EVERYTHING
Adaptation & Speciation 3
Explain the fundamental “paradox of sex” and the main hypotheses about why sexual reproduction is common in nature despite its many costs
Overall: The paradox of sex is that sexual reproduction is riskier, and has more disadvantages than asexual reproduction.
Asexual produce 2x more offspring & are easier.
Theories of why sexual reproduction is more common.
Sexual reproduction increases genetic diversity, which increases:
The likelihood of a species to produce offspring that can survive in various conditions.
The speed of reshuffling genes
Red Queen - More offspring will help fight against evolving pathogens and parasites.
Mullers Ratchet - With asexual reproduction, harmful mutations will persist over time(increasing genetic load). Sexual reproduction will have those mutations purged from natural selection.
Explain how differing reproductive strategies in males and females can result in differing selective pressures.
Overall: Males have a lot of sperm, so they focus on quantity of offspring not quality. Females have a few eggs, so they focus on quality of offspring not quality.
From this, males produce better in environments where selection favors mating opportunities. Whatever features allow for more mating opportunities will typically persist through generations.
Intrasexual Selection in Males(competition)
Females will produce better in environments that select for better quality care for their offspring. Whatever features allow for better quality offspring in these environments will persist for generations.
Intersexual Selection in Females(choice)
These differences lead to sexual dimorphism, the differences between males and females.
All of the above is typical, but the reverse can happen.
More
Evaluate the relationship between the operational sex ratio and the direction and intensity of sexual selection
OSR: Sexually Active Males / Sexually Active Females
Higher OSR -> Male-Biased OSR: more competition among males
Sexual Selection acts strongly on males leading to more traits that improve matability (combat, attractiveness). Intrasexual Selection in Males and Intersexual Selection in females,Lower OSR -> Female Biased OSR: competition among females for mates. Males choose, leading to sexual selection acting on females more. Intrasexual Selection in females and intersexual selection for males.
X-Gender Biased OSR-> more competition between x, increased intrasexual selection and sexual selection acts primarily on them. Intersexual selection acts on Y-Gender.
Higher OSR -> increased intensity of sexual selection & dimorphism.
Describe how sexual dimorphism can result from sexual selection
Sexual Selection is when certain traits evolve and develop in order to reproduce. These traits involve being better competitively and being more attractive. These traits often are different from the traits of the opposite sex, therefore sexual dimorphism exists.
Explain the circumstances that can lead to intersexual selection (mate choice) and intrasexual selection (mating competition)
Intrasexual Selection is when members of one sex compete against one another, which happens when OSR is biased(typically to males).
Intersexual Selection is when members of one sex choose of the sex, and it’s when OSR is biased towards the opposite sex.
Describe the process by which sexual selection can take place after mating
There is sperm competition, so sexual selection favors what sperm gets to fertilize. Females can play a part in this too.
Explain how sexual conflict can lead to antagonistic coevolution
Sexual Conflict - when female and male reproductive interests do not align.
Antagonistic Coevolution - when a sex evolves a trait to counteract the sexual conflict between them in order to reproduce.
Conflict Happens(lets say males benefit more from reproducing more, and females don’t) —> One Sex evolves trait —> Other Sex evolves countertrait first sex trait → cycle.
Senescence: (Aging) The process of gradual deterioration & decline in function that occurs with age.
Metapopulation: A group of separate populations of the same species that interact through occasional migration or gene flow.
Types of Speciation(when two populations cannot procreate)
Allopatric Speciation: When there is a geographic barrier that divides a population and over time they evolve differently to the point that they are two different species
Peripatric Speciation: When a small section gets isolated from the population, and then the same as allopatric speciation. More rapid evolution because it is a littler subset which will be less representative of the population
Vicariance: the formation of geographic barriers that
separate a population
Colonization & Dispersion:
Paripatric Speciation: When neighboring populations are unable to mate to do differences in neighboring conditions, but they are able to interact with each other.
Sympatric Speciation: When new species evolve in a population that is not geographically isolated.
Gametic Incompatibility - Sperm & Egg from different species fail to meet.
