BIOLOGY FOR AP COURSES Chapter 18 EVOLUTION AND

BIOLOGY FOR AP® COURSES Chapter 18 EVOLUTION AND THE ORIGIN OF SPECIES Power. Point Image Slideshow This work is licensed under a Creative Commons Attribution-Non. Commercial. Share. Alike 4. 0 International License.

DARWIN AND NATURAL SELECTION • Charles Darwin and the H. M. S. Beagle • Natural selection • Darwin’s postulates: • Most characteristics are heritable, passed from parent to offspring • More offspring are produced than can survive; there is competition for resources • Characteristics of offspring vary, and these variations are heritable. • Adaptation

DARWIN’S OBSERVATION Darwin observed that beak shape varies among finch species. He postulated that the beak of an ancestral species had adapted over time to equip the finches to acquire different food sources.

DARWIN AND WALLACE Both Charles Darwin and Alfred Wallace wrote scientific papers on natural selection that were presented together before the Linnean Society in 1858.

OVERVIEW: EVIDENCE OF EVOLUTION • Divergent evolution vs convergent evolution • Fossil record • Homologous structures • Vestigial structures • Biogeography • Molecular Biology

NATURAL VERSUS ARTIFICIAL SELECTION Our focus here is natural selection. Artificial selection occurs as well. a) Humans have been doing this for thousands of years a) Crops b) Domesticated animals b) We have chosen the phenotypes we want and breed those individuals, as well as creating more ideal hybrids and breeds – selective breeding c) Notably, in Darwin’s Origin of Species, he first draws attention to artificial selection (e. g. animal husbandry) before going in depth into natural selection.

HOMOLOGOUS STRUCTURES The similar construction of these appendages indicates that these organisms share a common ancestor.

CONVERGENCE The white winter coat of the arctic fox and the ptarmigan’s plumage are adaptations to their environments. (credit a: modification of work by Keith Morehouse) • These similarities occur not because of common ancestry, but because of similar selection pressures—the benefits of predators not seeing them. • Independently, similar phenotypes will evolve in distantly related species due to the same evolutionary pressures.

BIOGEOGRAPHY Development and presence of species based on location. For example: • Groups that evolved before Pangea broke up are distributed worldwide (albeit in different species) • Groups that developed after the breakup appear only in certain regions/continents (e. g. Australian marsupials and Madagascar lemurs) • Also evident (but usually less diverse) when species are separated by mountain ranges, large rivers, or other physical barriers.

MOLECULAR BIOLOGY DNA analysis (a more recent discovery) supports evolution • Closely related organisms have similar DNA • Evolution of new functions for proteins after mutations

MISCONCEPTIONS OF EVOLUTION • Evolution is just a theory • Individuals evolve • Evolution explains the origin of life • Organisms evolved on purpose

FORMATION OF NEW SPECIES • Species: a group of organisms that can interbreed and produce viable, fertile offspring • Hybrid: a cross between two species • Gene pool: a collection of all the variants of genes in a species

SPECIATION • Allopatric speciation – involves geographic isolation • Dispersal • Vicarience • Adaptive radiation • Sympatric speciation – occurs in the same geographical area • Chromosomal errors in cell division • Aneuploidy • Autopolyploidy • Allopolyploidy • Reproductive isolation • Prezygotic vs postzygotic barriers • Temporal Isolation • Habitat isolation • Behavioral isolation

SPECIATION • The only illustration in Darwin's On the Origin of Species: a diagram showing speciation events leading to biological diversity. The diagram shows similarities to phylogenetic charts that are drawn today to illustrate the relationships of species. • Modern elephants evolved from the Palaeomastodon, a species that lived in Egypt 35– 50 million years ago.

ALLOPATRIC SPECIATION The northern spotted owl and the Mexican spotted owl inhabit geographically separate locations with different climates and ecosystems. The owl is an example of incipient speciation. (credit “northern spotted owl”: modification of work by John and Karen Hollingsworth; credit “Mexican spotted owl”: modification of work by Bill Radke)

ALLOPATRIC SPECIATION Speciation can occur a) When groups become isolated geographically for long period of time b) Changes (mutations) in each group over time lead to the groups no longer being reproductively compatible Note: Sometimes gene flow reoccurs in an area when something that is isolating 2 groups is removed. Dispersal is when a few members of a species move to a new geographical area, Vicariance is when a natural situation arises to physically divide organisms.

ADAPTIVE RADIATION The honeycreeper birds illustrate adaptive radiation. From one original species of bird, multiple others evolved, each with its own distinctive characteristics.

SYMPATRIC SPECIATION • Speciation within the same physical location and conditions. • Arises from errors in chromosomes during cell division. • Aneuploidy: Two few chromosomes • Autopolyploidy: Two or more complete sets of chromosomes after division. Results from error in meiosis. • Allopolyploid: Gametes from two different species combine.

SYMPATRIC SPECIATION Aneuploidy results when the gametes have too many or too few chromosomes due to nondisjunction during meiosis. In the example shown here, the resulting offspring will have 2 n+1 or 2 n-1 chromosomes

SYMPATRIC SPECIATION Autopolyploidy results when mitosis is not followed by cytokinesis.

SYMPATRIC SPECIATION Alloploidy results when two species mate to produce viable offspring. In the example shown, a normal gamete from one species fuses with a polyploidy gamete from another. Two matings are necessary to produce viable offspring.

REPRODUCTIVE ISOLATION Prezygotic: • Temporal isolation – species have different breeding schedules • Habitat isolation – members of species move or are otherwise separated. • Behaviorial isolation – certain actions or behaviors (or the lack of them) impacts reproduction Postzygotic • Hybrid inviability – an embryo is produced, but cannot survive development • Hybrid sterility – different species can produce a viable offspring, but that offspring cannot reproduce

TEMPORAL ISOLATION These two related frog species exhibit temporal reproductive isolation. (a) Rana aurora breeds earlier in the year than (b) Rana boylii. (credit a: modification of work by Mark R. Jennings, USFWS; credit b: modification of work by Alessandro Catenazzi)

HABITAT ISOLATION Speciation can occur when two populations occupy different habitats. The habitats need not be far apart. The cricket (a) Gryllus pennsylvanicus prefers sandy soil, and the cricket (b) Gryllus firmus prefers loamy soil. The two species can live in close proximity, but because of their different soil preferences, they became genetically isolated.

GAMETIC BARRIER The shape of the male reproductive organ varies among male damselfly species, and is only compatible with the female of that species. Reproductive organ incompatibility keeps the species reproductively isolated.

GAMETIC BARRIER Some flowers have evolved to attract certain pollinators. The (a) wide foxglove flower is adapted for pollination by bees, while the (b) long, tube-shaped trumpet creeper flower is adapted for pollination by humming birds.

RECONNECTION • Hybrid zones: area where two closely related species interact and interbreed • Reinforcement: process where hybrids are less fit, and thus there is a nudge towards further divergence between the two species

HYBRID ZONE After speciation has occurred, the two separate but closely related species may continue to produce offspring in an area called the hybrid zone. Reinforcement, fusion, or stability may result, depending on reproductive barriers and the relative fitness of the hybrids.

RATES OF SPECIATION • Gradual speciation: species diverge gradually through time with small steps • Punctuated equilibrium: species exhibit a large change in a relatively short period of time followed by long periods of stasis

RATES OF SPECIATION In (a) gradual speciation, species diverge at a slow, steady pace as traits change incrementally. In (b) punctuated equilibrium, species diverge quickly and then remain unchanged for long periods of time.