Topic 8: Speciation

Question 1

what is meant by the term “species”?

Answer 1

populations that can interbreed with members of the same group in nature and produce viable, fertile offspring

Question 2

what is meant by the term “speciation”?

Answer 2

evolutionary process in which one species splits into 2+ species

Question 3

what is meant by the term “macroevolution”?

Answer 3

evolutionary change at or above species level

Question 4

what is meant by the term “microevolution”?

Answer 4

• evolutionary change at or below species level
• characterized by changes in the allele frequencies in a population over generations

Question 5

what is the “biological species concept (BSC)”?

Answer 5

populations can interbreed or have potential to interbreed with members of the same group in nature, and produce viable, fertile offspring

Question 6

what are key characteristics of the biological species concept (BSC)?

Answer 6

• focus on breeding over generation
• species are distinguished by reproductive isolation
• relies on actual or potential breeding
• gene flow between population of the same species contributes to unity of species

Question 7

how is reproductive isolation caused?

Answer 7

by reproductive barriers

Question 8

what is a reproductive barrier?

Answer 8

existence of biological factors that impede members of two species from producing viable, fertile offspring

Question 9

what are the two main categories of reproductive barriers?

Answer 9

• prezygotic barrier
• postzygotic barrier

Question 10

what is the prezygotic barrier?

Answer 10

• reproductive barrier that impedes mating between species or hinders fertilization if interspecies mating in attempted

Question 11

what are the main types of prezygotic barrier?

Answer 11

• habitat isolation
• temporal isolation
• behaviour isolation
• mechanical isolation
• gametic isolation

Question 12

what is meant by “habitat isolation”?

Answer 12

two species that live different habitats within the same location encounter each other rarely or not at all (gap in space)

Question 13

what is meant by “temporal isolation”?

Answer 13

two species that breed at different times, leading to rare or no encounters (gap in time)

Question 14

what is meant by “behaviour isolation”?

Answer 14

species use unique courtship rituals and other behaviours to attract mates (like the don’t speak the same language)

Question 15

what is meant by “mechanical isolation”?

Answer 15

anatomical differences prevent successful mating (ducks corkscrew dicks)

Question 16

what is meant by “gametic isolation”?

Answer 16

sperms of one species cannot fertilize the eggs of another species

Question 17

what is the postzygotic barrier?

Answer 17

a reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults

Question 18

what are the main categories of postzygotic barrier?

Answer 18

• reduced hybrid viability
• reduced hybrid fertility
  -hybrid breakdown

Question 19

what is meant by “reduced hybrid viability”?

Answer 19

genes from parents of different species may interact to impair the hybrid’s development or survival

Question 20

what is meant by “reduced hybrid fertility”?

Answer 20

hybrids may even be sterile and could not reproduce further, even if the hybrids survive

Question 21

what is meant by “hybrid breakdown”? what is a possible cause?

Answer 21

• reproductive failure that appears after the F2 generation of crosses between different species
• possible cause is accumulation of deleterious genetic traits (alleles)

Question 22

what does the term”zygote” mean?

Answer 22

fertilized eggs from union of reproductive cells

Question 23

what does the term “hybrids” mean?

Answer 23

offspring from the mating of two different species

Question 24

what are the limitations of BSC?

Answer 24

• cannot be applied to asexually reproducing organisms
• cannot be examined in most fossil species
• strong emphasis on the absence of gene flow between species (BSC implies that different species would not mate and produce viable offsprings, surviving offsprings do exist in nature)

Question 25

what is the morphological species concept?

Answer 25

- defines species in terms of measurable anatomical features

Question 26

what are the key features of the morphological species concept?

Answer 26

- observable and measurable features of a given species are distinct from other species - applicable to both extant and extinct organisms - applicable to both sexually and asexually reproducing organisms

Question 27

what is the ecological species concept?

Answer 27

defines species by ecological niches, which encompass how organisms of the same species interact with biological and abiotic aspects of their environment

Question 28

what are the key features of the ecological species concept?

