07. Species and Speciation

Question 1

What is a species?

Answer 1

A group of individuals that can exchange genetic material through interbreeding to produce fertile offspring.

Question 2

Biological species concept (BSC)

Answer 2

Species are groups of interbreeding populations that are reproductively isolated from other such groups

Question 3

Shortcomings of the biological species concept (4)

Answer 3

1. impossible/difficult to test
2. doesn’t apply to asexual organisms
3. doesn’t apply to extinct organisms
4. Conceptually challenging to deal with hybridization and ring species

Question 4

Hybridization

Answer 4

when separate species are still able to pass genes

Question 5

Ring species

Answer 5

contain populations that are reproductively isolated from each
other, but can still exchange genetic material through other linking populations

Question 6

Morphospecies Concept

Answer 6

The idea that members of the same species usually look like eachother
-also usually have similar DNA sequences

Question 7

Shortcomings of the morphospecies concept (2)

Answer 7

1. Fails when within-species variation is large

2. Fails when among-species variation is small

Question 8

Ecological species concept

Answer 8

The idea that there is one to one correspondence between a species and its niche

Question 9

Shortcoming of the ecological species concept

Answer 9

1. Ecologically distinct types exist within a population and can interbreed
2. Two populations have similar ecologies but are incapable of exchanging genetic material

Question 10

Phylogenetic species concept

Answer 10

The idea that members of a species all share a common ancestry and a common fate

Question 11

Shortcomings of the phylogenetic species concept

Answer 11

What degree of difference is required to separate species?

• Too course (all mammals come from common ancestor)
• Too fine (siblings and cousins descend from common ancestor)

Question 12

Pre-zygotic isolating factors

Answer 12

Act before fertilization

-barriers include: geographical/ecological, temporal, behavioural, mechanical, gametic

Question 13

Post-zygotic isolating factors

Answer 13

after fertilization

• failure of fertilized egg to develop into a fertile individual
• genetic incompatibility

Question 14

Ecological isolation

Answer 14

Two species encounter each other
rarely, or not at all, because they occupy different
habitats, even though not isolated by physical barriers

Question 15

Temporal isolation

Answer 15

Species that breed at different
times of the day, different seasons, or different
years cannot mix their gametes

Question 16

Behavioral isolation

Answer 16

-Courtship rituals and other behaviors
unique to a species are effective barriers to mating
-The attraction of different pollinators
prevents inter-species matings in plants

Question 17

Mechanical isolation

Answer 17

Morphological differences can

prevent successful completion of mating (lock and key)

Question 18

Gametic isolation

Answer 18

Sperm of one species may not be

able to fertilize eggs of another species

Question 19

Post-zygotic isolating factors

Answer 19

-reduced hybrid viability: Genes of the different parent species may interact
and impair the hybrid’s development or survival in its environment
-Reduced hybrid fertility: even if hybrids are vigorous, they may be sterile
-Hybrid breakdown: Some first-generation hybrids are fertile, but when
they mate with each other or with either parent species, offspring of
the next generation are feeble or sterile