Prezygotic vs Postzygotic Reproductive Barriers
Prezygotic - before fertilization ex.(mating behavior or timing)
Pre-mating and post-maring before fertilization
Postzygotic - after fertilization ex.(sterile offspring)
Hybrids
Reinforcement & Fusion are opposites
Reinforcement is when natural selection strengthens reproductive barriers, reducing hybrid formation. Reinforcement - Reduce
Fusion is when natural selection weakens the barriers, allowing for more hybrid formation. Fusion - Free
Zones
Primary Hybrid Zone -> When populations are initially diverging(still in contact), and typically during parapatric speciation, there is a hybrid zone of gradual genetic drift.
Secondary Hybrid Zone -> Previously separated populations come back into contact with each other, and fuse, allowing for interbreeding.
Defining Species Methods
Morphological Traits -
Benefits - easily observed
Drawbacks - members of the same species can be morphologically distinct, and members of different species can be morphologically similar(cryptic species)
Biological Species Concept - based on if they can produce fertile, viable offspring
Benefits - objective criterion, and reveals a lot about evolution
Drawbacks - not easily observed, don't work for asexual species, and hybrid species make it difficult.
Macroevolution 2
Appreciate what the fossil record offers the study of evolution; especially what is unique to the fossil record (the past is the key to the present).
The fossil record is the best direct evidence of old life on Earth, because it is the only evidence where you can see the changes.
Transitional forms seen in the fossil record provide evidence of descent with modification.
Transitional forms are forms with evidence of both ancestral and derived species, therefore showing evidence of evolution, or descent with modification. The transitional forms are species, not half of one or another, but evidence of the ancestral and derived species.
What is the overall pattern of marine diversity through time and how (what data) is this curve generated?
Generally, marine diversity increases over time, and it is shown through the Saposki Curve.
Sapkoksi Curve
It starts with a slow, steady rise throughout the Cambrian Period after the Cambrian Explosion (~541 mya), when most major animal groups first appeared. During the Ordovician Period (~485–444 mya), diversity rose sharply in the Great Ordovician Biodiversification Event before dropping during the End-Ordovician Mass Extinction, the first of the Big Five. Through the Silurian and Devonian, diversity recovered and leveled off, forming a long plateau during the Paleozoic Era. Then, the Permian Extinction (~252 mya), the largest mass extinction in Earth’s history, wiped out around 90–96% of marine species, causing a massive crash in diversity. In the Mesozoic Era, diversity rebounded rapidly during the Mesozoic Marine Revolution, driven by new predator-prey dynamics and modern marine groups. After the End-Cretaceous Extinction (~66 mya), diversity continued to rise steeply throughout the Cenozoic Era, reaching the highest levels of marine biodiversity observed today.
Appreciate biases and limitations of the fossil record.
Not all organisms fossil, and some fossil better than others. Harder ones typically get saved more. Temporal bias(time bias): certain time periods are studies more
Know the relationship between Standing Diversity, Origination, and Extinction.
Standing Diversity is the amount of a given species at a given time, origination is the increase of the species, and extinction is the decrease of the species. So if origination> extinction, standing diversity is increasing, and if origination<extinction, standing diversity is decreasing.
What is adaptive radiation and give an example or two.
Adaptive Radiation - The rapid diversification of species into many new species, adapting to a new niche. Usually happens when a new habitat opens up, or after a mass extinction. Darwin’s finches are a great example, so are Anolis lizards.
Explain the difference between background and mass extinction.
Background Extinction is the normal extinction rate of humanity. Mass extinction is caused by a catastrophic event.
Know what kinds of phenomena caused the P-T and K-Pg mass extinctions.
P-T extinction (Permian Extinction) was caused by volcanic eruptions, leading to increased CO2 and methane. Ocean acidification from this kills marine life.
K-Pg extinction (Dinosaur Extinction) was caused by an asteroid impact, which caused global cooling, killing the non-avian dinosaurs.
The fossil record can be a source of information about the tempo and mode of evolutionary change.
The fossil record reveals both the tempo (rate) and mode (pattern) of evolutionary change over time. It shows whether evolution occurred gradually or in rapid bursts (punctuated equilibrium), and whether species evolved by transformation (anagenesis) or branching (cladogenesis). By preserving sequences of organisms through time, fossils provide direct evidence for how and how fast evolution has occurred.
Anagenesis: Evolutionary change within a single lineage where one species gradually transforms into another without branching — the original species no longer exists once the new one forms. (Straight Line)
Cladogenesis: Evolutionary change that involves the splitting of one lineage into two or more new species, increasing overall biodiversity — this is branching evolution. (Branch)
Be able to read and interpret time by morphology plots.
