Classifications and Systematics Quiz

Classifications and Systematics

• Systematics is the scientific study of biological diversity and evolutionary history
• It's a comparative science
• Prior to binomial nomenclature, plant species had excessively long names
• All living organisms have a single, two-word Latin scientific name
• Only one correct scientific name applies to all individuals of a species, regardless of variations
• Many common names can be applied to different species, but only one common name can be assigned to a species

Introduction

• Taxonomy, phylogeny, and systematics are related parts of classifying species
• Taxonomy is the method of classifying and organizing living things based on their evolutionary relationships
• Phylogeny is the study of evolutionary relationships among organisms
• Systematics involves the study of the diversity and evolutionary relationships of organisms

Background

• Systematics is the science
• Binomial nomenclature assigns a unique two-word Latin name to every species
• Scientific names provide a clear and consistent way to identify organisms
• Common names are not consistently applied to all individuals of a particular species

Concepts (1 of 2)

• Phylogeny is the hereditary relationships of any group of organisms, depicting their evolutionary history
• At the end of the 19th century, taxonomists aimed to develop natural systems of classification
• Organisms closely related, phylogenetically, are grouped (natural classification)
• Phylogenetic relationships are used to assign plant names

Concepts (2 of 2)

• Modern plant systematics aims to interpret evolutionary lineages and produce accurate nomenclature (naming systems)

• Phylogeny is a real process; our current classifications are hypotheses, not definitive truths

• Our knowledge, limited and imperfect, leads to imperfect classifications

Development of Concepts of Evolution and Classification

• Modern classifications originate from ancient Greek thought
• Theophrastus, an ancient Greek philosopher and biologist, was the first to organize and classify plants
• Dioscorides, a Roman military surgeon, wrote an important ancient book on plant classification (Materia Medica)
• Linnaeus's system of binomial nomenclature was pivotal

Taxonomy

• Taxonomy is the scientific method for classifying the huge diversity of life on Earth
• It helps understand the evolutionary relationships between organisms
• Taxonomy documents biodiversity, and organizes and classifies lifeforms

Levels of Taxonomic Categories (1 of 3)

• Species is the fundamental taxonomic unit—individuals that can interbreed and produce viable offspring
• Members of a species can interbreed successfully but cannot interbreed with members of other species
• Closely-related species are grouped into genera
• Some species may interbreed to yield viable offspring

Levels of Taxonomic Categories (2 of 3)

• A group of species is monophyletic if all its members share a common ancestor
• All descendants of the common ancestor are in the same genus
• A group of species is polyphyletic if members share no common ancestor

Levels of Taxonomic Categories (3 of 3)

• The level above genus is family
• Taxon levels above family are order, class, division, and kingdom
• All but genus, species, and kingdom require specific suffixes

Cladistics (1 of 5)

• Distantly related plants evolved separately for a great deal of time
• Accumulation of mutations can result in slight resemblance even between distantly related species

Cladistics (2 of 5)

• Closely related species have descended from a common ancestor
• Similar features shared by closely-related organisms are synapomorphies (homologous features)
• Convergent evolution produces species that appear similar but do not share a common ancestor; in this case, similar structures are homoplasies (analogous features)

Cladistics (3 of 5)

• Distinguishing between homology (similarity due to common ancestry) and analogy (similarity due to convergent evolution) can be difficult

Cladistics (4 of 5)

• Studying lack of similarity can be challenging

Cladistics (5 of 5)

• Systematists try to consider as many features of organisms as possible in cladistic analysis
• Misleading information is accounted for; valid information is prioritized in analysis

Genealogy Versus Clades

• Genealogy charts genetic convergence of characters over a short period, while phylogeny charts evolutionary divergence over long periods

Cladograms (1 of 3)

• Cladograms are diagrams that represent evolutionary patterns using branches.

• Branching points (nodes) depict when a lineage diverges from another

• All offshoots from a branching point represent the descendants of that original group.

Cladograms (2 of 3)

• A paraphyletic group doesn't contain all descendants of a recent common ancestor.
• A derived condition (apomorphy) is a trait present in a group but not in their ancestor.
• Synapomorphies are used as criteria for constructing cladograms
• The principle of parsimony states that the simplest possible explanation is preferred

Cladograms (3 of 3)

• A clade comprises a species and its common ancestor
• A paraphyletic grouping excludes some descendants of the most recent common ancestor

Cladograms and Taxonomic Categories

• The species is the only taxonomic unit with an objective definition
• Species are defined based on their ability to interbreed successfully

Cacti and Evolutionary Diversification

• The cactus family (Cactaceae) has undergone extensive evolutionary diversification
• DNA sequencing has altered some traditional classifications

Other Types of Classification Systems

• Artificial systems group organisms based on observable characteristics, such as flower colors or leaf shapes, rather than evolutionary ancestry

Taxonomic Studies (2 of 2)

• The International Code of Botanical Nomenclature provides precise naming guidelines.
• The formal naming of a new plant species must include a designated type specimen

Major Lines of Evolution

• All life forms are grouped into three domains: Bacteria, Archaea, and Eukarya

Major Lines of Evolution (1 of 3)

• The origin of life is probably about 3.5 billion years ago
• The conversion of a prokaryote to a eukaryote was a significant step in evolution

Major Lines of Evolution (2 of 3)

• One clade later diverged into animals and fungi, while the other generated algae
• Some algae adapted to land approximately 400 million years ago
• Land-adapted algae formed the base of the plant kingdom(Plantae)

Major Lines of Evolution (3 of 3)

• Major evolutionary lineages diverged from early algae
• Simple non-vascular plants (e.g., mosses)
• Plants that do not produce seeds but possess vascular tissue (e.g., ferns)
• Seed-bearing vascular plants (e.g., gymnosperms, angiosperms)