Chordates
Tunicates
Hemichordates
Echinoderms
Arthropods
Tardigrades
Nematodes
Loricifera
Priapulida
Rotifers
Cycliophora
Annelids
Molluscs
Bryozoa
Brachiopods
Phoronids
Platyhelminthes
Biological diversity
• How many species are there?
• What is the taxonomic and geographical distribution of species number?
– Why do some groups have more species than others?
– Why are some parts of the world more species rich than others?
• What are the major divisions and characteristics of biological diversity?
– Bacteria v Eukaryotes
– Archae v Eubacteria
– Unicellular v multicellular
• What is the time-scale of evolution?
Insecta
751,000 described species
Plantae (Multicellular
Plants)
248,428 described species
Non-insect Arthropoda
(Mites, Spiders,
Crustaceans etc.)
123,151 described species
Mollusca (Mollusks)
50,000 described species
Fungi
46,983 described species
Protozoa
30,800 described species
Algae
26,900 described species
Pisces (Fish)
19,056 described species
Platyhelminthes (Flatworms)
12,200 described species
Nematoda (Roundworms)
12,000 described species
Annelida (Earthworms etc.)
12,000 described species
Aves (Birds)
9,040 described species
Coelenterata (Jellyfish, Corals,
Comb Jellies)
9,000 described species
Reptilia (Reptiles)
6,300 described species
Echinodermata (Starfish,
etc.)
6,100 described species
Porifera (Sponges)
5,000 described species
Monera (Bacteria, Blue-
green Algae)
4,760 described species
Amphibia (Amphibians)
4,184 described species
Mammalia (Mammals)
4,000 described species
Species richness distribution
Purvis and Hector (2000)
Species richness distributions
Purvis and Hector (2000)
Species-number models in ecology and systematics
• Species number reflects random process of speciation and extinction
– Branching process
• Distribution of population sizes likewise is a random process
• Innovations
– Factors such as phytophagy (insects), warm-blooded nature (mammals, birds), flight
(insects, etc.) enable new niches to be occupied
• Distinguishing hypotheses is made difficult by the fact that life has only evolved once
– Though comparing analogous structures (wings, phytophagy) is possible
All partitions are equally likely
Linnaean taxonomic hierarchy
Domain Eukaryota All nucleated organisms
Kingdom Metazoa All animals
Phylum Chordata All animals with backbone
Class Mammalia Warm-blooded milk-producing vertebrates
Order Primates Monkeys and apes
(Super)Family Hominoidea Great apes
Genus Homo
Species sapiens Other spp. (e.g. habilis, erectus, extinct)
• Carl Linnaeus: Swedish naturalist published Systema Naturae in 1735.
Taxonomic difficulties
• Assignment of a taxonomic level really reflects the systematist’s bias
– There is no biological meaning to the taxonomic scheme
• The mammalian order primates (including families, subfamilies and many
genii and species) is younger than the genus Drosophila
• Cladistic nomenclature represents each node of the phylogenetic tree
– BUT there are a lot of internal nodes
Features common to all life
• Replication of DNA/RNA
• Exchange of genetic material
• Cells and cytoplasm (lipid bilayer membrane)
• Gene expression and RNA translation machinery (ribosomes)
• Energy converter (takes in energy and uses it to make ‘order’)
• Evolution….