If morphology is changing steadily, then anagenesis is happening. If it isn’t changing, then stasis is happening, and if long periods of stasis are rapidly stopped, then it is punctuated equilibrium(cladogenesis).
The fossil record shows both gradual change as well as a pattern of stasis and punctuated change, the latter being more common.
Because of this, we can assume most species go through long periods of stasis, then rapid evolution.
Understand why stasis is interesting and what might cause it.
It challenges the idea that evolution is constant. There are many reasons to why it could happen:
Natural Selection could favor the current form.
Genetic Constraints
Constant habitat
Understand and explain the theory of Punctuated Equilibrium.
Punctuated Equilibrium is the idea that evolutionary change happens in rapid bursts, associated with speciation events, followed by long periods of stasis (little or no change).
Biodiversity 5
Major Divisions in the Tree of Life
Understanding developmental patterns, symmetry, body cavity, and segmentation is key to classifying animals.
Taxa Animalia is closely related to choanoflagellates.
Animal Classification & Evolutionary Relationships
1. Common Methods for Identifying Evolutionary Relationships
Fossils
Anatomical and physiological differences
Patterns in development
Genomic sequencing (increasingly relied upon by taxonomists)
2. Relationship between Choanoflagellates and Animals
Choanoflagellates are identified as the closest living relatives to animals due to their:
Singular posterior flagellum identical to collar cells in sponges.
Indication of a multicellular common ancestor.
Share molecular synapomorphies: Cadherins (adhesive molecules) and Tyrosine kinases (cell signaling).
Characteristics of Choanoflagellates:
Unicellular, funnel-shaped with sticky tentacles.
Capture bacteria through phagocytosis.
Sometimes form small colonies.
3. Defining Characteristics of Animals
Multicellular (not unique, also seen in other eukaryotes)
Heterotrophs (not unique to animals)
Possess a single posterior flagellum (similar to other opisthokonts)
Lack chitin (excludes them from being fungi)
Exhibit internal digestion (some parasites have lost this)
Mobile at certain life stages (similarity with plants and fungi)
Key synapomorphy: Presence of collagen (structural protein in extracellular matrix).
4. Early Animal Development & Tissue Layers
After fertilization, cleavage occurs:
Zygote divides into cells, forming a solid ball of cells which then rearranges into a hollow ball (blastula).
Blastula is one cell layer thick.
Gastrulation begins:
Invagination of cells forms two primary germ layers:
Inner layer: Endoderm
Outer layer: Ectoderm
The opening from invagination is the blastopore.
Diploblastic animals: Possess two tissue layers (endoderm and ectoderm).
Examples: Ctenophores (comb jellies), Cnidarians (jellyfish, corals, anemones, hydras).
Triploblastic animals: Possess three tissue layers (endoderm, mesoderm, ectoderm).
Includes bilaterians (protostomes and deuterostomes).
Significance of Mesoderm: Its distribution allows classification into three types of body cavities. It also plays a key role in the evolution of the neural crest in vertebrates.
5. Body Symmetry
Sponges: Lack any symmetry.
Radial symmetry: Symmetrical halves along any central axis (e.g., sea anemone).
Typically found in diploblastic animals.
Bilateral symmetry: Mirror image from a single plane (sagittal plane) from anterior to posterior (front to back).
Evolutionary significance: Supports active, directional movement.
Establishes orientation: Anterior (front), Posterior (back), Dorsal (top), Ventral (bottom).
Typically found in triploblastic animals, except for echinoderms (bilateral larvae, adult radial symmetry).
6. Cephalization
Definition: Concentration of sensory organs and neural tissue at the anterior end.
Evolutionary Advantage: Senses encounter the environment first, improving survival chances and enabling better sensory processing, coordinated movement, and hunting abilities.
7. Internal Body Cavity Organization (Coelom)
Three types of body cavities in triploblastic animals:
Acoelomates: No body cavity (solid tissue between ectoderm and endoderm).
Example: Flatworms (Platyhelminthes).
Pseudocoelomates: False coelom (cavity lined with mesoderm on outside only).
Example: Roundworms (Nematodes).
Coelomates: True coelom (both body wall and internal organs lined by mesoderm).
