Speciation I 23 PDF

9 Speciation I 23 Thursday, 21 December 2023 9 Specia)on I 23 13:23 Ernst mayr - studied birds of Melanesia, The species concept - populations of interbreeding organisms that are reproductively isolated from other groups Speciation being the process that leads to the evolution of this re...

9 Speciation I 23 Thursday, 21 December 2023 9 Specia)on I 23 13:23 Ernst mayr - studied birds of Melanesia, The species concept - populations of interbreeding organisms that are reproductively isolated from other groups Speciation being the process that leads to the evolution of this reproductive isolation between groups There are two mechanism in which this isolation occurs, pre and post mating Tigon and a liger And mule and donkey names - no idea the mix they are What does the existence of these animals mean for species definition? E.g., tigers and lions used to co exist but are now species. However these animals are sterile, so species definition leads to; having the need to produce non sterile offspring. Here this is post mating isolation mechanism, as hybrids are sterile. Mayr came up with the spcies concept, Dobzhansky came up with the isolating mechanism Mayr came up with the spcies concept, Dobzhansky came up with the isolating mechanism Isolating mechanism can occur before and after mating They are not however always perfect, as there is often hybrids made - shows not perfect, but their formation is very restricted, But normally hybrids don’t work well Two fish here living in lake Victoria, very closely related. Can see difference by colouration Did experiment of mate choice, in the two species in coloured and white light. Females couldn’t tell difference of colouration in Two fish here living in lake Victoria, very closely related. Can see difference by colouration Did experiment of mate choice, in the two species in coloured and white light. Females couldn’t tell difference of colouration in coloured light and hence cant tell two species apart. And hence may mate with these species in coloured light Pre mating isolation mechanism , by mate choice. Similar occurs in plants, two species - aquilegia species. Difference is how and when they're pollinated, Formosa in the day by bees hummingbirds fly's Pubescnes at night by moths Leads to restriction of transport of pollen between two species, But isn't impossible due to some bees and fly's visiting both pubescnes and formosa. Post mating isolation - hybrid just wont work - normally as they're sterile, either first or second generation Hatching rates of two butterflies species Hybrids of the two will hatch but not the F1 generation of the hybrid with a male Female are sterile Female hybrid with male normal butterfly The sterile hybrids are normally the ones with different sex chromosomes. The sterile hybrids are normally the ones with different sex chromosomes. E.g., males in mammals and in this case females Cases where hybrids seem okay, however they fall between niches in the wild and cant survive in the wild Ecological post zygotic isolation not genetics E.g., N.bebbianae, beetles which sub species specialise on certain plant species. In this experiment made hybrids of beetles which specialise in specific plants to make F1 , And then bred them back to pure form ( mated with a non hybrid again ) ( called backcross ) If you expose them to the wild, they cant feed properly. As these backcross species fall between niches. And seen by reduced growth rate Ecologically dependent not only due to genes Willow backcrosses do better on willow and bad on maple Vice versa for maple backcross If you expose them to the wild, they cant feed properly. As these backcross species fall between niches. And seen by reduced growth rate Ecologically dependent not only due to genes Limnetic and benthic sticklebacks in British Columbia Reared fish backcrosses and reared them in opposite species Benthic backcross does better in benthic conditions Limnetic backcross does better in limnetic conditions Showing there is a inadequacy in hybrids linked to environment How does speciation occur Sympatric and allopatrically Now apparently it is only really allopatric or parapatric Allopatric a single population becomes two by some barrier leading to comp Making two gene pools, and restriction of gene flow between the t Begins cladogenesis - creation of two lineages, Two populations may be able to get back into contact and even ov Range overlap starts low as they need to become two different sp Sympatric speciation Start with a range but there is a different availability of niche a single range plete separation two verlap again pecies then they get re introduced es in a range leading to separation within Two ends of a spectrum, w with complete and mixed separation Sympatric speciation Start with a range but there is a different availability of niche a single range To start range of small sub population is small with large over overlap reduces if other species begins to spread Range overlap starts large then reduces Paper looking at degree of sympatry. 1- Overlap 0. No overlap Compared to age Increasing pattern of overlap overtime, - suggest most speciatio Two ends of a spectrum, w es in a range leading to separation within rlap by large range and overtime this on is allopatric In the real world its really overlap of species, but no with complete and mixed separation y parapatry, where there is a bit of an ot so extreme like sympatry An empirical study into speciation - snapping shrimp A land snapped shut in this space, to stop movement between Carib In phylogeny you have P for pacific and C for Caribbean sea All appear and are separated by isthmus of Panama, most si Panama created/promoted speciation Lots of islands having some species of Anolas lizard Count of species against area of island bbean and pacific ocean ister species are C and P meaning isthmus of Count of species against area of island Big variation of number of species in islands Also big variation in size of islands Number of species really picks up at bigger islands If you look at where speciation occurs, there is none in s speciation at the bigger islands There are lizards but no speciation in sm This is because speciation is easier when the Also idea that allopatry is most dominant spe Patterns in Galapagos finches Crust in ocean is moving slightly Islands are being created on the left and worn away as you go rig Allows dating of islands at points in past Can also estimate species of finch's in past small islands until 10 to 4 power, and lots of mall islands ere is space eciation ght. As the crust moves Can also estimate species of finch's in past