EVOLUTION SPECIATION VOCABULARY REVIEW EVOLUTION CHANGE OVER TIME
EVOLUTION & SPECIATION
VOCABULARY REVIEW • EVOLUTION – CHANGE OVER TIME • NATURAL SELECTION - INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT ARE ABLE TO SURVIVE & REPRODUCE. – A. K. A. “SURVIVAL OF THE FITTEST”
NEW VOCABULARY • POPULATION – GROUP OF INDIVIDUALS OF SAME SPECIES THAT INTERBREED • GENE POOL – COMMON GROUP OF ALL GENES PRESENT IN A POPULATION
Gene Pool Combined genetic info. of all members Allele frequency is # of times alleles occur
Variation in Populations 2 processes can lead to this: Mutations change in DNA sequence Gene Shuffling – from sexual reproduction
Genetic Drift changes populations……. • Random change in allele frequency causes an allele to become common
• Founder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population
• Nonrandom mating: inbreeding and assortive mating (both shift frequencies of different genotypes)
• Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment
Sexual selection • Sexual dimorphism: secondary sex characteristic distinction • Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism
Evolution of Populations Occurs when there is a change in relative frequency of alleles
Phenotype Expression • Depends on how many genes control that trait
Single-Gene vs. Polygenic Traits Single-Gene: 2 Distinct Phenotypes (eg: tongue rolling) Polygenic: Many Phenotypes
Allele Frequencies Natural Selection Single Gene Traits Genetic Drift Polygenic Traits Directional Selection Stabilizing Selection Disruptive Selection
Natural Selection on Polygenic Traits • Shifts to middle range • Shifts to 2 extremes • Shifts to 1 extreme
Conditions needed for Genetic Equilibrium
SPECIATION • THE FORMATION OF NEW SPECIES • AS NEW SPECIES EVOVLVE, POPULATIONS BECOME REPRODUCTIVELY ISOLATED • REPRODUCTIVE ISOLATION – MEMBERS OF 2 POPULATIONS CANNOT INTERBREED & PRODUCE FERTILE OFFSPRING.
Allopatric Speciation • A few individuals of a species on the mainland – reach isolated island 1 – Speciation follows genetic divergence in a new habitat.
Allopatric Speciation • Later in time, a few individuals of the new species colonize island 2 – In this new habitat, speciation follows genetic divergence.
Allopatric Speciation • Speciation may also follow colonization of islands 3 and 4 • Invasion of island 1 by genetically different descendants of the ancestral species!
Honeycreeper Speciation • More than 20 species of Hawaiian honeycreepers have evolved – from a common ancestor as they adapted to diverse food sources on the islands
3 ISOLATING MECHANISMS……. . • BEHAVIORAL ISOLATION- CAPABLE OF BREEDING BUT HAVE DIFFERENCES IN COURTSHIP RITUALS (EX. MEADOWLARKS) • GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE RIVERS, MOUNTAINS, OR BODIES OF WATER (EX. SQUIRREL) • TEMPORAL ISOLATION – 2 OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES.
Table 23. 1 a
Subspecies • Separate populations of the same species can exist in isolation. • Over time the population of the same species can differ genetically because of adaptation to different living conditions. • Eventually different populations can become so different they can not interbreed successfully. • They are then considered to be separate species.
Tigon Result of male tiger and female lion mating incaptivity. Offspring are infertile. Separated both geographically and ecologically.
Liger Result of male lion and female tiger mating in captivity. Offspring are infertile.
Table 23. 1 b
Fig. 23. 6 Four species of leopard frogs: differ in their mating calls. Hybrids are inviable.
These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation.
Galápagos Finches • Darwin’s finches from the Galápagos Islands – arranged to show evolutionary relationships Insect eaters Berry eater Seed Cactus eaters – Notice that beak shape – varies depending on diet
Hawaiian Honeycreepers An example of adaptive radiation – these species all diverged from a common ancestor (founder species) FOUNDER SPECIES
SPECIATION IN DARWIN’S FINCHES • SPECIAITON IN THE GALAPAGOS FINCHES OCCURRED BY: - FOUNDING OF A NEW POPULATION, - GEOGRAPHIC ISOLATION which led to -REPRODUCTIVE ISOLATION and CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.
Evidence of Evolution Fossil Record provides evidence that living things have evolved Fossils show the history of life on earth and how different groups of organisms have changed over time
Flying Squirrel Sugar Glider Marsupial Mammals Convergent Evolution and Analogous Structures Placental mammals Mammalia Rat like common ancestor
Convergent Evolution • Similarities can evolve in organisms not closely related often because they live in the same or similar habitat. Ex. The wings of a bird and the wings of a bat These characteristics are called analogous structures.