Examples: Earthworms (Annelids), sea stars (Echinoderms), Chordates.
Movement and growth of organs in a true coelom is facilitated by the fluid-filled cavity.
Eumetazoans: Animals with True Tissues
Eumetazoans possess the synapomorphy of true tissues (nerve and muscle).
Eumetazoans Breakdown
Sponges (Porifera)
Synapomorphy: Presence of choanocytes (collar cells) and mineral spicules.
Body Plan: Asymmetrical; lacks true tissues and organs.
Feeding: Filter feeders utilizing water flow.
Skeleton: Composed of spicules (silica or calcium carbonate) and/or spongin fibers.
Other Features: Sessile; capable of both sexual and asexual reproduction.
Differences from Colonial Choanoflagellates: Sponges are multicellular with integrated choanocytes, whereas colonial choanoflagellates are groups of similar cells where each cell functions independently.
Ctenophores (Comb Jellies)
Synapomorphy: Presence of 8 ciliary “combs” for swimming.
Body Plan: Radial or biradial symmetry; diploblastic.
Feeding: Utilize colloblasts (sticky cells) for prey capture.
Movement: Utilize cilia for locomotion.
Other Features: Possess a complete flow-through gut (mouth and anal pores).
Cnidarians (e.g., Jellyfish, Corals, Sea Anemones, Hydras)
Synapomorphy: Cnidocytes, specialized stinging cells containing nematocysts for defense.
Body Plan: Radial symmetry; diploblastic (two tissue layers).
Body Forms: Polyp (sessile stalk with mouth/tentacles up) and medusa (free-swimming with mouth/tentacles down).
Anemones only reproduce via polyp stage.
Coral polyps live in communities and secrete calcium carbonate to form rocky reefs.
Nervous System: Simple nerve net without a brain.
Feeding: Carnivorous, using tentacles for capturing prey.
Reproduction: Polyp can bud off to become medusa; external fertilization in adults forms larval stage that develops into a polyp.
Hydra: Primarily reproduce asexually via budding but can reproduce sexually; capture prey using tentacles and nematocysts; some species form colonies with specialized functions.
Bilaterians
Synapomorphy: Triploblastic tissues with bilateral symmetry.
Evolutionary Significance of Flow-Through Gut: Digestive tract with separate mouth and anus. Efficient digestion from front to back, minimizing mixing. Allows continuous feeding capacity, specialized digestive regions, and supports higher metabolism for active lifestyles.
Divided into:
Protostomes
Deuterostomes
Protostomes vs. Deuterostomes
The fate of the blastopore distinguishes protostomes from deuterostomes.
Protostomes: "First mouth"
Synapomorphy: Blastopore develops into the mouth.
Contain an anterior brain with a ventral nervous system.
Subgroups: Lophotrochozoans and Ecdysozoans.
Deuterostomes: "Second mouth"
Synapomorphy: Blastopore develops into the anus; mouth forms from a second opening.
Have an anterior brain with a dorsal nervous system.
Include echinoderms (e.g., starfish) and chordates.
Subgroups of Protostomes
1. Lophotrochozoans
Identification: DNA evidence indicates unique links, supporting classification as a monophyletic clade.
Distinctive Features (present in some but not all members):
Trochophore larva: Characterized by a ciliated girdle used for swimming and feeding.
Lophophore: A collar of tentacles used in feeding and gas exchange (found in bryozoans and brachiopods).
Body Cavity: Generally coelomate, except for flatworms (acoelomate).
Breakdown:
Flatworms (Platyhelminthes)
Common Types: Planarians, Flukes, Tapeworms.
Body Plan: Acoelomate (lacks a body cavity); bilateral symmetry; triploblastic.
Digestive System: Incomplete (blind-gut; mouth and anus are the same opening) or absent (in parasitic forms, relying on hosts).
Circulatory System: Absent; relies on diffusion facilitated by flat shape.
Nervous System: Concentration of nerves near the head (cephalization) and ventral longitudinal nerves. Free-living species show increased perceptive capacity and regenerative capabilities (e.g., planarians).
Locomotion: Cilia or muscle contractions.
Reproduction: Often hermaphroditic; capable of regeneration.
Ecological Roles: Free-living flatworms are typically marine carnivores. Tapeworms and flukes are parasitic with complex life cycles involving multiple hosts. Some exhibit aposematic (warning) coloration indicating toxicity.
