Essentials of Biology Sylvia S. Mader Chapter 16 Lecture Outline Prepared by: Dr. Stephen Ebbs Southern Illinois University Carbondale Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16.1 Macroevolution Microevolution involves changes on the small scale at the level of gene pool alleles. In contrast, macroevolution involves evolution at the large scale as species originate, adapt to their environment, and possibly become extinct.

Defining Species Speciation is an evolutionary event that gives rise to new species. The biological species concept provides one definition of a species. A group of organisms that interbreed with each other and share the same gene pool. A group of organisms that produce fertile offspring. Each species is reproductively isolated from every other species.

Reproductive Barriers In order for species to be reproductively isolated, they must be separated by barriers which prevent gene flow. • Reproductive barriers are also called isolating mechanisms.

Reproductive Barriers (cont.)

Reproductive Barriers (cont.) • Prezygotic isolating mechanisms prevent reproduction and make fertilization unlikely. • Habitat isolation occurs when organisms cannot reproduce because they are in different habitats. • Temporal isolation occurs if the reproductive cycles of organisms occurs at different times.

Reproductive Barriers (cont.) The unique courtship patterns displayed by organisms can create behavioral isolation. • Mechanical isolation occurs when the genitalia are structurally incompatible. • Genetic isolation occurs when the fertilization does not occur, even when sperm and egg are brought together.

Reproductive Barriers (cont.) • Postzygotic isolating mechanisms prevent hybrid organisms from developing (zygote mortality) or reproducing (hybrid sterility). In the case of F2 fitness, even a hybrid organism develops and reproduces, but the offspring of the hybrid are sterile.

Reproductive Barriers (cont.)

Models of Speciation There are different ways in which the process of speciation can occur. In allopatric speciation, an ancestral population is geographically isolated, resulting in the evolution of separate species.

Models of Speciation (cont.)

Models of Speciation (cont.) • Sympatric speciation involves speciation without a geographic barrier. One example of sympatric speciation is polyploidy, found more often in plants. Polyploidy occurs when the number of chromosome sets increase to 3n or more.

Models of Speciation (cont.)

Adaptive Radiation • Adaptive radiation involves the evolution of several new species from an ancestral species. Adaptive radiation occurs as natural selection drives members of the ancestral species to adapt to several different environments.

Adaptive Radiation (cont.)

16.2 The History of Species The evolutionary history of a species, such as is origin and extinction is reflected in the fossil record. The study of fossils is called paleontology.

The Geological Timescale The geological timescale of the earth has been constructed by studying the fossils in the various strata of rock. Based upon the fossil record, the Earth’s history can be divided into segments. – Epochs are the shortest segments. A series of epochs form a period. Several periods comprise an era.

The Geological Timescale (cont.)

The Geological Timescale (cont.)

The Geological Timescale (cont.)

The Geological Timescale (cont.)

The Pace of Speciation One school of thought maintains that evolution is a gradual process, the gradualistic model. More commonly, new species occur suddenly in the fossil record followed by long periods of little change, a pattern called punctuated equilibrium.

The Pace of Speciation (cont.)

The Pace of Speciation (cont.)

Mass Extinction of Speciation Most species exist for a limited period of geological time and then become extinct. Within the fossil record there are also instances of mass extinctions. Evidence of six mass extinctions can be seen in the fossil record.

Mass Extinction of Speciation (cont.) There are two primary events that are believed to have contributed to these mass extinctions. The movement of the Earth’s surface via continental drift is one such event. • Plate tectonics provides the explanation for why continental drift occurs.

Mass Extinction of Speciation (cont.)

Mass Extinction of Speciation (cont.) Habitat changes caused by continental drift contributed to mass extinctions. The formation of the supercontinent Pangaea created dramatic changes. All the oceans were joined. The amount of coastline was greatly reduced. This effect continued until Pangaea broke apart and separated.

Mass Extinction of Speciation (cont.)

Mass Extinction of Speciation (cont.)

Mass Extinction of Speciation (cont.) A meteorite impact was another event that contributed to mass extinctions. The impact of a meteor in Central America is thought to have caused the Cretaceous extinction of the dinosaurs.

