Chapter 18 Organizing Information About Species

1. Chapter 18Organizing Information About Species

2. 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

3. Endangered: The Palila

4. Endangered: The Akekee

5. Extinct: The Poouli

6. 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

7. 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

8. Table 18-1 p296

9. 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

10. 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

11. Cladograms • Cladistic analysis produces a cladogram – an evolutionary treethat 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

12. earthworm tuna lizard mouse human earthworm multicellular tuna multicellular with a backbone lizard multicellular with a backbone and legs mouse multicellular with a backbone, legs, and hair human Figure 18-3 p297

13. 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

14. 1 2 3 pterosaur 1 2 chicken 3 2 3 penguin 1 2 1 3 4 stem reptile 5 porpoise 4 2 3 5 1 2 bat 3 4 5 1 2 3 4 5 human 1 2 3 4 5 elephant Figure 18-4 p298

15. 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

16. Morphological Convergence

17. 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)

18. 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

19. Comparison of an Amino Acid Sequence

20. 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

21. Comparison of a DNA Sequence

22. Cladogram Based On DNA Sequence

23. 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

24. 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

25. Comparison of Vertebrate Embryos

26. Hox Genes • Hox genes are homeotic genes of animals • The pattern of expression of Hox genesdetermines 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

27. Expression of the Antennapedia Gene

28. 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

29. Expression of the Hoxc6 Gene

30. 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

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

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

33. Diversity of Hawaiian Honeycreepers

34. Evolutionary Relationships Among Honeycreepers

35. 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

36. 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