1.IB BiologyOption DD2 Species and SpeciationAll syllabus statements IBO 2007All images CC or public domain or link to original material.Jason de Nysif I really have as bad an expression, asmy photograph gives me, how I can haveone single friend is surprising."

2. D.2.1 Define allele frequency and gene pool allele frequencygene pool Allele frequency is the proportion Noun: The total collection of of all copies of a gene that isdifferent alleles in an interbreeding made up of a particular gene population. variant (allele). ExampleSay if a recessive allele h made up2% of the total in a human then the dominant allele Hpopulation would make up 98%. The frequency for h would be expressed as 0.02 and for H 0.98 Recessive allele frequency + dominant allele frequency = 1 (for characteristics determined by two alleles) http://www.flickr.com/photos/limowreck666/171979083/ 3. D.2.2 State that evolution involves a change in allele frequency in a populations gene pool overa number of generations New combinations of alleles lead to new phenotypes that can then be selected for or against by the environment.This leads toevolutionary change inthe species 4. D.2.3 Discuss the definition of the term species What is a species? 5. D.2.3 Discuss the definition of the term species Ecological speciesThere are many definitions,A set of organisms adapted to a particular set of resources, called a niche, in the here are five!environment. Genetic species Based on similarity of DNA of individuals or populations. Having a common gene pool. Evolutionary species A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, some members may diverge from the main population and evolve into a subspecies.Lots to discuss if you get a Cladistic Species question about this! A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, members may diverge from one another: when such a divergence becomes sufficiently clear, the two populations are regarded as separate species. (This differs from the Evolutionary definition in that the parent species goes extinct when two new species are recognised). Breeding Species Two organisms that are able to reproduce naturally to produce fertile offspring of both sexes.http://en.wikipedia.org/wiki/Species 6. The genetic definition is most widelyused and works well for mostmulticellular organismsThe following 4 slides outline theexceptions: is anything ever simple in Biology? 7. Horsdoeuvre? It could be (ahem) physically impossiblefor members of thesame species to mate. Therefore they are genetically isolated. http://www.flickr.com/photos/lepetitblonde/2247963815/ 8. 1 : Lesser Black-backed Gull 2 : Siberian population Black-backed gull 3 : Heuglins gull 4 : Birulas Gull 5 : East Siberian Herring Gull 6 : American Herring Gull 7 : Herring GullRing Species:Adjacent populationscan interbreed but thepopulations at the endof the line cannot.1 and 7 cannotproduce offspring.Soclose and yet so far :( http://commons.wikimedia.org/wiki/File:Ring_species_seagull.svg 9. Hybrids are usually infertile and can not produce offspring together,for example the mule (63 chromosomes): a cross between a MaleWhy are 63horse (64 chromosomes) and a female donkey (62 chromosomes)chromosomes aproblem whenThe liger is a hybrid cross between a male Panthera leo (lion), and a female reproducing?Panthera tigris (tiger) and is denoted scientifically as:Panthera tigris Panthera leo. The tiglon is a hybrid cross between a female Panthera leo conversely (lion), and a male Panthera tigris (tiger) and is denotedscientifically as: Panthera leo Panthera tigris.Ligers and tiglons sometimesproduce offspring when matedback with a parent speciese.g. The hybrid of a male lionand a female tiglon is a li-tiglon! MADNESS!!http://xkcd.com/419/ 10. The genetic definitiononly applies to sexually Rats!reproducing organismsand doesnt apply tosingle-celled organisms http://www.flickr.com/photos/microagua/3721497804/ 11. Additionally:Fossil remains cant tell us whetherspecies were able to interbreed orproduce viable offspring so palaeontologists tend to use the cladistic definition http://www.flickr.com/photos/bruce_mcadam/1393218574/ 12. D.2.4 Describe three examples of barriers between gene pools The circumstances preventing different species from interbreeding are known as reproductive isolating mechanisms 13. Temporal isolationPinus radiata (Monterey Pine)MAX Pinus attenuata (Knobcone pine)Pollen ProductionJ F M A M J J A S O N D MonthPinus radiata and Pinus attenuata are prevented from hybridising becausethey have separate pollination times.They can be made to hybridise by pollinating them manually.