Speciation

Question 1

What is the basic unit of biodiversity?

Answer 1

Species

Question 2

How do definitions of a species change with fields in biology?

Answer 2

Taxonomy - mostly focus on ways for cataloguing and information retrieval
Phylogeny - definition mostly relates to relationships and history
Evolutionary biology - focuses on the evolutionary process

Question 3

What system did Linnaeus develop?

Answer 3

Hierarchical system: kingdom, phylum, class, order, family, genus and species

Question 4

Describe the taxonomic approach

Answer 4

Phenetic method (according to observable attributes)

• Describe the phenotype of the holotype and deposit specimen into a museum
• Other researchers compare their species to the holotype

Question 5

What is the problem with the taxonomic approach?

Answer 5

• Lead to organisms being occasionally described as being part of a different species when they are actually different populations connected by continuous variation or have phenotyhpic polymorphisms
• How much variation is ‘allowed’ within a species

Question 6

What is the biological species concept (Mayr)

Answer 6

Species are populations which are reproductively isolated

Question 7

What are the criteria for a species in the biological concept?

Answer 7

• Reproductive isolation
• Stabilised, well-integrated genotype
• Species-specific niche

Question 8

What are the advantages of the biological species concept?

Answer 8

• Make species as biological reality and not a taxonomists opinion
• Measurable and testable
• Can study speciation through reproductive isolation

Question 9

What are the issues with the biological species concept?

Answer 9

• How to define asexual species
• How to study and classify species from fossils
• Is reproductive isolation completely necessary?

Question 10

What is the phylogenetic definition of a species?

Answer 10

Smallest aggregate population/lineage which can be united by synapomorphic characters (shared derived characters)

Question 11

What is the phylogenetic definition of a species good for?

Answer 11

Fossils and asexual organisms

Question 12

What are Dobzhanky’s 2 classifications of mechanisms of reproductive isolation?

Answer 12

• pre-mating mechanisms which prevent the formation of hybrid zygotes by impeding gene flow before sperm/pollen transfer
• post-mating mechanisms can be pre-zygotic or post-zygotic

Question 13

Name 4 mechanisms of pre-mating reproductive isolation mechanisms

Answer 13

• Behavioural isolation
• Ecological isolation
• Mechanical isolation
• Mating system isolation

Question 14

Define behavioural isolation?

Answer 14

Differences which result in a lack of cross-attraction between species (does strong sexual selection result in speciation?)

Question 15

What are the 3 components of ecological isolation?

Answer 15

• Habitat isolation -> when species have a tendency to occupy different habitats in a general area resulting in a lack of gene transfer
• Temporal isolation -> different breeding times
• Pollinator isolation -> gene flow between angiosperms is reduced due to their different interactions with pollinators

Question 16

How do cicadas show temporal and behavioural isolation?

Answer 16

• Have developed different life cycle lengths (11, 13, 17 & 19 years) to avoid predator satiation which has separated them from ancestors
• Different mating calls to differentiate different cicadas with the same length lifecycle

Question 17

Give an example of pollination isolation

Answer 17

Closely related Mimulus species have different pollinator vectors due to different shapes which mostly seems to be controlled by a single gene

Question 18

Give 2 post-mating pre-zygotic barriers

Answer 18

1. Copulatory mating isolation -> where individual behaviour during copulation does not allow for normal fertilisation
2. Gametic isolation

Question 19

What are the 2 forms of gametic isolation?

Answer 19

Noncompetitive - Intrinsic problems with transfer/storage/fertilisations of heterospecific gametes in single fertilisations between individuals
Competitive - Heterospecific gametes are not properly transferred/stored when competing with gametes of the same species

Question 20

What are the two post-zygotic mechanisms of isolation?

Answer 20

1. Extrinsic factors - hybrids cannot adapt to ecological niche or cannot obtain mates as intermediate characteristics are unattractive
2. Intrinsic factors - could be hybrid inviability where difficulties cause full/partial lethality or hybrid sterility due to physiological (gametes/reproductive development) or behavioural (neurological lesions) factors

Question 21

Define polyploidy

Answer 21

A change in the number of chromosomes

Question 22

Name 2 types of polyploidy

Answer 22

autoploidy - duplicating of own chromosome

allopolyploidy - chromosome doubling of a hybrid

Question 23

How did Muller believe hybrid sterility evolved?

Answer 23

Through negative interactions between genes evolving independently of eachother

Question 24

What is Haldane’s rule?

Answer 24

When in the F1 offspring of two different animal races one sex is absent, rare or sterile, it is the heterozygous sex

Question 25

Name 4 possible explanations of Haldane’s rule

Answer 25

1. Male effects
2. Sex-linked genes evolve more quickly
3. Incompatibility between the X and Y
4. Combination of dominance effects and epistasis

Question 26

What is Coyne & Orr’s second rule of speciation?

Answer 26

The genes having the greatest effect on hybrid sterility and inviability are sex-linked

Question 27

Why is allopolyploidy frequently a cause of speciation in plants?

Answer 27

• Allopolyploids are immediately reproductively isolated from their parents
• Can originate more than once

Question 28

What is a homoploid hybrid?

Answer 28

When a recombinant that segregates from the initial hybrid is reproductively isolated from its parent species by a chromosomal barrier and/or an ecological barrier