Animal Characteristics and Evolution

Animal Characteristics

Ancestral Characters

• Features present before a species evolved.

• Examples:

  • Bones in fish are ancestral for amphibians, reptiles, birds, and mammals.

  • Lungs in fish are ancestral for amphibians, reptiles, birds, and mammals. Only six living species of fish have lungs; the rest have gills.

Shared Derived Characters

• Features distinguishing one group from another.

• Examples:

  • Bones are found only in vertebrates.

  • A dorsal nerve cord is found only in chordates.

  • Feathers are found only in birds and theropod dinosaurs.

  • Milk is the identifying characteristic of mammals, as is hair/fur.

  • Amniotic eggs and waterproof skin are shared derived characters for reptiles, birds, and mammals.

Body Symmetry

• Arrangement of the body.

• Examples:

  • Sponges have no symmetry.

  • Radially symmetrical animals have no head.

  • Bilaterally symmetrical animals have a head and a tail.

Body Tissues

• Layers in the body.

• Examples:

  • Sponges have no true tissues.

  • Jellyfish have two cell layers (diploblasts).

  • All other animals have three cell layers (triploblasts): ectoderm, mesoderm, and endoderm.

Body Cavities

• Arrangement of layers in the body.

• Animals with fewer than three tissue layers (Porifera, Cnidaria, Ctenophora) do not have body cavities.

• Among animals with three tissue layers:

  • Acoelomate: Platyhelminthes (Flatworms) have no spaces between tissue layers.

  • Pseudocoelomate: Nematoda (Roundworms) have a gap between the mesoderm and endoderm.

  • Coelomates: Annelida to chordates have a gap entirely within the mesoderm.

Nervous Systems

• Sponges do not have one.

• Cnidaria and Ctenophora have a nerve net.

• Platyhelminthes have a ladder-like system with ganglia and a brain.

• Nematoda to Arthropoda have several ganglia and a brain.

• Echinodermata have a nerve ring.

• Chordates have a dorsal nerve cord and a brain.

Circulatory Systems

• Sponges, Cnidaria, and Ctenophora do not have one.

• Nematoda to Arthropoda have an open circulatory system.

• Annelida and Cephalopoda (mollusca) have a closed circulatory system.

• Echinodermata have an open circulatory system.

• Chordata have a closed circulatory system.

Digestive Systems

• Sponges do not have one.

• Single-opening (two-way/incomplete) systems are present in Cnidaria, Ctenophora, and Platyhelminthes.

• Two-opening (one-way/complete) systems are present in Nematoda to Arthropoda, Echinodermata, and Chordata.

Amniotic Egg

• Waterproof egg originating in reptiles, present in birds and mammals.

• Allowed reptiles to reproduce away from water.

• The waterproof shell allows gas exchange but keeps water in.

• Mammals and birds inherited it from reptiles.

• Mammals:

  • Monotremes (platypus, echidna) lay eggs.

  • Marsupial eggs have a thin shell that disappears.

  • Placental mammal eggs never leave the mother’s body.

Cladogram

• Arrangement of organisms by shared traits and order of evolution.

• Example:

  • Organisms listed in evolutionary order: Jellyfish, beetle, mandarin fish, collared lizard, hummingbird, ocelot.

  • Traits include: Bilateral Symmetry, 3 tissue layers, brain/nerve cord, bones/endoskeleton, amniotic egg, warm-blooded, milk/fur/hair.

  • Any organism BEFORE a listed character does not have it, and all organisms AFTER do.

Dichotomous Key Example

• 1a. No bilateral symmetry: Jellyfish

• 1b. Bilateral symmetry: go to 2

• 2a. Not a vertebrate: Beetle

• 2b. Vertebrate: go to 3

• 3a. No amniotic eggs: Mandarin fish

• 3b. Amniotic eggs: go to 4

• 4a. Not warm-blooded: Collared lizard

• 4b. Warm-blooded: go to 5

• 5a. Feathers: Hummingbird

• 5b. Gives milk: Ocelot

Parallel Evolution

• When two species evolve similarly due to similar habitats.

• Results in organisms that seem stationary in relationship to each other.

• Example: Tasmanian Wolf vs. European Wolf

  • Both had distant relatives and evolved to their environment similarly.

• How it happens:

  • Isolation of primitive populations in similar environments.

  • They evolve similarly, but minor differences persist.

Artificial Selection

• Humans drive the evolutionary process by selective breeding.

• Usually not beneficial for survival in nature.

• Example: Over 150 breeds of dogs.

Evolution and Environmental Adaptation

• In nature, animals adapt to their environment.

• If the environment changes, they must adapt or move/go extinct.

Historical Figures in Evolution Theory

Aristotle

• Lived 384-322 BC.

• Employed descriptive visual examination for early classification.

• Encountered issues with classifying sponges and mushrooms.

Comparative Anatomists

• Systematic study grouping organisms by body plans (taxonomy).

• Questioned the diversity and similarities in body plans.

• Vestigial organs (tailbone, appendix, pelvic girdle in snakes) posed problems.

