Flashcards in Lecture 2: Vertebrate Origins And Evolution Deck (21)
Define Ontogeny and Teleology
- Ontogeny refers to the embryonic development of an organism as well as any developmental changes that occur after birth or hatching (i.e., reproductive maturation, aging, etc.)
- Teleology: The idea that characteristics develop because they are needed. Such as: Birds needed to fly, so they developed wings. Obviously teleology's mostly not true.
Describe Von Baer's law and explain how it might relate to modern views of vertebrate evolution and relationships
- Features that develop earliest in ontogeny are the oldest phylogenetically.
- Features that develop later in ontogeny are of more recent phylogenetic development.
- Features common to all members of a major taxonomic group develop earlier in ontogeny than do special features that distinguish subdivisions of the group.
Describe the synthetic theory of evolution and list it's first two components
- Organisms living today are not necessarily the same as those that lived in the past. Organisms living in the past are not necessarily the same as those living today. Based primarily on fossil record.
- Genetic diversity: All members of a population demonstrate genetic variation (identical twins may be an exception). Sources of genetic variability include: Sexual reproduction(Meiosis & Independent assortment and Crossing-over), recombination (Fertilization), and mutation
Describe the synthetic theory of evolution by listing it's 3rd component
- Theory of natural selection: Co-developed independently by Charles Darwin, who published On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life in 1859, and Alfred Russell Wallace.
- Components include Genetic Variability, which exists in sexually reproducing populations. Some members of the population may be better “fit” for a given environment than others. These individuals have a better chance of survival and of having fertile offspring. The genotypes in these species will become more frequent over the years. If the environment does not change, the population may reach genetic equilibrium, where evolution will be very slow, if it occurs at all.
Who came up with the theory of acquired characteristics. What are it's components?
- Developed by Jean Baptiste Lamarck.
- During its lifetime, an organism may develop anatomic changes in response to specific pressures it encounters.
- These acquired characteristics may then be passed on to its offspring.
- Judge's Verdict: ...ehhh, not quite.
Describe the characteristics of an Analogy
- Similarity in function in structures in two or more different species.
- Although the function is similar (i.e., wing of bird and wing of insect), neither the anatomy nor the embryological development is similar.
- Structures that are similar in function but that do not have a similar anatomical structure and/or embryological development are referred to as being analogous (noun = analogue). Organisms possessing these structures do not derive these structures from a common ancestor.
Describe the characteristics of a homology
- Structural similarity uniquely evolved (due to inheritance from a common ancestor or developed from a common embryonic anlage. The anatomy and development are similar, but function does not have to be similar.
- Of greater interest are those structures found in different organisms that are similar in their anatomical structure and embryological development and that may or may not be similar in function. Such structures are referred to as homologous. These structures are derived from an ancestor common to all organisms possessing these structures. An example to be considered are the set of middle ear bones in the human ear and certain elements of the upper and lower jaws found in fishes.
- Structural similarity in different organisms not due directly to inheritance from a common ancestor or development from a common embryonic anlage.
- Independent development of similar characteristics in lineages that inherit from a common ancestor a potential for such development but do not directly inherit the similar characteristics.
- Independent development of similar characters in two or more lineages even though they receive from the common ancestor neither the adaptations involved not characteristics that channel the development of those adaptations.
Compare paedomorphosis and neoteny and give examples of both
- Larval form does not metamorphose.
- Larval form becomes the adult form.
- Larval form develops gonads and becomes sexually mature.
- Example includes the Amphioxus
- Type of paedomorphosis
- Adult form retains one or more larval characteristics.
- Example includes the gills in salamanders
What geological period did vertebrates first appear. How long ago was this?
Paleozoic Era - Cambrian Period - About 570 million years ago
What were some characteristics of the common ancestor shared between echinoderms and chordates?
- Sessile or semi-sessile.
- Bilateral symmetry.
- Ciliated larval form.
- Ciliary feeders.
How could paedogenesis be used to explain the origin of vertebrates?
- Apart from echinoderms, the echinoderm ancestor appeared to have hemichordates (acorn worms) and stem chordates (or tunicates?) as descendants.