Analogous Structures • Wings of insects, birds and bats – serve the same function but differ considerably – in structure and embryological development
Divergent Evolution • Divergent evolution of a variety – of placental mammals from a common ancestor • Divergence accounts for descendants – that differ from their ancestors and from one another
Convergent Evolution • Convergent evolution takes place – when distantly related organisms give rise to species – that resemble one another – because they adapt – in comparable ways
Gradualism vs. Punctuated Equilibrium • Gradualism changes that take place over a long period of time. • Punctuated equilibrium are periods of rapid change separated by little or no change. © 2008 Paul Billiet ODWS
Punctuated Equilibrium
Gradualism
Tempo of Evolution
Cladistics and Cladograms • Traditionally, scientists have – depicted evolutionary relationships – with phylogenetic trees • in which the horizontal axis represents • anatomical differences • and the vertical axis denotes time • In contrast, a cladogram shows – the relationships among members of a clade • a group of organisms • including its most recent common ancestor • Cladistics focus on derived characteristics • sometimes called evolutionary novelties – as opposed to primitive characteristics
Phylogenetic Tree • A phylogenetic tree – showing the relationships – among various vertebrate animals
Cladogram • A cladogram showing inferred relationships • Some of the characteristics used – to construct this cladogram are indicated
Evolutionary Novelties All land-dwelling vertebrate animals – possess bone and paired limbs – so these characteristics are primitive – and of little use in establishing
Cladograms • Bats and birds fly, – which might suggest – a closer relationship – than to dogs • Dogs and birds – do not appear closely related • Hair and giving birth to live young – indicate that bats and dogs – are more closely related
Linnaean Classification Most inclusive • Kingdom – Phylum • Subphylum • the coyote, Canis latrans • Animalia – Chordata – Class v. Order • Family • Vertebrata – Mammalia • Canidae » Carnivora – Genus • Species Least inclusive – Canis • latrans
Classification —shared Characteristics • Subphylum vertebrata – including fishes, amphibians, reptiles, birds and mammals, – have a segmented vertebral column • Only warm- blooded animals with hair/fur and mammary glands are mammals
Coyote, Canis latrans • 18 orders of • • • mammals exist including order Carnivora The Family Canidae are doglike carnivores and the genus Canis includes only closely related species Coyote, Canis latrans, stands alone as a species
Cladistics for Fossils • Cladistics and cladograms work – well for living organisms, – but are trickier fossils • Care must be taken in determining – what are primitive verses derived characteristics, – especially in groups with poor fossil records • Paleontologists must be especially careful – of characteristics resulting – from convergent evolution
Evolutionary Trends • During evolution, all aspects of an organism • • • – do not change simultaneously A key feature we associate – with a descendant group might appear – before other features typical of that group For example, the oldest known bird – had feathers and the typical fused clavicles of birds, – but it also retained many reptile characteristics Mosaic evolution is the concept that – organisms possess recently evolved characteristics – as well as some features of their ancestral group
Phylogeny • Phylogeny is the evolutionary history – of a group of organisms • If sufficient fossil material is available, – paleontologists determine the phylogeny – and evolutionary trends for groups of organisms • For example, one trend in ammonoids • extinct relatives of squid and octopus – was the evolution – of an increasingly complex shell
Evolutionary Trends • Abundant fossils show the evolutionary trends of – the extinct Eocene mammals, Titanotheres • These relative of horses and rhinoceroses – evolved from small ancestors – to giants standing 2. 4 m at the shoulder – developed large horns – and the shape of their skull changed – Only 4 of the 16 known genera are show
Evolutionary Trends • Size increase is – one of the most common evolutionary trends • However, trends are complex – they might reverse – more than one can take place – at the same time at different rates • Trends in horses included – generally larger size • but size decreased in some now-extinct horses – changes in teeth and skull – lengthening legs – reduction in number of toes • These trends occurred at different rates
Adaptations • Evolutionary trends are a series of adaptations – to changing environment – or in response to exploitation of new habitats • Some organisms – show little evolutionary change – for long periods • Lingula is a brachiopod – with a shell, at least, – that has not changed – significantly since the Ordovician
“Living Fossils” • Several organisms have shown – little or no change for long periods • If these still exist as living organisms today – they are sometimes called living fossils • For example: – horseshoe crabs – Latrimaria (fish) – Gingko trees • Some of these are generalized and can live under a wide variety of enviroinments
A Living Fossil • Latimeria – belongs to a group of fish – once thought to have gone extinct – at the end of the Mesozoic Era A specimen was caught off the coast of East Africa in 1938
A Second Living Fossil • Ginkgos – have changed very little – for millions of years
Vestigial Structures • Vestigial structures are nonfunctional remnants – of structures in organisms that were functional in their • Why– do dogs ancestors have tiny, – functionless toes on their feet • Ancestral dogs had five (dewclaws)? toes – on each foot, – all of which contacted the ground • As they evolved – they became toe-walkers with only four toes on the ground – and the big toes and thumbs were lost or reduced
Remnants of Rear Limbs in Whales • The Eocene-aged whale, Basilosaurus, – had tiny vestigial back limbs – but it did not use limbs to support its body weight.