*Random fact: The Monterey pine is at risk in its native range butis one of the most common plantation trees in the world. If yousee a pine forest in Australia or NZ, it is probably Pinus radiatahttp://www.flickr.com/photos/alancleaver/4293345631/ 14. Ecological isolation The two species are in the same area, but live in different habitats I love mesome CaCO3 in my soilBlechhh! Acidic soilsare more mything Viola arvensisViola tricolorhttp://www.flickr.com/photos/annetanne/3035068940/http://www.flickr.com/photos/carinemily/644052381/ 15. Behavioural isolationAnimals exhibit courting behaviour (song, dance etc.) or release pheremones to attract mates. Individuals are only attracted to, and will only mate with, members of theopposite sex who perform the appropriate ritual or release the correct chemical.Yo! I dont like your music! Its like,totally mutual!http://www.flickr.com/photos/nrk-p3/2333221093/http://www.flickr.com/photos/rowelbg/2895578034/ 16. Mechanical isolationAnimal example:Different species of bush baby (Galago) have particular shapes for their genitaliaand they are physically incapable of copulation*.It is like a lock andkey.She says Werenot a good fit. In plants, mechanical isolation occurs What is that when different species have differentsupposed to pollinators that are not able to service mean? the flowers of other species *Take care when Googling Bush baby genitalia!http://www.flickr.com/photos/joachim_s_mueller/4113758487/ 17. Hybrid InviabilityRemember: Male Horse + Female Donkey = Mule Horse 2n = 64 sperm n = 32 Donkey 2n = 62 ovum n = 31 Sperm + Ovum = Mule zygote 32 + 31 = 63 Mule2n = 63 gamete n = ? Note: Sad eyeshttp://www.flickr.com/photos/pirateparrot/301798478/ 18. D.2.5 Explain how polyploidy can contribute to speciationSo far youve learnt that cells contain two homologous sets of chromosomes.Well.. that isnt always the case.It goes on:PentaploidHexaploidSeptaploidOctaploidEtc.up to:84-ploid and 1260chromosomes Ophioglossum reticulatum A small fern. The incredible thing is that this plant isable to carry out meiosis accurately with 1260 chromosomes to divvy up http://commons.wikimedia.org/wiki/File:Haploid,_diploid_,triploid_and_tetraploid.svg 19. How it happens: Remember:Self When non-disjunction occursfertilisation during meiosis in humans, an individual can end up with an extra chromosome or missing chromosomes. E.g. An extra chromosome 21 means Downs syndrome (see 4.2.4) Total non-disjunction, is when one of the two cells produced during Meiosis I gets all of the chromosomes. The other cell is not viable and is reabsorbed. This results in two (2n) daughter cells from meiosis instead of the usual four (n) daughter cells. See animationhttp://commons.wikimedia.org/wiki/File:Polyploidization.svg 20. Few polyploid organisms exist in the animal kingdom. Can you think of the reasons why not?Animal polyploid species include salamanders, goldfish andsalmon. However, polyploidy is a great source of speciation amongst plants.Polyploidy often leads toincreased size, resistance todisease and overall vigour.Many plants used by humans arepolyploid. Including cereal cropslike wheat.Polyploid crops generally havebigger fruits, seeds and storageorgans 21. Two versions of Polyploidy: Autopolyploidy* Allopolyploidy *This is not autopolyploidy http://www.flickr.com/photos/leapkye/3224058317/ 22. Autopolyploidy (Auto = self) Autopolyploids are polyploids with multiple chromosomesets derived from a single species as described a couple ofslides ago. Autopolyploids form following fusion of 2n gametes Autopolyploidy can be induced in plants using colchicine, achemical extracted from the autumn crocus. Autopolyploids with odd ploidys eg triploid or pentaploidhave trouble reproducing sexuallyWHY? That does not stop them from being good crops if they canbe propagated asexually 23. Allopolyploidy(Allo = different)Allopolyploids come about when a