Reproductive isolation

Reproductive isolating barriers Extrinsic vs intrinsic isolation [Blackboard: population genetics of assortative mating]

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 1 Reproductive isolation

n Why don't we see these in nature?

"leopon", “liger”, Panthera leo x pardus Panthera leo x tigris

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 2 Reproductive isolating barriers

n Prezygotic isolation: no hybrid zygote is formed

q Behavioural isolation: song, pheromone, courtship, size, ...

Darwin's finches, Podos 2001

Geospiza magnirostris

Geospiza fuliginosa

kHz 0.5 s

q Mechanical isolation: insect genitalia, flower morphology

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 3 Reproductive isolating barriers

n Prezygotic isolation

q Gametic isolation: cross-fertilization impossible or conspecific sperm / pollen precedence

Sea urchin spp: sympatric broadcast spawners

bindin: released to enter the vitelline envelope of the egg, rapidly diverges between species Echinometra (high replacement / silent substitution ratio; arms race?)

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 4 Reproductive isolating barriers

n Prezygotic isolation

q Ecological isolation (byproducts of adaptation) n Habitat isolation: breed in different habitats within cruising range n Allochronic isolation: breed at different times

apple race

Aquilegia formosa (vs A. pubescens) apple maggot fly hawthorn race Rhagoletis pomonella

n Pollinator (floral) isolation: different insect spp or different individuals (!)

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 5 Reproductive isolating barriers

n Postzygotic isolation: hybrid inviability or sterility

q Extrinsic postzygotic isolation: environment-dependent n Ecological: hybrids are selected against in nature (no niche) n Behavioural: hybrids cannot find appropriate mates (sexual selection)

Heliconius melpomene hybrid H. cydno d e k c a t s t d a r i n b o i y t r b o p o r Merrill et al. (2012) p ME F1 CY

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 6 Reproductive isolating barriers

n Postzygotic isolation: hybrid inviability or sterility

q Intrinsic postzygotic isolation: in any / in stressful environment n Hybrid inviability: death during development or reduced survival later n Hybrid sterility: no functional reproductive organs or incapable of courtship/parental care

Mule: horse (2n=64) x donkey (2n=62)

Agapornis roseicollis x A. personata fischeri female hybrids fail to build a nest / do not incubate

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 7 Extrinsic vs intrinsic isolation

How to tell apart extrinsic and intrinsic postzygotic isolation?

Threespine stickleback (Gasterosteus aculeatus) invaded freshwater lakes in Canada after the ice age

Benthic and limnetic morphs differ in morphology (large/small; jaws, gill rakers) diet (benthic invertebrates/zooplankton)

Trade-off between habitats:

Schluter (1995)

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 8 Extrinsic vs intrinsic isolation

Hypothesis: hybrids are not efficient in either habitat = extrinsic postzygotic isolation

1. F1 hybrids are viable and fertile in the laboratory

Hatfield & Schluter 1999

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 9 Extrinsic vs intrinsic isolation

2. F1 hybrids do poorly in both natural habitats

benthic limnetic F1 hybrid

Hatfield & Schluter 1999

- but is this because they are not adapted to either niche (extrinsic) or because they have intrinsic genetic incompatibilities that manifest only in stressful environments?

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 10 Extrinsic vs intrinsic isolation

3. Backcrosses: F1 x benthic ® BB, F1 x limnetic ® BL phenotypically closer to the parental forms:

if extrinsic, BB should do better in the littoral habitat

BL should do better in open water equal genetic incompatibilities:

if intrinsic, BB and BL should do equally badly in each habitat

Rundle 2002

SPECIATION / EVA KISDI / 2018 FALL / LECTURE 2 11