Evolution, Phylogenetics, and the Diversity of Life: Study Guide

Phylogenetics (Evolutionary Trees)

Understanding Phylogenetic Trees

Phylogenetic trees are diagrams that represent the evolutionary relationships among various species or groups. They help biologists infer who is related to whom and estimate how recently different species shared a common ancestor.

• Node: Represents a split in the tree, indicating a common ancestor of descendant lineages.

• Root: The most ancestral branch, representing the oldest common ancestor of all taxa in the tree.

• Tip: The endpoint of a branch, representing current (extant) species or taxa.

• Branch: A line connecting nodes or tips, representing an evolutionary lineage.

Key Trait Terms

• Synapomorphic: A shared, derived trait that is unique to a particular clade, indicating evolutionary relationships.

• Plesiomorphic: An ancestral trait present in a common ancestor but not unique to a particular group.

• Homology: Similarity due to shared ancestry, even if the function differs (e.g., vertebrate forelimbs).

• Homoplasy: Similarity not due to shared ancestry, but to convergent evolution or evolutionary reversals (e.g., wings in bats and birds).

Patterns in Evolution

• Convergent Evolution: Unrelated species independently evolve similar traits due to similar environmental pressures.

• Polytomy: A node with more than two descendant branches, indicating uncertainty about evolutionary relationships.

Example: The wings of birds and bats are a homoplasy (convergent evolution), while the forelimb bones are a homology.

Development & Genetics

Cell Differentiation and Gene Regulation

Developmental biology explores how a single cell gives rise to the complex structures of an organism. This process is controlled by the regulation of gene expression.

• Transcription Factors: Proteins that bind to DNA and regulate the transcription of genes, turning them on or off.

• Enhancers: DNA sequences that increase the likelihood of transcription of particular genes.

• Cytoplasmic Determinants: Molecules in the egg cytoplasm that influence the developmental fate of cells.

• Induction: The process by which one group of cells signals to another, influencing their development.

Major Cellular Processes

• Cell Division: The process by which cells replicate.

• Differentiation: The process by which cells become specialized in structure and function.

• Cell Movement: Cells migrate to new locations during development.

• Apoptosis: Programmed cell death, essential for proper development.

Big Idea: The complexity of multicellular organisms arises from the precise regulation of gene expression during development.

Origin of Life & Early Evolution

LUCA and Early Life Forms

The Last Universal Common Ancestor (LUCA) is the most recent population of organisms from which all organisms now living on Earth have a common descent.

• Autotrophs: Organisms that produce their own food from inorganic sources.

• Chemoautotrophs: Use chemical energy to synthesize organic compounds.

• Photoautotrophs: Use sunlight as an energy source to synthesize organic compounds.

Major Evolutionary Events

• Oxygenic Photosynthesis: The evolution of photosynthesis that produces oxygen, leading to the oxygenation of Earth's atmosphere.

Endosymbiosis Theory

The endosymbiotic theory explains the origin of eukaryotic cells from prokaryotic organisms.

• Mitochondria: Originated from aerobic bacteria engulfed by ancestral eukaryotes.

• Chloroplasts: Originated from cyanobacteria engulfed by ancestral eukaryotes.

• Primary Endosymbiosis: Direct engulfment of a prokaryote by a eukaryote.

• Secondary/Tertiary Endosymbiosis: Eukaryotes engulfing other eukaryotes that already contained endosymbionts.

Example: Modern plant cells contain both mitochondria and chloroplasts, each with their own DNA.

Plant Evolution

Major Groups of Plants

Plant evolution shows a trend from aquatic to terrestrial life, with increasing independence from water.

1. Green Algae

2. Nonvascular Plants (e.g., mosses)

3. Vascular Plants (e.g., ferns)

4. Seed Plants (e.g., gymnosperms and angiosperms)

Key Plant Adaptations

• Cuticle: Waxy layer that prevents water loss.

• Stomata: Pores for gas exchange.

• Vascular Tissue: Xylem and phloem for transport of water and nutrients.

• Lignin: Provides structural support.

• Seeds: Enable reproduction without water.

• Flowers/Fruits: Enhance reproductive success and seed dispersal.

Life Cycle Trends

• Haploid Dominant: Early plants (e.g., mosses) have a dominant gametophyte stage.

• Diploid Dominant: Advanced plants (e.g., angiosperms) have a dominant sporophyte stage.

• Alternation of Generations: Life cycle alternates between haploid (gametophyte) and diploid (sporophyte) stages.

Trend: Over evolutionary time, the gametophyte stage decreases and the sporophyte stage increases in prominence.

Fungi

Structure and Nutrition

Fungi are heterotrophic organisms that absorb nutrients from their environment. Their structure and life cycle are distinct from plants and animals.

• Hyphae: Thread-like filaments that make up the body of a fungus.

• Mycelium: A network of hyphae.

• Cell Wall: Composed of chitin.

Nutrition

• Heterotrophs: Obtain nutrients by absorption.

Life Cycle

1. Plasmogamy: Fusion of cytoplasm from two parent mycelia.

2. Heterokaryotic Stage: Cells contain two or more genetically distinct nuclei.

3. Karyogamy: Fusion of nuclei to form a diploid zygote.

Major Groups

• Ascomycota: Produce spores in asci (8 spores per ascus).

• Basidiomycota: Produce spores on basidia (4 spores per basidium).

Example: Yeasts (Ascomycota) and mushrooms (Basidiomycota).

Animal Evolution (Metazoa)

Early Animal Groups

• Porifera: Sponges, simple animals without true tissues.

• Cnidaria: Jellyfish and relatives, with radial symmetry and two tissue layers.

Body Types

• Diploblastic: Two embryonic tissue layers (ectoderm and endoderm).

• Triploblastic: Three embryonic tissue layers (ectoderm, mesoderm, endoderm).

Major Evolutionary Splits

• Protostomes: Mouth develops before anus during embryonic development.

• Deuterostomes: Anus develops before mouth.

Key Concepts

• Cephalization: Evolution of a head region with sensory organs.

• Bilateral Symmetry: Body plan with left and right sides.

• Hox Genes: Regulatory genes that control body plan development.

Big Evolutionary Ideas

Adaptive Radiation

Adaptive radiation is the rapid evolution of diversely adapted species from a common ancestor, often following the opening of new ecological niches.

Extinction

Extinction events eliminate species, creating opportunities for new species to evolve and diversify.

Cambrian Explosion

The Cambrian Explosion was a period of rapid evolutionary diversification of animals approximately 541 million years ago.

Life Cycle and Reproduction Trends

Evolutionary Trends in Reproduction

• Decreased dependence on water for reproduction (e.g., evolution of seeds and internal fertilization).

• Increased protection of the embryo (e.g., amniotic egg, seeds).

• Development of more complex reproductive structures (e.g., flowers, placenta).