Chapter 24Wednesday, February 3, 20162:19 PM Chapter 24: The Origin of Species -Defining Species-Originally, Latin for "kind"-Morphological species-Smallest set of organisms that look alike-Looks may deceiveEx. Eastern Meadowlark and Western - different speciesEx. Variations within the same speciesEx. Army ants, different "castes" but sisters in the same colony-Ecological species-A set of organisms adapted to a specific set of resourcesEx. Utilize different organic food sources-Phylogenetic species-Smallest distinct set of organisms that share a common ancestorEx. North and South American mountain lions-Biological species-Sets of populations whose members potentially interbreed in nature, to producefertile, viable young and do not successfully interbreed with other such groupsStay separate from other groups that interbreed with one anotherEx. Meadowlarks = different speciesEx. Humans = same speciesoBiological Species Concept-Members of same biological species:-Share the same gene poolThere is gene flow between populations-Are reproductively isolated from other species (cannot have gene flow)By natural biological barriers-Prezygotic or postzygotic-Reproduction has to produce fertile viable offspring-Prezygotic barriers-Prevent fertilization, that actually produces a zygoteHabitat (ecological) isolation-How a species is using the resources in the environment they live-Ex. Field/country mice never meet because of their different habitats, no chance of matingTemporal isolation-Mating at different times-Ex. FrogsBehavioral isolation-Females can distinguish the males even though theyare mating at the same time-Courtship cuesMechanical isolation-Insects have to mate end to end-Have to stay linked togetherGametic isolation-Gametes being released and gametes coming togetheroPostzygotic barriers Act after a hybrid zygote is formedReduced hybrid viability-Embryo fails to develop or is weak-Embryo may never develop very far, born but weak, feeble-Not able to reproduceReduced hybrid fertility: -Hybrid survives but is sterile (or almost so)-Infertile-Ex. MuleHybrid breakdown: -2nd generation hybrids are feeble or sterile-Ex. Wheato[24.3] -Problems with the Biological Species ConceptoFossil species-Have to use morphologicaloAsexual speciesoSometimes hybrids happen-How many genes are responsible for reproductive isolation?oMay be many genesoBut as few as one-Ex. Variation in one gene keeps 2 snail species from mating (gene changes direction of spiral, preventing mating - mechanical isolation) How Can New Species Form?-Speciation and EvolutionoSpeciation increases diversity of life (formation of new species)-Microevolution alone does not make more speciesMicroevolution = no increase in diversity of lifeMicroevolution with speciation = greater diversityoFossil record shows increased # of species-Gradual pattern of changeStart off with one species and slowly diverges ultimately forming two speciesSlow divergence as new species formEx. Butterflies-"Punctuated equilibrium"Brief period of rapid change as new species form= long period of stabilityEx. ButterfliesoSpeciation may occur with or without geographic separation-Allopatric speciation - geographic barrierCan account for vast majority of speciation, common-Sympatric speciation - doesn't require geographic barrier-Reference is to geography-Allopatric SpeciationoHow geographic separation makes a new species:-Keeps one population genetically isolated from the rest of the species-Physical barrier isolates one populationEx. Birds isolated on the island and barrier is the oceanEx. Small geographic distance, fish isolated in different pool,-Isolated population diverges genetically due to natural selection and/or genetic driftSubject to different environments, meaning different natural selection-During allopatry, biological reproductive barriers evolve, creating separate speciesNo reproductionOriginal and daughter species, new diversity, increase in diversityoHybrid zones may exist during allopatric speciation-Areas of contact may allow some matingLook back at the figures for examples of three possible outcomes*No prezygotic barriers or weak barriers-Three possible outcomesReinforcement (hybrids are weak/sterile, not successful)-Better and better, fewer hybrids in futureFusion (hybrids are healthy, 100% viable)-Gene pools come back together, two species are fusing togetherStable hybridization zone-Hybrids continue to be formed, but other factors keep gene pools separatedoEvidence for this process-Shrimp speciation and the IsthmusShrimp in Panama area, land bridge formed millions years ago15 species living on both sides of PanamaClosest related "sister species" live on opposite sides of land bridge-Divergence of species A and B from north and south-Barrier allowed divergence and speciation into 30 species-Mosquitofish in BahamasIsolated populations under different predator pressures also form reproductive barriers-Difference in morphology-Under high predation, pond with predators had wider tails for length, for burst of speed to escape predators-Pond without predators have sleek bodySleek bodied preferred sleekWide bodied preferred wideSeparation in natural selection, yielded less cross-mating (reproductive barrier)-Fruit fly populationsFlies isolated and raised on different foods showed mate-preference divergence (starch medium and maltose medium)Mating preference based on their food typeNo mating based on origin of population-Sympatric Speciationo= speciation in same geographical area-Gene pools become isolated in other ways-Very rare process, esp. in animalsoIsolated behaviorally by sexual selection-Female chooses same species of male under normal light-Female chooses male at random under monochromatic light-=> female choice maintains gene flow barrier-Animals onlyMales will have characteristics different from the femalesMay have led to two different speciesEx. Females pick mate on the basis of visual cues-Used monochromatic light and chose male species at random-Females actually use visual cues for matesOutcome: female choice maintains the two speciesoIsolated by habitat differentiation-Plant or animal populations isolated by use of different resourcesEx. Apple maggot fly-Hawthorn mistaken with apple fruitoIsolated by polyploidy-(complete nondisjunction) cell division errors duplicate entire genomeInstead of