Speciation Flashcards
What is a species?
Populations between which there is no or very little gene flow
What is speciation?
Origin of reproductive barrier among population that permit the maintenance of genetic and phenotypic distinctiveness in geographic proximity
What are the three ways allopatric speciation can occur?
When a core species colonise new habitat.
When a continuous distribution gets fragmented (e.g. island chains, like Drosophila flies in Hawaiian archipelago).
Ring species: where the middle is unsuitable, colonise as they move round, when come back two separate species
What is an example where ring species have occurred?
Eurasian Greenish Warbler, multivariate statistical analysis, shows large change in song characteristics, no longer recognise each others songs.
Who suggested allopatric speciation was the main driver of speciation?
Ernst Mayr
What would we expect to see in real world data if allopatric speciation holds?
Anciently derived sister groups to have overlapping regions because sufficient differences have occurred so that they are able to inhabit the same areas without the gene flow collapsing), more recently derived groups have non overlapping regions.
What are the Nerodia snakes?
Snakes in N. America. Have polymorphic colour variation depending on habitat. Limestone areas are plain whilst areas high in vegetation are banded. The mainlaind is 100% banded, as you start to move towards the islands plain more frequent but still intermediates and banded ones, why no fixation becuase ongoing movement from mainland to island, continual gene flow!
How did oil seed rape come about?
Ploidy speciation
What two veg where used, how many chromosomes did they have?
Cabbage (18) and turnips (20)
Why were the two vegetable sterile at first?
Because they had odd number of chromsomes but a failure of meiosis results in new plants with 38 chromosomes.
What is anagenesis?
Speciation without splitting. Change through time. No division of lineages. Accumulation of changes within same lineage so if we take samples from different time points there would be sufficient genetic differences that we’d consider them separate species.
What is sympatry?
When species are within cruising range of one another
Who suggested sympatric speciation might occur?
John Maynard Smith
How did John Maynard Smith say that sympatric speciation could happen?
When you have two slightly different niches and different alleles are favoured at either one
What idea does sympatric speciation rest on?
Genotype fitness landscape
What is an example of ecological speciation?
Sparkleberry/apple maggot fly. Found from Mexico up to US breeds on fruit of several trees, apple, sour cherry, hawthorn. Different forms specialise on to different host plants. Conditions that would favour reproductive isolation due to different emergence times of larva. (fruit in different seasons) reduces chance of contact.
How did ecological speciation occur?
Was continuous then fragmented. Changes on chromosomes 1-3 that are associated with diapause and emergence times. Fly is polymorphic for different emergence times. 150ya explosion in agriculture and orchard development so new potential hosts to be exploited by the flies with the relevant polymorphisms. Allopatry a while ago and introduction of new host resource to facilitate sympatric speciation
What is another example of sympatric speciation?
Threespine stickleback in N.America. benthic form chunkier more armouring, Limnetic less so, habitats surface whilst benthic inhabits the deep bit. In each habitat different resources drive divergence and phenotypic difference. If they do meet and breed offspring have poor fitness as phenotype will not be specialised to either habitat
What are pre-zygotic barriers?
Arise from being in different habitats, from phenological source, reproducing at different times of year. Sexual isolation
What are post-zygotic barriers?
Occurs after mating, after hybrid offspring are generated, selection against migrant and hybrids because phenotype has lower fitness in habitat
What is post?
Barriers arise due to genetic incompatibilities
