Evolutionary Developmental Biology, History of Life, Animal and Plant Diversity, and Ecology

Evolutionary Developmental Biology

Integration of Genetics, Biochemistry, Cell Biology, and Evolution

Evolutionary developmental biology ("evo-devo") explores how developmental processes and gene regulation shape evolutionary changes in organisms. It integrates multiple biological disciplines to understand how organisms are built from a single cell and how changes in gene regulation drive evolutionary innovation.

• Developmental genes control the formation and specialization of cells, tissues, and organs.

• All cells in an organism have the same DNA; differences arise from gene expression, not from different genes.

• Cell fate is determined by location in the embryo, often influenced by chemical gradients called morphogens.

• Genes activate other genes in a sequence, forming gene cascades that guide development step by step.

Hox Genes and Body Plan Specification

Hox genes are master control genes that specify the identity and position of body segments. They are highly conserved across species and arranged in clusters, showing colinearity (gene order matches body position).

• Mutations in hox genes can cause dramatic changes, such as the antennapedia mutation in flies (antenna replaced by legs).

• Similar hox genes are found in flies, mice, and humans; mouse hox genes can function in flies.

• Hox genes regulate other genes but do not build structures directly; they signal and activate pathways.

Gene Duplication and Evolutionary Innovation

Gene duplication creates extra copies of genes, providing material for evolutionary innovation. Duplicated genes can mutate and acquire new functions, forming gene families.

• Gene duplication occurs via unequal crossing over or polyploidy.

• Example: globin genes (hemoglobin family) have multiple copies expressed at different developmental stages; fetal hemoglobin has higher oxygen affinity.

• Small genetic changes, especially in regulatory genes, can lead to large morphological effects.

History of Life

Major Transitions in Earth's History

Life evolved over 4.6 billion years ago, with major transitions including the origin of life, oxygenation, rise of eukaryotes, multicellularity, and animal diversification.

• Hadean: Earth forms, no life yet.

• Archean: First prokaryotes (anaerobic), photosynthesis appears (cyanobacteria), oxygen accumulates.

• Proterozoic: Rise of eukaryotes and multicellularity.

• Cambrian Explosion: Rapid diversification of animal phyla.

Origin of Eukaryotes: Serial Endosymbiosis Theory (SET)

Eukaryotic cells formed when one cell engulfed another, leading to organelles like mitochondria and chloroplasts.

• Mitochondria derived from purple bacteria; chloroplasts from cyanobacteria.

• Evidence: circular DNA, similar membranes to bacteria.

Multicellularity and Surface Area/Volume Challenges

Multicellularity required solving surface area/volume (SA/V) problems for efficient nutrient exchange and waste removal.

• As size increases, SA/V ratio decreases, making exchange harder.

• Solutions: circulatory systems, specialized structures, division of labor.

Cambrian Explosion: Causes and Consequences

The Cambrian Explosion was a rapid diversification of animal life, not the origin of animals. It was driven by both intrinsic (genetic) and extrinsic (environmental) factors.

• Intrinsic: hox gene duplication increased developmental complexity.

• Extrinsic: oxygen increase allowed larger bodies and active lifestyles; mass extinctions opened niches.

• Predator-prey arms race accelerated evolution.

Animal Diversity and Classification

Major Features and Classification Criteria

Animals are multicellular, heterotrophic, ingest food, are mobile at some stage, and digest internally. Classification is based on:

• Presence of true tissues

• Type of symmetry (radial vs bilateral)

• Blastopore fate (mouth vs anus)

• Molting to grow (ecdysis)

Key Animal Groups

• Porifera (sponges): No true tissues, no symmetry, sessile, filter feeders. Key structure: choanocytes.

• Cnidaria (jellyfish, corals): Diploblastic, radial symmetry, alternating life cycles (medusa and polyp), stinging cells (cnidocytes).

• Protostomes: Mouth forms first. Includes lophotrochozoans (annelids, flatworms, molluscs) and ecdysozoans (nematodes, arthropods).

• Deuterostomes: Anus forms first. Includes echinoderms (sea stars) and chordates (vertebrates).

Examples of Animal Phyla

• Platyhelminthes (flatworms): Bilateral symmetry, triploblastic, lophotrochozoans.

• Annelida (segmented worms): Bilateral symmetry, triploblastic, segmentation increases complexity.

• Nematodes (roundworms): Bilateral symmetry, triploblastic, ecdysozoan, many are parasites.

• Arthropods: Exoskeleton, jointed appendages, most diverse phylum (insects, arachnids, crustaceans).

• Echinodermata: Bilateral symmetry in larvae, radial in adults, endoskeleton, tube feet.

• Chordata: Dorsal hollow nerve cord, notochord, pharyngeal gill slits, post-anal tail.

