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Lecture #3 – Origin of Species 1 Key Concepts: • • • • • • Species concepts Development of reproductive isolation Patterns of speciation Macroevolution Human evolution Evolution continues….. 2 My pet peeve is…. specie “Species” is both singular and plural 3 Major Species Concepts • Biological • Morphological • Phylogenetic Diagram – variation in beaks between species 4 Biological species – the basic standard for separating species (Ernst Mayr, 1942) • Species are defined by natural reproductive isolation Individuals that can produce successful offspring are considered the same species Image – Sarracenia rubra Image – Sarracenia flava ≠ 5 Critical Thinking • Biological species are defined by natural reproductive isolation Individuals that can produce successful offspring are considered the same species • Definition doesn't always work – why not??? 6 Critical Thinking • Biological species are defined by natural reproductive isolation Individuals that can produce successful offspring are considered the same species • Definition doesn't always work 7 Morphological species – the first way to separate species (Linnaeus, ~1750 & others) • Species are defined by differences in form Individuals with the same morphology and/or anatomy are considered the same species Image – Hymenocallis coronaria Image – Hymenocallis floridana ≠ 8 Critical Thinking • Morphological species are defined by differences in form Individuals with the same morphology and/or anatomy are considered the same species • Definition doesn't always work – why not??? 9 Critical Thinking • Morphological species are defined by differences in form Individuals with the same morphology and/or anatomy are considered the same species • Definition doesn't always work 10 Phylogenetic species – the new standard for separating species??? • Species are defined based on evolutionary history Species defined by the smallest monophyletic group in an evolutionary tree Monophyletic = lineage is derived from a common ancestor • Definition doesn't always work Don’t have good phylogenies for all species or groups Also, imperfect agreement on interpretations 11 Development And Maintenance Of Reproductive Isolation It is generally accepted that natural reproductive isolation defines and preserves separate species in sexually reproducing organisms • What constitutes a barrier to reproduction? • How do reproductive barriers develop? 12 Pre-zygotic Barriers • Remember, the zygote is the fertilized egg cell The first cell of the new offspring • Pre-zygotic barriers prevent the formation of the zygote • Natural, evolved incompatibilities prevent successful fertilization Habitat isolation Behavioral isolation Temporal isolation Structural isolation Chemical isolation Image – blue-footed boobies mating behavior 13 Critical Thinking • Natural, evolved incompatibilities prevent successful fertilization • Think of some examples of: Habitat isolation Behavioral isolation Temporal isolation Structural isolation Chemical isolation 14 Critical Thinking • • • • • Habitat isolation – Behavioral isolation – Temporal isolation – Structural isolation – Chemical isolation – 15 Post-zygotic Barriers • Post-zygotic barriers prevent successful development of offspring Hybrids don’t develop properly Hybrids don’t reach sexual maturity Hybrids don’t produce viable gametes Hybrid lineages fail over time • Natural genetic incompatibilities prevent successful long-term reproduction Horse x Donkey = robust but sterile Mule 16 Critical Thinking The Darwinian fitness of an individual is measured by a. its ability to reproduce. b. how long it lives. c. the number of mates it attracts. d. the number of its offspring that survive to reproduce. e. its physical strength. 17 Critical Thinking The Darwinian fitness of an individual is measured by a. its ability to reproduce. b. how long it lives. c. the number of mates it attracts. d. the number of its offspring that survive to reproduce. e. its physical strength. 18 Patterns of Speciation Barriers result from separations that persist long enough that eventually new species have developed Diagram – different species of fish in separated ponds 19 Patterns of Speciation • Pattern depends on the mechanism of gene flow interruption Allopatric speciation occurs when populations are separated by a geographical barrier Sympatric speciation occurs in the absence of a geographic barrier 20 Critical Thinking • Allopatric speciation occurs when populations are separated by a geographical barrier • Such as???? • How could such barriers form??? 21 Critical Thinking • Allopatric speciation occurs when populations are separated by a geographical barrier • How could such barriers form??? 22 Critical Thinking • Allopatric speciation occurs when populations are separated by a geographical barrier • How could such barriers form??? 23 Critical Thinking 24 Allopatric Speciation • Once populations are physically isolated, speciation may occur due to all the evolutionary processes we talked about earlier Selection Drift Selective mating Mutation 25 Critical Thinking • What if the isolated population is small??? • What if the isolated population is from edge of the range of the original population??? 26 Critical Thinking • What if the isolated population is small??? • What if the isolated population is from edge of the range of the original population??? 27 Critical Thinking • What if the isolated population is small??? • What if the isolated population is from edge of the range of the original population??? 28 Birds??? Plants???? Allopatric Speciation due to geographic separation Images – different species of chipmunk on either side of the Grand Canyon 29 Speciation may, or may not, occur… Diagram – sympatric allopatric either sympatric again or not. 30 Sympatric Speciation • Occurs when a population becomes reproductively isolated without geographic barriers Mutations or selection pressures that lead to changes in behavior, habitat, food source, phenology…. Errors in meiosis that lead to polyploidy (some plants can be selffertile, vegetative reproduction) Hybrids that develop into fertile populations through vegetative reproduction (mostly plants) Diagram – sympatric speciation in a forest environment 31 Sympatric Speciation • Occurs when a population becomes reproductively isolated without geographic barriers Mutations or selection pressures that lead to changes in behavior, habitat, food source, phenology…. Diagram – meiosis errors Errors in meiosis that lead to polyploidy (mostly plants) Hybrids