sterile F1 hybrid doubles all of itschromosomes and becomes fertile.For example, Triticale is the hybrid ofwheat (Triticum turgidum) and rye + =(Secale cereale). It combines sought-after characteristics of the parents, butthe initial hybrids were sterile untildoubling of the number ofWheatRyeTriticalechromosomes occurred Remember the poor sterile mule with 63chromosomes? Imagine if we could somehow induce sperm andova with 126 chromosomes Voila! The mule born would be fertile.Of course, it would need to be done a couple oftimes to get a few mules to breed togetherhttp://en.wikipedia.org/wiki/File:Wheat,_rye,_triticale_montage.jpghttp://jonathanturley.org/2009/03/01/a-happy-mule/ 24. D.2.6 Compare allopatric and sympatric speciation Allopatric speciation (Allo = different, patric = fatherland) This arises when a species is subject to geographic isolation. This can occur when a population is split by: A river A mountain rangeGene flow is cut off between the two split A desertpopulations and they can evolve in different A roaddirections (See animations below) The sea etc.RememberDarwinsfinches?http://commons.wikimedia.org/wiki/File:Darwin%27s_finches_by_Gould.jpg 25. Once the populations have been separated into two gene pools theycan diverge through natural selectionor through random genetic drifthttp://upload.wikimedia.org/wikipedia/commons/b/b6/Random_sampling_genetic_drift.gif 26. Allopatric speciation of Drosophila in the labEven when the geographic barrieris removed, the populations are stillgenetically isolated 27. Sympatric speciation(Sym = same, patric = fatherland)The formation of two or more descendantspecies from a single ancestral species alloccupying the same geographic location. Whether it actually happens is still contested.Find a pair of species that are thought to have diverged by sympatric speciation http://etc.usf.edu/clipart/2200/2288/salamander_1.htm 28. Diagrammaticcomparisonhttp://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Speciation_modes.svg/500px-Speciation_modes.svg.png 29. D.2.7 Outline the process of adaptive radiation Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits with which they can exploit a range of divergent environments. Wikipedia Think Darwins finches (AGAIN!) They originated from a population of an ancestral species that flew or were blown to the Galapagos islands from mainland South America. They colonised the islands and (while geographically isolated) evolved via natural selection to have beaks that suited the types of food available on their islands.Their beaks arehomologous structures inthat they have evolvedfrom a common structure to have different functions. 30. D.2.8 Compare convergent and divergent evolutionWhat do humans, octopi and box jellyfish have in common?http://www.flickr.com/photos/jlambus/2303592201/ 31. We all have complexcamera* eyes. They evolvedindependently inorganisms only verydistantly related.They are an exampleof convergent evolution Complex eyes have evolved 50 to 100 times!*Camera means room 32. Convergent evolution describes the acquisition ofthe same biological trait in unrelated lineages.Other (random!) examples include:- Penguins in the southern hemisphere and Auks in the northern hemisphere both use wings as flippers Little Auk- Echolocation in bats, toothed whales and shrews to capture prey. It even http://commons.wikimedia.org/wiki/File:AlleA evolved independently twice amongst the bats- Super strong jaws on different genuses of ants (Trapjaw )- Flight/gliding in birds, pterosaurs, bats, insects and flying fish! Little Penguinhttp://commons.wikimedia.org/wiki/File:Little_penguin_Eudyptula_minor.jpg 33. Im including this image because I mentioned bats twice on the last slide and bats are awesome! * *Whatever hes saying, its ultrasonichttp://www.flickr.com/photos/furryscalyman/673915993/ 34. Features that come about by convergent evolution are known asanalogous structureshttp://www.flickr.com/photos/sniffette/6705872/http://www.flickr.com/photos/volk/1038089969/ http://www.flickr.com/photos/jaybock/4006029348/http://www.flickr.com/photos/martynr/76538849/sizes/o/in/photostream/ 35. Divergent Evolution is another way of saying adaptive radiation (D.2.7).As natural selection acts on two or more species that have