Introduction to phylogenetics, the protostomes and the deuterostomes Flashcards
Define a clade.
A monophyletic group, including a common ancestor and all its descendants.
Define a paraphyletic group.
A common ancestor and some of its descendants.
Define a metazoan.
A multicellular eukaryote, an ‘animal’.
When do the metazoans originate from?
The Cambrian Explosion.
When was the Cambrian explosion?
540mya
Define a heterotroph.
An organism that derives its nutrients from complex organic sources.
Approximately how many metazoan phyla are there?
~30-40
How many species of metazoan are there?
~1.3million.
What proportion of metazoans are insects?
2/3
What percentage of all metazoans are coleoptera (beetles)?
1/4.
Approximately how many species of mammal are there?
4000
What kind of data is the new animal phylogeny based on?
Molecular
What kind of data were old style cladograms based on?
Morphological data from the fossil record and living specimens.
What are 2 benefits of using morphological data?
- Helps us to group animals for which we cannot get any DNA
- Helps us to determine ancestral states
Morphological and molecular data are now used in combination with each other. True or false?
True.
What are the 2 categories of metazoan?
- Bilateria
2. Non-bilateria
Define a bilaterian.
An organism with bilateral symmetry and 3 germ layers.
Define cephalisation.
The concentration of sensory organs and nervous control at the anterior of the animal.
What are the most basal metazoans?
Ctenophores (comb jellies)
It is thought that ctenophores evolved muscles and neurons by parallel evolution to the rest of metazoa. What does this mean?
Where the same trait evolves in distinct but related groups that descend from the same ancestor.
The bilaterians are split into the protostomes and deuterostomes. What 2 groups make up the protostomes?
- Lophotrochozoa
2. Ecdysozoa
Which forms first in protostomes, the mouth or the anus?
The mouth forms first from the blastopore.
What kind of cleavage do protostomes have?
Spiral cleavage
In protostomes, the mesoderm is formed by…?
Schizocoely.
The bilaterians are split into the protostomes and deuterostomes. What 2 groups make up the deuterostomes?
- Ambulacraria
2. Chordata
What groups make up the ambulacraria?
The echinoderms and hemichordates.
The larvae of echinoderms have bilateral symmetry. What kind of symmetry do the adults have?
Pentaradial
What are the skeletons of echinoderms made from?
Their skeletons are calcitic and made from CaCO3 (calcium carbonate)
What is ‘stereom mesh’?
The structure of echinoderm skeletons.
Pharangial slits (gill slits) are typical of all chordates. True or false?
True.
Which gene controls the formation of pharangial slits?
Patch19
Where is patch19 expressed?
In the developing gills of chordates and during the gill patterning of hemichordates.
Which 3 groups make up the chordates?
- Cephalochordata
- Urochordata
- Vertebrata
In the deuterostomes which forms first, the mouth or anus?
The anus forms from the blastopore.
What kind of cleavage do deuterostomes undergo?
Radial.
In deuterostomes the mesoderm is formed by…?
Enterocoely.
Deuterostomes have trimery. What does this mean?
3 fluid-filled coeloms.
The echinoderms are the most primitive bilaterian clade. Which was the next to evolve?
The hemichordates.
Which was the last of the 3 major bilaterian clades to evolve?
Chordata.
The echinoderms and hemichordates are largely motile. True or false?
False - they are mostly sessile (sedentary).
How many taxa of echinoderms are there?
5
How many taxa of hemichordates are there?
2
Most chordates have a notochord to protect their dorsal hollow nerve chord. What are the vertebrate equivalents of these?
A backbone protecting the spinal cord.
Within the chordates, which group is more closely related to the vertebrates?
The urochordates.
Why was it previously thought that vertebrates were more closely related to the cephalochordates? What does this say about urochordates?
They both have fish-like larval stages. Urochordates may also have had a fish-like larval stage that has been lost in regressive evolution.
Urochordates display multiple instances of regressive evolution. Give an example.
They have lost some HOX genes.
What is characteristic about the dorsal-ventral axis in both invertebrates and vertebrates?
Invertebrates have their hollow nerve cord/notochords on the ventral side, whereas it is on the dorsal side of vertebrates.
The xenoturbella and acoelomorpha were both misclassified as what group?
Platyhelminthes, which are protostomes.
Xenoturbella and acoelomorpha underwent DNA analysis and were then classified as molluscs. Why was this wrong?
The mollusc DNA came from their stomach contents.
Now, after mtDNA anaylsis, what are xenoturbella and acoelomorpha both thought to be? Why is this controversial?
Deuterostomes, but xenoturbella is missing the patch19 gene that determines the pharangial slits in chordates.
Scientists are unsure where Chaetognaths should be placed as they have a) deuterostomic and b) protostomic qualities. What are they?
a) Radial cleavage and enterocoely
b) The NAD5 gene in mtDNA
Lophophorates are now classified with the protostomes. Why was it previously thought they were deuterostomes?
They possess a lophophore feeding structure, similar to that in hemichordates which are deuterostomes.
How was it confirmed that lophophorates are in fact protostomes?
The possess a NAD5 gene
The pogonophores were thought to be deuterostomes because they display trimery. Why was this wrong?
Pogonophores actually have 20+ coelomic cavities, much like protostomic annelids, however most of these are hidden in the substrate.
How must the binomial name of organisms be written?
In italics.
How can you identify a word is indicative of a family?
It ends in -ae
What is phylogenetics?
The sistergroup relations between taxa based on their genetics, i.e. how closely related they are
When do phylogenetic trees date back to?
1837.
Define cladistics.
The study of shared physical and morphological characters.
What is sexual dichromatism?
A difference in colour/patterning between the sexes.
In phylogenetics, what is the root of a tree?
The ancestor of all the organisms in that tree.
In phylogenetics, what is an internal node of a tree?
Hypothetical ancestors, where 2 branches connect.
In phylogenetics, what are the terminal nodes?
The most recent organism in the tree where a lineage ends.
If a tree is fully resolved, what does this mean about the relationships?
There is complete certainty of the relationships.
If a tree is partially resolved, what does this mean about the relationships?
There is some doubt.
Define polytomy.
Where a node splits into more than 2 branches.
There are 2 types of polytomy. What are they? Explain them.
- Hard: a simultaneous speciation event where there is complete certainty of relationships
- Soft: unsure of the relationships between organisms
Define a synapomorphy.
A shared derived character, displayed by the ancestor and all its descendants.
What is an ultrametric tree?
One where the time scale is indicated.
Define a plesiomorphy.
An ancestral morphology that has been lost in some of the descendants.
Define an autopomorphy.
A unique character state used for identification.
Define a homoplasy.
Homologous characteristics resulting fom convergent evolution. ‘The same feature from a different ancestral morphology’.
Why are homoplasies misleading?
They make it look like organisms are related when they aren’t.
