2 1. Ways at Classifying Species Biological species conceptPopulation that has the potential to interbreed and produce viable, fertile offspring but unable to produce viable fertile offspring with members of other populations
3 Other Species Concepts MorphologicalBased on shape, size, etc.Ecologicalin terms ecological nichePhylogeneticin terms of unique genetic history
4 2. Biological Species Barriers Prezygotic barriersImpedes fertilization of ovaPostzygotic barriersPrevents hybrid zygote from developing
5 Individuals of different species Prezygotic and postzygotic barriersFigure 24.4Prezygotic barriers impede mating or hinder fertilization if mating does occurIndividuals of different speciesMating attemptHabitat isolationTemporal isolationBehavioral isolationMechanical isolationHABITAT ISOLATIONTEMPORAL ISOLATIONBEHAVIORAL ISOLATIONMECHANICAL ISOLATION(b)(a)(c)(d)(e)(f)(g)
7 Speciation can occur in 2 ways AllopatricSympatric(a)Allopatric speciation. A population forms a newspecies while geographically isolated from its parent population.(b)Sympatric speciation. A small population becomes a new species without geographic separation.Figure 24.5 A, B
8 3. Formation of Species: Allopatric Allopatric speciationPopulation is divided into 2 or more geographically isolated subpopulations
9 Geographic separation evolutionary change during the period of separationFigure 24.6A. harrisiA. leucurus
10 Allopatric speciation Reproductive isolationFigure 24.7Initial population of fruit flies (Drosphila Pseudoobscura)Some flies raised on starch mediumSome flies raised on maltose mediumMating experiments after several generationsEXPERIMENTDiane Dodd, of Yale University, divided a fruit-fly population, raising some populations on a starch medium and others on a maltose medium. After many generations, natural selection resulted in divergent evolution: Populations raised on starch digested starch more efficiently, while those raised on maltose digested maltose more efficiently. Dodd then put flies from the same or different populations in mating cages and measured mating frequencies.
11 3. Formation of Species: Sympatric Sympatric speciationGeographically overlapping populations
12 PolyploidyExtra sets of chromosomes f/ accidents during cell division
13 Autopolyploid More than two chromosome sets, f/ same species Figure 24.82n = 64n = 122n4nFailure of cell division in a cell of a growing diploid plant after chromosome duplication gives rise to a tetraploid branch or other tissue.Gametes produced by flowers on this branch will be diploid.Offspring with tetraploid karyotypes may be viable and fertile—a new biological species.
14 AllopolyploidMultiple sets of chromosomes derived from different speciesFigure 24.9Meiotic error;chromosomenumber notreduced from2n to nUnreduced gametewith 4 chromosomesHybrid with7 chromosomeswith 7 chromosomesViable fertile hybrid(allopolyploid)Normal gameten = 3Species A2n = 4Species B2n = 62n = 10
16 Sexual Selection Cichlid fish Sympatric speciation f/ nonrandom mating due to sexual selectionFigure 24.10Researchers from the University of Leiden placed males and females of Pundamilia pundamilia and P. nyererei together in two aquarium tanks, one with natural light and one with a monochromatic orange lamp. Under normal light, the two species are noticeably different in coloration; under monochromatic orange light, the two species appear identical in color. The researchers then observed the mating choices of the fish in each tank.EXPERIMENTP. nyerereiNormal lightMonochromaticorange lightP. pundamiliaUnder normal light, females of each species mated only with males of their own species. But under orange light, females of each species mated indiscriminately with males of both species. The resulting hybrids were viable and fertile.RESULTSThe researchers concluded that mate choice by females based on coloration is the main reproductive barrier that normally keeps the gene pools of these two species separate. Since the species can still interbreed when this prezygotic behavioral barrier is breached in the laboratory, the genetic divergence between the species is likely to be small. This suggests that speciation in nature has occurred relatively recently.CONCLUSION
17 Allopatric speciation Speciation due to geographic isolationSympatric speciationBarrier isolates a subset of a population without geographic separation
18 5. Adaptive Radiation Adaptive radiation Evolution of diversely adapted species from a common ancestor upon introduction to new environmentFigure 24.11
19 Argyroxiphium sandwicense Hawaiian archipelagoShowcase of adaptive radiationFigure 24.12Dubautia laxaDubautia waialealaeKAUA'I5.1millionyearsO'AHU3.7LANAIMOLOKA'I1.3 million yearsMAUIHAWAI'I0.4Argyroxiphium sandwicenseDubautia scabraDubautia linearisN