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