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BIOS 2061 Lecture NotesMain Ideas Evolution and Introduction to the Vertebrates Evolutionary Model  Not a theory2 Core Concepts: 1. Life originated spontaneously from non-life 2. New kinds of life can and did originate from pre-existing kinds by:  Mutations  Natural selection Tested in 3 differen...

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BIOS 2061 Lecture Notes Main Ideas

Evolution and Introduction to the Vertebrates

Evolutionary Model

2 Core Concepts:



Not a theory

1. Life originated spontaneously from non-life 2. New kinds of life can and did originate from pre-existing kinds by: 

Mutations



Natural selection

Tested in 3 different ways: 1. By experiments with simulated pre-biotic conditions on Earth 2. Studies of Earth’s living creatures Mutations

3. Studies of Earth’s prehistoric creatures 1. New variations arise as genetic mutations but most are ‘neutral mutations’ and hence not immediately acted on by natural selection Eg. 200+ mutant forms of Haemoglobin molecule in humans alone, but as long as mutations don’t interfere with heme group, there will be no negative impact on the owner of the mutation 

Some mutations can be harmful to the specie (not normally passed on)



Some single mutations (eg. Hox gene Antennapedia) are not very adaptive but an indication of the ability of a single gene mutation to cause major changes in body form

2. Evidence that natural selection can change the frequency of different genetic variations? 

All factors determine which young survive to reproduce are called ‘natural selection’



There are 3 basic kinds of natural selection o

Random or accidental natural selection: may have nothing to do with th relative ‘fitness’ of the particular individuals who survive

o

Directed natural selection: such that it drives change in the population eg. Peppered Moth

o

Natural selection can be a stabilizing force that works to stop evolutionary change that would otherwise reduce the fitness of a welladapted population in a stable environment

3. Evidence to support new species developing as a consequence of mutations/natural selection 

Mechanism must lead to reproductive isolation eg. Geographic barriers such as rivers, mountains or deserts and/or tectonic plates o

Plate Tectonics: last 225M years of Earth mindlessly messing with vertebrate distributions

o

Ecological isolation: Rhagoletis Pomonella (Apple Maggot Flies): 1. Hawthorn fruit fliy: fly’s natural food ripen in August 2. Apples: introduced to North America in 1765 and ripen in July 3. By 1865 apples became infested 4. Now are 2 different kinds of Apple Maggot Flies, one that eats Hawthorn and breed in August, and one that eats Apples and breeds

in July o

Chromosomal Speciation (aneuploidy): new species can result from chromosomal mutations without natural selection driving it – 47% of

Other Evidence of

flowering plants appear to have originated this way Comparative Morphology: Vertebrates comes from the basic common body



plan found in all of them,

Evolution

o

Eg. Forelimb of all vertebrates has the same basic structural elements because they were inherited from a CA

Comparative Embryology: developmental paths and patterns in all vertebrate



o

Eg. Ear region of mammals develops in a way that clearly reflects the descent of mammals from reptiles

‘Missing Links’: unite different but hypothetically related kinds of animals and



plants o

Eg. Porbainognathus and Diarthrognathus are double-jawed missing links between modern reptiles and modern animals. Both had condition that is new dentary/squamosal (mammal) jaw joint as well as the old quadrate/articular (reptile jaw system

Testing the Model

o

Fish/Amphibian Link: Tiktaalik Rosae 375MYO

o

Land-dwelling mammals and modern whales: Ambulocetus

o

Lizard and snakes: primitive Cretaceous snake from Brazil Tetrapodophis

o Human and Chimp: Australopithecines There is still debate about how fast new species can evolve Two different processes 1. Gradual Speciation 2. Punctuated Equilibrium 

Rapid speciation event



Rapid change in shape



Long period of ‘stasis’ Approx. 55,000 living vertebrates



Approx. 1000x that amount are extinct



Radiated over the last 500MY



Now 12 unique radiation

 Who are Vertebrates

5 Foci in this course 1. Chordate Ancestors (pre but not vertebrates) 2. ‘Fish’ then and now 3. ‘Amphibians’ and ‘Reptiles’ 4. Birds Phylum Chordata Contains vertebrates

Archaic Chordates

5. Mammals – origins and early groups, monotremes, marsupials, placentals Share unique derived ‘vertebrate-like’ features 

Notochord, hollow nerve cord, pharyngeal gill slits, post-anal tail



Features are often evident only in the larval stage

 These features earmark them as ‘photo-vertebrates’ Stiffening rod along their backs Emu Bay, Kangaroo Island, South Australia all have approx. 55MYO Vetulicolians aka ‘Blind Flappers’ (some also found in Canada and Greenland

Case Study: Cephalochordates: Lancelets (Amphioxus) 

Only 22 species world-wide (8 in Australia)



5cm long, mud-burrowing, filter-feeders fish like body shape as adults



Live several kms off-shore so are rarely encountered

Cephalochordate

 

Name refers to notochord extending into the head region V-shaped myomeres (muscle blocks)