Mollusks (e.g., Snails, Clams, Squids, Octopuses)
Synapomorphy: Muscular foot, visceral mass, and mantle.
Body Plan: Unsegmented coelomates; triploblastic with bilateral symmetry.
Coelom: True coelomate.
Digestive System: Complete with mouth and anus.
Circulatory System: Typically open in most, closed in cephalopods (for efficient oxygen transport).
Locomotion: Via muscular foot or jet propulsion (cephalopods).
Reproduction: Primarily sexual.
Variations in Body Plans:
Foot: Gastropods (broad, flat foot for crawling), Bivalves (wedge-shaped foot for burrowing), Cephalopods (modified into arms and tentacles for mobility and feeding).
Visceral Mass: Present in all; varies in shape according to lifestyle needs (spiral shapes in gastropods, compressed in bivalves).
Mantle: Gastropods (single coiled shell and respiratory cavity), Bivalves (two shells with a large cavity for feeding), Cephalopods (forms body wall, aids in jet propulsion; internal or absent shell).
Key Takeaway: Consistent basic body parts (foot, visceral mass, mantle) exhibit significant modifications across molluscan taxa according to ecological niches and lifestyles.
Annelids (Segmented Worms)
Examples: Earthworms, Leeches, Polychaetes.
Body Plan: Segmented body (metamerism); triploblastic with bilateral symmetry.
Coelom: True coelomate, divided by septa.
Digestive System: Complete flow-through gut with specialized regions (crop, gizzard, intestine).
Circulatory System: Closed.
Locomotion: Circular and longitudinal muscles with chitinous bristles (setae).
Reproduction: Sexual reproduction with some hermaphrodites.
Functions of Segmentation: Enhances body organization and movement through hydrostatic pressure and rigid support.
2. Ecdysozoans
Synapomorphy: Shedding of exoskeletons (ecdysis).
Body Cavity: Coelomate, except for roundworms (pseudocoelomate).
Breakdown:
Nematodes (Roundworms)
Synapomorphy: Pseudocoelomate.
Arthropods
Characteristics: Joint appendages.
Breakdown:
Trilobites
Myriapods
Chelicerates
Pancrustaceans (divided into Crustacea and Insecta)
Biodiversity 6
Overview of Ecdysozoans
Ecdysozoans are a diverse superphylum of protostome animals, characterized by molting.
Focus on two major groups: nematodes and arthropods.
Arthropods are the most diverse group of animals within ecdysozoans, primarily due to adaptations of their hardened exoskeleton and segmented bodies, which have allowed them to colonize diverse ecological niches.
Definition of Ecdysozoans
Synapomorphy: All ecdysozoans molt their exoskeleton or cuticle during growth or metamorphosis. This process, known as ecdysis, is essential for growth, as their rigid external covering does not expand.
Ecdysis: A Greek term meaning "get out of", directly referring to the process of shedding the outer layer.
Cuticle Characteristics
Nematodes:
Possess a permeable cuticle that allows for gas and water exchange directly through their body surface.
Due to this permeability, they must reside in moist environments to avoid desiccation and maintain osmotic balance.
Arthropods:
Their cuticle forms a hardened exoskeleton, reinforced internally and externally, often featuring a waxy layer for effective waterproofing.
This exoskeleton serves as robust protection against predators and physical damage, and provides crucial structural reinforcement and attachment points for muscles. It is primarily composed of chitin (a strong polysaccharide similar to cellulose), which is largely responsible for the immense diversity and evolutionary success of arthropods.
Nematodes (Round Worms)
Characteristics:
Possess a thin cuticle that limits their movement largely to wriggling, as it lacks the specialized joints found in arthropods.
Have a complete digestive tract with two openings—a mouth and an anus—allowing for a continuous, flow-through gut, which is more efficient than the sac-like gut of flatworms.
Pseudocoelomate structure: Their mesoderm lines one side of the coelom (body cavity) but does not fully line the digestive tract, in contrast to true coelomates. This fluid-filled pseudocoelom acts as a hydrostatic skeleton, providing support and aiding movement.
Unsegmented body structure, meaning their bodies lack repetitive segments found in annelids or arthropods.
Exhibit cephalization, with a distinct head region containing sensory organs and a brain, and feature a prominent ventral nerve cord running along their body.
