2 18.1 Bye Bye BirdieOver millions of years, unique forms and behaviors evolved in many different lineages of Hawaiian finches – the Hawaiian honeycreepersVariations in traits allowed the birds to exploit special opportunities presented by their island habitatsPolynesians arrived on the Hawaiian Islands around 1000 A.D. – followed by Europeans in 1778
3 The Hawaiian Honeycreepers By 1778 at least 43 honeycreeper species that had thrived on the Hawaiian islands before humans arrived were extinctConservation efforts began in the 1960s, but 26 more species have since disappeared – today, 35 of the remaining 68 species are endangeredThey are pressured by invasive, non-native species of plants and animals, and by rising global temperatures that allow disease-bearing mosquitoes to invade higher-altitude habitats
4 Endangered: The Palila The palila (Loxioides bailleui) has an adaptation that allows it to feedmainly on the seeds of the mamane plant. The seeds are toxic to mostother birds. The one remaining palila population is declining becausemamane plants are being trampled by cows and gnawed to death bygoats and sheep. Only about 1,200 palila remained in 2010.
5 Endangered: The Akekee The unusual lower bill of the akekee (Loxops caeruleirostris) points toone side, allowing this bird to pry open buds that harbor insects. Avianmalaria carried by mosquitoes to higher altitudes is decimating the lastpopulation of this species. Between 2000 and 2007, the number ofakekee plummeted from 7,839 birds to 3,536.
6 Extinct: The Poouli This male poouli (Melamprosops phaeosoma)— rare, old, and missingan eye—died in 2004from avian malaria. Therewere two other poouli aliveat the time, but neither hasbeen seen since then.
7 18.2 PhylogenyEvolutionary history can be reconstructed by studying shared, heritable traitsPhylogeny is the evolutionary history of a species or a group of species – a kind of genealogy that follows a lineage’s evolutionary relationships through time
8 CharactersEach species bears evidence of its own unique evolutionary history in its charactersA character is any heritable physical, behavioral, or biochemical feature that can be measured or quantifiedExamples: Number of segments in a backbone, the nucleotide sequence of ribosomal RNA
10 Traditional Classification Traditional classification groups organisms based on shared characters, such as feathers in birdsTraditional classification does not always reflect phylogeny – species that appear very similar are not necessarily closely related
11 Evolutionary Classification Evolutionary biologists try to pinpoint the source of shared characters: a common ancestorCommon ancestry is determined by derived traits – characters present in a group, but not in that group’s ancestorsA group whose members share one or more defining derived traits is called a clade – a monophyletic group consisting of an ancestor with a derived trait, and all of its descendants
12 CladisticsMaking hypotheses about evolutionary relationships among clades is called cladisticsParsimony analysis is used to find the simplest and most likely evolutionary pathway – the one in which defining derived traits evolved the fewest number of times
13 Parsimony AnalysisFigure 18.2 A simple example of parsimony analysis, using the data in Table There are three possible evolutionary relationships among a bird, bat, and dolphin. The scenario that is most likely to be correct is the one in which the derived traits (in red) would have arisen the fewest number of times.
14 Parsimony AnalysisFigure 18.2 A simple example of parsimony analysis, using the data in Table There are three possible evolutionary relationships among a bird, bat, and dolphin. The scenario that is most likely to be correct is the one in which the derived traits (in red) would have arisen the fewest number of times.
15 Parsimony AnalysisFigure 18.2 A simple example of parsimony analysis, using the data in Table There are three possible evolutionary relationships among a bird, bat, and dolphin. The scenario that is most likely to be correct is the one in which the derived traits (in red) would have arisen the fewest number of times.
16 CladogramsCladistic analysis produces a cladogram – an evolutionary tree that diagrams evolutionary trends and patternsData from an outgroup (a species not closely related to any member of the group) may be included to “root” the treeEach line represents a lineage, which may branch into two lineages at a node – a common ancestor of two lineagesEvery branch on a cladogram is a clade; the two lineages that emerge from a node are sister groups
17 multicellular with a backbone earthwormtunalizardmousehumanearthwormmulticellulartunamulticellular with a backbonelizardmulticellular with a backbone and legsFigure 18.3 Animated An example of a cladogram.mousemulticellular with a backbone, legs, and hairhumanFigure 18-3 p297
18 ANIMATED FIGURE: Interpreting a cladogram To play movie you must be in Slide Show ModePC Users: Please wait for content to load, then click to playMac Users: CLICK HERE
19 Take-Home Message: How do evolutionary biologists study life’s diversity? Evolutionary biologists study phylogeny to understand how all species are connected by shared ancestryA clade is a monophyletic group whose members share one or more derived traits; cladistics is a method of making hypotheses about evolutionary relationships among cladesCladograms and other evolutionary tree diagrams are hypotheses based on our best understanding of the evolutionary history of a group of organisms
20 18.3 Comparing Form and Function Physical similarities are often evidence of shared ancestry, but sometimes a trait evolves independently in two groupsIn many cases, comparative morphology can be used to unravel evolutionary relationships
21 Morphological Divergence Homologous structures are similar body parts in separate lineages that evolved in a common ancestorHomologous structures may be used for different purposes, but the same genes direct their developmentChange from the body form of a common ancestor is an evolutionary pattern called morphological divergenceExample: Vertebrate forelimbs vary in size, shape, and function, but are alike in structure
22 123pterosaur12chicken323penguin123145stem reptileporpoise234512Figure 18.4 Morphological divergence among vertebrate forelimbs, starting with the bones of a stem reptile. The number and position of many skeletal elements were preserved when these diverse forms evolved; notice the bones of the fore-arms. Certain bones were lost over time in some of the lineages (compare the digits numbered 1 through 5). Drawings are not to scale.bat34152345human12345elephantFigure 18-4 p298