Geologists

• Discovered earth had layers of rock and sand.

• Found similar rock layers around the world.

• Observed that fossils were found only in certain layers.

• Fossils got older and simpler as they dug deeper.

• Older digs showed more marine organisms.

• Observed extinct creatures in the fossil record.

Theories in Geology

• Theory of Catastrophism: Catastrophes occur regularly (earthquakes, volcanoes, etc.).

• Theory of Uniformity: Slow, gradual change makes sense.

• Both theories are used together.

Fathers of Evolution Theory Before Darwin

George Cuvier (1769-1832)

• Founded vertebrate paleontology.

• Believed in the Theory of Catastrophism.

  • Based on abrupt changes in the fossil record.

  • Believed in a singular creation.

  • After catastrophes, survivors repopulated the world.

  • New organisms appeared after successive catastrophes.

Charles Lyell (1797-1875)

• Developed the Theory of Uniformity.

• Believed in gradual change over billions of years.

• His book "Principles of Geology" influenced Darwin and Wallace.

Jean Baptise Lamarck

• Proposed the Theory of Acquired Traits.

  • If a body part needed to change, it would grow.

  • Offspring would inherit the changed part.

  • The force to change was a "drive to perfection".

  • The environment caused change.

  • This theory is no longer accepted.

Thomas Malthus (1766-1834)

• Developed the Principle of Population.

  • Humans produce more offspring than can survive.

  • Resources cannot support the population.

  • Competition increases, leading to starvation and wars.

  • Influenced Darwin and Wallace.

Natural Selection

• When a population evolves, allele frequencies change.

• The environment is the driving force behind natural selection.

• Advantageous traits become adaptations, enhancing survival and reproduction (fitness).

Adaptations

• The process that selects specific traits as an advantage is not random.

• An adaptation in one environment may be a disadvantage in another.

Genetic Variation

• A gene pool without much variation limits a species’ ability to adapt.

• If populations do not adapt, they may become extinct.

• Note: Populations change, not individuals.

Rates of Evolution

• Gradualism: Slow changes over long periods.

• Punctuated Equilibrium: Rapid initial change followed by stability.

Examples of Adaptations

Camouflage

• The ability to blend into the environment.

Mimicry

• Resemblance of an animal or plant to another animal, plant, or object.

• Example: Sea slug and flatworm mimicry; bumblebee mimicry; Hawk Moth caterpillar mimicry.

Sexual Selection

• Selection based on traits that attract mates.

Interpreting Graphs

• Y-axis plots the number of individuals with a trait.

• X-axis plots the variety of traits.

How Species Form

• Changes in a population’s gene pool.

• Gene Flow (Migration).

• Genetic Drift (Chance) – significant in small populations.

• Nonrandom Mating.

• Sexual Selection.

Types of Natural Selection

• Stabilizing Selection: Favors the average trait.

  • Example: Wild rabbit coat color, human head size at birth.

• Directional Selection: Favors one extreme.

  • Example: Polar bear fur color, whale leg size, giraffe neck length.

• Disruptive Selection: Favors both extremes.

  • Example: Salmon size.

Isolating Mechanisms

• Geographic Isolation: Different areas, different selective pressures.

• Reproductive Isolation:

  • Prezygotic: Mating calls & rituals, habits, temporal.

  • Postzygotic: Gamete survival, zygote survival, embryonic survival, infertile offspring.

Evolutionary Patterns

Divergent Evolution

• Organisms become more different over time.

• Example: Polar bear, black bear, grizzly bear.

• Caused by physical or social/behavioral isolation.

Convergent Evolution

• Organisms under similar selective pressures become similar, even if not closely related.

• Examples: Shark vs. Porpoise; Cactus vs. Euphorbia; Tasmanian Wolf vs. European Wolf.

• Results from using similar resources or isolation in similar environments.

Co-Evolution

• Two organisms mutually adapt to changes in each other.

• Example: Ichneumon wasp & orchid.

Artificial Selection

• Humans drive evolution via selective breeding.

Speciation

Natural Selection

• Only organisms suited to an environment are selected for.

Types of Selection:

• Stabilizing

• Directional

• Disruptive

Isolating Mechanisms

• Geographic

• Reproductive (Prezygotic & Postzygotic)

Hardy-Weinberg Principle

• Evolution is a change in genetic composition from one generation to the next.

Hardy-Weinberg Equation

• $P^2 + 2PQ + Q^2 = 1$

• Where:

  • $P$ = % of dominant allele in population

  • $Q$ = % of recessive allele in population

  • $P + Q = 1$

  • $P^2$ = homozygous dominant frequency

  • $Q^2$ = homozygous recessive frequency

  • $2PQ$ = heterozygous frequency

What Hardy-Weinberg Tells Us

• Allele frequency in offspring if there is no evolution.

• Changes in allele frequency indicate evolution.

What Causes Evolution?

• Sexual selection

• Gene Flow (Immigration/Emmigration)

• Random accidents & small populations.

• Birth Rates