16.3 Classification of Species Organisms are classified (organized) based upon their evolutionary relationship. The branch of science that deals with the classification of organisms is taxonomy. • Taxonomists give each species a scientific name, also called the binomial name.

16.3 Classification of Species (cont.) The scientific name consists of a genus and species. Peas: Genus = Pisum; species = sativa Humans: Genus = Homo; species = sapiens The species name is also called the specific epithet.

16.3 Classification of Species (cont.) Taxonomists use several hierarchical categories to classify organisms. Species Genus Family Order Class Phylum Kingdom Domain Most inclusive Least inclusive

16.3 Classification of Species (cont.)

16.3 Classification of Species (cont.) Organisms are classified into the different categories based upon shared structural, chromosomal, or molecular features. These categories may also be divided into three additional subcategories, creating more than 30 categories in total.

Classification and Phylogeny Taxonomy and the classification of species are part of systematics, the study of organismal diversity. A goal of systematics is to establish the evolutionary history (phylogeny) of a group of organisms. One aspect of systematics is to identify groups (taxa) of organisms with common ancestors.

Classification and Phylogeny (cont.) The classification of organisms and their common ancestry can be illustrated with a phylogenetic tree. This tree is assembled based upon the shared characters of different groups or organisms.

Classification and Phylogeny (cont.)

Classification and Phylogeny (cont.) If the character is present in the common ancestor and all taxa within that group, it is called a primitive character. If the character is limited to a specific line of descent it is a derived character.

Tracing Phylogeny Several types of data are used to determine the evolutionary relationship between organisms. Details from the fossil record Homology Molecular data This information can be used to determine the sequence of common ancestors for a particular organism.

Tracing Phylogeny (cont.) The homology of certain characters in organisms is indicative of common ancestry and can be used to classify organisms. However this can be complicated by convergent evolution for that character.

Tracing Phylogeny (cont.) • Analogous structures may have arisen from convergent evolution, but are not derived from a common ancestor. Similarly, parallel evolution may lead to the same character in different species not derived from the same common ancestor.

Tracing Phylogeny (cont.) Since speciation occurs when mutations change genes, DNA information can be used to classify organisms. Closely related organisms have genes with closely related sequences. The greater the divergence in gene sequence, the greater the evolutionary distance between the organisms.

Tracing Phylogeny (cont.)

Cladistic Systematics • Cladistics strives to produce testable hypotheses about the evolutionary relationships between organisms. Systematic information is used to classify and arrange organisms in a phylogenetic tree called a cladogram. A cladogram can be used to trace the evolutionary history of a group.

Cladistic Systematics (cont.)

Cladistic Systematics (cont.) The guiding principle of cladistics is parsimony, which states that the least number of assumptions is the most probable. This means that the cladogram is constructed to minimize the number of evolutionary changes.

Cladistic Systematics (cont.) Within a cladogram, a clade is an evolutionary branch that includes a common ancestor and all its descendents. Clades are nested together to show how characters emerge as evolution progresses. Since cladograms objectively arrange the data, their structure can address specific hypotheses about the evolutionary relationship of groups.

Cladistic Systematics (cont.)

Traditionalists Versus Cladists • Traditional systematists use a greater range of information to draw conclusions about the evolutionary relationship between organismal groups. Traditional systematists also believe that organisms need not be classified based upon their common ancestor.

Traditionalists Versus Cladists (cont.) The phylogenetic trees constructed by traditional systematists provide a different view of the relationship between organisms.

Traditionalists Versus Cladists (cont.)

Traditionalists Versus Cladists (cont.)

Classification Systems Classification systems evolve just as species do. Until recently, most biologists used a five-kingdom system of classification. Animalia Plantae Fungi Protista Monera

Classification Systems (cont.) However, molecular and cellular data has revealed problems with the five kingdom system. Based upon that data, a three-domain system has been proposed instead. Bacteria Archaea Eukarya

Classification Systems (cont.)

Classification Systems (cont.)

Classification Systems (cont.)