BIOL 152 1st Edition Lecture 5 Outline of Last Lecture I Exploring evolutionary processes a Natural Selection i Darwin and Wallace 1 Observations generate hypotheses 2 Artificial selection as a proxy for natural selection ii Directional Disruptive Stabilizing b Mating System Influences i Sexual selections ii Non random mating c Immigration Emigration d Population Size Genetic Drif II Species and Speciation a Biodiversity b Maintaining continuous variation i Gene flow Outline of Current Lecture I Speciation and species a Isolation These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute i Prezygotic ii Postzygotic b Case Study Rhagoletispomonella i Life cycle ii Parasites iii Hawthorns 1 Small fruit 2 High nutritional value 3 Maggots barely burrow 4 High wasp mortality 5 Late ripening iv Apples 1 Large fruit 2 Low nutritional value 3 Maggots burrow deep 4 Low wasp mortality 5 Early ripening v Types of species 1 Biological 2 Ecological 3 Morphological 4 Phylogenetic vi Types of isolating mechanisms 1 Postzygotic a Hybrid inviable or sterile 2 Prezygotic a Geographical b Mechanical c Ecological d Behavioral vii Types of speciation 1 Allopatric 2 Sympatric didn t get to within lecture Current Lecture Maintaining Continuous Variation Sympatry living in the same place Interbreeding o Gene flow moving genetic variants within and between populations Maintaining DIScontinuous variation Preventing gene flow Isolation o Prezygotic Preventing fertilization o Postzygotic Fertilization product inviable or sterile zygote first cell in new generation Isolation Speciation Isolated populations accumulate changes o Populations diverge o Recognized as species A Case Study in Speciation Crataegus sp Hawthorn trees are native to North America Rhagoletispomonella Hawthorn maggot fly North America native House fly size Larvae eat Hawthorn fruit Life Cycle of the maggot fly Female lays eggs in fruit Maggots hatch o Feed on fruit Fruit with maggots drop from trees o Pupation occurs within soil Adult flies emerge from soil o Fly to trees o Mate on fruit s surface There are parasites Parasitoid wasp lay eggs in maggot bodies o Paralyzing and killing maggots Hawthorn Features Native to North America Small fruits Apple Features Domesticated apples introduced in the 1600s Most widely grown fruit Large compared to Hawthorn fruit Larvae of rhagoletis started feeding on commercial apples Rhagoletishost shif First noted apple infestation 1864 Are all flies capable of doing this Apple vs Hawthorn A Maggot s Perspective Apple is large 220x more food than Hawthorn Hawthorn fruit is more nutritious o Survival rate is higher with Hawthorn Parasite POV Apples are thicker more protection Maggots burrow to avoid wasps Maggots on apples carry fewer wasp eggs Today Hawthorn and Apple maggot flies o Morphologically indistinguishable o BUT genetically distinct No geographic isolation or physical separation of the two populations Maggot flies show mating preferences o Hawthorn flies prefer to mate on Hawthorn fruit o Apple flies prefer to mate on Apple fruit o 4 6 hybridization between populations Hybrids are viable and fertile o No postzygotic barriers Timing of host fruit ripening Leads to temporal separation of the flies Are the flies separate species The answer can change with the definition you use of species Biological Species Definition Species a group of interbreeding natural populations whose members can produce viable fertile offspring and that are reproductively isolated from other such groups Ecological Species Definition Species a set of organisms exploiting a single niche Key aspects of this definition are resources exploited and the habitat occupied by the members of a species Morphological Species Definition Species a set of individuals with similar morphological features The key aspect is what the members look like Individuals of a species are morphologically similar to each other Phylogenetic Species Definition Species a unique lineage or a terminal branch on a phylogenetic tree Species are defined by their uniquely derived features and shared ancestry Three Outcomes with renewed or continued contact between two populations 1 Individuals interbreed readily no speciation 2 Individuals do not interbreed species boundaries enhanced 3 Individuals interbreed but offspring have reduced fitness speciation in progress What maintains gene flow barriers Postzygotic barriers o Zygote inviability o Hybrid sterility partial or full Ex Horse x donkey mule sterile Prezygotic barriers o Geographical separation allopatry o Mechanical Isolation Ex Milkweed flower Lock and Key reproduction takes much mechanical cooperation o Ecological isolation Ex complexity of a tropical forest o Behavioral isolation Ex Orchid Flowers How do species originate Natural Selection o Adaptation to novel habits Geographic Isolation o Allopatric Speciation Peripheral isolation Probably most common speciation pathway o Proposed by Ernst Mayr Sympatric speciation o Probably specialized and infrequent
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