BIO 102: Speciation and Macroevolution

Morphological species concept

Based on diagnostic features and physical (anatomical) characteristics.

What are the advantages of the Morphological species concept?

Useful for organisms that can be easily observed

What are the disadvantages of the Morphological species concept?

Limited; not useful for microbial or extinct organisms, and struggles with cryptic species.

Evolutionary Species Concept

Based on diagnostic features of organisms sharing an evolutionary lineage

What are the advantages of the Evolutionary species concept?

Helpful for suggesting speciation in extinct lineages.

Considers small transitional changes insufficient for a new species unless accompanied by abrupt changes.

Justifies hybrids with genetic variations as part of the same species.

What are the disadvantages of the Evolutionary species concept?

Conclusions are tentative because fossil remains typically lack soft tissues.

Phylogenetic species concept

A concept based on an organism's relation to a shared common ancestor between different species.

What type of evidence does the Phylogenetic Species Concept incorporate?

Morphological, behavioral, and genetic evidence.

What tool is used to illustrate relationships in the Phylogenetic Species Concept?

A phylogenetic tree.

What are the advantages of the Phylogenetic species concept?

Integrates multiple lines of evidence (e.g., DNA sequencing used to redefine giraffe species).

Biologic Species Concept

A concept based on the ability of organisms to interbreed in reproductive isolation.

What is a key requirement for organisms under the Biologic Species Concept?

They must produce fertile offspring in nature.

What are the advantages of the Biological species concept?

Clearly defines species by reproductive isolation.

What are the disadvantages of the Biological species concept?

Limited to sexually reproducing organisms and not useful for fossils.

Phylogeny

An organism's evolutionary history and is often represented using a phylogenetic tree model.

Reproductive isolation

When organisms do not reproduce because of physiological, behavioral, or genetic processes.

Prezygotic Isolating Mechanisms

Prevent mating attempts or make fertilization unsuccessful.

Habitat Isolation

Species occupy different habitats

Temporal Isolation

Species reproduce at different times (different seasons or times of day)

Behavioral Isolation

Species have different courtship patterns, songs, calls, pheromones, or signals.

Mechanical Isolation

Genitalia or floral structures are incompatible or unsuitable for one another.

Gamete Isolation

Gametes meet but do not fuse to form a zygote.

What are the different prezygotic isolating mechanisms?

Habitat, temporal, behavioral, mechanical, gamete

Postzygotic Isolating Mechanisms

prevent hybrid offspring from developing or breeding

What are the types of postzygotic isolating mechanisms?

Hybrid inviability and hybrid sterility

Hybrid Inviability (Zygote Mortality)

Fertilization occurs, but the hybrid zygote is not viable and does not survive (e.g., sheep-goat hybrids dying in utero)

What is hybrid sterility?

A condition where the hybrid zygote develops into an adult but is sterile and incapable of reproducing.

Give an example of hybrid sterility.

A mule, which is a hybrid of a horse and a donkey.

What is F2 fitness in the context of hybridization?

F2 fitness is a postzygotic mechanism where hybrids are fertile, but their F2 offspring have reduced fitness.

What are the Modes of speciation?

Geographical isolation, allopatric speciation, sympatric speciation

Geographic isolation

common between organisms and resultsfrom biogeography (a geographical barrier)

Allopatric speciation?

The generation of new species resulting from geographic isolation via a geographical barrier.

What allows microevolutionary changes to accumulate over time in allopatric speciation?

Physical separation.

Give an example of allopatric speciation.

Ensatina salamanders separated by California's Central Valley.

What reinforces pre- and postzygotic barriers in allopatric speciation?

Natural selection.

What is sympatric speciation?

The generation of new species through methods other than geographic isolation.

What is a common method through which sympatric speciation occurs?

Polyploidy (chromosome numbers >2n).

Disadvantage of sympatric speciation

much harder to observe in nature

Autoploidy

A new polyploid species arises from a single diploid species (from itself)

Alloploidy

A new polyploid species arises from two different species through hybridization and chromosome doubling.

Convergent evolution

It occurs when independent organisms experience a similar set of environmental pressures and evolve similar forms through natural selection.

Can you give an example of convergent evolution?

Cichlid fish species in two different African lakes.

Coevolution

Coevolution occurs when two organisms adapt to benefit each other or adapt in direct response to selective pressures from each other.

What is an example of mutualism in coevolution?

An example of mutualism in coevolution is the relationship between flowering plants and their pollinators.

How do bats and hawkmoths demonstrate coevolution?

Bats and hawkmoths demonstrate coevolution by modifying echolocation frequencies in response to each other.

In what ways can macroevolution be observed?

gradualistic equilibrium model and the punctuated equilibrium model

Gradualistic Equilibrium Model

A model where reproductively isolated groups slowly and steadily adapt over time until they are considered different species.

What happens once groups are reproductively isolated in the Gradualistic Equilibrium Model?

They slowly and steadily adapt over time.

What type of environments does the Gradualistic Equilibrium Model occur best in?

Stable, consistent environments.

What does the Gradualistic Equilibrium Model feature?

Many transitional forms.

Punctuated Equilibrium Model feature?

Model that features abrupt, rapid environmental changes that result in fast speciation.

What is a characteristic of the Punctuated Equilibrium Model regarding transitional forms?

It has very few transitional forms.

Can both the Punctuated Equilibrium Model and other models occur simultaneously in the wild?

Yes, both models can occur in the wild, potentially simultaneously.

Macroevolution

Evolutionary changes resulting in the formation of one or more new species on a large scale. (NOT goal-oriented)

How is macroevolution best observed?

Within the fossil record.

What process is involved in macroevolution?

The origin of new species (speciation).