[UCSB SUMMER ‘26] EEMB 2 - Evolution: Week 3 Set

What is speciation?

The evolution of reproductively isolated species through accumulation of genetic changes that create significant differences between populations.

What is an incipient species?

A population in the process of diverging toward full reproductive isolation.

What does gene flow have to do with mechanisms of speciation?

Speciation modes differ largely in how much gene flow persists while populations diverge.

What is the Biological Species Concept?

Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.

Who is associated with the Biological Species Concept?

Ernst Mayr.

What is a major limitation of the Biological Species Concept?

It works poorly or not at all for asexual organisms and cannot be directly applied to many fossils.

What is the Morphological Species Concept?

Species are distinguished by structural/morphological characteristics.

What is a limitation of the Morphological Species Concept?

Within-species variation, developmental changes, and sexual dimorphism can make boundaries ambiguous.

What is the Paleontological Species Concept?

Species are morphologically discrete groups identified in the fossil record.

What is a limitation of the Paleontological Species Concept?

The fossil record is incomplete and many organisms fossilize poorly.

What is the Ecological Species Concept?

Species are distinguished by their ecological niches.

Who is associated with the Ecological Species Concept?

Leigh Van Valen.

What is a limitation of the Ecological Species Concept?

Niches can be difficult to define and may be flexible.

What is the Phylogenetic Species Concept?

Species are sets of organisms with a unique genetic/evolutionary history identified using phenotypic and molecular comparisons.

What types of data can support the Phylogenetic Species Concept?

Phenotypic traits and molecular methods such as DNA barcoding, mitochondrial DNA, molecular clocks, and computational comparisons.

What is a limitation of the Phylogenetic Species Concept?

It can be difficult to decide how much genetic difference is enough to define a species.

Why is 16S rRNA useful for prokaryotic classification?

It is nearly universal in bacteria and contains conserved regions plus variable regions useful for estimating divergence.

What is a molecular clock?

Using rates of sequence change to estimate evolutionary divergence time.

What is an OTU?

Operational Taxonomic Unit; a practical microbial grouping based on molecular similarity.

What 16S rRNA difference threshold is highlighted in the E. coli example?

Historically, more than about 3% difference was used as a standard for recognizing different microbial species/OTUs.

What is allopatric speciation?

Speciation with little gene flow because a physical/geographic barrier separates populations.

How does allopatric speciation proceed?

A barrier reduces gene flow; mutation, selection, and drift produce divergence; reproductive isolation evolves; speciation is complete when interbreeding no longer occurs.

Why are small isolated populations especially prone to allopatric speciation?

Drift is stronger, selection can differ, and gene flow is limited.

What is peripatric speciation?

A form of speciation in a small peripheral isolate with very rare gene flow.

Why is the founder effect especially relevant to peripatric speciation?

A small number of colonists carry an unrepresentative gene pool and experience strong drift in a new environment.

What is parapatric speciation?

Neighboring populations diverge despite some gene flow, often along an environmental gradient, while remaining in contact along a border.

What is a hybrid zone in parapatric speciation?

The contact region where differentiated neighboring populations interbreed and produce hybrids.

What is sympatric speciation?

Formation of new species within the same geographic area despite substantial potential gene flow and no physical barrier.

What mechanisms can generate sympatric speciation?

Polyploidy, ecological/habitat specialization, disruptive selection, and sexual selection/assortative mating.

What is polyploidy?

Having more than two complete sets of chromosomes.

Why can polyploidy cause immediate reproductive isolation?

Polyploids often cannot produce fertile offspring with diploid ancestors because chromosome pairing is disrupted.

What is autopolyploidy?

Polyploidy in which extra chromosome sets come from the same species.

How can autopolyploidy arise?

Nondisjunction during gamete formation can create unreduced gametes; a meiotic error can produce a fertile 4N lineage.

What happens in a 2N × 4N cross?

It can produce 3N offspring that are sterile, creating reproductive isolation between 2N and 4N lineages.

What is allopolyploidy?

Polyploidy in which chromosome sets come from different species.

What is hybridization's initial outcome?

A usually sterile hybrid.

How can chromosome doubling affect hybrids?

It can restore pairing and fertility, producing a new reproductively isolated polyploid lineage.

Where is allopolyploidy especially common?

In plants, such as oats, cotton, potatoes, tobacco, and wheat.

How can ecological specialization drive sympatric speciation?

A subpopulation begins exploiting a different resource or habitat within the same area.

What is the role of divergent selection and assortative mating in sympatric speciation?

They can reduce gene flow.

What example illustrates sympatric speciation in Midas cichlids?

In Nicaraguan crater lakes, benthic and limnetic ecomorphs diverged.

What is positive assortative mating's role in sympatric speciation?

Preference for similar mates reduces gene exchange between diverging ecological forms.

What is adaptive radiation?

Evolution of an ancestral lineage into many descendant species differing in morphology, physiology, or behavior.

What are examples of adaptive radiation?

Galápagos island iguanas and Hawaiian honeycreepers.

What is gradualism in speciation?

Genetic and reproductive divergence accumulates gradually over long periods.

What is punctuated equilibrium?

Relatively rapid speciation when barriers arise quickly, producing long periods of little change.

How does macroevolution relate to microevolution?

Repeated microevolutionary divergence and speciation produce large-scale evolutionary patterns.

What is phylogeny?

The evolutionary history and relationships of organisms or lineages.

What is a phylogenetic tree?

A branching diagram representing hypotheses about evolutionary relationships.

What does a node represent on a phylogenetic tree?

A common ancestor and a lineage-splitting event.

What is a sister group?

Two descendant lineages that split from the same immediate node.

What is an outgroup?

The most closely related lineage outside the focal group.

What is a clade?

An ancestor and all of its descendants.

What is a monophyletic group?

A group containing a common ancestor and all of its descendants.

What is a paraphyletic group?

A group containing a common ancestor but excluding one or more descendant lineages.

What is a polyphyletic group?

A grouping that combines taxa from different evolutionary lineages.

What is a plesiomorphy?

An ancestral character state.

What is an apomorphy?

A derived character state.

What is a synapomorphy?

A shared derived character that diagnoses a clade.

Why are synapomorphies useful for tree construction?

They identify shared derived ancestry.

What is parsimony in phylogenetics?

Preference for the tree requiring the fewest evolutionary changes.

What is a polytomy?

A node with more than two descendant branches.

Does left-to-right tip order on a tree indicate evolutionary advancement?

No.

Do longer branches always mean more evolutionary time?

No.

Does the number of visible tips necessarily equal true diversity?

No.

What does common descent mean?

All living and extinct species trace ancestry through branching lineages.

How should you decide which species concept to use?

Match the method to the organisms and evidence available.

What mode of speciation occurs when a canyon splits one population?

Allopatric speciation.

What mode of speciation occurs when five colonists establish an isolated population?

Peripatric speciation.

What mode of speciation occurs with neighboring grass populations diverging but hybridizing?

Parapatric speciation.

What mode of speciation occurs when a new plant species appears after chromosome doubling?

Sympatric speciation by polyploidy.

What classification includes an ancestor and every descendant?

Monophyletic.

What kind of character is a shared trait evolved before the focal clade?

Plesiomorphy.

What is a shared derived trait appearing in a common ancestor and all descendants?

Synapomorphy.

Are species concepts interchangeable and universally valid?

No.