept t African elephants, what is the complicating evidence?

There is some evidence of hybrid offspring between forest and savanna elephants, suggesting they are not completely reproductively isolated

Applying the morphospecies Concept to african elephants, what is the evidence?

Clear anatomical differences support separating them; the tusk/shape, number of toenails, body size, and skull dimensions all differ

Applying the Phylogenetic species Concept to African elephants, what does the DNA evidence show

DNA sequences show forms and savanna elephants from distinct monophyletic groups, providing strong evidence that they are separate species

What does the elephant debate teach us aboutt the species concepts?

DNA evidence (Phylogenetic) often helps resolve conflicts between reproductive data (Biological) and physical data(Morphological)

what two conditions are ideal for fossil formation

1. Rapid burial (by sediment, mud, tar)

2. Slow decomposition (often in low-oxygen environments)

Which organisms are most likely to be preserved?

Species with hard parts (bones, shells), that were abundant, widespread, and long lived

Ex. We have many fossilized clams (hard shells, common) but almost no fossilized worms (soft bodies)

What are transitional features 

Traits in a fossil species that are intermediate between those of its ancestors and its descendants

Ex. Tiktaalik had both fish-like fins and scales, and tetrapod-like ribs and a neck

What are the missing links, like Archaeopteryx and Tiktaalik

fossil species demonstrate a clear evolutionary link between two major groups

Ex. Archaeopteryx links dinosaurs (teeth, bony tail) and birds (feathers, wishbone). Tiktaalik links (fins, gills) and tetrapods (flat head, wrist bones)

What is Homology?

A similarity in different species exists because they descended from a common ancestor

Genetic Homology

Similarity in DNA, RNA, or amino acid sequences between different species

What is the ost fundamental genetic homology shared by almost all life

The Genetic Code itself—the same rules for translating DNA into proteins

How do genetic Similarities show evolutionary relationships

The number of genetic differences (in amino acid sequences) corresponds to how closely related species are

Ex. Humans have fewer amino acid differences with chimpanzees than with cats, showing a closer relationship to chimps

Developmental Homology

Similarity in embryonic structures or developmental process

What is a key example of developmental homology in vertebrate embryos?

Early embryos of chicks, humans, and cats all have tails and pharyngeal pouches, suggesting a shared aquatic ancestor

Structural Homology

Similarity in adult body structures

Ex. The similar bone structure (one bone, two bones, many bones, digits) in the human arm, the cat leg, the whale flipper, and the bat wing

Vestigial Traits

Remnants of features that served a function in an organisms ancestors but have little or no function in modern descendants

Ex. Hip bones in whales and pythons (vestiges of when their ancestors had legs)

What is Internal Consistency in evolution?

The observation that data from independent sources agree in supporting predictions made by evolutionary theory

How do relative and Absolute Dating provide internal consistency for phylogenies

Relative Dating: Places fossils in a sequence (older vs. younger layers)

Absolute Dating: Provides numerical ages for rocks

Connection: Both methods confirm the same order of appearance for species that is predicted by phylogenetic species

How does the whale evolution show internal consistency?

1. DNA (Genetic Homology): Links whales to hippos.

2. Fossils (Structural Homology): Show a series of transitional forms from land-dwelling to aquatic mammals.

3. Vestigial Traits: Modern whales retain vestigial hip bones.

How do different types of homlogy help build a phylogeny?

They provide different data sets (DNA, embryos, bones) that all point to the same pattern of common ancestry, making the phylogenetic hypothesis strong and consistent