Radiations of cichlids in major lakes
malawi - 400 spp
tangaykia - 200 spp
victoria - 500 spp
cichlids phylogeny
- 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
lca of haplochromines
river fish lived 1.8mya
- 1000 descendent spp
- 1 mil years evo in galapagos finch = 14 finch spp.
cichlid migration
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
cichlid anomoly in lake victoria
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.
mtDNA analsyis in lake victoria
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
Lake victoria cichlids relationship with other cichlids
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
Lake malawi cichlid speciation
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
allopatric speciation
due to geographical or physical barrier inhibiting gene flow
lake malawi allopatric speciation of cichlids
- 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
sympatric speciation
due to other mechanisms micro-ecological, behavioural etc inhibiting gene flow
sympatric speciation in cichlids
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
sympatric and allopatric speciation in cichlisd
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
what are male egg spots
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
sympatric speciation of colour
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.
LV water column
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.
what is the LWS opsin gene
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
P and H alleles of LWS opsin gene
P allele = best at 544 blue
H allele = best at 550 red
H found in deeper
P is found in shallower
Sympatric speciation in crater lakes
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
flycatcher species history
collared flycatcher and pied flycatcher diverged less than 2mya due to cycles of glaciation in eurasia.
- still hybridise in contact
flycatcher genomics experiment
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
flycatcher genomic results
• 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.
Dobzhansy and muller`
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.
Incompatibility genes in dorsophila
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
