Macroevolution and Phylogenies

Flashcards covering macroevolution vs. microevolution, Hardy-Weinberg equilibrium calculations, mechanisms of allopatric and sympatric speciation, polyploidy, secondary contact outcomes, and phylogenetic tree construction principles.

How does microevolution differ from macroevolution?

Microevolution refers to changes in the frequency of an allele within a population, whereas macroevolution refers to changes in lineages over time and includes evolution across the history of life.

What is the relationship between microevolution and macroevolution?

Microevolution can lead to macroevolution.

In the pearl oyster Pinctada margaritifera, what phenotypes and pearl colors correspond to the $B$ and $b$ alleles?

The black wild-type allele ($B$) is dominant and produces black "peacock" pearls, while the recessive orange allele ($b$) produces an orange mantle morphotype that makes grey-yellow pearls.

In a sample of $100$ Pinctada margaritifera oysters with $40$ homozygous black ($BB$), $20$ heterozygous black ($Bb$), and $40$ homozygous orange ($bb$), what are the observed genotype frequencies?

The observed genotype frequencies are $BB = \frac{40}{100} = 0.4$, $Bb = \frac{20}{100} = 0.2$, and $bb = \frac{40}{100} = 0.4$.

For a sample of $100$ oysters containing $40$ $BB$, $20$ $Bb$, and $40$ $bb$, what are the calculated allele frequencies for $B$ and $b$?

The allele frequencies are $B = \frac{40 \times 2 + 20}{200} = 0.5$ and $b = \frac{40 \times 2 + 20}{200} = 0.5$.

What are the expected genotype frequencies under Hardy-Weinberg equilibrium for allele frequencies $B = 0.5$ and $b = 0.5$, and is the observed oyster population in equilibrium?

Expected genotype frequencies are $BB = 0.5^2 = 0.25$, $Bb = 2 \times 0.5 \times 0.5 = 0.5$, and $bb = 0.5^2 = 0.25$. The population is not in equilibrium because heterozygotes are much less common than expected ($0.2$ observed vs $0.5$ expected) and both homozygotes are more common ($0.4$ observed vs $0.25$ expected).

What biological explanations account for the deviation from Hardy-Weinberg equilibrium in the surveyed Pinctada margaritifera population?

Black and orange phenotypes are not mating randomly, or selection is removing heterozygotes from the population.

What initial condition causes speciation to begin?

Speciation begins when gene flow between populations is reduced or eliminated.

Is natural selection strictly required for speciation to occur?

False. Speciation does not require natural selection, as other evolutionary mechanisms such as genetic drift or chromosome mutations can drive it.

What is allopatric speciation?

Speciation that begins with physical isolation.

What is vicariance?

A physical splitting of habitat.

What is sympatric speciation?

Speciation that occurs while populations live in the same geographic area.

How can extrinsic factors drive sympatric speciation?

Extrinsic factors such as disruptive selection can cause populations to diverge due to different ecological niches and/or mate preferences.

Is disruptive selection more important during allopatric speciation or sympatric speciation?

Sympatric speciation.

How can intrinsic factors cause sympatric speciation, and in what kingdom is this especially common?

Intrinsic factors such as chromosome mutations (polyploidization) can lead to near instant speciation, which is common in plants.

How are autopolyploids formed, and why are triploid offspring sterile?

Autopolyploids form when a mutation in a single individual doubles the amount of chromosomes. When a tetraploid gamete combines with a diploid gamete, it forms a triploid cell that cannot undergo meiosis evenly, making it sterile.

How does allopolyploidy restore fertility in hybrid offspring?

Haploid gametes from two different species combine to make an otherwise sterile hybrid. An error in mitosis before meiosis doubles the number of chromosomes, giving the cell homologous pairs that can line up during meiosis.

What can happen during population fusion if one species is forced into the niche of another and hybrids are less fit?

Natural selection may cause one of the merged species to go effectively "extinct" as their alleles are completely lost.

What is reinforcement when isolated populations re-establish contact?

When differences developed in separation result in less fit hybrids, natural selection acts against hybrids upon secondary contact to further reinforce speciation.

What are two potential outcomes regarding hybrid persistence when isolated populations come into contact?

Permanent hybrid zones may form, or the hybrids may become species of their own.

What problematic assumptions are built into Hennig's method of constructing phylogenetic trees from data matrices?

It assumes that all currently observed shared traits are derived from a common ancestor (homologies) and that traits never reverse themselves.

What is the difference between homology and homoplasy?

Homology refers to traits shared because of common ancestry, whereas homoplasy refers to shared traits that evolved independently due to convergent evolution.

How does the principle of parsimony identify the best phylogenetic tree hypothesis?

It counts the number of character changes required to produce each tree pattern; the tree requiring the fewest overall character changes is hypothesized to reflect reality.

What characteristics make ribosomal RNA (rRNA) genes useful for molecular phylogenetics?

They are present in all living things and represent non-protein coding regions.

What makes mitochondrial DNA particularly useful for phylogenetic analysis compared to nuclear DNA?

Mitochondrial DNA evolves faster than nuclear DNA, making it ideal for studying closely related species.

Why do amino acid sequences evolve more slowly than DNA, and what evolutionary depth are they suited for?

They evolve more slowly because of codon redundancy, making them ideal for deep evolutionary comparisons.

What two historical processes shaped the diversity of life over the past approximately $500\text{ mya}$?

Adaptive radiations and extinctions.