Chapter 24: Origin of Species

Question 1

Speciation

Answer 1

The process by which one species splits into two

Question 2

Microevolution vs. macroevolution

Answer 2

Microevolution is the change over time in allele frequencies in a population

Macroevolution is the brad pattern of evolution above the species level

Question 3

Biological species concept

Answer 3

A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring

Do NOT produce viable, fertile offspring with members of other species

Question 4

Reproductive isolation

Answer 4

Barriers that impede members of two species from interbreeding and producing viable, fertile offspring

Prezygotic barriers- block fertilization from occuring by either impeding members of different species from attempting to mate, preventing attempted mating, or hindering fertilization if mating is successful

Postzygotic barriers- contribute towards reporductive isolation after the hybrid zygote is formed such as through developmental errors or infertile offspring

Question 5

Prezygotic barriers

Answer 5

1. Habitat isolation- two species occupy different habitats and rarely if ever come into contact
2. Temporal isolation- two species may breed during different times of day of different seasons
3. Behavioral isolation- courtship rituals may vary and be a barrier between even closely related species
4. Mechanical isolation- morphological differences prevent mating
5. Gametic isolation- sperm from one species may not be able to fertilize the eggs of another species

Question 6

Postzygotic barriers

Answer 6

1. Reduced hybrid viability- genes of different parent species may interact in ways that impair the hybrid’s development or survival
2. Reduced hybrid fertility- viable hybrids may be sterile
3. Hybrid breakdown- some first-generation hybrids are viable and fertile but when they mate with one another or either parent species, the next generation are feeble or sterile

Question 7

Morphological species concept

Answer 7

Distinguishes species by body shape and other structural features

Question 8

Ecological species concept

Answer 8

Defines a species in terms of its ecological niche- the sum of how members of a species interact with the nonliving and living parts of the environment

Question 9

Allopatric speciation

Answer 9

“Other country”

Gene flow is interrupted when a population is divided into geographically isolated subpopulations; more common

Question 10

Sympatric speciation

Answer 10

“Same country”

Speciation occurs in populations that live in the same geographic area; less common

Can occur is gene flow is reduced by factors such as:

• Polyploidy- autopolyploidy and allopolyploidy
• Sexual selection
• Habitat differentiation

Question 11

Polyploidy

Speciation

Answer 11

A condition where a species has an extra set of chromosomes

Two distinct forms:

1. Autopolyploid- an individual that has more than two chromosome sets that derived from a single species
2. Allopolyploid- descendents from a sterile hybrid polyploid that become fertile when mating with each other but NOT either patent species

Question 12

Hybrid zone

Answer 12

A region where members of different species meet and mate producing some hybrid offspring

Three possible outcomes:

1. Reinforcement of barriers- when hybrids are less fit than members of their parent species
2. Fusion of species- two species fuse into a single species due to excessive gene flow as a result of weak reproductive barriers
3. Stability- hybrids continue to be produced

Question 13

Models of speciation tempos

Answer 13

Punctuated model- new species change dramatically relatively quickly followed by a long period of apparent stasis; pattern is termed punctuated equilibria

Gradual model- Species diverge slowly and steadily over a long period of time