Lecture 4: Speciation

Question 1

Population

Answer 1

Group of potentially interbreeding individuals of the same species
(i.e., coexisting in the same place and time).

Question 2

Species

Answer 2

-a group of individuals capable of interbreeding AND reproductively isolated from other groups.
-May consist of several populations,
all capable of interbreeding, but rarely (or never actually) having the opportunity.

Question 3

Biological Species Concept

Answer 3

• Group of individuals capable of interbreeding that are reproductively isolated from other groups and produce fertile offspring (red wing bird vs blacking bird)
• because using a biological trait, the ability to interbreed, as foundation for the definition

Question 4

Problems with Biological species Concept (in practice)

Answer 4

(1) can be hard to tell members of the same species from appearance alone
-some species are sexually dimorphic (males/females look different)
-morphology can also be polymorphic (many forms or patterns)
(2) we rarely watch who actually interbreeds. we use clues from morphology but clues can be deceptive.
-also tricky because people can force some species to interbreed that don’t in nature (Liger, Cama)
-some organisms never reproduce sexually to begin with (wasps that have bacterium that cause
every member of species to be female)

*DNA sequencing has become tool of choice

Question 5

3 Critical Processes that are necessary for new species

Answer 5

(1) Isolation/seperation
(2) Genetic Divergence
(3) Reproductive Isolation

Question 6

Speciation

Answer 6

Isolation followed by genetic divergence.

(1) one population becomes separated into 2 (often by physical barrier but not always)
(2) each population independently experiences natural selection (may also experience mutation and genetic drift but NO GENE FLOW)

*Gene flow usually reduces differences between populations.

Question 7

Ways populations can be isolated

Answer 7

(1) Allopathic (different countries): a physical barrier arises that prevents interbreeding; considered usual start to speciation
ie - Grand Canyon: Harris Antelope Squirrel (south rim) vs white tailed antelope squirrel (North rim)
(2) Sympatric Speciation (same countries): no physical barrier arises, interbreeding stop for another reason possibly temporal
ie - Hawthorne Fruit fly: mutation led some flies to be attracted to and lay eggs on apple instead
-speciation began (isolation in time) then genetic divergence.

Question 8

Barriers to Speciation

Answer 8

(1) Prezygotic

(2) Postzygotic

Question 9

Prezygotic barriers

Answer 9

barriers that stop the zygote from forming

(a) barriers in space or time (Spacial or Temporal)
(b) behavioral isolation: females or males reject mate of the other population/species

Question 10

zygote

Answer 10

an egg cell after fusion of the egg and sperm nucleus (ie 1st cell of new organism)

Question 11

Postzygotic

Answer 11

occurs after zygote formation

(a) hybrid inviability: 2 kinds of parents = zygotes either don’t develop or die
(b) hybrid sterility: hybrid survive but are sterile (ie - mule from a horse and donkey)

Question 12

Summary of Speciation

Answer 12

(1) one population becomes divided into two and there’s no gene flow
(2) populations become more genetically different over time
(3) no longer successfully mate if come back together