lecture 13

Question 1

What is a species?

Answer 1

There’s a huge range of variation of all sorts of traits both within species and between species

Question 2

Can a single universal definition be used for all species?

Answer 2

no

Question 3

What is meant by some lineages diversify into many many species, in a very short amount of time

Answer 3

some species diversify faster than others

Question 4

Example: huge radiation of cichlids in African Great Lakes

Answer 4

(250, 700, & 800+ species in Lakes Tanganyika, Victoria & Malawi)
hyperdivere
we see lots of species that arose in a short time
happened in less than 10 million years

Question 5

Example: Tropheus cichlid species complex in Lake Tanganyika

Answer 5

isolated and found in different parts of the lake differences in color

Question 6

Biological Species Concept

Answer 6

• Species are groups of interbreeding (or potentially interbreeding) individuals that are reproductively isolated from other such groups
• Isolation does not necessarily have to be complete (just very strong) and if there is rare gene flow between distinct species, it does not result in much mixing (some mixing, its okay just it does not result in much mixing)

Question 7

reproductively isolated

Answer 7

reproductive isolation is all things that keep related thing from exchanging genes

Question 8

What two things are important processes and sources of diversity & adaptation

Answer 8

hybridization (& introgression)

Example of the EPAS1 allele! (adaptation in Tibetans that arose from ancient Denisovan introgession)

Question 9

Biological Species Concept: Challenges & Problematic Cases

Answer 9

For many organisms, it can be very difficult to demonstrate reproductive isolation (organisms are hard to do experiments with them) (but can we get some clues by analyzing DNA sequences?)

Question 10

How does one define species for organisms that do not have sexual reproduction (e.g. prokaryotes), or for fossils?

Answer 10

fossils and organisms with no sexual reproduction are hard to use

Question 11

why is speciation hard to study

Answer 11

doesnt happen over night and lots of switch back and forth

Question 12

SPECIATION IS A COMPLEX & DYNAMIC CONTINUUM (how it works) ?look at diagram

Answer 12

1. One species: polymorphism, but no isolation
   - lots of gene flow
2. Reduced (but not completely) gene flow: incipient species?
   - geographical barriers
3. Complete (or near complete?) reproductive isolation
4. Accumulation of differences (and isolating barriers) independent of initial isolation

Question 13

Allopatric speciation

Answer 13

complete geographic isolation (no gene flow), most common form of speciation

Question 14

Sympatric speciation

Answer 14

occurring without geographic isolation, while populations are still exchanging genes
- controversial: less common & more difficult to demonstrate

Question 15

why is it hard to determine whether and when there was geographic separation or not

Answer 15

Species ranges are dynamic
can switch from Allopatric to sympatric and vice versa

Question 16

Major types of isolating barriers

Answer 16

1. Premating
2. Postmating, prezygotic
3. Postzygotic

Question 17

Premating

Answer 17

(no mating occurs)
- ecological
- behavioural

keep related individuals from mating, they never encounter eachother
- different habitat
- different diet
- different migration patterns
- different reproduction times

Question 18

Example: Southern capuchino seedeaters

Answer 18

• 10 species in less than a million years (very fast), with largely overlapping ranges (sympatric)
• Differ primarily in male plumage coloration and song (similar ecologically)
  ?? all one experiment?

Question 19

was there genetic differentiation

Answer 19

No genetic differentiation, except for 3 gene regions (only 12 genes)
3 genes are associated with pigmentation genes
- TYRP1
- OCA2
- HERC2

Question 20

was there evidence of hybridization

Answer 20

no

Question 21

what was the males respond

Answer 21

Males respond most aggressively to song and plumage of the individuals of the same species

Question 22

what was the result of seeing if the males will respond to songs of different songs and plumage

Answer 22

more aggressive towards males of their own species and didnt find other species as competition

Question 23

Postmating, prezygotic

Answer 23

mating occurs but there is no
fertilization
no hybrids being produced

Question 24

what are the differences between the beetle species Carabus maiyasanus and Carabus iwawakianus

Answer 24

major differences is male gentialia and characteristics

Question 25

what was Teiji Sota and Kohei Kubota experiment

Answer 25

performed crosses in all possible combinations of beetles

Question 26

what were Teiji Sota and Kohei Kubota results

Answer 26

iw x ma ma x iw
- mortality due to damage to female reproductive damage
- they died

negative reproductive effects between these closely related species still keeping them separate

Question 27

Postzygotic

Answer 27

hybrids are produced but they are unfit
- ecological inviability
- hybrid inviability
- hybrid sterility
- eg. Mules are hybrids between donkeys & horses, and are sterile

Question 28

Example: Hybrid Heliconius butterflies

Answer 28

Hybrid butterflies are attacked more by birds
- hybrids live and are fertile but they are unfit

• hybrids get targeted more bc of their wing color
• both closely related parents show they are poison by wing color but the hybrid doesnt have the same wing warning as its parents and get eaten

Question 29

More than one barrier can contribute to isolation: e.g. Drosophila sechellia

Answer 29

• Endemic on the Seychelles islands in the Indian Ocean, closest relatives (D. mauritiana & D. simulans) found on African mainland and other Indian Ocean islands
• Premating isolation (ecological): a) on isolated islands, b) specializes on toxic morinda fruit
• Postzygotic isolation: produces hybrid sterile males when mating with D. mauritiana and D. simulans

Question 30

Bateson-Dobzhansky-Muller model of hybrid incompatibility

Answer 30

incompatibilities will accumulate over time (and later incompatibilities don’t necessarily have anything to do with the processes that drove speciation in the first place)
*look at slide 28

Question 31

Divergent Evolution of Duplicate
Genes Leads to Genetic Incompatibilities Within A. thaliana

Answer 31

looking at variation within a species
* Crossed two different strains of Arabidopsis thaliana
* Some specific combinations did not work (no successful offspring produced)

Plants that are homozygous for At1g71920 from green and homozygous for At5g10330 from purple die

if not homo you have problems

Question 32

Major takeaways from A. thaliana experiment

Answer 32

• At1g71920 and At5g10330 are duplicated genes (HPA1 & HPA2) that code for histidinol-phosphate amino-transferase, an essential step in histidine biosynthesis
• At1g71920 in green has a premature stop codon
• At5g10330 in purple has a large deletion

fine on their own but when combined the incompatibilities will have problems

• At1g71920 in green, and At5g10330 in purple are the kinds of incompatibilities that could result in speciation