Bacteria, Archaea, Protists, and Fungi

Three Domains of Life

Life is divided into three domains: Bacteria, Archaea, and Eukarya.

• Bacteria: Prokaryotic, single-celled, reproduce via binary fission, diverse metabolism.

• Archaea: Prokaryotic, single-celled, often extremophiles, genetically distinct from bacteria.

• Eukarya: Nucleus and organelles, includes protists, fungi, plants, and animals.

Bacterial Structure and Metabolism

• Cell wall (may have capsule), pili for attachment, flagella for movement.

• Gram-positive: thick cell wall (purple); Gram-negative: thin wall and outer membrane (pink).

• Reproduction: binary fission, horizontal gene transfer, sporulation.

• Metabolism: aerobes (need O2), anaerobes (no O2), fermentation, nitrogen fixation.

Protists and Fungi

• Protists: Diverse, mostly aquatic, paraphyletic group. Includes animal-like (protozoa), plant-like (algae), and fungus-like (molds).

• Fungi: Eukaryotic, heterotrophic, absorb nutrients, major decomposers, reproduce via spores.

• Symbiosis: mycorrhizae (fungus-plant roots), lichens (fungus-algae/cyanobacteria).

• Cell walls made of chitin (not cellulose).

Fungal Phyla

Phylum	Key Features	Examples
Chytrids	Water and soil	Chytridiomycosis
Zygomycetes	Fast-growing molds	Bread mold
Glomeromycetes	Plant symbiosis	Mycorrhizae
Ascomycetes	Morels, truffles, yeast	Baker's yeast
Basidiomycetes	Mushrooms, toadstools	Button mushroom

Plant Diversity and Adaptations

Evolution and Major Groups

Plants evolved from green algae and are multicellular, photoautotrophic, with cell walls made of cellulose. They protect embryos and have adaptations for life on land.

• Four major groups: nonvascular plants, vascular seedless plants, gymnosperms, angiosperms.

• Key adaptations: cuticle (prevents water loss), vascular tissue (transport), seeds, pollen, flowers.

Alternation of Generations

Plants alternate between haploid (gametophyte) and diploid (sporophyte) stages.

• Sporophyte (2n) produces spores via meiosis.

• Spores divide by mitosis into gametophytes (n).

• Gametophytes produce gametes by mitosis.

• Gametes unite (fertilization) to form zygote (2n), which becomes sporophyte.

Plant Groups and Reproduction

• Bryophytes: Nonvascular, small, need water for reproduction (mosses, liverworts).

• Vascular plants: Xylem (water up), phloem (sugar down), reproduce with spores (ferns, horsetails).

• Gymnosperms: Naked seeds, no flowers or fruit, pollen replaces need for water (conifers).

• Angiosperms: Flowering plants, seeds enclosed in fruit, most diverse group.

Pollination and Genetic Diversity

• Pollination: transfer of pollen from anther to stigma.

• Self-fertilization (selfing) vs outcrossing (different plants).

• Plants prevent selfing via temporal, spatial, and molecular mechanisms.

• Coevolution: plants and pollinators evolve together.

Ecology: Interactions and Organization

Levels of Organization

• Individual: Single organism.

• Population: Group of same species.

• Community: Populations of different species interacting.

• Ecosystem: All living (biotic) and nonliving (abiotic) factors in an area.

Types of Species Interactions

Interaction Type	Effect on Species 1	Effect on Species 2	Example
Mutualism	+	+	Mycorrhizae
Commensalism	+	0	Birds nesting in trees
Competition	-	-	Plants competing for light
Consumption (Predation, Herbivory, Parasitism)	+	-	Wolf eating deer

Predation, Defense, and Coevolution

• Predation exerts strong selective pressure; prey evolve defenses (camouflage, warning coloration, mimicry, mechanical, chemical, behavioral).

• Mimicry: Batesian (harmless mimics harmful), Müllerian (both harmful look similar).

• Coevolution: reciprocal evolutionary changes between interacting species (e.g., predator-prey arms race).

• Red Queen Hypothesis: species must continually evolve to maintain fitness relative to others.

• Cospeciation: host and parasite evolve together.

Summary Table: Domains and Major Groups

Domain	Cell Type	Key Features	Examples
Bacteria	Prokaryotic	No nucleus, cell wall, binary fission	Cyanobacteria
Archaea	Prokaryotic	Extreme environments, unique genetics	Thermophiles
Eukarya	Eukaryotic	Nucleus, organelles, multicellular	Plants, animals, fungi, protists

Additional info: Academic context was added to clarify developmental biology, evolutionary transitions, and ecological interactions. Key terms and examples were expanded for clarity and completeness.