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BIOL1407_Sp25_PhylogenyHistoryOfLife Notes 6
Taxonomy and Systematics
Taxonomy: The naming and classification of species.
Systematics: Focuses on determining evolutionary relationships (phylogeny).
Hawaiian Geology and Biodiversity
Young volcanic islands (Hawai’i) serve as an experiment showing how evolution generates biodiversity.
Evidence from geology, phylogeny, and biogeography is used to understand biodiversity development.
Hierarchical Classification
Introduced by Linnaeus, grouping species into categories: domain, kingdom, phylum, class, order, family, genus, species.
Taxon: A taxonomic unit at any level; not comparable across lineages.
Linking Classification and Phylogeny
Phylogenetic trees: Represent evolutionary history and can differ from Linnaean classifications.
Sister taxa share a common ancestor; branch points represent divergence of species.
Phylogenetic Tree Features
Rooted trees: Include a branch for the last common ancestor.
Basal taxon: Diverges early in the history of a group.
Polytomy: A branch point where more than two groups emerge.
Applications of Phylogenetics
Used to identify close relatives for conservation and improvement, and to understand pathogens.
Inferring Phylogenies
Homology: Similarity due to common ancestry; important for phylogenetic relationships.
Homoplasy: Similarity not due to common ancestry (e.g., convergent evolution).
Major Phylogenetic Concepts
Identification of homologous characters is essential for accurate classification.
Monophyletic groups: Include an ancestor and all its descendants; provide more information in classification.
Paraphyletic: Include an ancestor and some descendants.
Polyphyletic: Distantly related species without a common ancestor.
Origin of Life and Early Earth
Hypothesis of life's origin: abiotic synthesis of organic molecules leading to simple cells.
Miller-Urey experiment (1953) showed organic molecules could form under early Earth conditions.
Key stages of life's origin: formation of macromolecules, protocells, self-replicating RNA.
Key Events in Life's History
Origin of prokaryotic organisms, unicellular and multicellular eukaryotes.
Rise of atmospheric oxygen and colonization of land by plants and animals.
Mass Extinctions
Extinctions can be caused by rapid environmental changes; reveal ecological shifts and adaptive radiations.
Current extinction rate: 100 to 1000 times higher than background rates due to human activity.
Evolutionary Developmental Biology
Macroevolution: Cumulative effects of microevolution over generations.
Developmental genes play a crucial role in body form changes.
Minor changes in gene expression can lead to significant morphological differences (e.g., heterochrony).
Conclusions on Evolution
Evolution involves both long-term processes and rapid changes in response to environmental pressures.
Taxonomy and Systematics
Taxonomy
Taxonomy is the science of naming and classifying species into hierarchical categories based on shared characteristics and evolutionary relationships. It plays a crucial role in organizing biological diversity and is fundamental for biological research and communication.
Systematics
Systematics focuses on understanding the evolutionary relationships among species, known as phylogeny. It employs various data types such as morphological, genetic, and behavioral traits to construct phylogenetic trees, illustrating the evolutionary history and connections among organisms.
Hawaiian Geology and Biodiversity
The Hawaiian Islands, being relatively young volcanic islands, provide a unique natural laboratory for studying evolution and biodiversity. Their isolation has led to the development of numerous endemic species, showcasing adaptive radiation as species evolve to fill various ecological niches.
Researching the geological history of these islands offers insights into the patterns of colonization and diversification that contribute to Hawaii’s rich biodiversity. Evidence from geology, including lava flow ages and island formation, coupled with phylogenetic studies, aids in understanding these processes.
Hierarchical Classification
Introduced by Carl Linnaeus in the 18th century, hierarchical classification organizes living things into a nested system of categories: domain, kingdom, phylum, class, order, family, genus, and species. This system provides a standardized naming convention, known as binomial nomenclature, where each species is given a two-part name.
A taxon is any group of organisms at any level of this hierarchy and can consist of single species or multiple related species, making comparisons across lineages complex and informative.
Linking Classification and Phylogeny
Phylogenetic trees visually represent evolutionary histories, constructed through analysis of morphological and genetic data. These trees can differ significantly from Linnaean classifications as they reveal relationships based on ancestry rather than solely on features.
Sister taxa represent groups that share a common ancestor and are informative for understanding evolutionary divisions, with branch points or nodes depicting the divergence of species.
Phylogenetic Tree Features
Rooted trees include a branch representing the last common ancestor of all species included in the tree, offering a clear method for tracing lineages.
A basal taxon diverges early in a group’s evolutionary history and often serves as a reference point for comparisons among other taxa.
Polytomy occurs at branch points where more than two descendant groups emerge simultaneously, indicating uncertainty in evolutionary relationships.
Applications of Phylogenetics
Phylogenetic methods are invaluable in conservation biology for identifying genetically close relatives vital for breeding programs and conservation strategies. They also enhance understanding of pathogen evolution, leading to better management of diseases.
Inferring Phylogenies
Homology refers to traits shared due to common ancestry, which are critical for constructing accurate phylogenetic relationships. However, understanding the homoplasy, or similarities not resulting from common ancestry, such as those arising from convergent evolution, is equally important.
Major Phylogenetic Concepts
Identifying homologous characters is essential for accurate classification, as they reflect true evolutionary relationships.
Monophyletic groups include an ancestor and all its descendants, providing a clearer representation of evolutionary change compared to paraphyletic and polyphyletic groups.
Paraphyletic groups include an ancestor and some, but not all, descendants, while polyphyletic groups consist of unrelated organisms that lack a common ancestor, complicating classification efforts.
Origin of Life and Early Earth
The hypothesis regarding the origins of life posits that organic molecules were formed abiotically under the conditions of early Earth, leading to the emergence of simple cellular structures.
The landmark Miller-Urey experiment conducted in 1953 demonstrated that organic compounds could form under simulated primitive Earth conditions, bolstering theories on abiogenesis.
Key stages in the origin of life involve the formation of macromolecules that eventually combined to form protocells. This was a crucial step towards the development of self-replicating molecules such as RNA, which may have been a precursor to DNA.
Key Events in Life's History
Significant events include the emergence of prokaryotic organisms, followed by the rise of unicellular and multicellular eukaryotes. The increase in atmospheric oxygen and the colonization of terrestrial environments by plants (and later, animals) marked pivotal shifts in Earth's biosphere.
Mass Extinctions
Various mass extinctions have resulted from rapid environmental changes, often leading to extensive biodiversity loss. These events reveal ecological shifts and enable discussions about adaptive radiations where surviving species diversify to fill available niches. Current extinction rates, attributed largely to human activity, are estimated to be 100 to 1000 times higher than natural background rates, indicating a biodiversity crisis.
Evolutionary Developmental Biology
Macroevolution represents the cumulative changes from microevolution that accumulate over generations, shaping groups of organisms significantly.
Developmental genes are pivotal in driving morphological changes throughout evolution. Even minor shifts in gene expression can result in substantial morphological differences, a concept illustrated by heterochrony, which examines changes in the timing of developmental events.
Conclusions on Evolution
Overall, evolution is characterized by both gradual changes that occur over extended periods and rapid responses to environmental pressures, illustrating the complex dynamics that shape the diversity of life on Earth.
