10.28 Reproductive Isolation

Question 1

What is a species?

Answer 1

“Groups of interbreeding natural populations that are reproductively isolated from other such groups”.

Question 2

Pre-zygotic isolation

Answer 2

Union of egg and sperm never occurs because gametes never encounter one another.

Question 3

Post-zygotic isolation

Answer 3

Egg and sperm encounter one another but the zygote is either not viable or gives rise to individuals with low fitness.

Question 4

Gametic isolation

Answer 4

• Pre-zygotic.
• Occurs when incompatibilities in gametes do not permit viable fertilization.
• Can be caused by dif in number of chromosomes ot chemical signals required for gamete function + development.
• Example: pollen transferred to stigma of another species will not form pollen tube and therefore not pollinate the ovule.

Question 5

Mechanical isolation

Answer 5

• Pre-zygotic.
• Appendage A does not mesh with slot B.
• Lock and key type structure.
• Very common in arthropods, like dragonflies.

Question 6

Temporal isolation

Answer 6

When the peaks of sexual activity in different species do not overlap in time.

E.g. frog breeding periods.

Question 7

Behavioral isolation

Answer 7

• E.g. different cicada calls.
• Can occur when displays and rituals become intimately related to reproductive act.

Question 8

Ecological isolation

Answer 8

• Pre-zygotic
• When environmental preference reduces frequency of interbreeding.
• E.g. apple maggots prefer to lay eggs in fruit they grew up in.

Question 9

Allopatric speciation

Answer 9

Complete separation of populations.

Question 10

Parapatric speciation

Answer 10

Line occurs in broadly continuous region.

E.g. environmental gradients or humans preferring language.

Question 11

Sympatric speciation

Answer 11

No spatial separation, but reproductive isolation occurs.

E.g. flies preferring different host plants.