1. Chapter 18 Organizing Information About Species

2. 18.1 Bye Bye Birdie
Over millions of years, unique forms and behaviors evolved in many different lineages of Hawaiian finches – the Hawaiian honeycreepers
Variations in traits allowed the birds to exploit special opportunities presented by their island habitats
Polynesians 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 extinct
Conservation efforts began in the 1960s, but 26 more species have since disappeared – today, 35 of the remaining 68 species are endangered
They 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 feed
mainly on the seeds of the mamane plant. The seeds are toxic to most
other birds. The one remaining palila population is declining because
mamane plants are being trampled by cows and gnawed to death by
goats and sheep. Only about 1,200 palila remained in 2010.

5. Endangered: The Akekee
The unusual lower bill of the akekee (Loxops caeruleirostris) points to
one side, allowing this bird to pry open buds that harbor insects. Avian
malaria carried by mosquitoes to higher altitudes is decimating the last
population of this species. Between 2000 and 2007, the number of
akekee plummeted from 7,839 birds to 3,536.

6. Extinct: The Poouli This male poouli (Melamprosops phaeosoma)—
rare, old, and missing
an eye—died in 2004
from avian malaria. There
were two other poouli alive
at the time, but neither has
been seen since then.

7. 18.2 Phylogeny
Evolutionary history can be reconstructed by studying shared, heritable traits
Phylogeny 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. Characters
Each species bears evidence of its own unique evolutionary history in its characters
A character is any heritable physical, behavioral, or biochemical feature that can be measured or quantified
Examples: Number of segments in a backbone, the nucleotide sequence of ribosomal RNA

9. Table 18-1 p296

10. Traditional Classification
Traditional classification groups organisms based on shared characters, such as feathers in birds
Traditional 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 ancestor
Common ancestry is determined by derived traits – characters present in a group, but not in that group’s ancestors
A 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. Cladistics
Making hypotheses about evolutionary relationships among clades is called cladistics
Parsimony 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 Analysis
Figure 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 Analysis
Figure 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 Analysis
Figure 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. Cladograms
Cladistic analysis produces a cladogram – an evolutionary tree that diagrams evolutionary trends and patterns
Data from an outgroup (a species not closely related to any member of the group) may be included to “root” the tree
Each line represents a lineage, which may branch into two lineages at a node – a common ancestor of two lineages
Every branch on a cladogram is a clade; the two lineages that emerge from a node are sister groups

17. multicellular with a backbone
earthworm
tuna
lizard
mouse
human
earthworm
multicellular
tuna
multicellular with a backbone
lizard
multicellular with a backbone and legs
Figure 18.3 Animated An example of a cladogram.
mouse
multicellular with a backbone, legs, and hair
human
Figure 18-3 p297

18. ANIMATED FIGURE: Interpreting a cladogram
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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 ancestry
A clade is a monophyletic group whose members share one or more derived traits; cladistics is a method of making hypotheses about evolutionary relationships among clades
Cladograms 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 groups
In 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 ancestor
Homologous structures may be used for different purposes, but the same genes direct their development
Change from the body form of a common ancestor is an evolutionary pattern called morphological divergence
Example: Vertebrate forelimbs vary in size, shape, and function, but are alike in structure

22. 1 2 3
pterosaur 1 2
chicken 3 2 3
penguin 1 2 3 1 4 5
stem reptile
porpoise 2 3 4 5 1 2
Figure 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.
bat 3 4 1 5 2 3 4 5
human 1 2 3 4 5
elephant
Figure 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 pressures
The independent evolution of similar body parts in different lineages is called morphological convergence
Example: Bird, bat, and insect wings all perform the same function, but are derived from different structures

24. Morphological Convergence

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 Clocks
A molecular clock is used to estimate how long ago two lineages diverged by comparing DNA or protein sequences
Over time, neutral mutations that have no effect on survival or reproduction accumulate at a constant rate
The accumulation of neutral mutations in the DNA of a lineage act as a molecular clock
The 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 all
Comparing the nucleotide sequence of a gene or the amino acid sequence of a protein can provide evidence of an evolutionary relationship
Generally, 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

29. Comparison of an Amino Acid Sequence

30. DNA Comparisons
DNA from nuclei, mitochondria, and chloroplasts can be used in nucleotide comparisons
Mitochondria 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

31. Comparison of a DNA Sequence

32. Cladogram Based On DNA Sequence

33. Take-Home Message: How does biochemistry reflect evolutionary history?
Mutations change the nucleotide sequence of a lineage’s DNA over time
Lineages 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 genes
A 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 development
Example: 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 genes
Differences are brought about by variations in expression patterns of master genes that govern development
Example: 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

37. Comparison of Vertebrate Embryos

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 axis
Hox genes occur in clusters on a chromosome, in the order in which they are expressed in a developing embryo
Example: Legs develop wherever the antennapedia gene is expressed in an embryo

39. Expression of the Antennapedia Gene

40. Vertebrate Hox Genes
In vertebrates, expression of the Hoxc6 gene causes ribs to develop on vertebrae of the back – not the neck or tail
The Dlx gene encodes a transcription factor that signals embryonic cells to form buds that give rise to appendages
Hox genes suppress Dlx expression in all parts of an embryo that will not have appendages

41. Expression of the Hoxc6 Gene

42. Persistent Juvenile Features
A chimpanzee skull and a human skull appear quite similar an early stage
As development continues, both skulls change shape as different parts grow at different rates
A human adult skull is proportioned more like the skull of an infant chimpanzee than the skull of an adult chimpanzee
Human evolution involved changes that caused traits typical of juvenile stages to persist into adulthood

43. Proportional Changes During Skull Development: Chimpanzee
adult
proportions in infant

44. Proportional Changes During Skull Development: Human
proportions in infant
adult

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 time
Some 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
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48. 18.6 Applications of Phylogeny Research
Studies of phylogeny reveal how species relate to one another and to species that are now extinct
We use information about phylogeny to understand how to preserve the species that exist today

49. Conservation Biology
The reservoir of genetic diversity among Hawaiian honeycreepers is diminishing along with its numbers
Lowered diversity means the group as a whole is less resilient to change, and more likely to suffer species losses
Deciphering honeycreeper phylogeny can tell us which ones are most valuable in terms of preserving genetic diversity

50. Diversity of Hawaiian Honeycreepers

51. Evolutionary Relationships Among Honeycreepers

52. Conservation Biology (cont.)
Cladistics analyses are also used to correlate past evolutionary divergences with behavior and dispersal patterns of existing populations
Example: A cladistic analysis of mitochondrial DNA sequences suggests that blue wildebeest populations are genetically less similar than they should be
Using a combination of data, conservation biologists can recommend measures to improve gene flow

53. Medical Applications
Researchers study the evolution of infectious agents by grouping their biochemical characters into clades
Example: 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 ancestry
Among other applications, phylogeny research can help us preserve species in danger of becoming extinct, and to understand the spread of infectious diseases