Homology Homologous Structures – structures in different species that are similar because of common ancestry.

Analogy Analogous Structures – similarity in structures due to adaptations from similar evolutionary pressures (convergent evolution) and not a common ancestor.

Convergent evolution occurs when similar environmental pressures and natural selection Produce similar (analogous) adaptations in organisms from different evolutionary lineages Australian Mole –marsupial mammal North American Mole – placental mammal

Sorting Homology from Analogy A potential misconception in constructing a phylogeny Is similarity due to convergent evolution, called analogy, rather than shared ancestry Ex: Humans, gorillas, and ravens have the ability to problem-solve, and are highly intelligent. Humans and gorillas share ancestry: homology. Ravens are in a separate phylum (birds), so developed their intelligence separately from humans.

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

“KLADOS” = Greek word meaning “BRANCH” or “SPROUT” Cladogram - a shows pattern of shared, inherited characteristics; a “graphic organizer” based on measurable traits and not evolutionary relationships.

Cladogram for Transportation Wheels are the most ancestral (oldest). Wings are the most derived (newest).

Construct a Cladogram for Us!

Gorilla Four limbs Fur No tail

Tiger Four limbs Fur Tail

Lizard Four limbs Tail

Fish Tail

Chimpanzee Four limbs Fur No tail

Clade With 4 Limbs

Clade With Fur

Clade With No Tail

Characteristics (Traits) for Constructing this Cladogram Tail is the most ancestral Four limbs is the oldest derived trait Fur is a later derived trait Loss of tail is the most derived trait

One Possible Cladogram Four Limbs

Where’s the Tail? How do we know the gorilla and chimpanzee have lost their tail? Sometimes cladists must compare embryological development and internal anatomy to determine relatedness. May not be exactly the same structures.

Coccyx- Primate Vestigial Tails Human Pelvic Girdle Gorilla Pelvic Girdle Vestigial Structure - historical remnants of a structure that has little or no use in a modern organism but had a function in ancestors.

A Vertebrate Cladogram Vertebrae Lancelet Outgroup

What is the shared primitive character for this clade? Ans: Birds Mammals Reptile Amphibian Fish Four Limbs Amniotic Egg Endothermic Fur Feathers Vertebrae Lancelet Outgroup What is the shared primitive character for this clade? Ans:

Birds Mammals Reptile Amphibian Fish Four Limbs Amniotic Egg Endothermic Fur Feathers Vertebrae Lancelet Outgroup What is the shared derived character for amphibians, reptiles, birds & mammals? Ans: Four Limbs For reptiles, birds & mammals? Ans: Amniotic Egg

Phylogenetic Trees and Timing A cladogram is not a phylogenetic tree; may need more information (fossils, molecular systemics, etc.). Any chronology represented by the branching pattern of a phylogenetic tree Is relative rather than absolute in terms of representing the timing of divergences.

Phylograms In a phylogram: The length of a branch reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage. A phylogram of homologous hedgehog genes. Outgroup

Ultrametric Trees In an ultrametric tree: The branching pattern is the same as in a phylogram, but all the branches that can be traced from the common ancestor to the present are of equal length. Outgroup

A Rule about Phylogenetic Trees William of Ockham – 14th Cent. English philosopher, stated that, when all qualities of hypotheses are equal, the simplest explanation for a phenomenon is usually correct; Occam’s Razor: "entities must not be multiplied beyond necessity" (entia non sunt multiplicanda praeter necessitatem). Parsimony – stingy, economical, fewest complications.

Phylogenetic Trees are Hypotheses Among phylogenetic hypotheses The most parsimonious tree is the one that requires the fewest evolutionary events to have occurred in the form of shared derived characters. The best hypotheses for phylogenetic trees Are those that fit the most data: morphological, molecular, and fossil.

The Case of the 4- Chambered Heart: Analogous vs. Homologous Type of heart arose twice independenly. Not the most parsimonious. Crocodilians

Molecular Clocks A molecular clock: Is a yardstick for measuring the absolute time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve at constant rates. The rRNA genes change very slowly; good clocks for distant time measurments (millions of years). Mitochondrial DNA (mtDNA) changes quickly and useful in recent evolutionary changes; used to explore the relationships of groups of humans (thousands of years).

Overview: Welcome to Your Kingdom The animal kingdom Extends far beyond humans and other animals we usually encounter

Several characteristics of animals Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers Several characteristics of animals Sufficiently define the group

The history of animals may span more than a billion years The animal kingdom includes not only great diversity of living species But the even greater diversity of extinct ones as well

The common ancestor of living animals May have lived 1.2 billion–800 million years ago May have resembled modern choanoflagellates, protists that are the closest living relatives of animals. Single cell Stalk

Animals can be characterized by “body plans” One way in which zoologists categorize the diversity of animals Is according to general features of morphology and development A group of animal species That share the same level of organizational complexity is known as a grade; grade is not necessarily a clade (may not be monophyletic)

Patterns of Organization 4 Ways of Animal Organization: Symmetry (Asymmetry, Radial, Bilateral) Tissue Organization (Diploblastic, Triploblastic) Body Cavity Development (Acoelomate, Pseudocoelomate, Coelomate) Embryological Development (Protostome and Deuterostome)