How does speciation progress Pops of a single species become reproductively isolated from each other Over time these isolated pops begin to genetically diverge Changes in gene pool within pops relative to allele freq for diff traits One possibility genetic divergence results in inability of one pop to breed with another speciation has occurred OR the genetic divergence is not enough to prevent interbreeding successful offspring viable OR successful breeding can occur but not always it is tough to tell if speciation Partial isolation often leads to selection against mating Why Reproduction is energetically expensive mating with a member of other isolated pop can lead to infertile offspring no offspring wasted effort energy dead end particularly an issue if produce once a year or once in lifetime Partial isolation Most breeding events result in no offspring a few do produce offspring In some cases these offspring are fertile Breeding between individuals from the 2 pops lost reproductive effort Often leads to new traits becoming important in mate selection Reinforcement After initial genetic divergence of pops if they come back together other isolating mechanisms begin to arise and prevent interbreeding Maintaining genetic diffs Ex European flycatchers some areas of 2 isolated pops overlap can lead to some offspring produced Very low survival from egg to juvenile Female produce fewer viable eggs when they interbreed Reinforcement occurs in overlapping range thru changes in plumage feather color significantly decreases interbreeding Speciation can occur through genetic drift Separation of random groups of individuals into distinct isolated pops Often thru founder effect Ex Hawaiian fruit flies each island has distinct species group based on morphology habitat behavior Adaptive radiation rapid production of new species recently evolved from same common ancestor founder effect natural selection Ex few birds on an island lots of food and no competition come back years later to many birds and low food availability high competition for preferred food Some individuals shift to alternative food and never go back to old Ex natural dams forming lakes in a river have a single common ancestral species competition for food leads to new pops competition for breeding habitat leads to some shifted habitats habitat range adaptive radiation in Alpine buttercups 14 species in New Zealand driven by periodic isolation and environmental change increased speciation rate and few competitors and diverse when glaciers recede growth moves across mountain ranges again when glaciers present they prevent growth Allopatric speciation species separated geographically ex isolated island kingfishers vs mainland kingfishers much less common than sympatric Than adaptive radiation Sympatric speciation occurs without geographic separation Imagine mutation occurs shell coiling changes direction leads to mechanical isolation Sympatric speciation example fruit flies went from doing behavioral dancing on Hawthorn trees to doing it on apple trees which are similar maybe by wind and never went back Example 2 anoles speciation can occur as a function of natural selection anoles living on tree trunk competition for food space some anoles shift habitat to ground and don t switch back this separation can lead to genetic divergence can lead to speciation Speciation can occur rapidly or take a very long time millions of years RAPID EVOLUTION punctuated equilibrium short bursts of evolutionary change resulting in speciation often thru mutation SLOW EVOLUTION gradualism change occurs gradually over a long period of time intermediate forms Extinction Vastly more extinct species than currently existing species When it happens new niches open up allowing for population separation Can happen due to small changes in environment anthropogenic alteration and genetic divergence of habitats drought or famine Can occur thru catastrophe Chapter 23 Systematics Phylogenetics etc Systematics method of classifying naming orgs within an evolutionary framework Goals inventory of all living things universal system of naming orgs taxonomy determining evolutionary relationships among orgs Phylogenetics technique tool for reconstructing evolutionary relationships based on common ancestry Carolus Linnaeus Systema Naturae book binomial nomenclature suggested all names be in Latin universal language each org has 2 word name genus species Ex Homo sapiens Hierarchical nomenclature kingdom phylum class order family genus species Carl Woese prokaryotes vs eukaryotes pro lack membrane bound nucleus eu have one domain should precede kingdom 3 domains Bacteria Archaea Eukarya Archaea more similar to eukaryotes Phylogenetic trees cladograms main trunk with branches coming off it organismal organization based on evolutionary relationships common ancestor at the base relative position of branches based on shared characteristics Viruses considered nonliving orgs lack the ability to replicate on their own generalization of viruses all small 22 250nm infect all domains all carry genome RNA or DNA all possess a capsid capsid outer protein covering that encases genetic info in virus Plant virus helical capsid Animal virus Adenovirus icosahedral projections called antigens help with host recognition Bacterial virus bacteriophage icosahedral head helical tail Animal virus Influenza envelope virus studded with antigens encases helical capsid around RNA Bacteriophages viruses that invade bacteria DNA viruses small viral particles or virions icosahedral head helical tail use both lytic cycle and lysogenic cycle fig in textbook Lytic 1 Attachement virus attaches to bacterium 2 Penetration injects viral DNA into cell 3 Synthesis viral DNA hijacks the bacterial genome turns on cellular replication protein synthesis 4 Assembly new virions assemble 5 Release cell lysis new virions are released from cell go infect more cells Lysogenic non destructive bacterial cell lives 1 Integration occurs after attachment and penetration viral DNA incorporated into bacterial genome prophage 2 Propagation when bacterial DNA replicates so does viral DNA 3 Stress happens at some point bacterial starvation toxin environmental change etc Induction viral DNA becomes active cell goes into lytic cycle 4 Phage conversion bacterial host becomes virulent infectious toxic following infection by bacteriophage lysogenic cycle where a portion of viral genome is expressed leads to toxin production by the
View Full Document
Unlocking...