Lecture 9

Question 1

what was the confusion about the link between micro and macroevolution?

Answer 1

can processes of microevolution lead to macroevolution?

Question 2

taxonomic (morphological) species concept

Answer 2

based primarily on distinct measurable differences

Question 3

biological species concept

Answer 3

based on inter-fertility among individuals

Question 4

why is it so hard to define a species?

Answer 4

concepts vary among groups of organisms and among scientists. There is no universal species concept.
- geographic isolation alone is NOT sufficient
- isolation does NOT have to be absolute (what cutoff?)

Question 5

Darwin’s definition of a species

Answer 5

groups of organisms that are sufficiently similar in phenotype

Question 6

Ernst Meyer’s view on distinguishing species

Answer 6

reproductive isolation as key to distinguishing species

Question 7

what species does the BSC not apply to?

Answer 7

does not apply well for bacteria, asexuals, highly self-fertilising species…or fossils

Question 8

allopatric speciation

Answer 8

often called geographic speciation
- due to involvement of geographical isolation
- much more common and easier to evolve

Question 9

stages where reproductive isolation can occur

Answer 9

pre-zygotic:
- finding a compatible mate and mating
- fertilisation
post-zygotic:
- development and growth of zygote (F1)
- adult survival & reproduction
- growth, survival, reproduction of offspring (F2)

Question 10

pre-zygotic barriers

Answer 10

prevent mating or fertilisation so no zygote is formed:
- geographical, ecological
- temporal, behavioural (mate recognition)
- mechanical (genital stricture compatibility)
- cellular (sperm-egg compatibility)

Question 11

use Rhagoletis pomonella (Apple Maggot Flies) as an example of pre-zygotic isolation

Answer 11

• host shift after arrival of domesticated applies in 1800s
• differences in timing of host planting fruiting (apple vs hawthorn)
• different timing of fly mating on preferred host plant)
• reduces fly gene flow by 94% in sympatry (same region)

Question 12

describe pre-zygotic isolation in abalone

Answer 12

binding of sperm lysin protein to egg vitelline envelope receptor (VERL) required for fertilization (molecular lock and key)
Lysin/VERL interaction has coevolved
– Different evolutionary changes in different species
– Causes reproductive isolation due to fertilization
incompatibility

Question 13

post-zygotic barriers

Answer 13

prevent proper functioning of zygotes
once they are formed
* Caused by combinations of genes with low fitness in the
hybrid
* Arise as an indirect byproduct of evolution acting
separately in different populations (cannot be directly
favored by natural selection)

Question 14

intrinsic post-zygotic barriers vs extrinsic post-zygotic barriers

Answer 14

Intrinsic Post‐zygotic Barriers:
* Inviability, sterility, or abnormal development of hybrids
Extrinsic Post‐zygotic Barriers:
* Ecological mismatch of hybrid phenotype to environment

Question 15

example of intrinsic post-zygotic isolation

Answer 15

Mule is a sterile hybrid cross of:
* Male donkey (62 chromosomes)
* Female horse (64 chromosomes)

Hinny is a sterile hybrid of:
* Male horse (64 chromosomes)
* Female donkey (62 chromosomes)

Question 16

relation between genetic distance and post-zygotic isolation in fruit flies

Answer 16

• The more that fly pairs are genetically differentiated,
  the more likely they are to be reproductively isolated

Question 17

example of extrinsic post-zygotic isolation

Answer 17

aposematic helicons butterflies
Hybrids have aberrant colour patterns
* Higher predation risk
* Lower mating success

Question 18

local adaptation by different populations can lead to

Answer 18

reproductive isolation and speciation

Question 19

distinct evolutionary responses happen due to

Answer 19

different selective pressures

Question 20

is local adaptation necessary for speciation?

Answer 20

Local adaptation not absolutely necessary, but accelerates population divergence and
evolution of RI

Question 21

describe sticklebacks in marine and freshwater environments

Answer 21

In marine environment:
– Bony armor protects against large fish predation
In freshwater:
– Loss of armor increases growth rate
– Greater winter survival
– Earlier breeding

Question 22

so, can microevolution lead to macroevolution?

Answer 22

yes - as populations diverge genetically as a result of evolutionary forces
(mutation, natural selection, genetic drift), they become reproductively
isolate

Question 23

define and describe adaptive radiation

Answer 23

The evolution of ecological and phenotypic diversity within a rapidly multiplying lineage
– Originates from a single common ancestor
– The process results in an array of many species
– The species differ in traits allowing exploitation of a range of habitats and resources

Question 24

Four features commonly identify an adaptive radiation

Answer 24

1) Recent common ancestry from a single species
2) Phenotype‐environment correlation
3) Trait utility
4) Rapid speciation

Question 25

define ecological opportunity

Answer 25

the absence (or reduction) of competition for resources

Question 25

two things that cause adaptive radiation

Answer 25

ecological opportunity and high propensity for speciation

Question 27

how does ecological opportunity come about?

Answer 27

Colonization of competition‐free regions (e.g., islands, lakes, or continents)
Extinction (which can eliminate competitors)
Key innovation (evolution of a trait that provides access to new resources)

Question 28

high propensity for speciation

Answer 28

RI evolves more readily in some clades than others

Question 29

define hybridisation

Answer 29

The exchange of genes between species as a result of occasional inter‐species mating
– Sometimes can reverse speciation process to merge two groups into one

Question 30

how does hybridisation vary across the tree of life?

Answer 30

common in plants and fish, rare in mammals

Question 31

how can hybridisation result in complex patterns of variation?

Answer 31

Can be evolutionarily significant for speciation, especially by polyploidy

Question 32

define polyploidy

Answer 32

Describes an organism, tissue, or cell with more than
two complete sets of homologous chromosomes

Question 33

define and describe allopolyploidy

Answer 33

Allopolyploidy (e.g. AA x AA -> AA AA)
– Arises from duplicated karyotype following
hybridization between species
– Commonest type of polyploidy

Question 34

define and describe autopolyploidy

Answer 34

Autopolyploidy (e.g. AA -> AA AA)
– Arises from duplicated karyotype within a species
(e.g. non‐disjunction)

Question 35

describe how allopolyploid hybridisation comes about

Answer 35

1. Two species mate and produce an F1 hybrid
   offspring (genotype AA*)
2. F1 hybrid offspring produces unreduced diploid
   gametes (genotype AA*) due to meiotic
   nondisjunction
3. Diploid gametes combine to produce tetraploid
   F2 offspring
4. Tetraploid is fertile, but is reproductively
   isolated from parental species

Question 36

evolutionary significance of polyploidy

Answer 36

Polyploids are reproductively isolated from their
diploid parents
– Hence a form of sympatric speciation
* Polyploids exhibit novel phenotypes
– Allows exploitation of new habitats
* Polyploids often show hybrid vigor due to
heterozygosity, particularly in allopolyploids
* Polyploid origin for ~50% of flowering plants
– Many crop plants & invasive species
Evolutionary Significance of Hybridization© BIO120 Fall 2024

Question 37

draw the speciation continuum