Big Idea 1 Ch. 25 - Phylogeny

Overview: Investigating the Tree of Life Phylogeny is the evolutionary history of a species or group of related species To get information about ancient organisms and their relationship to current species, biologists draw on the fossil record

Systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. used to understand the evolutionary history of life on Earth Systematists use morphological, biochemical, and molecular comparisons to infer evolutionary relationships (they also examine fossils)

The Fossil Record Sedimentary rocks are the richest source of fossils Soft Haven’t been heated or melted like igneous and metamorphic Sedimentary rocks are deposited into layers called strata

LE 25-3 Rivers carry sediment to the ocean. Sedimentary rock layers containing fossils form on the ocean floor. Over time, new strata are deposited, containing fossils from each time period. As sea levels change and the seafloor is pushed upward, sedimentary rocks are exposed. Erosion reveals strata and fossils. Younger stratum with more recent fossils Older stratum with older fossils

The fossil record is based on the sequence in which fossils have accumulated in such strata Fossils reveal ancestral characteristics that may have been lost over time

LE 25-4 Leaf fossil, about 40 million years ago Petrified trees in Arizona, about 190 million years old Insects preserved whole in amber Dinosaur bones being excavated from sandstone Casts of ammonites, about 375 million years old Boy standing in a 150-million-year-old dinosaur track in Colorado Tusks of a 23,000-year-old mammoth, frozen whole in Siberian ice

Morphological and Molecular Homologies In addition to fossils, phylogenetic history can be inferred from morphological and molecular similarities in living organisms Organisms with very similar morphologies or similar DNA sequences are likely to be more closely related than organisms with vastly different structures or sequences

Sorting Homology from Analogy In constructing a phylogeny, systematists need to distinguish whether a similarity is the result of homology or analogy Homology is similarity due to shared ancestry Analogy is similarity due to convergent evolution (the evolution of similar traits in unrelated lineages) Ex – opossums have opposable thumbs like primates, even though they aren’t related

Convergent evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages

Evaluating Molecular Homologies Systematists use computer programs and mathematical tools when analyzing comparable DNA segments from different organisms

LE 25-6 1 2 Deletion 1 2 Insertion 1 2 1 2

Phylogenetic systematics connects classification with evolutionary history Taxonomy is the ordered division of organisms into categories based on characteristics used to assess similarities and differences (putting things into groups based on similarities) In 1748, Carolus Linnaeus published a system of taxonomy based on resemblances. Two key features of his system remain useful today: two-part names for species and hierarchical classification

Binomial Nomenclature Cont. Rules: All living things are given a two-part name. The first part of the name identifies the genus The second part of the name identifies the species *Both parts together name the species (not the specific epithet alone) The genus is ALWAYS capitalized and the species is ALWAYS lowercase Both words are ALWAYS either italicized or underlined Latin or Greek

Hierarchical Classification Linnaeus introduced a system for grouping species in increasingly broad categories *the more levels shared, the more organisms will have in common and the more closely related they will be

LE 25-8 Panthera pardus Species Panthera Genus Felidae Family Carnivora Order Mammalia Class Chordata Phylum Animalia Kingdom Eukarya Domain

Linking Classification and Phylogeny Systematists depict evolutionary relationships in branching phylogenetic trees Each branch point represents the divergence of two species “Deeper” branch points represent progressively greater amounts of divergence

LE 25-9 Panthera pardus (leopard) Mephitis mephitis (striped skunk) Lutra lutra (European otter) Canis familiaris (domestic dog) Canis lupus (wolf) Species Genus Panthera Mephitis Lutra Canis Family Felidae Mustelidae Canidae Order Carnivora

Phylogenetic systematics informs the construction of phylogenetic trees based on shared characteristics A cladogram depicts patterns of shared characteristics among taxa Takes characteristics of certain organisms and putting together a hyposthesis of how you think they may be related A clade is a group of species that includes an ancestral species and all its descendants Clades can be nested in larger clades, but not all groupings or organisms qualify as clades Cladistics studies resemblances among clades Primative to derived characteristics

Types of clades: monophyletic, signifying that it consists of the ancestor species and all its descendants A paraphyletic grouping consists of an ancestral species and some, but not all, of the descendants A polyphyletic grouping consists of various species that lack a common ancestor

Shared Primitive and Shared Derived Characteristics In cladistic analysis, clades are defined by their evolutionary novelties A shared primitive character is a character that is shared beyond the taxon we are trying to define A shared derived character is an evolutionary novelty unique to a particular clade derived is when a trait shows up that was NOT present in a common ancestor. ancestral/primitive characters WERE present in a common ancestor. E.G. Among primates, the relatively shortened and straight spine of a gorilla is a derived trait (it was not present in the common ancestor of all primates). However, the shortened spine of a gorilla is ancestral to apes (it is present in all apes and in the common ancestor of apes).

Outgroups An outgroup is a species or group of species that is closely related to the ingroup, the various species being studied “one of these things is not like the other” Systematists compare each ingroup species with the outgroup to differentiate between shared derived and shared primitive characteristics Outgroup comparison assumes that homologies shared by the outgroup and ingroup must be primitive characters that predate the divergence of both groups from a common ancestor It enables us to focus on characters derived at various branch points in the evolution of a clade

LE 25-11 TAXA (outgroup) Salamander Lancelet Lamprey Leopard Turtle Tuna Turtle Hair Amniotic (shelled) egg CHARACTERS Four walking legs Hinged jaws Vertebral column (backbone) Character table Leopard Turtle Hair Salamander Amniotic egg Tuna Four walking legs Lamprey Hinged jaws Lancelet (outgroup) Vertebral column Cladogram

Phylograms A phylogram is a phylogenetic tree that indicates the amount of evolution in addition to the branching order. the length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage

Phylogenetic Trees as Hypotheses The best hypotheses for phylogenetic trees fit the most data: morphological, molecular, and fossil Sometimes the best hypothesis is not the most parsimonious (simplest, fewest changes)

LE 25-16 Lizard Bird Mammal Four-chambered heart Mammal-bird clade Lizard-bird clade

The Universal Tree of Life The tree of life is divided into three great clades called domains: Bacteria, Archaea, and Eukarya The early history of these domains is not yet clear