- The primitive tunicates gave rise to modern tunicates. But the larval tunicate forms gave rise to both cephalochordates and vertebrates. The fact that cephalochordates and vertebrates share similarities to these larval tunicates is an indicator of paeodogenesis.
(Can't think of a better way to do this)
Describe The First Half of the characteristics of the Amphioxus
- The most representative member of cephalochordates.
- Found in warm, shallow, marine environments, the body form of both the larva and the adult is elongated, flattened, and tapered at both ends.
- They would burrow into sand so that only their head is exposed and filter microscopic food particles out of the water using a ciliary pump and pharyngeal gill slits.
- Larval forms similar to adults but lack gonads. They lacked paired fins/limbs and jaws, and possessed a well-developed notochord but no vertebral column.
- The cells of the notochord are stacked flattened discs of paramyosin muscle similar to adductor muscles of clams. The notochord extends from the tip of the head to the tip of the tail.
- Nerve cord lies dorsal to the notochord but does not have a cranial enlargement (brain)
Give More Facts about the cephalochordate, amphioxus.
They lack cartilage or bone. There are “V”-shaped muscle segments (myomeres) that flank the notochord and are used for swimming. The cranial end of the animal consists of a conspicuous tubular pharynx equipped with a row of pharyngeal slits on either side. The mouth opens into the pharynx. The gill slits do not open to the exterior but into an internal cavity surrounding the pharynx called the atrium. The atrium opens to the exterior via the atriopore.
- A groove, the endostyle, is located in the floor of the pharynx and secretes a thin film of mucous that covers the inside of the gill slits and traps food particles, conveying them into the intestine from the pharynx.
How many classes of urochordates are there?
What's the most common class?
Three, but we rarely ever talk about two of them. The important one is the ascidiacea, often referred to as a Sea Squirt or Tunicate. As an adult, these are sessile bags of liquid so useless and boring most people thought it was a plant for a while.
- Also, since you asked, the adult doesn't have a notochord or a dorsal hollow nerve tube, but they Do have a Pharynx! So that's cool! Right?
Note: The larva has all three of these.
Describe the adult appearance of the sea squirt/tunicate
Well I can tell you what it Doesn't Look Like: A vertebrate! Or even a chordate! But it does like two short hoses called siphons coming out of it. Passing through it would go Incurrent Siphon into the pharynx with a few filtration slits, into the intestine into the atriopore into the exurrent siphon.
- The Outer Wall of this guy is made of a cellulose-like polysaccharide called TUNICIN. This is unique/rare. Beneath the outer wall/tunic is the Mantle, which has all the dermal epithelium and connective tissue.
- Sea squirts are called that because they shoot water out of both holes. Water is also drawn into the the incurrent siphon using cilliary action.
Bored with Urochordates yet? Good!
Now discuss their digestive tract
You might think it enters through the incurrent siphon. But it doesn't. Instead they enter through those slits in the pharynx and enter into the atrium chamber, which leads out the atriopore and excurrent siphon. Useless stuff and waste material goes right out the atriopore. Food particles stay behind and enter the intestine.
Pointless note: Tunicates start out as larval tadpoles and then go through metamorphosis in order to become their boring selves. The other two (unidentified) urochordates remain in their larval stage until death.
What happens to the urochordate larva during metamorphosis?
Upon finding a suitable substrate, the head of the larva, equipped with adhesive, sucker-like structures, attaches to the substrate.
- The tail then immediately collapses like an accordion, eliminating the notochord and most of the nerve cord.
- The pharynx is expanded considerably and takes up most of the volume of the adult.
- The remnants of the neural tube forms a ganglion in the adult form.
- Gonads then develop and the transformation is completed.
Define a clade (cladistics)
- Phylogenetic systematics is based on evolutionary lineages called clades (thus it is also referred to as cladistics).
- A clade is a monophyletic group made up of an ancestor and all of its descendants.
- These groups can only be identified on the basis of derived characters.
- A character is an anatomical feature of an organism.
- Apomorphies, also called derived characters is a character that differs from the ancestral condition
- Synapomorphies are derived characters that are shared by several lineages
- Plesiomorphies are ancestral characters that are retained by the descendents of the ancestors.
- Symplesiomorphies are ancestral characters shared by more than one lineage.