Speciation and Reproductive Isolation

Question 1

Perfection in adaptation?

Answer 1

Adaptation is rarely perfect

Question 2

Pre-zygotic mechanisms for reproductive isolation

Answer 2

1. Geographic Isolation (allopatric speciation)
2. Gametic isolation
3. Mechanical isolation
4. temporal
5. behavioral
6. ecological preferences and mating isolation (apple maggot)

Question 3

Mechanical isolation

Answer 3

1. simply put, male “parts” don’t fit female “parts” (e.g. dragonflies, beetles, bush babies)
2. flowering plants & specificity in their pollinators

Question 4

temporal mechanisms for pre-zygotic isolation

Answer 4

inter-species differences in timing of reproduction

Question 5

behavioral mechanisms for pre-zygotic isolation

Answer 5

mating rituals, displays, songs, etc.

Question 6

post-zygotic mechanisms for reproductive isolation

Answer 6

1. zygote mortality
2. hybrid inviability
3. hybrid sterility
4. low hybrid fitness (survivorship)

Question 7

3 Geographic Models of Speciation

Answer 7

1. Allopatry
2. Parapatry, “ring species”
3. Sympatry

Question 8

Sympatry

Answer 8

i.e. no geographic speciation

Question 9

How do geographically isolated populations diverge?

Answer 9

1. natural selection adjusts population to local environment
2. genetic drift (mutations)
3. founder effect

Question 10

Other important effects of small population size

Answer 10

1. Founder effect
2. Bottleneck effect

examples: including Amish, cheetahs

Question 11

Biological species concept

Answer 11

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

1. Groups of populations that can exchange genes (actually or potentially)
2. Produce fertile offspring
3. Reproductively isolated from other such groups
4. As long as two forms interbreed, they cannot diverge
5. If two forms DO NOT interbreed, each can develop different adaptations

Question 12

Pre-zygotic isolation

Answer 12

union of egg and sperm never occurs because gametes never encounter one another

Question 13

Post-zygotic isolation

Answer 13

egg and sperm encounter one another but the zygote is either not viable or gives rise to individuals that cannot reproduce or that have very low fitness

Question 14

Zygote

Answer 14

cell formed by the union of male (a sperm) and female (an ovum) sex cells. The zygote develops into the embryo following the instructions encoded in its genetic material, the DNA.

Question 15

Allopatry

Answer 15

physical barrier separating species

Question 16

Parapatry

Answer 16

“ring species” i.e. grass adapting to rivers with heavy metals whereas the grass in clean rivers don’t need to

Question 17

Sympatry

Answer 17

i.e. no geographic separation - genetic polymorphism

Question 18

How do geographically isolated populations diverge?

Answer 18

1. natural selection adjusts population to local environment
2. genetic drift (mutations, unpredictable allele fluctuations), is more prevalent in smaller populations
3. founder effect

Question 19

founder effect

Answer 19

when a few individuals from a larger population interbreed, results in a more limited gene pool (ex: the Amish population with heritable genetic conditions such as polydactyly, dwarfism, twins). The genetic variety in the original main population is preserved (new subpopulation has a different allele frequency than the original population!)

Question 20

bottleneck effect

Answer 20

when a large population decreases in size (could be due to hunting, home environment getting destroyed, etc), resulting in a lack of genetic diversity (survivors of the bottleneck effect tend to lack genetic diversity themselves. Ex: the inbreeding among remaining Florida panthers results in more genetic disorders and birth defects)

Question 21

hybrid inviability

Answer 21

occurs when gametes fuse, development progresses, but the offspring cannot survive to adulthood

Question 22

hybrid sterility

Answer 22

when gametes fuse, development progresses, but the offspring cannot survive to adulthood

Question 23

low hybrid fitness

Answer 23

when gametes fuse, development progresses, and offspring survive to adulthood and can reproduce, but have very low fitness in the wild

Question 24

gametic isolation

Answer 24

a type of prezygotic barrier where the gametes (egg and sperm) come into contact, but no fertilization takes place (e.g. tubes sprouting from pollen grains)