Allopatric speciation - 2
Allopatric speciation in nature Ring species Allopatric speciation in the lab Parallel speciation in nature [Blackboard: population genetics of natural selection 2]
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 1 Allopatric speciation
Platanus
P. occidentalis Eastern N America P. orientalis SE Europe, SW Asia
P. x hispanica (hybrida) "London plane“, fertile hybrid
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 2 Allopatric speciation
n When is allopatric speciation complete?
q isolation only by a geographic barrier is not considered speciation
q secondary contact, reproductive isolation in sympatry
q no hybridization in the lab? sufficient but not necessary
q morphological / genetic differentiation? not enough for BSC!
n Can we prove that speciation occurred in allopatry?
q if currently sympatric, did a geographic barrier exist in the past?
q if currently allopatric, are they biological species?
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 3 Allopatric speciation in nature
n Known geographic barrier: The Isthmus of Panama closed 3 My ago Alpheus (snapping shrimp, Knowlton et al 1993)
behavioural isolation (white=strong) mtDNA
C=Caribbean, P=Pacific sister spp 3-10 My old, older spp are living deeper
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 4 Allopatric speciation in nature
n Sister species are often allopatric
(hybridize) Diadema mtDNA tree (Lessios et al. 2001)
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 5 Ring species
Larus argentatus - L. fuscus greenish warbler (Phylloscopus trochiloides) circumpolar, overlap in N Europe around Tibet and the Himalayas
interbreeding between adjacent populations, reproductive isolation in sympatry
- are these “good” species? gene flow still exists via the ring - if the ring is continuous, this is not allopatric speciation - the ring shows discontinuities in real examples (e.g. sudden change of allozyme frequencies) – past allopatry?
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 6 Allopatric speciation in the lab?
n Experimental lines subject to divergent selection Drosophila: DDT resistant vs control lines maintained for 40 years in isolation (Boake et al. 2003)
Multiple choice mating test (expect 1:1:1:1 under random mating)
s 40 2
g 35 35 n χ =16.85* i
t 30 30
a - pleiotropy? 23 m 25
f - hitchhiking? 20 o 15 r 15 - independent evolution e
b 10
m 5 e.g. by genetic drift? u n 0 genes responsible for Res x Res Cont x Cont Res x Cont Cont x Res isolation and for resistance weak prezygotic isolation (no postzygotic) are on different chromosomes
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 7 Allopatric speciation in the lab?
Melon fly (Bactrocera cucurbitae, Miyatake & Shimizu 1999)
Selected lines: Diurnal mating activity short development -1 short development -2 long development -1 long development -2 pleiotropy "clock genes"
Multiple-choice mating tests no drift hitchhiking unlikely
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 8 Modes of allopatric speciation
n Vicariant speciation: isolated populations of reasonably large size
n Peripatric speciation: a small population becomes isolated or an isolated habitat patch ("island") is colonised
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 9 Modes of allopatric speciation
n Several islands: natural replicates J
q isolates from the same main population may differ due to sampling (founder effect) and may evolve into different species
q or may follow similar evolutionary pathways and become one (polyphyletic) species = parallel speciation strong evidence for adaptive speciation
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 10 Parallel speciation
n Stickleback (Gasterosteus aculeatus) benthic - limnetic species pair, two biological species across 6 lakes q single origin of benthic + limnetic? q sympatric speciation in each lake? q double invasion of low-lying lakes?
microsatellite DNA, nearby lakes max. likelihood tree B = benthic L = limnetic S = solitary M = marine Taylor & McPhail 2000
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 11 Parallel speciation
Are alternative trees worse? significant = rejected
double invasion (some sympatric speciation cannot be ruled out)
multiple origin of benthic-limnetic pairs: polyphyletic species parallel speciation
SPECIATION / EVA KISDI / 2018 FALL / LECTURE 6 12