Speciation

Question 1

Define morphological convergence.

Answer 1

Species evolve to look the same but are only distantly related.

Question 2

Morphological convergence creates cryptic variation. Define cryptic variation.

Answer 2

That which is undetectable in the phenotype and only evident from genetic studies.

Question 3

Both extinct and extant species need to be taken into account when assessing diversity. True or false?

Answer 3

True.

Question 4

Define speciation.

Answer 4

Whereby populations become reproductively isolated from each other, gene flow is stopped. These populations then diverge and accumulate differences, forming a new species.

Question 5

What is the species continuum?

Answer 5

A scale ranging from high to low species diversity.

Question 6

There are 3 different concepts of what a species is. What are they?

Answer 6

1. Morphological concept
2. Phylogenetic concept
   3, Biological concept

Question 7

Explain the morphological concept of a species.

Answer 7

Species are groups of organisms that look similar.

Question 8

Explain the phylogenetic concept of a species.

Answer 8

Species are the smallest sets of organisms sharing a common ancestor.

Question 9

Explain the biological concept of a species.

Answer 9

Species are groups of interbreeding organisms that are reproductively isolated from other groups.

Question 10

What is an advantage to the biological concept of a species?

Answer 10

It does not rely on morphology which can be misleading.

Question 11

What are disadvantages to the biological concept of a species? List 4.

Answer 11

1. It cannot be applied to asexual species
2. Does not account for temporary geographical boundaries
3. It cannot be applied to the fossil record
4. It does not account for hybridisation

Question 12

Which of the 3 concepts of a species is the most widely accepted?

Answer 12

The biological concept.

Question 13

Species can become reproductively isolated at 2 major stages. What are they?

Answer 13

1. Pre-zygotic: before mating

2, Post-zygotic: after mating

Question 14

Pre-zygotic isolation can occur for geographic reasons. Give an example of this.

Answer 14

If two organisms live either side of a physical barrier, they will never meet and won’t mate.

Question 15

Pre-zygotic isolation can occur for a) behavioural or b) mechanistic reasons reasons. Give an example of each.

Answer 15

a) Spawning times are different, e.g. in corals, so gametes never meet
b) Genitalia are not compatible

Question 16

Post-zygotic isolation can occur for genetic reasons. Give an example.

Answer 16

Chromosome rearrangements mean that chromosomes are unable to recombine at meiosis and hybrids are unviable.

Question 17

What does the Dobzhansky-Muller model show?

Answer 17

Explains that when two species diverge from a common ancestor, they acquire and fix different mutations. This means the chromosomes of both species are unable to recombine at meiosis.

Question 18

What is Haldane’s rule?

Answer 18

The heterogametic sex in F1 hybrids, the progeny of 2 different species, is often sterile.

Question 19

Explain how Haldane’s rule works.

Answer 19

The maladapted traits of sex chromosomes are not masked in the homozygous state, thus mutations accumulate that often lead to infertility.

Question 20

Post-zygotic isolation can occur for ecological reasons. Give an example.

Answer 20

Hybrids are less fit and thus are outcompeted.

Question 21

Define allopatric speciation.

Answer 21

Where a physical boundary forms between populations, causing them to diverge.

Question 22

Give an example of allopatric speciation.

Answer 22

The Isthmus of Panama: the Caribbean and Pacific plates collided and volcanoes created the land mass of Costa Rica and Panama. Speciation of marine life occurred in the Caribbean sea and Pacific Ocean, an example species being the Alpheus snapping shrimp.

Question 23

Define peripatric speciation.

Answer 23

The formation of islands.

Question 24

Why are populations split by allo or peripatric speciation susceptible to genetic drift?

Answer 24

They are much smaller.

Question 25

Define parapatric speciation.

Answer 25

A gradient of environmental variation forms across a landscape.

Question 26

Define sympatric speciation.

Answer 26

A series of microenvironments form within the main environment.

Question 27

In para and sympatric habitats, random mating could homogenise initial species divergence. What prevents this?

Answer 27

Selection.

Question 28

In para or sympatric habitats, species can be separated temporally. Give an example.

Answer 28

Apple maggots have 2 host plants: the ancestral hawthorn and the derived apple tree, and thus have diversified into two species, one that prefers each. Hybrids show no preference thus selection acts to separate them. The timings of their lifecycle reflect the blossoming times of their preferred plants, which are different. Thus they are separated temporally from mating.

Question 29

What causes the preference for different plants in apple maggots?

Answer 29

An olfactory preference.

Question 30

In para or sympatric habitats, species can be separated spatially. Give an example.

Answer 30

Crater lake cichlids can be limnetic, living in light, open surface waters, or benthic. This separates them spatially so they do not interbreed.

Question 31

Why has predation affected the spatial separation of crater lake cichlids?

Answer 31

Crayfish predation has caused the benthic species to stray into limnetic zones to avoid being eaten. Now there is increased gene flow between the populations.

Question 32

Define the Wallace effect.

Answer 32

A positive feedback loop whereby hybrids are less fit than either parent species, thus affecting mate choice. Either species favours members of their own species as a potential mate, thus hybrids do not get to mate.

Question 33

Isolation mechanisms do not occur together. True or false?

Answer 33

False - multiple isolation mechanisms often act in speciation. For example species may first become geographically then reproductively isolated.

Question 34

Define an introgression event.

Answer 34

A rare occurrence of gene flow.