BG26

Question 1

Radiations of cichlids in major lakes

Answer 1

malawi - 400 spp
tangaykia - 200 spp
victoria - 500 spp

Question 2

cichlids phylogeny

Answer 2

• most cichlids are in the haplochromines sub-family (endemic of eastern and southern africa
• tanganyika = oldest and most diverse fauna - not all monophyletic
• malawi and victoria - monophyletic radiations of haplochromines
• tanganykia seems to be source of malawi and victoria cichlids
• malawi = monphyletic
  victoria = shallower/younger technically not a rift lake

Question 3

lca of haplochromines

Answer 3

river fish lived 1.8mya

• 1000 descendent spp
• 1 mil years evo in galapagos finch = 14 finch spp.

Question 4

cichlid migration

Answer 4

malawi -> tanganyika = 324km

• lakes now have own drainage basin so unclear how fish migrated.
• hypothessi that they flew, fish eagle etc carries into swamps along the way

Question 5

cichlid anomoly in lake victoria

Answer 5

recently formed= 500ka
but dried out, perhaps completely 15ka
- impies 500 species in 15k years
- impossible to show it dried out completely, could have been pockets/ponds that remained in large expanses.

Question 6

mtDNA analsyis in lake victoria

Answer 6

victoria fish mostly originated from lake kevo fish
- mtDNA suggests LV is not monophyletic
- LK56 haplotype gives rise to LV76 and LV77/92 lineages seperately.
LV separated from LK65 98-133ka
- not all lineages evolved in situ

** suggest LV is not totally monophyletic

Question 7

Lake victoria cichlids relationship with other cichlids

Answer 7

part of a species flock

• includes lk which now drains into lt
• lk may have drained into lv before virunga mountains appeared 30ka years ago

Question 8

Lake malawi cichlid speciation

Answer 8

many near shore islands have endemic species of cichlids

• islands were dry 150 years ago
• lm is steep lake sensitive to climatic fluctuations
• lms water levels dropped dramatically >100m; 25ka, 1ka, 500 years ago

** implied high rates of speciation

Question 9

allopatric speciation

Answer 9

due to geographical or physical barrier inhibiting gene flow

Question 10

lake malawi allopatric speciation of cichlids

Answer 10

• many lm species seem to have speciated in allopatry.

P. zebra = algae eater

• species likes rocks which can be found up and down lake separated by a long stretch of sandy bottom
• variant p.z complex spp at different rocks up and down the lake which are isoalted
• sandy stretches = geographical barriers

Question 11

sympatric speciation

Answer 11

due to other mechanisms micro-ecological, behavioural etc inhibiting gene flow

Question 12

sympatric speciation in cichlids

Answer 12

castles

• many haplochromine males make elaborate sandcastle bowers to woo females
• castles are species specific in form, females wont respond to wrong kind
• sexual selection results in behavioural isolation

Question 13

sympatric and allopatric speciation in cichlisd

Answer 13

mouthbrooders

• most african cichlids are maternal mouthbrooders
• females take eggs in their mouths and get fertilised there.
• females brood them while they are vulnerable until late juveniles
• promotes phillopatry - tendancy of offspring to stay where they are born rather than scatter as planktonic larvae = allopatry

Question 14

what are male egg spots

Answer 14

males have markings on their anal fin which are the same size and colour as eggs
- appear so to females
- as male does shimmying dance the spots wave and movement induces female to lay eggs or assume shes left some behind
female opens her mouth to reach for eggs and male releases sperm

Question 15

sympatric speciation of colour

Answer 15

LV
P. pundamilla (blue) and P. nyererei (red) -lives further from shore and deeper than pundamilla
but both live within 500m of each other
- no sign of geographical barrier
males differ in breeding colour

• to be visible in deeper water P. nyereri are red
• to be visible in shallower water (where the blue part of the spectrum is dominant) P. pundamilla are blue.

Question 16

LV water column

Answer 16

at greater depths in lv water column blue part of spectrum drops out and appears black
- spectrum attenuation is specific to LV due to particulates.
whereas in clear water, long wavelength red drops out first and short blue drops out last.

Question 17

what is the LWS opsin gene

Answer 17

encodes an eye pigment required for colour perception

• this is polymorphic in the two species
• with different functional properties - what part of spectrum it can absorb

Question 18

P and H alleles of LWS opsin gene

Answer 18

P allele = best at 544 blue
H allele = best at 550 red

H found in deeper
P is found in shallower

Question 19

Sympatric speciation in crater lakes

Answer 19

700-meter crater lake in tanzania has yellow littoral (shore) shore morph and blue benthic (deep) morph

genome sequencing reveals 98 genomic islands of high differentiation between morphs

• low fst
• reveals recent speciatiion is just begginigng with no fixed alellic differences yet

Question 20

flycatcher species history

Answer 20

collared flycatcher and pied flycatcher diverged less than 2mya due to cycles of glaciation in eurasia.
- still hybridise in contact

Question 21

flycatcher genomics experiment

Answer 21

10 birds of each species sequenced and they examined the the density of fixed differences per bp for 200kb windows across the genome to determine divergence

Question 22

flycatcher genomic results

Answer 22

• 50 ‘divergence islands’ were identified which have
1. Reduced levels of nt diversity.
2. Skewed allele frequency spectra
3. Elevated levels of linkage D.
4. Reduced proportions of shared polymorphisms in both species, Indicative of parallel episodes of selection.
• They’re close to centromeres and telomeres suggesting that repeat structures may drive species divergence.

Question 23

Dobzhansy and muller`

Answer 23

1930
proposed that hybrid incompatibilities that contribute to speciation are caused by interactions between genes that have functioanlly diverged between hybridising species
- results in redcued fitness of the hybrid
-functional divergence between hybridising species
- dependence of a pair og genes on each other to cause their incompatibility.

Question 24

Incompatibility genes in dorsophila

Answer 24

simulan and melanogaster can be crossed, but sometimes F1 is lethal.
- two HI genes: Hmr and Lhr identified which contribute to hybrid incompatibility.
LoF mutations in either allow viable crosses
- particualr type epistasis

Question 25

what does Hmr encode

Answer 25

a rapidly evolving proteins in MADF class of DNA binding proteins

Question 26

what does Lhr encode

Answer 26

a protein with BESS domains that mediate protein-protein interaction often with MADF domains

Question 27

what may cause hybridisation incompatibility.

Answer 27

alter chromosome morphology and chromatin strucutre in hybrids due to cumulative effects of species specific differences

Question 28

Sisphean cycle

Answer 28

finches respond to new selection pressures -> fluctuating enviro causes changes in selection -> ^^

Question 29

sisphean cycle relative to finches

finch phylogeny

Answer 29

finches species are always cycling, species we see now havent always been there
current finches are more closely related to each other indicating recent radition - 100-300ka?
- ABBA bABA show 30% of genomes are due to recent hybridisation

Question 30

what is partly responsible for difference between sharp and blunt beaks in finches

Answer 30

ALX1 - homeobox TF implicated in craniofacial patterning.