Speciation II 23 - Past Paper Notes PDF

10 Speciation II 23 Friday, 29 December 2023 10 Specia*on… 22:17 Modes of speciation = how speciation can occur Summary of modes of speciation Genetic drift was suggested by Mayr, that drift could cause speciation On many small islands you find different species to mainland. In New Guinea...

10 Speciation II 23 Friday, 29 December 2023 10 Specia*on… 22:17 Modes of speciation = how speciation can occur Summary of modes of speciation Genetic drift was suggested by Mayr, that drift could cause speciation On many small islands you find different species to mainland. In New Guinea, Many of these species confined to the islands, some have range on mainland have range on mainland Initial variability from species, Genetic founder affect removes variation, which get pounded as small genetic variability in small populat do badly Then genetic variation increases back to normal With a difference genetic composition to original spe causing hybrid incompatibility and speciation Experimental evidence Single male and female in 100 vials and bred them for 12-14 Extreme bottleneck - only 2 individuals from a po Hypothesis - tested whether individuals were more w Assortative or disassortative mating? Figure shows there's ( centred at 0 ) no overall shift to m force in speciation. Will drift produce the changes that create speciation? E.g., changes of mate choice ts tions ecies, Its unlikely that difference that make speciation are this process But it is testable in lab 4 generations opulation willing to mate with individuals in own or other vials mate assortatively- so drift isn't a main driving Figure shows there's ( centred at 0 ) no overall shift to m force in speciation. A mechanism that does bare an effect and is important - polyp Polyploid = 3 or more sets of chromsone 2 sets of chromosome is normal but can get doublings 2n > 4 hybrid mating's 2n and 4n would produce 3n offspring which are sterile and speciation However sometimes 3n species survive so there can be gene flo 2-4% speciation of events but more common in plants ( up t Links to hybrid speciation Two separate parental species, that produce hybrids. That in some cases hybrids seem to be able to function, particul mate assortatively- so drift isn't a main driving ploid speciation 4n > 8n, occurs by mistakes in meiosis and d hence this techincally gives up instant ow between these 'species' Different blackberries have different chromosome numbers Also in goldfish lizards and frogs to 20%) Commercially large salmon are 3x ( hybrid between 2 and 4n) larly in extreme environments Two separate parental species, that produce hybrids. That in some cases hybrids seem to be able to function, particul E.g., two sunflower species H.annuus and petiolaris And their hybrids grow in extreme conditions Large chunks of hybrids chromosomes are from parents DNA Hybrids can produce divesrity Italian sparrow is hybrid from Spanish and house sparrow Seems to have occurred in different places across the med, giving 60% house sparrow 40% Spanish sparrow larly in extreme environments A g rise to one species of bird Cichlid adaptive radiation in Africa Shown that in this part of africa, Many populations have met and fish ended up meeting each ot Lead to diversification of cichlids around this area can be se Nile and congo genomes mixing ther due to river capture een in phylogeny Speciation driven by selection Uniform selection - the process mutation order being the mechanism of this Then divergent natural selection - ecological speciation Dobzhansky muller model Population with different locus a and b Dobzhansky muller model Population with different locus a and b If its split somehow ( allopatric model ) Overtime mutation occurs - regarded as stochastic ( random ) Order of mutations that occur in two populations are hence differe If advantageous it goes to fixation If at some point the two populations come back into contact Any hybrid offspring will be AaBb, and big A and big B have never in may confer a fitness cost. This model can hold true if se E.g., with or without predato Parallel evolution is when another population when same thing o loci and alleles change in same way - expected to be in same env Different environment - going to different genotypes - dive Note - mutation order also matters here Same environment - going to different genotypes - uniform entn nteracted in a genetic network, and election is same or different in two different populations ors and as you have different order of mutations it doesntmatter occurs in different population - same viroment ergent selection - ecological speciation m selection ( mutation order speciation ) Same environment - going to different genotypes - uniform Same environment - same genetic change - parallel evolutio Its hard to establish if the environment are the same for unifor Its easy to say if there different But not the same Senecio lautus occurs in Australia and different forms based m selection ( mutation order speciation ) on rm selection d on where it grows e.g., headland and dune Regular pattern occurring in Australia of different forms Phylogeny suggests this occurs locally Note there are two clades When comparing reproductive isolation in different locations When comparing reproductive isolation in different locations Different ecotypes in different clades have strong reproductive is Share same environment but don’t produce offspring - sugges solation sts mutation order selection Species separated somehow Can get different environments in two populatio You may get divergence - by product m Reducing likelihood of mating betweee In secondary contact you can get reinfor ons e,g., wet and dry etc mechanism, - species evolving to place where they are now en species ( e.g., the shape of fish stopping mating ) rcement due to lower fitness of mating producing hybrids Flies living on starch or maltose and many generations pu At end of experiment looking at individuals and w If they will mate across environmental divide Flies from different environments are less willing to m Flies from same environment are more willing to mate ushed through these who they're willing to mate with mate with each other e with each other Divergent selection is affecting mate choice That divergent selection results in speciation 4 predictions from this 4 predictions from this 1. Environments different and selection is different, repro difference 2. Selection reduces hybrid fitness, due to trade offs in ( ecological reason ) 3. Traits under selection produce by product mechanis and fuel reproductive isolation ) 4. With similar environments, you expect populatio likely to diverge, than in different environments ( only if environment is driving isolation ) - because of m oductive isolation increases with this these hybrids as they fall between niches sm ( traits lead to difference in mate choice ons evolve in the same way, and these are less mutation order speciaiton ) Change in ecological traits over time with divergence and Correlation of genetic divergence and ecological traits First prediction from model - that isolation increases with differ rence in enviroments First prediction from model - that isolation increases with differ Different eco types of whitefish are seen You get a big benthic form and a small pygmy form Across a set of different pairs of lakes, there is correlation distinctions Chance of gene flow reduces as morphological differe Ecological and genetic traits change together rence in enviroments between morphological and genetic entiation increases Predictions 2 - ecological selection reduces hybrid fitness Hybrid fitness is largely driven by interaction with environment Non functioning of the backcrosses have different fitness out Tells that ecology matters for fitness of hybirds t tcomes due to the different enviroments Tells that ecology matters for fitness of hybirds Prediction 3 - traits under selection lead to by product mecha Galapagos finches Variation in beak shape, leads to variation in songs Correlation to song and shape of beak Song important as mate choice que and hence mating choice a Another example Affect of body size in sticklebacks as mate choice anism affected by ecological traits Affect of body size in sticklebacks as mate choice Sticklebacks from small population like to mate with small bodie See when there is low difference in size higher m Comparing matings in stickleback Find that stickleback from similar size, even from different ec es stickleback mating choice cotypes, still mate with each other