BIOLOGICAL DIVERSITY EXAM 2 LECTURE TEXTBOOK NOTES BIODIVERSITY CHAPTER TWENTY TWO THE ORIGIN OF SPECIES lecture 9 17 Macroevolution speciation 1 2 formation of new species can happen by two ways transformation over time of one species into another splitting of particular ancestral species into two or more descendant species traditionally morphology use of physical characteristics was used to designate species can cause difficulties and morphology does not work when there is a sexual dimorphism female looks different from male Ernst Mayr 1904 2005 biological species concept natural populations that are reproductively isolated from other such groups two distinct groups species is defined as groups of actually or potentially interbreeding 1 one group that is interbreeding 2 another group that will not breed with the other reproduction is not possible ways species organisms can split and be isolated disease decrease in population size geographic geological continental shift climate change behavioral mating calls fitness reproduction union of egg and sperm creating a zygote through fertilization pre zygotic reproductive isolation table 22 1 usually multiple things in play mechanical isolation impossible for reproduction mating to occur lock and key mechanism body mismatch ex ground beetles males have copulatory pieces and females match perfectly key and lock mechanism shape is mechanical isolation geographic isolation mating could occur but does not necessarily work barriers to organismal movement or reproduction patrick movement ex pollen no gene flow under these circumstances lakes valleys oceans mountains predators manmade structures like roads dams buildings cities conditions climate deserts any structure that prevents two organisms from being together ex desert pup fish live in isolated small streams and have generally very small habitats Death Valley to be specific 10 species of pupfish there and each is isolated in its own significant selective pressures DNA genetic analysis demonstrates that species are all closely related possibly due to common ancestry pool stream that is very hot and incredibly saline ecological isolation mating could happen but it doesn t organisms living in the same location where there is some specific ecological factor habitat preference that prevents organisms coming together and breeding ex anoles small lizards found in most tropical habitats they re very habitat specific and adapted to their environment they rarely leave their habitat therefore breeding is not likely at all behavioral isolation breeding could happen but does not some aspect of organismal interaction song dance ritualized movements that differs between species and makes breeding unlikely ex birds and insects fireflies species specific light patterns temporal isolation mating is possible but doesn t occur breeding of similar species occurs at different times of the year no chance of interbreeding true for animals and plants ex crickets Gryllus veletis that only call and mate during the spring and Gryllus pennsylvanicus only calls and mates in the fall both are very similar genetically however they have different breeding seasons prevention of gamete fusion NO GAMETE FUSION no fertilization mating occurs but sperm not get into the egg toxic environment for sperm sperm is killed by biochemical agents sperm cannot penetrate the egg biochemical environment sperm gets lost and swims around randomly main reason for biological isolation post zygotic reproductive isolation hybrid inviability fertilization occurs but there is such an accumulation of genetic defects that it results in death of the offspring before or soon after birth hybrid infertility fertilization occurs off spring survives develops into adulthood but is sterile and incapable of producing offspring themselves this can be partial ex mule result of horse and donkey mules are born strong and reach adulthood but are completely infertile ex tigers and lions often times there is more than one isolating mechanism in zoos lions and tigers were traditionally kept in the same enclosures often produced offspring most of the hybrids are sterile and cannot produce their own offspring but there is a handful that is fertile hybrid infertility 1 Speciation Requires Multiple Steps reproductive isolation populations of a single species become isolated from each other and over time those populations diverge become different as they evolve relative to their gene pool allele frequencies associated with particular traits if allele frequency is different trait frequency will be different could occur through natural selection as the environment may differ between populations if isolated there is ZERO gene flow no interbreeding between populations mutations will differ between populations that are isolated assuming mutation is not detrimental to the population it will change allele frequency genetic drift can limit the allele diversity in newly isolated populations founder effect differences in allele diversity in populations become fixed particular alleles for particular genes become increasingly common significant in a population at this point each population is limited in its ability to respond to new selective pressures driven by its allele diversity ex Hawaiian fruit flies hundreds of species and each species has elaborate mating rituals dancing song females will only respond to individuals from their own species courtship rituals of males of their own species 2 other isolating mechanisms evolve maintaining differences genetic divergence the longer two populations are separated the more likely it is that they will reach differences selection against mating particularly if there are costs associated with interbreeding ex hybrid infertility inviability reproduction is very energy expensive mating with a member of the isolated population that maybe has been brought back together somehow is a dead end reinforcement after the divergence of populations other isolating mechanisms prevent reduce interbreeding series of characteristics that arise and decrease the likelihood of interbreeding if interbreeding is lost allows for maintenance of genetic differences ex collared and pied flycatcher birds have a hybrid zone where hybridization does occur some hybrid infertility and some hybrid inviability when pied collared mate decreased egg production and decreased survival from egg to juvenile Speciation as a Function of Natural Selection small population
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