|
List the two objectives of Phylogenetics |
|
a)To understand how one animal evolves from another.
b) To discover the relationships of kinds of animals |
| |
|
Define, "kind" |
|
A kind is a phylum. A phylum represents animals having the same fundamental body plan. |
| |
|
List the two traditions of phylogenetics |
|
- Use objective (a) to derive objective (b): This represents the classical approach via the study of morphology and development.
- Use objective (b) to derive objective (a): This represents the modern approach via study of DNA sequence
|
| |
The Classical approach:
-Main assumption?
-Commonly used features?
|
|
-Fundamental aspects of body plan are unlikely to have arisen independently in different lines of descent.
-Features: Body symmetry, coelom presence, mode of coelom formation, segmentation, number of germ layers, early embryonic development, etc.
|
| |
The Classical approach cont:
-Main trends?
|
|
Main line of metazoan evolution has invovled an increase in complexity through the addition and elaboration of features.
-Radial->Bilaterial->cephalized
-Acoelomate->psuedocoelmoate->coelomate
-Gastric cavity->through-gut
-diploblastic->triploblastic
-Cell groups->tissues->organs
-Open body cavity->segmentation
|
| |
Acoelomate->psuedocoelomate->coelomate:
-Define. Provide example.
-List features from exterior->interior.
|
|
-Acoelomate:Have no body cavity at all. Organs have direct contact with the epithelium. Semi-solid mesodermal tissues between the gut and body wall hold their organs in place. E.g. Flatworms.
-Psuedocoelomate:fully functional body cavity. Tissue derived from mesoderm only partly
lines the fluid filled body cavity of these animals. Thus, although
organs are held in place loosely, they are not as well organized as in
a coelomate. All pseudocoelomates are protostomes; however, not all protostomes are pseudocoelomates. E.g. roundworm.
-Coelomate:have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm (one of the three primary tissue layers).
The complete mesoderm lining allows organs to be attached to each other
so that they can be suspended in a particular order while still being
able to move freely within the cavity. Most bilateral animals,
including all the vertebrates, are coelomates. |
| |
|
Describe the evolutionary advance of tissue organization as defined by classical approach |
|
See image |
| |
Classical phylogeny (Adouette)
-Place the following on the phylogeny:
Bilateria, Radiata, Acoelomate, Psuedocoelomate, Coelomate, Protostome, Lophophorate, Deuterostome
|
|
See image |
| |
Classical phylogeny (Halanych 2004)
-Place following:
Metazoa, Bilateria, aschelminthes, deuterostomia, protostomia; Mesozoa, Porifera, coelenterata, chordata, lophophorata, articulata, athropoda
|
|
See image
|
| |
Main features of classical phylogeny: Porifera
-Monophyletic and basal, criterion? |
|
Cellular grade of construction |
| |
Main features of classical phylogeny: Coelenterata
-Sister group of bilateria, criterion?
|
|
diploblastic tissue grade |
| |
Main features of classical phylogeny: Platyhelminthes
-Basal bilateria, criterion?
|
|
Solid body lacking coelom |
| |
Main features of classical phylogeny: Aschelminthes
-Sister group of coelomates, criterion?
|
|
Pseudocoelomates: Body cavity not lined with mesoderm |
| |
Main features of classical phylogeny: Coelomates -Protostomes and Deuterostomes are the 2 monophyletic groups of coelomates, criterion?
|
|
Mode of cleavage, blastopore fate, coelom formation |
| |
Main features of classical phylogeny: Deuterostomes
-Echinoderms and lophophorates are deuterostomes, criterion?
|
|
Blastopore fate |
| |
Main features of classical phylogeny: Articulata
-Annelida and Athropoda form clade Articulata, criterion?
|
|
Segmentation |
| |
Molecular approach to phylogeny:
-Define. Strengths? Weaknesses?
|
|
-Infer phylogeny from obtained DNA sequences
-Strengths:4 unambiguously scored characters (i.e. ATCG), characters common to all organisms, characters represent directly the transmission of genetic info
-Weaknesses:Sporadic sampling, liability to artefact, drawing of implausible scenarios
|
| |
Modern phylogeny
-Place the following:
Metazoa, Bilateria, Deuterostomia, Lophotrochozoa, Ecdysozoa; Sponges, Chordata, , Arthropoda; Ambulacraria, Gnathifera, Panarthropoda, Nematoida, Scalidophora; Platyzoa
|
|
See image |
| |
|
New features of modern phylogeny? |
|
-Porifera is basal but may be paraphyletic
-Cnidaria is sister group of bilateria:Coelentera is invalid. Position of ctenophora and placazoa is uncertain.
-Platyhelminthes is derived protostome group: acoeloa prolly basal bileterian; platyhelminthes prolly polyphyletic
-Deuterostomata confirmed to consist of Tunicata+Chordata+Echinodermata; Lophophorates are not deuterostomes.
-Protostomia=Lophotrochozoa+ecdysozoa:elimination of articulata and coelomata->implies separate origins of segmentation.
-Platyzoa replaces aschelminthes and places acoelomate and psuedocoelomate as clade within lophotrochozoa: If acoelomate condition primitive in bilateria, imply that coelom arose independently in protostomes and deuterostomes.
-New major clades (eg syndermata, scalidophora etc)
|
| |
Overview of Halanych's modern phylogeny
-Place following groups:
Arthropoda, Annelida, Chordata, Choanoflagellata, Cnidaria, Echinodermata, Nematoda, Mollusca, Platyhelminthes, Porifera,
|
|
See image. |
| |
|
apomorphy |
|
A character state derived by evolution from an ancestral state (plesiomorphy). A novel evolutionary trait.
Also see synapomorphy, autapomorphy |
| |
|
plesiomorphy |
|
An ancestral character state. A trait from which an evolutionary novelty (apomorphy) is derived.
Also see symplesiomorphy. |
| |
|
symplesiomorphy |
|
A shared ancestral character state (plesiomorphy). A trait that is shared by two or more groups due to inheritance from a distant common ancestor.
Symplesiomorphies are common to all the descendants of a distant common ancestor, and they cannot be used to infer close evolutionary relationships between subsets of these descendants. |
| |
|
synapomorphy |
|
A shared derived character state (apomorphy). A novel evolutionary trait that is shared by two or more groups due to inheritance from an immediate common ancestor.
Synapomorphies are used by phylogenetic biologists to infer close evolutionary relationships between organisms. |
| |
|
autapomorphy |
|
A uniquely-derived character state. An apomorphy that is unique to a single terminal taxon.
Compare to synapomorphy.
|
| |
|
monophyletic: (monophyly) |
|
A group of organisms that includes their most recent common ancestor and all of its descendents. (cf. paraphyletic, polyphyletic) |
| |
|
paraphyletic: (paraphyly) |
|
A group of organisms that includes their most recent common ancestor and some but not all of its descendents. (cf. monophyletic; technically speaking, the distinction between polyphyletic and paraphyletic is not as clear as it might seem.) |
| |
|
polyphyletic |
|
A group of organisms that does not include their most recent common ancestor. (cf. monophyletic; technically speaking, the distinction between polyphyletic and paraphyletic is not as clear as it might seem.) |
| |
|
polytomy: (polytomies) |
|
A branch point on a tree that has more than two immediate descendents.
-Could represent a lack of knowledge.
-Or, Rapid speciation.
|
| |