Answer 28

- individual of the same species share similar preferences/tolerances to habitat conditions - species are grouped/separated by partitioning of ecological niches - applicable to both sexually and asexually reproducing organisms

Question 29

what is the phylogenetic species concept?

Answer 29

define a species as the smallest group of individuals on a phylogeny

Question 30

what are the key features of the phylogenetic species concept?

Answer 30

- based on evolutionary history and shared ancestry - species can be one of the tips/terminal taxa on phylogeny - applicable to sexually and asexually reproducing organisms

Question 31

why can describing phylogenetic species be difficult?

Answer 31

- phylogenies are update frequently - tips can be expanded into a monophyletic group

Question 32

what are the two categories of speciations based on whether or not geographic separation is present?

Answer 32

- allopatric speciation (geographically separated populations) - sympatric speciation

Question 33

what is allopatric speciation?

Answer 33

- involves two geographically separated populations - formation of new species in populations that are geographically isolated from one another, and gene flow is interrupted

Question 34

what is supporting evidence for allopatric speciation?

Answer 34

number of species is higher in regions with many geographic barriers

Question 35

whether a geographic construct is geographic barrier depends on what?

Answer 35

how the population migrates

Question 36

what are the two ways that lead to geographic isolation ?

Answer 36

- dispersal - vicariance

Question 37

what is meant by the term "dispersal"?

Answer 37

- movement of individuals away from the rest of the population - the movement sometimes expands the geographic range of a population or species

Question 38

what is meant by the term "vicariance"?

Answer 38

- range of a species is split by change in the environment, creating two subpopulations - subpopulations may be subjected to different selective agents and pressures

Question 39

what is sympatric speciation? key characteristics and the general process?

Answer 39

- formation of new species in populations that live in the same geographic area - new species are established only when reproductive isolation is fully established - general process: geographic barrier is absent but some individuals stop interbreeding with others in population (stopping gene flow on a local level)

Question 40

what are the types of mechanisms for sympatric speciation?

Answer 40

- habitat differentiation (under disruptive selection) - sexual selection

Question 41

what is "habitat differentiation (under disruptive selection)"?

Answer 41

- subpopulations of the same species adapt to different environments, leading to reproductive isolation (reproductive barriers can be either prezygotic or postzygotic)

Question 42

what is "sexual selection"?

Answer 42

- individuals with certain inherited characteristics are more likely than others to obtain mates (this selection for traits leads to increased mating, can lead to sexual dimorphism, traits can be deleterious to survival of the individuals) - can be seen as a form of natural selection for mating success & can drive sympatric speciation

Question 43

what are "hybrid zones"?

Answer 43

- a geographic region in which members of different species meet and mate, producing at least some offspring of mixed ancestry

Question 44

can hybrid zones be partial overlap in ranges of two species?

Answer 44

yes

Question 45

true or false: hybrids are often less fit, but can sometimes lead to speciation

Answer 45

true

Question 46

what are the three possible outcomes of hybrid zones?

Answer 46

(1) reinforcement (2) fusion (3) stability

Question 47

what is meant by the term "reinforcement"? what does this lead to?

Answer 47

- hybrid offsprings are less fit than the parents, and natural selection removed hybrids - leads to the strengthening of reproductive barriers (prezygotic)

Question 48

what is meant by the term "fusion"? what does this lead to?

Answer 48

- hybrid offsprings are as fit as the parents, and gene flow can be maintained between hybrids and parent populations in substantial and stable ways - reproductive barrier is weakened and eventually removed

Question 49

what is meant by the term "stability"? what does this lead to?

Answer 49

- hybrid offspring are continuously formed by the parents, and gene flow can be maintained between the parent populations in substantial and stable ways -stability may lead to fusion

Question 50

can speciation occur with and without natural selection?

Answer 50

- yes - accumulation of genotypic difference leads to speciation - natural selection acts on traits of the new species - new species deemed unfit would be removed