Size range:
Most nematodes are microscopic, often found in soil and water, but some parasitic species can grow up to 9 meters long, particularly those living inside large hosts like whales.
Ecological roles: They fulfill various ecological roles, including scavengers breaking down organic matter, predators of microscopic organisms, and significant parasites (e.g., hookworm in humans, which can cause anemia).
Model organism: Caenorhabditis elegans (C. elegans):
Matures in just 3 days, making it an ideal candidate for rapid genetic and developmental studies in laboratory settings.
Its transparent body allows for direct observation of internal organ development and cell changes without invasive procedures.
Has a completely mapped cell fate, meaning the developmental lineage of every cell is known. This has been crucial for groundbreaking research on apoptosis (programmed cell death) and the development of GFP (Green Fluorescent Protein) technology, both of which were recognized with Nobel Prizes (in 2002 and 2008, respectively).
Arthropods
A highly diverse group that prominently includes insects, crustaceans, spiders, centipedes, and millipedes.
Synapomorphy: Characterized by the presence of jointed appendages (derived from Greek "arthro" for joint and "pod" for appendage), which enable flexible and specialized movements for locomotion, feeding, and sensory perception.
Structure:
Exoskeleton: A thick and rigid cuticle primarily composed of chitin. While tough, it is strategically thinned at the joints, allowing for precise movement of appendages via attached muscles.
Body segmented: Their bodies are composed of repeating segments, each of which can bear a pair of appendages. These appendages are highly adaptable and may be modified to serve various functions beyond just legs, such as antennae, mouthparts, or gills.
Regulatory genes, such as Hox genes, play a critical role in controlling the development and formation of these diverse appendages along the body axis.
Example: Insects like Drosophila typically exhibit a distinct body plan with six walking legs, whereas myriapods, such as centipedes and millipedes, often have many more legs due to less tagmatization.
Fusions of segments often lead to distinct body regions (e.g., head, thorax, abdomen), a process called tagmatization, which results in various specialized adaptations across different arthropod taxa, optimizing function for specific lifestyles.
Diversity of Arthropods
Trilobites:
An extinct group of aquatic arthropods that first appeared in the Early Cambrian period and persisted until the end of the Permian extinction event. They are among the earliest known arthropods.
Represented by over 17,000 described fossil species, making them exceptionally significant in paleontology for understanding early animal diversity and evolution.
Myriapods:
Characterized by two distinct body regions: a head and a flexible, elongated trunk.
Centipedes: Are carnivorous predators. Their first pair of legs is notably modified into venomous fangs (forcipules) used to subdue prey.
Millipedes: Primarily herbivorous or detritivorous. They appear to have two pairs of legs per body segment, which is a result of the fusion of two embryonic segments during development.
Chelicerates:
This group includes familiar terrestrial arthropods like ticks, mites, spiders, and scorpions. They are uniquely characterized by the presence of chelicerae, specialized pincer-like or fanged mouthparts used primarily for grasping or piercing prey.
Typically possess four pairs of walking legs. Spiders, specifically, use their specialized chelicerae to inject venom into their prey.
Pancrustacea:
A clade that groups insects and crustaceans together, reflecting their close evolutionary relationship.
Crustaceans, which are the dominant marine arthropods, possess a high number of highly versatile appendages modified for various functions such as manipulating food, walking on the seafloor, and swimming through water.
Insects:
The most diverse group within arthropods, with over 1 million species described and many more yet to be identified.
Characterized by a three-part body plan (head, thorax, and abdomen) and typically six legs attached to the thorax. Their appendages are incredibly diverse and may be modified for flight (wings), jumping, grasping, or sensory perception.
Due to their hard exoskeleton, insects cannot exchange gases directly through their body surface; instead, they utilize a system of spiracles (external openings) and internal air sacs connected to tracheal tubes for efficient respiration.
A notable model organism in genetics is Drosophila melanogaster (fruit fly), which has been instrumental in research on developmental regulatory genes, genetics, and heredity.
Echinoderms
Echinoderms are part of the Deuterostomia clade, indicating they are closely related to chordates (which include vertebrates) based on shared embryonic developmental patterns (e.g., radial cleavage, blastopore forms the anus).
They are mostly marine animals and predominantly benthic, meaning they live on the sea floor.
