Lecture 12 - Speciation Flashcards
Mechanical isolation
Structural incompatibility of the reproductive organs between two species
Copulatory behavioral isolation
Behaviour of individual during copulation is insufficient to allow normal fertilisation
Gametic isolation
Transferred gametes cannot effect fertilization
What are the 3 different types of post-mating pre-zygotic barriers?
Mechanical isolation
Copulatory behavioural isolation
Gametic isolation
Example of mechanical isolation
The males of two species of Japanese carabid beetles have different shape and size of copulatory pieces causing tearing of the females reproductive organs and sometimes killing her (65% reproductive isolation)
How common is mechanical isolation in animals?
Not very common
What is an example of copulatory behavioral isolation?
Males of different species of drosophila have different shaped posterior lobe of the genital arch
Stimulates the female differently
If the female is not stimulated correctly the sperm is expelled
What are the two different types of gametic isolation?
Non-competitive gametic isolation (intrinsic factors)
Competitive gametic isolation: conspecific sperm precedence
Example of conspecific sperm/pollen precedence
D.Simulans female inseminated by both D.simulans and D.mauritania males produced almost no hybrdis (even when hetero-specific male is secound to mate)
Hybrid inviability
The hybrid zygote dies due to genetic incompatibilities
Hybrid sterility
The hybrid zygote survives, but is unable to produce viable progeny
Two types of post-zygotic barriers?
Extrinsic - isolation depends on environment
Intrinsic - developmental problem in hybrids that is independent from the environment
What are the two types of Extrinsic post-zygotic barriers?
Ecological inviability and behavioural sterlitiy
Ecological inviability
Hybrids suffer lower viability because cannot fin an appropriate ecological niche
Behavioral sterility
Hybrids are less fertile than the parental species because cannot obtain mates
Two types of intrinsic post-zygotic barriers
Hybrid inviability - developmental difficulties cause hybrid lethality
Hybrid sterility - physiological or behavioural
Example of ecological inviability in plants
Sagebush has two types: one that grows in the mountains and one that grows in the basin
hybrids show a lower fitness in both environments
Example of ecological inviability in animals
butterflies H.melpomene and H.cydno
Have colors that show they are unpalatable
Hybrids change this colour pattern and means they are eaten more
Example of behavioral sterility
Hybrids of Chrysoperla sps. will produce intermediate songs that are discriminated against by the females of both parental species
is extrinsic isolation fixed? give an example
No
Darwin’s finches in the Galapagos, before and after el nino even. The climactic phenomenon had an impact on the seed size on the islands and therefore altered beak morphology
How easy is it to distinguish between extrinsic and intrinsic post-zygotic isolation? give an example
Hard
Two species of mouse hybrids more prone to intestinal parasites (extrinsic) due to reduced genetic resistance (intrinsic) to parasitism
Examples of hybrid sterality
Mule (horse and donkey)
Zedonk (zebra and donkey)
Haldanes rule
If the reproductive isolation barriers are incomplete, the heterogametic (XY) sex will show the strongest isolation
The male is XY in mammals and most insects
The female is XY in butterflies and birds
Dominance theory
Hybrid heterogametic are affected by X-linked incompatible genes either dominant or recessive (see example in notes)
