EEB 390 - Exam 2 - Winter 2025

Gene flow (migration)

Has a dizzying array of possible effects

Interacts with both drift and selection

Viability selection

fitness differences due to differential rates of survival/mortality (surviving to reproductive age)

Fecundity selection

selection on the number of offspring produced

What animal triggered Darwin to think of sexual selection?

The sight of a feather in a peacock's tail

Sexual selection

differential reproductive success resulting from

intrasexual

competition for mates among the same sex

intersexual

attraction to the opposite sex (mate choice)

How does selection operate differently for each sex?

Males (cheap gametes) compete for access to eggs

Females (expensive gametes) invest heavily in each offspring and be choosy

Mating signals first and foremost allow for what

communicating and choosing correct species identity

Direct benefits for females

benefits that affect a particular female directly (food, nest, protection)

Indirect benefits for females

benefits that affect the genetic quality of a particular female's offspring

indicator traits

Assumes that the signals arehonest (signal really means they have good traits—no cheaters!)

Good Genes theories

sexual selection is fundamentally a product of natural selection

Handicap Principle

Ornaments are costly to produce and wear, so they must be indicators of vigor

Runaway Selection

Positive feedback and linkage disequilibrium between ornament and preference = explosive evolutionary "runaway" of both trait and preference

Ex. Females with preference for long tails tend to mate with long-tailed males. Therefore, offspring tend to have the genes for both long tails and the preference for the trait

Lande-Kirkpatrick ("LK") model

mathematical exploration of "Runaway selection"

Darwin's really "Dangerous Idea"

Animal preference may simply be a preference - rather than a product of natural selection to prefer an indicator trait

Evolutionary species concept

a lineage that maintains a unique identity over time (most agreed upon in principal)

Phenetic species (morphospecies) concept

an approach to determining species boundaries in which species are identified as clusters of phenotypically similar individuals or populations

Biological species concept

species are composed of actually or potentially interbreeding individuals that are reproductively isolated

Phylogenetic species concept

species is the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent

Hybrid Zone

Incomplete reproductive isolation can lead to stable hybrid zones

Can provide a window into the speciation process

Reproductive isolation

mechanisms that prevent members of different species from producing offspring

Prezygotic isolating mechanisms

isolating mechanisms that:

1) prevent mating or

2) prevent fertilization if mating has occurred

Postzygotic isolating mechanisms

reproductive isolating mechanisms that occur after fertilization

Examples of Prezygotic isolating mechanisms

1) Mate choice

2) Ecological (i.e. different pollinators because of morphology)

3) Mechanical (i.e. incompatible sex organs)

Examples of Postzygotic isolating mechanisms

1) Hybrid inviability (i.e. hybrids have lower fitness than either parental species in a shared environment) extrinsic

2) Hybrid inviability/sterility (often due to structural differences between chromosomes) intrinsic

Dobzhansky-Müller incompatibility

a general framework for understanding hybrid malfitness

Allopatric Speciation

Occurring in geographically isolated areas. Cannot interbreed due to geographic separation. Gene flow cannot occur because of physical separation.

Sympatric speciation

Occurring together in the same area.

Parapatric

Involves a spatial reduction of gene flow, but no geographic boundary. Usually associated with an ecological gradient

Ecomorph

body types/traits correlated with specific habitat utilization

Ecological isolation

divide up a resource or divide up time for reproduction

Reinforcement

selection against hybrids that reduces the frequency of hybrids and can complete speciation

Gene flow can lead to _____ across multiple spaces

homogenization

Founder event or Peripheral Isolate speciation

When a small population becomes isolated and diverges

What is required for evolution by natural selection?

Variation, heritability, natural selection

The stronger the divergence of selection pressures between locations...

the more differentiation can happen in the face of gene flow

"Mutation-order" speciation

Mutations were selected for within populations, but do not signify adaptive divergence between populations

"sister" species

species and their closest relative

Phylogeography

Studying divergence at the "tips" of the tree of life

FST (fixation index)

proportion of the total genetic variance contained in a subpopulation relative to the total genetic variance. Values can range from 0 to 1. High FST implies a considerable degree of differentiation among populations (isolated groups = 1).