Excludes viruses
The deep splits
Eukaryota Archaea Eubacteria
KingdomsMetazoaPlantaeProtistaFungi
EuryarhcaeotaCrenarchaeota
ProteobacteriaChlamydiasSpirochaetesGram-positiveCyanobacteria
Prokaryota
Largely unresolved – probably many horizontaltransfer events. Archaea may be polyphyletic
Prokaryote v Eukaryote
Prokaryote
No nucleusSingle coiled chromosome with few associated proteinsBacterial cell wallNo organelles17s RNA
Eukaryote
DNA in nucleusChromosomes with many proteins (histones)No cell wallOrganelles (mitochondria, chloroplasts)18s RNA
Archaea v Eubacteria
Eubacteria Archaea Eukaryota
No histones Histones associated Histoneswith DNA
One RNA polymerase Several Several
Formyl-methionine as Methionine Methioninestart codon
Rare and unusual introns Some splicing introns Spliceosomal introns
The eukaryotes
• Protists
– Unicellular, enormously diverse
– Many important human pathogens (Plasmodium, Giardia)
• Fungi
– Networks of hyphae, saprophytes
– Many important agricultural pests (rusts, smuts, mildew)
• Plants and green algae
– Generate energy through photosynthesis (chlorophyll)
• Animals
– Consumers
ciliate dinoflagellate diatom Green alga
Red algaChlorarachniophyte
Euglena
Endosymbiosis
• Mitochondria and chloroplasts are descendants of bacteria that lived within the cells of early
eukaryotes
– Have their own genomes (circular)
– Have prokaryote-like ribosome subunits and membrane proteins
– No histones
– Most genes lost or migrated to the nucleus
• Other symbioses at earlier stages
– Tryptophan producing Buchnera in aphids
– Rhizobium nitrogen fixing in legumes
– Wolbachia
Mitochondriafromproteobacteria
Chloroplastsfromcyanobacteria
Specialisations of multicellular life
• Differentiation of cell types
• Coordinated development
• Self / non-self recognition
Platyhelminthes(flatworms, tapeworms, flukes) Mollusca
(snails, clams, squid)Annelida(worms, leeches)
Arthropoda(insects, crustaceans, millipedes)
Echinodermata(starfish, sea-urchins, sea-cucumbers)
Chordata(fish, amphibians, reptiles, birds, mammals)
Loricifera Tardigrade Bryozoa
Brachiopods Nemertea Micrognathozoa
Colonial life
Siphonophore Sponge
Grades of body plan
Cell layerNon-living tissue/space
Third layer can differentiate to provide internal organs
Two-layerCnidariaCtenophoresPlatyhelmintes
Pseudo-coelomatesNematodesRotifers
CoelomatesMolluscsAnnelidsEchinodermsChordates
Specialisations of animals
• Specialised cell types (nerves, muscles)
• Motility (as oppose to mobility)
• Self / non-self cell recognition
– Immune systems
• Individual-individual communication
– Chemical, visual, olfactory, auditory
• Social organisation
Polyploidy of early vertebrates
Ancestral vertebrate and all invertebrates
First round of polyploidisation (Amphioxus?)
Second round of polyploidisation
Differentiation, loss and rearrangement of genes
Plant groupsLiverworts
Mosses
Club-mosses
Ferns
Cycads
Conifers
Ginkgos
Welwitschia
Flowering plants
Relative genome size: prokaryotes
Organism Genome size (Mb) Gene number
E. coli 4.6 4288
Mycoplasma genitalium 0.58 470
Buchnera spp. 0.64 583
Chlamydia pneumoniae 1.23 1052
Salmonella typhi 4.8 4600
Methanococcus jannaschii 1.67 1682
Yersinia pestis 4.65 4012
Relative genome sizes: eukaryotes
Genes reported [1]
Predicted genes
Genome kilobases
Fruitfly 25,728 35% 116,109
Human 30-40,000 61% 3,118,900
Mouse 24,948 (an extra 94,075) --
Mosquito 12,687 91% 231,408
Arabidopsis 28,129 -- 117,429
C. elegans 22,705 78% 100,270
Yeast 7,222 32% 12,156
Zebrafish 20,062 -- --
source: euGenes
The C value paradox
• Haploid DNA content in a cell can be measured by flow cytometry
• In multicellular eukaryotes, there is no correlation between gene number and DNA
content of cells
– Drosophila 0.18
– Human 3.19
– Grasshopper 13.4
– Lungfish 140
• What is the value of the extra DNA?
– Nuclear volume: more DNA correlates strongly with larger cells
– None: DNA is a self-promoting opportunist which naturally increases unless
checked by the time and energy demands of replication and transcription
– (transposons, introns, LINES, SINES)
Geological eras and epochs
Time-line of life on earth
Origin of life
3800MY
Multicellularlife
1000MY
Cambrianexplosion
530MY
First landplants
First vertebrates
2500MY
Oxygen appears
410MY
First insects
Time-line of life on earth II
Firsttetrapods
360MY
FirstPrimates
60MY
Chimp/Humansplit
Modernhumans
5MY 0.1MY
Firstbirds
170MY
K/Textinction
100MY65MY
FirstMammals
Age of thedinosaurs
210MY
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