Evolution in Living Organisms • Small-scale evolution can be observed today. • For example – adaptations of some plants to contaminated soils – insects and rodents developing resistance to new insecticides and pesticides – development of antibiotic-resistant strains of bacteria • Variations in these populations – allowed some variant types – to live and reproduce, – bringing about a genetic change
What do We Learn from Fossils? • The fossil record consists – of first appearances of various organisms – through time • One-celled organisms appeared – before multicelled ones – plants appeared before animals – invertebrates before vertebrates • Fish appeared first followed – in succession by amphibians, – reptiles, mammals, and birds
Advent of Various Vertebrates • Times when major groups of vertebrates appeared in the fossil record • Thickness of spindles shows relative abundance
Fossils Are Common • Fossils are much more common • • – than many people realize However the origin and initial diversification – of a group is generally the most poorly represented But fossils showing the diversification – of horses, rhinoceroses, and tapirs – from a common ancestor are known as are ones showing the origin – of birds from reptiles and the evolution – of whales from a land-dwelling ancestor
Horses and Their Relatives • This cladogram shows the relationship among – tapirs, rhinoceroses, and horses
Horses and Their Relatives • These might seem an odd assortment of animals • • • – but fossils and studies of living animals – indicate that they shared a common ancestor As we trace these animals back – in the fossil record, – differentiating one from the other – becomes increasingly difficult The earliest members of each group – are remarkably similar, – differing mostly in size and details of their teeth As their diversification proceeded – the differences became more apparent
Never Enough • Of course, we will never have enough fossils – to document the evolutionary history – of all living creatures simply because fossilization – is an incomplete process • The remains of some organisms – are more likely to be preserved than those of others – and accumulation of sediments – varies in both space and time • But several other kinds of evidence – support the concept of evolution – including molecular biology and paleontology
Big Question!!! §How did life arise on the big blue planet? ? § Scientists attempt to answer this question scientifically.
Big Bang Theory § A cosmic explosion that hurled matter and in all directions created the universe 10 -20 billion years ago § Evidence: it explains why distant galaxies are traveling away from us at great speeds. Cosmic radiation from the explosion can be observed § The Big Bang theory probably will never be proven; consequentially, leaving a number of tough, unanswered questions.
What was early earth like? §Earth was Hot!! §Little or no oxygen §Gasses in atmosphere: §Hydrogen cyanide (poison to you!) §Hydrogen sulfide §Carbon dioxide §Carbon monoxide §Nitrogen
So how did the earth get oxygen? § Some of that oxygen was generated by photosynthetic cyanobacteria § Some came from the chemical separation of water molecules into oxygen and hydrogen.
§ Oxygen drove some life forms to extinction § Others evolved ways of using oxygen for respiration
How did life begin? Miller and Urey’s Experiment § Passed sparks through a mixture of hydrogen methane ammonia and water § This produced amino acids – the building blocks of life
Miller’s experiment suggests that lightning could have produced amino acids
How can simple amino acids result in life? 1. Formation of microspheres § Large organic molecules can sometimes form tiny proteinoid microspheres § Store and release energy, selectively permeable membranes, may have acquired more characteristics of living cells
nd 2 Hypothesis for Life Evolution of RNA to DNA • RNA was assembled from simple organic molecules in a primordial soup • RNA was able to replicate itself and eventually form DNA • Not scientifically proven to be possible
The Bubble Model
rd 3 Theory of Life Endosymbiotic theory §eukaryotic cells arose from living communities formed by prokaryotic organisms §Ancient prokaryotes entered primitive eukaryotic cells and remained there as organelles
• Prokaryotes are chemosynthetic. • Photosynthetic prokaryotes (cyanobacteria) release oxygen into the water, once saturated move into atmosphere. • Evolution of eukaryotes then multicelluar organisms. • Formation of ozone allowed organisms to move to land
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