arisen from acommon ancestor, they become phenotypically different.It gives rise to homologous structures, features that now look differentor have a different purpose for each species that has evolved 36. http://commons.wikimedia.org/wiki/File:Evolution_pl.png 37. Divergent evolution Convergent evolutionTimeParent species Parent Parent (common ancestor) speciesspecies 38. D.2.9 Discuss ideas on the pace of evolution including gradualism and punctuated evolution Phyletic Gradualism, as the name suggests, is the idea that evolution occurs at a slow-but- steady pace. Punctuated Equilibrium is the idea that, for most of the time, species are stable. But every now and then there is a disruptive event that prompts rapid change.The slope of the line indicates rate of change. Vertical lines = little/no change Horizontal lines = very rapid change 39. Gradualism is the older idea. Darwin is one of theoriginators of the concept,borrowing from his friend Charles Lyell. Darwin recognised however that not all species evolve at the same rate all of the time "I think case must be that one generation shouldhave as many living as now. To do this and to have asmany species in same genus (as is) requiresextinction . Thus between A + B the immense gap ofrelation. C + B the finest gradation. B+D rathergreater distinction. Thus genera would be formed.Bearing relation" (next page begins) "to ancienttypes with several extinct forms" http://commons.wikimedia.org/wiki/File:Darwin_tree.png 40. Punctuated equilibrium was first proposed by palaeontologists Niles Eldredge and Stephen Jay Gould in 1972. They were the first to suggest that species did not change for long periods of time but were in stasis until events punctuated (disrupted) the equilibrium (balance)Richard Dawkins is a prominent critic of the theoryTOK: Find out more: What evidence are the two theories based on? Gould (deceased) and Dawkins have both becomepopular writers. How does this affect the weight oftheir opinion: In the scientific community? In the wider community?http://www.flickr.com/photos/ideonexus/4022727065/http://www.flickr.com/photos/mrccos/288136783/sizes/m/in/photostream/ 41. Revisiting the tree for punctuatedequilibrium it should be noted that thesudden speciation events are onlysudden in terms of geological time. Theywould still take many generations andpossibly thousands of years.The periods of stasis may beexplained by stabilising selection The punctuation could be explained by directional selection or disruptive selection 42. You should be able to understand and interpret these diagrams.Practise sketching them.The downward facing arrows indicate selection pressure against individualswith that morphologyStabilisingDirectional DisruptiveBeforeAfterAll images CC Andrew Colvin 43. Darwins Finches (again!) are an example of disruptive selection A B Short-beaked birds (A) and long-beaked birds (B) were able to exploit different food sources and this selection pressure led to the evolution of two specieshttp://www.flickr.com/photos/kookr/2917861361/ 44. Lake Turkana (Kenya,Ethiopia) contains severalspecies of snails that havea fossil record showingThe periods of changelong periods with little coincide with timeschange followed by when the water level ofsudden changethe lake dropped and it(punctuated equilibrium) became a series of smaller lakes. What happens then?http://en.wikipedia.org/wiki/File:Lake_turkana_satellite.jpg 45. Thats right: geographic isolationSmaller gene pools aremore susceptible todirectional selectionBy the time lake levelsSo evolution of the recovered and theisolated populations maypopulations werebe faster than when theyunited, isolatingwere one big happy gene mechanisms were inpoolplace that preventedhybridisation 46. After each extinction event, the number of genera has bounced back Phanerozoic_Biodiversity.svg 47. The K/T extinction event (250 MA at theCretaceous-Tertiary boundary) wiped outover half the genera, including most ofthe dinosaurs.A layer of iridium has been found insediments laid down at that time all overthe globe. Iridium is in higherconcentrations in meteorites than onEarth generally.Therefore it is postulated that a largemeteor or comet hit the Earth andcaused the extinction.Individuals in the species that