Chapter 18.2 Notes

Phylogenetics Scientists who study systematics are interested in phylogeny, or the ancestral relationships between species. Grouping organisms by similarity is often assumed to reflect phylogeny, but inferring phylogeny is complex in practice. Reconstructing a species’ phylogeny is like trying to draw a huge family tree over millions of generations.

Phylogenetics, continued Not all similar characteristics are inherited from a common ancestor. Consider the wings of an insect and the wings of a bird. Both enable flight, but the structures of the two wings differ. Fossil evidence also shows that insects with wings existed long before birds appeared.

Phylogenetics, continued Through the process of convergent evolution, similarities may evolve in groups that are not closely related. Similar features may evolve because the groups have adopted similar habitats or lifestyles. Similarities that arise through convergent evolution are called analogous characters.

Phylogenetics, continued Grouping organisms by similarities is subjective. Some scientists may think one character is important, while another scientist does not. For example, systematists historically placed birds in a separate class from reptiles, giving importance to characters like feathers.

Cladistics, continued Cladistics is a method of analysis that infers phylogenies by careful comparisons of shared characteristics. Cladistics focuses on finding characters that are shared between different groups because of shared ancestry. A shared character is defined as ancestral if it is thought to have evolved in a common ancestor of both groups. A derived character is one that evolved in one group but not the other.

Cladistics, continued For example, the production of seeds is a character that is present in all living conifers and flowering plants, and some prehistoric plants. Seed production is a shared ancestral character among those groups. The production of flowers is a derived character that is only shared by flowering plants.

Cladistics, continued A cladogram is a phylogenetic tree that is drawn in a specific way. Organisms are grouped together through identification of their shared derived characters. All groups that arise from one point on a cladogram belong to a clade. A clade is a set of groups that are related by descent from a single ancestral lineage.

Cladistics, continued Each clade is usually compared with an outgroup, or group that lacks some of the shared characteristics. The next slide shows a cladogram of different types of plants. Conifers and flowering plants form a clade. Ferns form the outgroup.

Cladogram: Major Groups of Plants

Inferring Evolutionary Relatedness, Morphological Evidence Morphology refers to the physical structure or anatomy of organisms.

Inferring Evolutionary Relatedness, continued An important part of morphology in multicellular species is the pattern of development from embryo to adult. Organisms that share ancestral genes often show similarities during the process of development. For example, the jaw of an adult develops from the same part of an embryo in every vertebrate species.

Inferring Evolutionary Relatedness, continued Molecular Evidence Scientists can now use genetic information to infer phylogenies. Recall that as genes are passed on from generation to generation, mutations occur. Some mutations may be passed on to all species that have a common ancestor.

Inferring Evolutionary Relatedness, continued Evidence of Order and Time Cladistics can determine only the relative order of divergence, or branching, in a phylogenetic tree. The fossil record can often be used to infer the actual time when a group may have begun to “branch off.” For example, using cladistics, scientists have identified lancelets as the closest relative of vertebrates.

Inferring Evolutionary Relatedness, continued Inference Using Parsimony Modern systematists use the principle of parsimony to construct phylogenetic trees. This principle holds that the simplest explanation for something is the most reasonable, unless strong evidence exists against that explanation. Given two possible cladograms, the one that implies the fewest character changes between points is preferred.

Scientific Naming of Organisms The first name is the organism’s genus. The second name is the organism’s species. The genus is always capitalized; the species is always lowercase. The entire name is either printed in italics or underlined.

Scientific Naming of Organisms Ex. What is the scientific name of this organism? Its genus is Homo. Its species is sapiens. Its scientific name is Homo sapiens.

Scientific Naming of Organisms In longer names, the genus name can be abbreviated to a single capital letter. For example, this organism is known as Carcharadon carcharias. This can be shortened to C. carcharias.

Scientific Naming of Organisms So, what do you call this organism? Puma concolor!

Three Domains for all organisms Bacteria common members = bacteria contains Kingdoms: Eubacteria Eukarya common members = eukaryotes contains Kingdoms: Protista, Fungi, Plantae, and Animalia Archea common members = archea contains Kingdoms: Archaebacteria

Kingdoms are defined by the following characteristics Cell type : prokaryotic or eukaryotic cell walls : have a cell wall or don’t have a cell wall body type : unicellular or multicellular nutrition : autotrophic (makes their own food) or heterotroph (gets nutrition from other organisms) Genetics : DNA, RNA, or proteins

SIX KINGDOMS

The Six Kingdoms Eubacteria Unicellular, prokaryotic organisms. They can be autotrophs or hertertrophs. Eubacteria have thick cell walls. Ex. Cyanobacteria, E. coli

The Six Kingdoms Archaebacteria Unicellular, prokaryotic organisms. They can be autotrophs or hertertrophs. They live in very harsh, extreme conditions, like volcanoes or other places without oxygen. Ex. Methanogens, thermophiles

The Six Kingdoms Protista Most are unicellular, eukaryotic organisms. Protists can be autotrophs or hertertrophs. Some plant-like; some animal- like; some fungus-like Live in moist environments Ex. amoeba, algae, paramecium

The Six Kingdoms Fungi Most are Multicellular, eukaryotic organisms. Fungi are heterotrophic decomposers. Absorbs nutrients obtained by decomposing dead organisms and wastes Ex. mushrooms, mold, yeast, penicillin

The Six Kingdoms Plantae Multicellular, eukaryotic organisms. Plant cells have cell walls containing cellulose. Plants are autotrophic. Photosynthesize. Tissues organized into organs and organ systems. Instead of phyla, plants are classified into divisions. Ex. moss, ferns, trees, gymnosperms, angiosperms

The Six Kingdoms Animalia Multicellular, eukaryotic organisms. Animal cells do not have cell walls. Animals are heterotrophic. Animalia is the largest of the six kingdoms. Tissues organized into organs and complex organ systems. Ex. insects, fish, YOU