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
Algae
Reptilia (Reptiles)
751,000 described species
26,900 described species
6,300 described species
Plantae (Multicellular Plants)
Pisces (Fish)
Echinodermata (Starfish, etc.)
248,428 described species
19,056 described species
6,100 described species
Non-insect Arthropoda (Mites,
Platyhelminthes (Flatworms)
Porifera (Sponges)
Spiders, Crustaceans etc.)
12,200 described species
5,000 described species
123,151 described species
Nematoda (Roundworms)
Monera (Bacteria, Blue-green
Mollusca (Mollusks)
12,000 described species
Algae)
50,000 described species
Annelida (Earthworms etc.)
4,760 described species
Fungi
12,000 described species
Amphibia (Amphibians)
46,983 described species
Aves (Birds)
4,184 described species
Protozoa
9,040 described species
Mammalia (Mammals)
30,800 described species
Coelenterata (Jellyfish, Corals, Comb
4,000 described species
Jellies)
9,000 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
All partitions are equally likely
•
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
Linnaean taxonomic hierarchy
•
Carl Linnaeus: Swedish naturalist published Systema Naturae in 1735.
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)
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
Largely unresolved – probably many horizontal
transfer events. Archaea may be polyphyletic
Prokaryota
Eukaryota
Kingdoms
Metazoa
Plantae
Protista
Fungi
Archaea
Euryarhcaeota
Crenarchaeota
Eubacteria
Proteobacteria
Chlamydias
Spirochaetes
Gram-positive
Cyanobacteria
Prokaryote v Eukaryote
Prokaryote
Eukaryote
No nucleus
Single coiled chromosome with few
associated proteins
Bacterial cell wall
No organelles
17s RNA
DNA in nucleus
Chromosomes with many proteins (histones)
No cell wall
Organelles (mitochondria, chloroplasts)
18s RNA
Archaea v Eubacteria
Eubacteria
Archaea
Eukaryota
No histones
Histones associated
with DNA
Histones
One RNA polymerase
Several
Several
Formyl-methionine as
start codon
Methionine
Methionine
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
Chlorarachniophyte
Euglena
ciliate
Red alga
dinoflagellate
diatom
Green alga
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
Mitochondria
from
proteobacteria
•
Other symbioses at earlier stages
– Tryptophan producing Buchnera in aphids
– Rhizobium nitrogen fixing in legumes
– Wolbachia
Chloroplasts
from
cyanobacteria
Specialisations of multicellular life
•
Differentiation of cell types
•
Coordinated development
•
Self / non-self recognition
Platyhelminthes
(flatworms, tapeworms, flukes)
Arthropoda
(insects, crustaceans,
millipedes)
Mollusca
(snails, clams, squid)
Echinodermata
(starfish, sea-urchins,
sea-cucumbers)
Annelida
(worms, leeches)
Chordata
(fish, amphibians,
reptiles, birds, mammals)
Loricifera
Brachiopods
Tardigrade
Nemertea
Bryozoa
Micrognathozoa
Colonial life
Siphonophore
Sponge
Grades of body plan
Non-living tissue/space
Cell layer
Two-layer
Cnidaria
Ctenophores
Platyhelmintes
Pseudo-coelomates
Nematodes
Rotifers
Coelomates
Molluscs
Annelids
Echinoderms
Chordates
Third layer can differentiate to provide
internal organs
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 groups
Liverworts
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
Oxygen appears
Multicellular Cambrian
life explosion
First land
plants
First
insects
First
vertebrates
3800MY
2500MY
1000MY 530MY
410MY
Time-line of life on earth II
First
tetrapods
Age of the
dinosaurs
First
birds
First
Mammals
360MY
210MY 170MY
First
Modern
Primates humans
K/T
extinction
100MY
60MY
65MY
Chimp/
Human
split
5MY
0.1MY