23 Morphological Convergence Analogous structures are body parts that look alike but did not evolve in a shared ancestor – they evolved independently in lineages subject to the same environmental pressuresThe independent evolution of similar body parts in different lineages is called morphological convergenceExample: Bird, bat, and insect wings all perform the same function, but are derived from different structures
25 Take-Home Message: What does comparative morphology reveal about phylogeny? In morphological divergence, a body part inherited from a common ancestor becomes modified differently in different lines of descent (homologous structures)In morphological convergence, body parts that appear alike evolved independently in different lineages, not in a common ancestor (analogous structures)
26 18.4 Comparing Biochemistry The kind and number of biochemical similarities among species are clues about evolutionary relationships
27 Molecular ClocksA molecular clock is used to estimate how long ago two lineages diverged by comparing DNA or protein sequencesOver time, neutral mutations that have no effect on survival or reproduction accumulate at a constant rateThe accumulation of neutral mutations in the DNA of a lineage act as a molecular clockThe number of differences between genomes can be used to estimate the relative times of divergence
28 DNA and Protein Sequence Comparisons Some essential genes are highly conserved (their DNA sequences have changed very little over evolutionary time) – other genes are not conserved at allComparing the nucleotide sequence of a gene or the amino acid sequence of a protein can provide evidence of an evolutionary relationshipGenerally, two species with many identical proteins are likely to be close relatives – the number of amino acid differences give us an idea of evolutionary relationships
30 DNA ComparisonsDNA from nuclei, mitochondria, and chloroplasts can be used in nucleotide comparisonsMitochondria are inherited intact from a single parent, usually the mother – any differences in mitochondrial DNA sequences between maternally related individuals are due to mutations, not genetic recombination during fertilization
33 Take-Home Message: How does biochemistry reflect evolutionary history? Mutations change the nucleotide sequence of a lineage’s DNA over timeLineages that diverged long ago have more differences between their DNA and amino acid sequences than do lineages that diverged more recently
34 18.5 Comparing Patterns of Development Similar patterns of embryonic development are an outcome of highly conserved master genesA mutation in a master gene typically halts development
35 Similar Forms in Plants Homeotic genes encode transcription factors that determine details of body form during embryonic developmentExample: A floral identity gene, Apetala1, affects petal formation across many different lineages – it is likely that this gene evolved in a shared ancestor
36 Developmental Comparisons in Animals The embryos of many vertebrate species develop in similar ways – directed by the very same genesDifferences are brought about by variations in expression patterns of master genes that govern developmentExample: All vertebrates go through a stage in which they have four limb buds, a tail, and a series of somites – divisions of the body that give rise to a backbone
38 Hox Genes Hox genes are homeotic genes of animals The pattern of expression of Hox genes determines the identity of particular zones along the body axisHox genes occur in clusters on a chromosome, in the order in which they are expressed in a developing embryoExample: Legs develop wherever the antennapedia gene is expressed in an embryo
40 Vertebrate Hox GenesIn vertebrates, expression of the Hoxc6 gene causes ribs to develop on vertebrae of the back – not the neck or tailThe Dlx gene encodes a transcription factor that signals embryonic cells to form buds that give rise to appendagesHox genes suppress Dlx expression in all parts of an embryo that will not have appendages
42 Persistent Juvenile Features A chimpanzee skull and a human skull appear quite similar an early stageAs development continues, both skulls change shape as different parts grow at different ratesA human adult skull is proportioned more like the skull of an infant chimpanzee than the skull of an adult chimpanzeeHuman evolution involved changes that caused traits typical of juvenile stages to persist into adulthood
43 Proportional Changes During Skull Development: Chimpanzee adultproportions in infant
44 Proportional Changes During Skull Development: Human proportions in infantadult
45 Persistent Juvenile Traits in Salamanders In axolotls, external gills and other larval traits persist into adulthood
46 Take-Home Message: Why are similarities in development indicative of shared ancestry? Similarities in patterns of development are the result of master genes that have been conserved over evolutionary timeSome differences between closely related species are a result of master gene mutations that change the rate or onset of development
47 ANIMATED FIGURE: Mutation and proportional changes To play movie you must be in Slide Show ModePC Users: Please wait for content to load, then click to playMac Users: CLICK HERE
48 18.6 Applications of Phylogeny Research Studies of phylogeny reveal how species relate to one another and to species that are now extinctWe use information about phylogeny to understand how to preserve the species that exist today
49 Conservation BiologyThe reservoir of genetic diversity among Hawaiian honeycreepers is diminishing along with its numbersLowered diversity means the group as a whole is less resilient to change, and more likely to suffer species lossesDeciphering honeycreeper phylogeny can tell us which ones are most valuable in terms of preserving genetic diversity
52 Conservation Biology (cont.) Cladistics analyses are also used to correlate past evolutionary divergences with behavior and dispersal patterns of existing populationsExample: A cladistic analysis of mitochondrial DNA sequences suggests that blue wildebeest populations are genetically less similar than they should beUsing a combination of data, conservation biologists can recommend measures to improve gene flow
53 Medical ApplicationsResearchers study the evolution of infectious agents by grouping their biochemical characters into cladesExample: A phylogenetic analysis of H5N1 influenza virus isolated from pigs showed that the virus “jumped” from birds to pigs at least three times since 2005, and that one group had acquired the potential to be transmitted among humans
54 Take-Home Message: How is studying phylogeny useful? Phylogeny research is yielding an ever more specific and accurate picture of how all life is related by shared ancestryAmong other applications, phylogeny research can help us preserve species in danger of becoming extinct, and to understand the spread of infectious diseases