Exhibit various feeding modes:
Sea lilies (crinoids) are filter feeders, capturing suspended organic matter from the water column.
Brittle stars and sea cucumbers typically act as scavengers, feeding on detritus.
Sea urchins graze on algae and other organic material found on rocky surfaces.
Starfish are primarily predatory, often preying on bivalves, snails, or other echinoderms.
Synapomorphies:
Water vascular system with numerous tube feet: This unique hydraulic system is used for locomotion, feeding, gas exchange, and waste excretion, operating through changes in water pressure.
Pentaradial symmetry as adults: Their bodies are typically organized around a central axis in multiples of five. Interestingly, this is a secondary adaptation, as their larvae always exhibit ciliated bilateral symmetry before undergoing metamorphosis to their adult form.
Calcified endoskeleton of ossicles: They possess an internal skeleton composed of numerous small, interlocking calcium carbonate plates called ossicles, which provide support and protection, often bearing spines.
Oral-aboral axis with mutable connective tissue: Their body axis runs from the mouth (oral) on the underside to the anus (aboral) on the top. They feature mutable connective tissue that can rapidly change its rigidity, allowing them to dramatically alter their body posture, detach limbs, or firmly anchor themselves, enhancing their adaptability and ecological success.
Major Groups of Echinoderms
Starfish (Class Asteroidea):
Often keystone predators in marine ecosystems, meaning their presence is crucial for maintaining biodiversity within their communities. They use their strong tube feet not only for locomotion but also to pry open the shells of their prey.
Brittle Stars (Class Ophiuroidea):
Characterized by slender, flexible arms that are distinct from their central disc, enabling more rapid arm movements for locomotion. They are primarily scavengers, using their tube feet mostly for gathering food particles rather than movement.
Crinoids (Class Crinoidea):
Include sea lilies (sessile, attached to the seafloor by a stalk) and feather stars (motile, pelagic, unattached). Both forms feed as filter feeders, using their feathery arms to capture plankton and detritus.
Sea Urchins and Sand Dollars (Class Echinoidea):
Distinctively lack arms but maintain their characteristic pentaradial symmetry. Their spherical (sea urchins) or flattened (sand dollars) bodies are covered in movable spines used for protection against predators, camouflage, and sometimes for locomotion.
Aristotle's lantern: A complex, five-part feeding structure unique to sea urchins, described by Aristotle. It comprises ossicles and muscles, allowing them to scrape algae and other food from surfaces using sharp, calcareous teeth.
Sea Cucumbers (Class Holothuroidea):
Exhibiting secondary bilateral symmetry, their bodies are elongated along the oral-aboral axis, giving them a worm-like appearance despite their echinoderm affinities. They possess well-developed tube feet often restricted to specific bands for crawling and specialized tentacles near their mouths for food sensing and collection.
They display evolutionary adaptations, such as loss of pigmentation and increased antenna length, similar to convergent evolution observed in cave-dwelling arthropods, reflecting adaptations to low-light or detritus-rich environments.
Topic: The Tree of Life and the Clade of Plants.
Focus on biological diversity, evolutionary forces, and challenges in transitioning to land.
Course Context
The study of plants is vast; entire courses and majors exist.
Today's focus: different life cycles and alternation of generations in plants.
Discuss the role of novel traits such as the vascular system, seeds, and flowers.
Learning objectives include:
Describing plant diversity
Understanding complex life cycles
Learning about ecological adaptations
The Tree of Life
Reference the tree of life on the Canvas website for classifications and taxa information.
Plants are connected to other taxa through a basal eukaryote polytomy alongside protists (discussed in Biodiversity 2).
Simplified Tree of Life
Includes bacteria, archaea, and eukaryotes.
Details the placement of plants within the eukaryotic clade and relation to other groups like fungi, which will be discussed in Biodiversity 4.
Plant Synapomorphies
Definition: Synapomorphy for the plant clade = presence of chloroplasts from primary endosymbiosis of a cyanobacterium.
Evidence:
Chloroplast structure: has two membranes (original cyanobacterium and eukaryotic engulfment).
Chloroplast’s DNA: circular chromosome akin to cyanobacteria.
Importance: This event was singular and foundational for all plant chloroplasts, leading to two basal lineages (glaucophytes and red algae) and all green plants.