survived couldmove into the empty ecological niches anddirectional selection led to rapid evolution http://www.flickr.com/photos/53402955@N08/4928503884/in/photostream/ 48. D.2.10 Describe one example of transient polymorphism Darwins finches. Have little to do with this point (for a change!). Instead, the peppered moths (Biston betularia) are the best known example Polymorphism is the existence of two or more different forms of a species Poly = many morphism = shapesPrior to 1840 peppered moths in Britain were light grey with dark spotsto blend in with the grey lichen that grew on the trees in their habitathttp://www.flickr.com/photos/wildhastings/4720082589/ 49. The first dark variant wasreported in 1848 and by1895 most of them wereblack.The term industrialmelanism was coined.Soot and acid rain fromthe burning of coalchanged the colour orthe trees that the mothsrested on.Directional selection didthe rest. http://www.flickr.com/photos/naturalhistoryman/817332984/ 50. Before long the majority weredark.This situation reversed after 1956when Britain instituted the cleanair act. Less coal was burnt andmost trees returned to theiroriginal colour.Now in polluted areas mostmoths are dark and in rural areasmost moths are light.They are not distinct speciesbecause they still interbreed.The theory that natural selectiondue to predation was the causeof these changes has beenconfirmed experimentally byDr HBD Kettlewell 51. D.2.10 Describe sickle cell anaemia as an example of balanced polymorphism Sickle cell anaemia occurs when a single-base mutation in the gene that codes for haemoglobin causes the amino acid valine to be produced in a particular spot rather than glutamic acid.Valine is non-polar, unlike glutamic acid,and this causes the mutant variety ofhaemoglobin (haemoglobin S) to crystalliseat low concentrations of oxygen.This in turn pulls the red blood cell into asickle shape. It is less able to carry oxygenand can get stuck in small capillaries,causing blockages, pain and damage.Homozygous individuals (HbS HbS) aresubject to a debilitating condition and havea shortened life expectancy 52. On the brighter side, while individuals who are heterozygous (HbA HbS) will havesome mutant haemoglobin. They can lead normal lives. As a benefit, they areresistant to malaria as the plasmodium parasite that causes it is not able to usesickle cells to reproduce.Individuals that are homozygous normal (HbA HbA) have no sickle cellsand no resistance to malaria.Historical distribution of malaria Distribution of the sickle cell trait 53. HbA HbAHaemoglobin: NormalRBCs: Normal Heterozygous:Heterozygous: O2 Capacity: Normal Sickle cell traitSickle cell trait Malaria resistance: None HbA HbS Haemoglobin: A SA S50% normal, 50% mutant RBCs: Usually normal, sickle when [O2] lowA AA SA S S SO2 Capacity: Mild anaemia Malaria resistance: Moderate HbS HbS Haemoglobin: mutant RBCs: Sickle O2 Capacity: Severe anaemia Malaria Resistance: HighHomozygous: Heterozygous: Homozygous:NormalSickle cell traitSickle Anaemia 25% chance50% chance25% chance http://en.wikipedia.org/wiki/File:Autorecessive.svg 54. This is an example of balancing selection and balanced polymorphism People who are homozygous for sickle cell are severely anaemic and have less chance of surviving to reproduce. Likewise individuals homozygous for normal haemoglobin are likely to contract malaria and are less likely to survive.Heterozygous individuals have whatis termed heterozygote advantage. They are the most likely to surviveand reproduce.Therefore both alleles are maintained in the population http://en.wikipedia.org/wiki/File:Plasmodium.jpghttp://en.wikipedia.org/wiki/File:Sicklecells.jpg http://commons.wikimedia.org/wiki/File:Simple_balance_scales-01.jpg 55. Hypotheticals:France has the greatest number of sickle cell sufferers in Europe becauseof immigration from its former African and Caribbean colonies.What do you expect will happen to the sickle cell allele in France overtime given: 1. no more immigration, 2. modern medicine, 3. and the absence of malaria?What do you expect will happen to the sickle cell allele in West Africa overtime if: We eradicate malaria?Or We develop medication that helps all sickle cell sufferers live normally 56. Further information: