Evolution and Speciation Flashcards

Question

Isolated populations | Biogeography

Answer 1

Islands such as the Galápagos or Hawaiian archipelagos contain species that are closely related to those on nearby continents but have evolved distinct characteristics due to geographic isolation. - Remote islands (e.g. Galápagos) often have many endemic species, species that are only found in a specific area and are not found elsewhere on Earth

Answer 2

Species that are only found in a specific area and are not found elsewhere on Earth

Answer 3

The geographical distribution of living and fossil species assists in the reconstruction of evolutionary histories. Understanding continental movement and the distribution of living species allows us to predict when and where different groups evolved. - For example, marsupials are found almost exclusively in Australia, while placental mammals dominate other continents - This pattern is explained by the historical separation of land masses (continental drift), which isolated South American and Australian populations and allowed them to evolve independently.

Answer 4

The change in allele frequencies in populations over generations - Individuals represent different combinations of alleles drawn from the gene pool, that is, from all the alleles present in all individuals in the population

Answer 5

Mutation or Gene Duplication

Answer 6

Changes in an individual’s DNA sequence - **Occur Randomly** - Creates new alleles - Causes: i) small-scale (e.g. point mutation) or chromosomal (e.g. insertion/deletion) errors in DNA replication; ii) structural damage to DNA (e.g. radiation) - Can only be inherited if it impacts gametes **Can be deleterious (‘bad’), neutral, or advantageous (‘good’) in the current environment**

Answer 7

**Mutations occur relatively infrequently in populations** Eukaryotes have much faster evolution rates Mutation rates are much lower in prokaryotes. - However, mutations accumulate quickly in prokaryotes because they have very short generation times.

Answer 8

1. Mutation 2. Sexual Reproduction

Answer 9

Sexual reproduction amplifies genetic variation by **creating new combinations of existing alleles** - **Recombination** of homologous chromosomes during meiosis shuffles existing genetic material to create new combinations of alleles - Recombination is often more impactful than mutation in generating genetic variation within sexually reproducing populations over **short timescales**

Answer 10

**Natural selection, genetic drift, and gene flow** are the mechanisms that cause changes in allele frequencies in populations Note: **Only natural selection causes adaptive evolution** - Genetic drift and gene flow are random

Answer 11

The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals

Answer 12

1. Directional selection 1. Disruptive selection 1. Stabilizing selection

Answer 13

Favours individuals that differ from the current mean phenotype of a population **in one direction** - Under directional selection, a population’s genetic variance shifts toward a new phenotype with higher relative fitness when exposed to selection pressures - **Occurs in response to consistent selective pressure**, i.e. a steady change in the environment

Answer 14

Favours individuals at **both extremes of the phenotypic range** - Intermediate (average) phenotypes have lower fitness than either extreme phenotype - **maintains genetic variation in populations** - Ex. Beak size in birds - Some may be drastically large or small based on food availibility

Answer 15

Favours **intermediate or common phenotypes** by selecting against extreme phenotypes that deviate from the current population mean - Stabilizing selection **reduces genetic variation in a population** and maintains the population’s mean phenotype - Very Common - Removes deleterious mutations

Answer 16

Random changes in allele frequencies in a population - **More likely in small populations** - Rare alleles are more likely to be lost due to genetic drift - causes evolutionary change but **does not create adaptations** (non-adaptive)

Answer 17

The bottleneck effect is a sudden reduction in population size due to a change in the environment - Population size is reduced within its natural range Allele frequency in the next generation is different than the previous generation Examples: - Cheetas - Greater Prairie Chickens

Answer 18

Occurs when a few individuals become isolated from a larger population - Allele frequency in the original large population is unchanged The small founding population has a **small fraction** of the total gene pool present in the original population - Allele frequencies in the small founder population differ from those in the larger originating population - e.g. increased frequency of Huntington’s Disease in human populations founded by small groups of European migrants

Answer 19

1. Genetic drift has the largest impact on small populations. 2. Genetic drift causes allele frequencies to change at random. 3. Genetic drift can lead to a loss of genetic variation within populations. 4. Genetic drift can cause harmful alleles to become fixed in small populations.

Answer 20

The movement of alleles between populations of a species - Alleles can be transferred through the movement of fertile individuals (e.g. dispersal of animals or seeds) or gametes (e.g. pollen) Gene flow can **introduce new variation** into the receiving Gene flow reduces variation **between populations** over time.

Answer 21

**Trick Question**: It can make it better or worse **Decreasing** - Occurs when the immigration of alleles that decrease fitness is more rapid than natural selection for alleles that increase fitness - Maladaptive traits are passed along **Increasing** - Examlple: the spread of alleles for resistance to insecticides

Answer 22

1. Natural selection (adaptive) 2. Genetic drift (non-adaptive) 3. Gene flow (non-adaptive) Other factors that bring about evolutionary change: - **Extirpation** of populations reduces a species’ genetic diversity. - **Global extinction** of a species (complete loss of genetic diversity).

Answer 23

Genetic variation that does not confer a selective advantage or disadvantage. - Natural selection does not affect the frequency of neutral mutations Maintained by: - Mutation. - Recombination (crossing-over of chromosomes during meiosis). - Independent assortment (of alleles) during meiosis. - Random mating between individuals (sexual reproduction). - Random fertilization (sexual reproduction). - Recessive alleles are hidden from selection in heterozygote individuals. - Disruptive selection (natural selection). - Gene flow (between populations). - Balancing selection.

Answer 24

A form of natural selection that maintains genetic diversity by **favouring stable frequencies of multiple alleles** in the gene pool of a population Mechanisms: - **Temporal or spatial variation** (the need for different alleles at different locations or points in time) - **Heterozygote Advantage** (organisms with two dofferent alleles have the advantage, ie. sickle cell disease) - **Frequency-dependent selection** (fitness of the alleles depends on lack of others with the same allele ie. scale eating fish) - Often is a result of interactions between species (predation, parasitism, or competition)

Answer 25

1. Adaptations and the genes responsible for them only need to be “good enough” to enable reproduction. 2. Natural selection has no goals 3. Natural selection only acts on existing variation 4. Historical constraints limit natural selection 5. Adaptations are compromises 6. Chance events (genetic drift, gene flow) and environmental variability limit natural selection

Answer 26

The distinction between micro- and macroevolution is arbitrary. - They are fundamentally identical processes on different time scale - **Between microevolution and macroevolution is speciation**, the process by which one species splits into two species over time **Microevolution** - evolution at the population level **Macroevolution** - broad patterns of evolutionary change above the species level

Answer 27

**Macroevolution** - broad patterns of evolutionary change above the species level - Macroevolution is evolutionary changes occurring on geological time scales. - Includes - Novel traits (ex. wings in birds) - Origin of new groups - Mass extinctions

Answer 28

A species is a group of individuals that can interbreed, producing viable (healthy and fertile) offspring, and are reproductively isolated from other species - Members of the same species can exchange genes (through reproduction), which keeps the group unified as a species - **BSC is based on the potential to interbreed rather than physical similarity**

Answer 29

**Not applicable to fossils or asexual organisms**: We can't use BSC for species that reproduce without mating (like bacteria) or for extinct species that we only know through fossils. **Gene flow between species**: While BSC focuses on reproductive isolation (absence of gene flow), sometimes gene flow can occur between different species (hybridization).

Answer 30

**Biological Species Concept (BSC)** - If they can have babies and their babies can have babies **Morphological Species Concept** - It they look similar enough **Ecological Species Concept** - If they have the same job (niche) and live in the same environments **Phylogenetic Species Concept** - The smallest group of individuals with a common ancestor

Answer 31

identifies a species **based on their physical appearance or structural traits**. - Members of a species share a set of characteristics that make them look similar and distinguishable from other species. - **It applies to sexual and asexual organisms but relies on subjective criteria**.

Answer 32

Defines a species by its role in the environment, known as its **ecological niche**, how the species interacts with other organisms and its habitat - Members of the same species will have similar preferences and tolerances for environmental conditions, like temperature or food sources. - This concept also **applies to both sexual and asexual species**. - For example, Canada lynx (Lynx canadensis) and bobcat (Lynx rufus) hybridize in the wild, especially in regions where their ranges overlap, but occupy distinct ecological niches that define them as separate species

Answer 33

Defines a species as **the smallest group of individuals that share a common ancestor**, based on evolutionary history - This concept **applies to sexual and asexual organisms** and is particularly **useful for analyzing evolutionary relationships** - For example, giraffes were previously considered a single species, but recent phylogenetic analyses have revealed that giraffes consist of four distinct species

Answer 34

Biological factors (barriers) that prevent two species from interbreeding and producing fertile offspring (hybrids). - Reproductive isolation keeps species distinct from each other under BSC Reproductive isolation can happen before or after fertilization - **Prezygotic barriers** occur before fertilization and prevent mating or the formation of a zygote (fertilized egg). - **Postzygotic** barriers occur after fertilization, where hybrids may be sterile or not survive long enough to reproduce.

Answer 35

- Impeding different species from attempting to mate. - **Habitat isolation** (don't live in the same space) - **Temporal isolation** (don't mate at the same time) - **Behavioural isolation** (mating rituals keep animals of different species from mating - ANIMAL ONLY) - Preventing the successful completion of mating. - **Mechanical isolation** (Square peg, round hole. Don't think about it) - Preventing fertilization if mating is successful - **Gametic isolation** (Fertilization is unable to happen)

Answer 36

**Reduced hybrid viability**: genes of the different parent species may interact to impair the hybrid’s development or survival **Reduced hybrid fertility**: even if hybrids are vigorous, they may be sterile (ex. mules) **Hybrid breakdown**: some 1st-generation hybrids are vigorous and fertile, but when these hybrids mate with one another or with either parent species, offspring of subsequent generations are feeble or sterile

Answer 37

Some 1st-generation hybrids are vigorous and fertile, but when these hybrids mate with one another or with either parent species, offspring of subsequent generations are feeble or sterile. - Hybrids are eventually eliminated from the population by natural selection - Ex. , different strains of cultivated rice have accumulated different mutant recessive alleles at two loci after divergence from a common ancestor - Hybrids between them are vigorous and fertile, but plants in the subsequent generations carrying too many recessive alleles are small and sterile

Answer 38

**The evolution of new species following the geographic isolation of two or more subpopulations of an ancestral species** When a population is **geographically divided** into two or more isolated groups that are **prevented from interbreeding** - Regions with many geographic barriers (e.g. mountains, rivers, etc) typically have more species than regions with fewer barriers Geographic isolation arises via: - **Dispersal**: where a small population becomes isolated at the edge of a larger population. - **Vicariance**: the range of a species is split by a change in the environment, creating two subpopulations

Answer 39

**False** Barriers to reproduction must be intrinsic; separation itself is not a biological barrier

Answer 40

**The evolution of a new species from an ancestral species while both continue to inhabit the same geographic region** - Speciation without geographic separation - For sympatric speciation to occur the subpopulations occupying the same geographic region must become reproductively isolated from each other Overlapping subpopulations can become reproductively isolated from each other by: - **Chromosomal errors** during meiosis or hybridization of closely related species. - Polyploidy and hybrid speciation. - **Natural selection for reproductive isolation**. - Habitat differentiation (often by disruptive selection). - Sexual selection (non-random mating)

Answer 41

When changes in the number of chromosome sets (polyploidy) create genetically distinct descendants that are reproductively isolated from parental forms. - Occurs infrequently in animals (usually lethal) - Common among plants

Answer 42

When interbreeding between two related species creates genetically distinct descendants that are reproductively isolated from the parent species - Some hybrid species form by polyploidization.

Answer 43

Polyploids have a different number of chromosome sets than their parental forms - Polyploids can only interbreed with individuals of the same ploidy - Polyploidy can produce new sympatric species within a single generation Polyploids arise from: - Hybridization of related species to form allopolyploids (hybrid speciation). - Chromosomal error during meiosis forming autopolyploids.

Answer 44

A species with multiple sets of chromosomes **derived from the hybridization of different species** - Allopolyploid hybrids have double the number of chromosome sets than the parent species - Ex. Wheat

Answer 45

An autopolyploid is an individual with more than two chromosome sets, **derived from one species** - Can arise spontaneously by genome doubling or by fusion of 2n gametes (failure of cell division during meiosis creates gametes with double the number of chromosomes) - Example autopolyploids: alfalfa and potato (both tetraploids, 4n)

Answer 46

Hybridization between related species is a trigger for polyploidization, forming allopolyploids Hybrid speciation can also occur with no change in chromosome number (ploidy), which is known as **homoploid hybrid speciation** - **Homoploids** arise when hybridization produces novel combinations of genes that can adapt hybrids to new habitats that cause them to be reproductively isolated from parental populations

Answer 47

Homoploids arise when hybridization produces novel combinations of genes that can adapt hybrids to new habitats that cause them to be reproductively isolated from parental populations

Answer 48

Natural selection for reproductive isolation between subpopulations can occur after the appearance of new ecological niches. Example: Apple maggot flies (Rhagoletis pomonella) can live on native hawthorn trees as well as more recently introduced apple trees. - Habitat differentiation (apple fruit vs. hawthorn fruit) increases reproductive isolation between subpopulations

Answer 49

Natural selection for reproductive isolation between subpopulations can occur under sexual selection. - Sexual selection occurs when individuals with certain inherited characteristics are more likely than other individuals to obtain mates - Often results in sexual dimorphism: marked differences between the sexes in secondary sexual characteristics

Answer 50

Hybridization occurs when species with **incomplete reproductive barriers** interbreed, resulting in hybrid offspring - These hybrids may have reduced fertility or survival, or they may be fully viable and fertile, depending on the extent of genetic divergence **Hybrid zones can sometimes form where the ranges of the two species overlap**, allowing for limited interbreeding between genetically distinct populations - A hybrid zone can occur in a single band where adjacent species meet - Altering environmental conditions can cause the band to shift

Answer 51

1. **Reinforcment** (hybrids are less fit, **reinforcing reproductive barriers**.) 2. **Fusion** (Hybrids are fit for reproduction, species recombine. **Weakens reproductive barriers**) 3. **Stability** (continued formation of hybrid individuals, but the hybrids are not more fit than the parents, so species remain seperate)

Answer 52

Speciation rates vary widely. - Speciation is generally considered to be a gradual process. - Estimates of the duration of speciation range from 4,000 years (e.g. cichlid fish) to 40 million years (some beetle taxa). - The calculated average time for speciation in plants and animals is ~6.5 million years. **Speciation begins only after gene flow between populations is interrupted, not after a given time**

Answer 53

**True** - Once gene flow is interrupted, the populations must diverge genetically to become reproductively isolated. - This must occur before another event causes gene flow to resume, thus stopping speciation. - Speciation may occur more rapidly under allopatric speciation, than under sympatric speciation.

Evolution and Speciation Flashcards

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