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 node, 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 present in an ancestor and all its descendants, indicating evolutionary relationships.

• Plesiomorphic: An ancestral trait that is present in a common ancestor but may not be 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, often resulting from convergent evolution (e.g., wings in bats and insects).

Patterns in Evolution

• Convergent Evolution: The independent evolution of similar traits in unrelated lineages, often 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, 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 a multicellular organism. This process is tightly regulated by genetic mechanisms.

• Transcription Factors: Proteins that bind to DNA and regulate gene expression by turning genes on or off.

• Enhancers: DNA sequences that increase the transcription of associated 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: The migration of cells to new locations during development.

• Apoptosis: Programmed cell death, essential for proper development and removal of unnecessary cells.

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 produce food.

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.

• Secondary/Tertiary Endosymbiosis: Engulfment of a eukaryote that already contains endosymbionts.

Example: Modern plant cells contain chloroplasts derived from cyanobacteria via primary endosymbiosis.

Plant Evolution

Major Groups of Plants

Plant evolution shows a progression from aquatic to increasingly terrestrial forms, with key adaptations for life on land.

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 life cycle dominated by the gametophyte (haploid) stage.

• Diploid Dominant: Advanced plants (e.g., angiosperms) have a life cycle dominated by the sporophyte (diploid) stage.

• Alternation of Generations: Life cycle alternates between haploid and diploid stages.

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

Fungi

Structure and Nutrition

Fungi are a diverse group of heterotrophic organisms that absorb nutrients from their environment.

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

• Mycelium: A network of hyphae.

• Cell Wall: Composed of chitin, providing structural support.

• Heterotrophs: Obtain nutrients by absorption.

Fungal 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 Fungal Groups

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

• Basidiomycota: Produce spores on club-shaped structures called basidia (4 spores per basidium).

Group	Spore Structure	Number of Spores
Ascomycota	Asci	8
Basidiomycota	Basidia	4

Animal Evolution (Metazoa)

Major Animal Groups and Body Plans

Animal evolution is marked by increasing complexity in body structure and development.

• Porifera: Sponges, simple animals without true tissues.

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

Body Types

• Diploblastic: Animals with two germ layers (ectoderm and endoderm).

• Triploblastic: Animals with three germ layers (ectoderm, mesoderm, endoderm).

Developmental Patterns

• Protostomes: Mouth develops before anus during embryonic development.

• Deuterostomes: Anus develops before mouth.

Key Evolutionary Concepts

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

• Bilateral Symmetry: Body plan with left and right sides that are mirror images.

• Hox Genes: Regulatory genes that control body plan development along the anterior-posterior axis.

Big Evolutionary Ideas

Adaptive Radiation, Extinction, and the Cambrian Explosion

• Adaptive Radiation: Rapid evolution of many diverse species from a common ancestor, often following the opening of new ecological niches.

• Extinction: The loss of species, which can create opportunities for new species to evolve.

• Cambrian Explosion: A period (~541 million years ago) of rapid diversification of animal life.

Life Cycle and Reproduction Trends

Evolutionary Trends in Reproduction

Over evolutionary time, reproductive strategies have shifted to reduce dependence on water and increase protection of offspring.

• Less Water Needed for Reproduction: Evolution of seeds and internal fertilization.

• More Protection of Embryo: Development of structures like seeds, eggs, and placentas.

• More Complex Structures: Evolution of specialized reproductive organs and parental care.