Number of island steadily increases Which is followed in pattern of finches speciation increasing as Stating allopatry is important There are exceptions to this - best example of sympatric speciat Either hawthorn or app Feeds on fruits of different hawthorn species in North America Some Made a shift to apples from hawthorns, left their maggot Different species of fly have become differentiated, As many stay within just hawthorns or apples, most species are popping up tion in apple magot ( hawthorn ) fly ple fly's ts there Other example of sympatric speciation - cichlids in crater lakes Two different species in this lake of cichlids one is benthic ( plankton in open water Benthic, limnetic split - different pharyngeal jaws clear mor This appears to have occurred within the lake Hence sympatric speciation can be seen to occur bu A ring species is a situation in which two populations w same region and connected by a geographic ring of po Birds have expanded different ways and birds who even c recognising each other even though they are close A halfway houses - ring species big insects of bottom ) one limnetic - rphological difference. ut is rare which do not interbreed are living in the opulations that can interbreed. come into contact blue and red circles aren't Birds have expanded different ways and birds who even c recognising each other even though they are close A halfway houses - ring species Ring around Tibetan plateau - greenish warblers Two different migratory routes - east and west around Himala places like Russia Males have different songs based on which migratory route Song is linked to range and where they are Experiment Reponses of local birds to recordings of different distance awa After some distance around the ring shows lack of response to Open circles - are similar geographic distance but males recognise each other across hybrid zone. come into contact blue and red circles aren't ayas, to then breed north of this in Asia. In e they take and where you breed in Asia ay o calls ( the solid rings ) s nearby to each other but they still don’t Open circles - are similar geographic distance but males recognise each other across hybrid zone. Development of increasing genetic divergence of birds w s nearby to each other but they still don’t with distance acorss rings Stages of speciation as it takes a long time Cant really obvserrve it But you can observe speciation indirectly by seeing how iso far apart they are But you can observe speciation indirectly by seeing how iso far apart they are Plant species - silene Some pairs older than others Genetic distances is basically an indicator of time - time divergenc Can estimate likeliness pairs can mate with each other - and invert 1 = no hybrids 0 = pair of species hybridises freely See reproductive isolation increases over time - obvious Same graph with drosophila species Time of separation in any species olated species are by seeing how genetically ce t to get isolation index Average index increases after isolation In broad evolutionary terms, a by-product is a characterist simply because it happened to be structurally a with an adaptation via historical constraints. An Model of how speciation occurs At start - allopatric divergence occurs and may go on forever But if they don't come back together you don't know if they're You can get pairs of species back in contact but maintain this sp by reinforcement Reinforcement occurs due to hybrid species having reduced fitn selection favours parents who don’t mate with other species Reinforcement is selection against making mistakes in mating their grandchildren number is reduced tic of an organism that evolved and inextricably associated nd different species or not peciation by reinforcement via sympatric ness compared to normal genotypes, so - mating with different species, so that Reinforcement is selection against making mistakes in mating their grandchildren number is reduced Can get differences developing in allopatric phase due to diffe exist. Selection may no favour difference but favours adapting in dif Mosquito fish in bahamas You get lagoons with fish communites, you get places where mo based on other fish in lagoons - mating with different species, so that erence of environment in which gene pools fferent ways osquito fish have high or low predations Morphological differences between the fish in high and low preda Different shapes of these fish Then took individuals from along the axis and see if they would m ation mate with each other Individuals with more similar shape are more likely to mate w Selection is acting through predation, favouring different shap preference This is the by product mechanism Reproductive isolation builds in allopatry (dark product of adaptation to alternative environme Reinforcement of premating isolation, driven by reduced hybrid process during the sympatric phase (light shaded). Reinforcement t is selection for not making mistakes in mate sel Study into different fly catchers - collared and pied, into their h Pure or mixed in high But when the hybrids in F1 lay eggs their offspring is reduced female hybrid fertility Selection chooses against mates with wrong species ( previou with each other pes which leads to changes in mate shaded) as an incidental byents (by-product mechanism) d fitness, completes the speciation lection hatching rates ( the grand offspring) due to reduced usly mentioned in reinforcement ) But when the hybrids in F1 lay eggs their offspring is reduced female hybrid fertility Selection chooses against mates with wrong species ( previou You get exaggeration of difference between males where they oc Pied fly catcher in allopatry are males are black and white But in sympatry the males are brown and white like the females Brown males is a derived character Mate choice by females in sympatric areas When you get similar birds ( both black ) females sometimes ge This is why sympatry birds are brown as their grandkids wont be ( the grand offspring) due to reduced usly mentioned in reinforcement ) ccur in sympatry, et the wrong bird e infertile. This is why sympatry birds are brown as their grandkids wont be The hybrids are infertile, if you do mate choice experiments, yo Selection against making choice across species Stickle backs e infertile. ou get reduced choices between species Stickle backs F1 hybrids living in different areas Growth rate of pure ecotype is higher. Hybrids incur reduced fitness Females generally don’t differentiate between benthic and limne But females from benthic type don’t with limnetic from other p There is selection against choosing opposite species etic males populations