FST of 0

1 Subpopulation contains entire genetic variance of entire population

FST of 1

1 subpopulation is MISSING a lot of overall genetic variance

Hybrid zone studies

Trying to understand the outcomes of secondary contact and the evolution of reproductive isolation

three steps to building a phylogeny

1. Collect character data from each taxon

2. Align those characters into a matrix showing similarity

3. Use some method of inferring relationships from the matrix data

Maximum Parsimony

minimize the number of changes (maximize parsimony) needed to produce the observed tip states

Maximum likelihood

statistical approach used to find the model that maximizes the likelihood of seeing the data

Maximum Likelihood for phylogenetics:

statistical approach used to find the best phylogenetic tree that uses an explicit model of molecular evolution

Bayesian inference

Calculates the probability of the model given the data

Bootstrapping analyses

a statistical technique involving the resampling of data to assess the confidence in a phylogeny

incomplete lineage sorting

when ancestral genetic variation is retained through speciation events

Coalescent theory

developed to study gene-genealogical relationships by tracing the ancestry of gene copies in populations

Coalescence point

the point on a gene tree (the ancestral gene copy) that delineates the most recent common ancestor of the genes being studied in a population

Discordance

when different genes tell distinct stories even though they evolved under a shared history

Biomarkers

molecular evidence of life (e.g., microbial metabolism) in the fossil record

Prebiotic Soup Hypothesis

the idea that the earliest life emerged in a "soup-like" liquid environment, drawing upon energy from cosmic rays, volcanic eruptions, and the Earth's internal heat

Miller-Urey experiment (1952)

Methane, ammonia and hydrogen mixed with boiling water and simulated lightning. Reactions produced over 20 amino acids!

Ribozymes

RNA molecules with enzymatic function (discovered 1980s)

RNA world

a hypothetical period in the evolution of life when RNA served as rudimentary genes and the sole catalytic molecules

Protocell

a cell-like entity that predated cellular life-forms in the history of life

LUCA

Last Universal Common Ancestor (3.5-3.8 billion years ago)

Minimal gene set

hypothetical minimal number of genes

necessary to allow for cellular-based life (about 200)

Horizontal Gene Transfer

Movement of genetic material between individuals (not

parents/offspring) - common in early history of life

Snowball Earth set stage for origin of Eukaryotes

Eukaryotes: cells have a nucleus and other organelles enclosed within membranes (can be uni- or multicellularorganisms)

Who are animals most closely related to?

Fungi and then Amoeba

First eukaryotes:~1.8 billion yearsago• Initial radiation ofanimals: 800million years ago• Initial radiation ofland plants: 500million years ago

First eukaryotes

Endosymbiosis

a mutually beneficial relationship in which one organism lives within the body, often within the cell, of another (chloroplasts are cyanobacteria)

Slime molds

unicellular protists with facultative sociality (paraphyletic)

Taphonomy

study of the fossilization process

FAD & LAD

First appearance date and last appearance date

Macroevolution

Evolutionary change at or above the species level

Diversification

proliferation of phylogenetic (and ecological) diversity over time

Number of plants vs fungi species

500,000 plants and 100,000 fungi species

Lichen

a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi (usually one basidio and one asco!) in a symbiotic relationship

Sepkoski curves

Simple (but data-rich!!) visualizations of biodiversity changes over geologic time

Endemic

species unique to a defined geographic location

Biomes

geographically and climatically defined regions with similar environments

Vicariance

process by which the geographical

range of a population or species is split by the formation of a physical or biotic barrier

Dispersal

process by which a population or species moves individuals or propagules from one area to another

Groups that don't follow latitudinal diversity gradient

salamanders, crayfish, penguins, shorebirds, a few others

Species-Area relationship

Larger (and nearshore) islands have more species

Island biogeography

field within biogeography that examines the factors that affect the species richness of isolated natural communities

Unregulated diversification rate (S-E)

essentially exponential growth

Living Fossils

Single, long branches sister to "more successful" radiations

Imbalance

refers to the distribution of taxa among the different clades of a phylogeny - are they similar or different?

Branching times

the timings of speciation events

More dead hybrids = higher RI

Thick: _______ species

Thin: _______ species

sympatric, allopatric

Key innovation

phenotypic or genotypic trait associated with an increase in diversification (i.e. flowers)

High pollinator specificity

Potential for rapid coevolution of floral traits & pollinators: Rapid speciation

Passive trend

Lower barrier to something like size (evolution won't allow it to go lower)

Active trend

Each lineage tends to increase in body size

Species selection

where only certain species—those possessing a certain trait - survive over long periods of time and therefore

drive evolutionary trend in a trait

anagenetic change

speciation without splitting

Punctuated equilibrium vs phyletic gradualism

punctuated equilibrium: abrupt change

phyletic gradualism: species arise through constant slow change

Stasis

a period of little to no evolutionary change

Preadaption

shift in the function - but not morphology - of a trait during evolution

Why do non-amniote have large flat heads

Buccal pumping - pumping in air with mouth

Costal Ventilation

Amniotic breathing opens up head shape diversity

Key innovations

Amniote, Costal ventilation, flight, milk (mammary gland)