that develop into fertile populations through vegetative reproduction (mostly plants) 32 Polyploidy – one mechanism for sympatric speciation Diagram – errors in meiosis can lead to polyploids Some plants can be self-fertile, or vegetative 33 reproduction can produce multiple fertile individuals Sympatric Speciation • Occurs when a population becomes reproductively isolated without geographic barriers Mutations or selection pressures that lead to changes in behavior, habitat, food source, phenology…. Errors in meiosis that lead to polyploidy (some plants can be self-fertile, vegetative reproduction) Hybrids that develop into fertile populations through vegetative reproduction (mostly plants) 34 Speciation is NOT a Given • Must have an interruption to gene flow PLUS • Must have enough change in the separated populations to provide a barrier to reproduction 35 Endemic Species and Adaptive Radiation • Endemic species = restricted in distribution to a particular place, generally because they evolved in place Volcanic island chains often contain many endemic species No biota until they were colonized by a few individuals (founder effect) • These small populations then evolved into new species Allopatric speciation due to the geographic barrier from the founder effect • But also…… 36 Endemic Species and Adaptive Radiation • Many new species develop that are adapted to the diverse new habitats found in such islands Sympatric speciation No geographic barriers Adaptive radiation into new habitats 37 Adaptive Radiation Galapagos finches and Hawaiian honeycreepers Diagrams – adaptive radiation in birds 38 Adaptive Radiation is a common theme – both between and within lineages Diagram – mass extinctions over the past 2.5 billion years Diagram – diversification of mammals after extinction of the dinosaurs 39 Mass Extinction Events Mammals Critical Thinking • Humans have initiated a mass extinction event • Will life cease to exist on the planet??? • Can we destroy the planet??? 40 Critical Thinking • Humans have initiated a mass extinction event • Will life cease to exist on the planet??? • Can we destroy the planet??? 41 Critical Thinking • Humans have initiated a mass extinction event • Will life cease to exist on the planet??? • Can we destroy the planet??? 42 Speciation is a Constant • When migration, isolation or other selection pressures force divergence, reproductive isolation can eventually lead to speciation Speciation might be gradual or abrupt (punctuated equilibrium) Transitions (either gradual or abrupt) may or may not be captured in the fossil record 43 Macroevolution: larger-scale changes in organisms Also contributes to speciation • Small, population-scale changes can accumulate • Exaptations – traits can be co-opted Feathers for thermoregulation feathers for flight • Large phenotypic changes can result from small changes in regulatory genes Control over the timing and length of developmental events, or the spatial organization 44 of body parts Critical Thinking Was the evolution of the modern horse a series of directed events ???? Diagram – phylogeny of the modern horse 45 Critical Thinking Was the evolution of the modern horse a series of directed events??? 46 Selection is a series of gates!!! 47 A Preview of the Taxonomic Hierarchy: this is how we classify diversity Taxonomic Category Example (taxon) Domain Eukarya = all eukaryotic organisms Kingdom Plantae, also Metaphyta = all plants Division (phylum) Magnoliophyta = all angiosperms Class Liliopsida = all monocots Order Asparagales = related families (Orchidaceae, Iridaceae, etc) Family Orchidaceae = related genera (Platanthera, Spiranthes, etc) Genus Platanthera = related species (P. ciliaris, P. integra, etc) Specific name/epithet ciliaris = one species 48 Images – the yellow fringed orchid 49 Platanthera ciliaris Humans can also be classified! • Domain – eukarya • Kingdom – animal • Phylum – chordates Sub-phylum – vertebrates • • • • • Class – mammals Order – primates Family – hominoids Genus – Homo Specific epithet – sapiens 50 Phyla in the Animal Kingdom: Diagram – from this slide to slide #65 – phylogenies of the animal kingdom, showing the classification of humans through the taxonomic hierarchy from the phyla to the families in the primate order 51 Phyla in the Animal Kingdom: Chordates 52 Sub-phyla in the Chordate Phylum: 53 Sub-phyla in the Chordate Phylum: Vertebrates Sub-phylum 54 Classes in the Vertebrate Subphylum: Sub-phylum 55 Classes in the Vertebrate Subphylum: Mammals Sub-phylum 56 Close-up: Classes in the Vertebrate Sub-phylum 57 Orders in the Mammal Class: 58 Orders in the Mammal Class: Primates 59 Families in the Primate Order: 60 Families in the Primate Order: Hominoids 61 Some key steps in the evolution of primates – note that our last common ancestor with other modern primates was 6 to 10 MILLION years ago Loss of dinosaurs, Rise of mammals 62 Critical Thinking • Is your uncle a monkey??? 63 Critical Thinking • Is your uncle a monkey??? 64 65 Two key steps – bi-pedalism and large brain Diagram – phylogeny of humans, same diagram on slide #73 66 Critical Thinking • Why is bi-pedalism so important? 67 Critical Thinking • Why is bi-pedalism so important? 68 Images – human fossil and fossil footprints 69 Critical Thinking • Why is a large brain so important? 70 Critical Thinking • Why is a large brain so important? 71 The fossil record shows changes in our species over time • The path of human evolution is not ladderlike • We are currently a mono-specific family, but…. • Human phylogeny reveals many extinct lineages We are animals We are subject to natural selection There is a record! 72 All but one lineage of hominids are extinct 73 Out of Africa – Human Migration Diagram – multi-regional vs. “out of Africa” hypotheses for human migration patterns; same diagram on following 2 slides 74 Critical Thinking How would you test these alternate hypotheses??? 75 Critical Thinking 76 Evolution is a Constant • Constant supply of genetic variation + constant application of selection pressures All species are in some degree of flux • New species are constantly diverging ….and going extinct • At any given time, we are just looking at a cross section of the process A slice through the crown of a multidimensional tree • Evolution is NOT finished! 77 ….as the tree grows, so grows the tree of life… 78 Questions??? ….as the tree grows, so grows the tree of life… Key Concepts: • Species concepts • Development of reproductive isolation • Patterns of speciation • Macroevolution • Human evolution • Evolution continues….. 79