Further Endosymbiotic Events
Secondary and tertiary symbiotic events involving green algae and red algae explained. Examples include:
Euglenids (secondary endosymbiosis of green algae)
Stramenopiles and alveolates (secondary endosymbiosis of red algae)
Dinoflagellates (tertiary endosymbiosis of red algae)
Corals and dinoflagellates relationship (quaternary endosymbiosis).
Relationships Among Major Plant Clades
Four major plant clades:
Green plants (green)
Land plants (orange)
Vascular plants (blue)
Seed plants (gold)
Relationships also demonstrated in an indented classification format spanning glaucophytes and red algae to green plants, with key examples (liverworts, lycophytes, etc.).
Glaucophytes
Characteristics: Unicellular algae, rare, freshwater-living, significant for evolutionary study regarding chloroplasts, only reproduce asexually.
Red Algae
Characteristics: Unicellular or multicellular (mostly multicellular), marine and photosynthesize short-wavelength light due to red pigments; important as the sister group to green plants.
Note: Without chlorophyll b, red algae do not belong to the green plant clade.
Uses: Nori (sushi), agar.
Green Plants
Characteristics: Defined by the presence of chlorophyll b and starch.
Importance of Chlorophyll b:
Expands range of light absorption in photosynthesis, growing in varied light conditions.
Allows for energy storage improvements.
Questions posed regarding evolution traits such as chlorophyll b and starch evolution as synapomorphies for green plants.
Transition from Water to Land
Overview: Challenges faced include desiccation, physical support, nutrient transport, gamete protection, and UV exposure.
Evolution of adaptations:
Waxy cuticle to reduce water loss.
Embryo retention to protect developing offspring.
Vascular systems (phloem and xylem) to support larger structures and transport.
Stomata for regulation of gas exchange and water conservation.
Alternation of Generations
Defined: A critical process where plants alternate between haploid (gametophyte) and diploid (sporophyte) stages.
Diploid sporophyte produces haploid spores by meiosis; haploid gametophyte produces gametes by mitosis.
Describes specific transitions between generations in non-vascular (large gametophyte) and vascular plants (larger sporophyte).
Vascular Plants
Defined by the presence of vascular systems for water and nutrient transport.
Include lycophytes (with microphylls) and ferns (with megaphylls).
Seed Plants
Two major seed types discussed:
Gymnosperms (exposed seeds) vs. Angiosperms (enclosed seeds).
Key reproductive aspects (double fertilization unique to angiosperms) described.
Key Plant Characteristics
Glaucophytes: Microalgae with primitive features.
Red Algae: Redistributes light absorption in deep waters; critical in marine environments.
Green Algae / Green Plants: Unified by chlorophyll b and starch storage; pivotal for land adaptation.
Land Plants: Transitioned from water; require specific reproductive adaptations.
Non-Vascular vs. Vascular: Estimation of gametophyte versus sporophyte dominance laid out.
Fungi and Opisthokonts Overview
Learning objectives regarding fungal synapomorphies and relation to other taxa.
Refresh trees of life in context of recent discussions about cell structure and evolution of multicellularity.
Fungal Synapomorphies
Key traits include:
Chitin in cell walls
Absorptive heterotrophy defined with examples of their ecological roles.
Classification of Fungi
Major taxa within fungi includes microsporidia, chytrids, arbuscular mycorrhizae, and dikarya.
Dikarya includes distinct reproductive structures (ascomycota and basidiomycota).
Fungi Ecology
Discussed absorption processes: saprobic, parasitic, and predatory modes.
Mutualistic relationships illustrated, particularly with plants (mycorrhizae).
Final Review
The evolution and ecological significance of lichen were emphasized.
Lichens as mutualists photographed in varying conditions were highlighted for their role in pioneer ecosystems.
Concluded with specific questions to reinforce understanding and ensure mastery of the material.
Key Terms to Know
Synapomorphy: Trait shared by a group; crucial for defining taxa.
Alternation of Generations: Lifecycle difference showcased between haploid and diploid stages in plant development.
Di- and Dikaryon: Terms denoting different genetic structures in fungal reproduction.
Chitin and Absorptive Heterotrophy: Central to understanding fungal biology.
Endosymbiosis: Central role in the evolutionary narrative of both chloroplasts and mitochondria across groups.
Mycorrhizae: Defined critical mutualism with plants; pivotal in nutrient acquisition for terrestrial flora.