Features



Dorsal nerve-cord



Notochord-supports myomeres, helps burrowing



Simple eye; no brain



Respiration by diffusion



Pharyngeal gills used for filter-feeding – food is retained and passed back to intestines; water is extruded through slits to atrium and out via the

Shared Features with other chordates

atriopore (not the anus) Shared anatomical features 

Segmented muscle blocks along body



Blood moves ventral to dorsal through gills



Metameric gill arches



Caudal tail fin

Reasons why they evolved 

Urochordates

Increased mobility: o

Able to find new areas for food and breeding

o

Escape predators



o Catch prey Name means notochord in tail region only



Have the defining chordate features (notochord, dorsal nerve cord and pharyngeal slits)



Chordate traits often occur in larval form only; adults are very different



Approx. 1300 species worldwide



3 orders 1. Ascidiacea 2. Thaliacea 3. Larvacea



Ascidians are most common and diverse

Case Study: Haikouichthys

Vertebrate Chordates



530MYO



Oldest known chordate, craniate (has a head) and maybe first vertebrate

 Has a head, notochord, gill slit and post-anal tail Differ from lancelets in that: 

Gills are used for respiration, not for filtering food



Hemoglobin in blood



W-shaped muscles



Heads and sense organs



Digestive organs (liver, pancreas, etc)



Kidneys used for osmoregulation

Probably adaptive reasons: 

Increased ability to get food



Increased awareness of world



Better use of food



Salt-control = world domination?



Vertebrates have vertebrate and cranium (usually fused anterior vertebrae) – the cranium encloses the brain and sense organs



Unique embryonic tissue: the ‘neural crest’ – develops into range of

specialised vertebrate tissues Classification and Cladistics Jawless Fish



80 species worldwide



Agnathans



Hagfish and lampreys



Hagfish



Most primitive vertebrates



Sediment feeders and parasite



Changed little in last 500MY

 

3 hagfish and 6 lampreys in Australia 900 species worldwide



400 sharks, 450 rays, 50 ratfish



Cartilaginous skeletons



Features are 450MYO

 

200 sharks and 117 rays in Australia Comprise 50% of all vertebrate species



Name means ‘ray finned’



From seahorses to marlin



Radiated c. 400MYA

 

4000+ species in Australia Includes lungfish, probably precursors to land animals



Diverged from other fish – c. 410MYA

 

Only 8 extant species (1 Australian) Salamanders, frogs, caecilians



4600 species



Semiaquatic with metamorphic phase



Tetrapod body plan



Permeable skin

 

200+ species in Australia 260 living species



Appeared c. 250MYA



Semi-aquatic



Amniotic egg



Unique shell (modified bone) and skeleton

 

21 species in Australia 4500 species



Began to radiate c. 245MYA



Diapsid skull (2 temporal openings)



Australia has high diversity



800 species in Australia

Sharks and Rays 

Chondrichthyes

Ray-Finned Fish 

Actinopterygii

Lobe-Finned Fishes 

Sarcopterygii

Amphibians

Turtles 

Chelonia

Snakes and Lizards 

Lepidosaurs

Crocodiles and



21 species (2 Australian)

Alligators



Part of the archosaur group, includes dinosaurs and birds

 Crocodilia Birds

 

Very ancient features 9700 species



Best studied group



Also part of the archosaur group



First birds appeared c. 200MYA

 

770 species in Australia 4500 species in world



First mammal appears c. 220MYA



3 modern radiations



Aves

Mammals 

Mammalia

1. Monotremes 2. Marsupials 3. Placentals How to Classify the Vertebrates

Classification System

 285 species in Australia, most unique Species are all interrelated through evolutionary processes 

Share common ancestors



Share many common traits

What classification system can reflect natural, evolutionary and interrelationships?  Linnaeus’ 1758 binomial nomenclature, genus and species for 10,000 species

we have

o 

Eg. Homo Sapiens Linnaeus, 1758

Expanding into the 7 groupings: o

Kingdom, phylum, class, order, family, genus, species

o

Known as Linnaean systematics



Genus and species names ITALICS or UNDERLINE



Genus name starts with Upper Case



Species name always lowercase

Limitations of Linnaean System 



Groupings created subjectively o

Regardless of ancestry

o

Evolutionary relationships are not considered

o

All traits treated equally no matter how they arose

Doesn’t always reflect natural groupings o

Eg. Reptilia (crocodiles and lizards

Linnaean System and Phenetics 

Compares numbers of shared characters



All traits treated equally

Problem with Phenetic Approach 

Doesn’t reflect/consider evolutionary processes



Huge numbers of characters required to uncover likely relationships



Can’t distinguish traits that have evolved more than once i.e. Convergent

Classification System



evolution Should recognize that some species evolved at different rates

we need



Should avoid grouping based on superficial similarities

Cladistics/Phylogeneti

 

Should group together animals that are most closely related Developed in 1950s by Willi Hennig

c Systematics



Identifies lineages derived from a single ancestor



Recognizes special traits that define groups



Creates phylogenetic trees like family trees which clearly identify common ancestors Systematics should reflect relatedness alone i.e. systematics should be



phylogenetic Unambiguous definition of relatedness:



o Monophyletic



Groups/Clades

Two taxa are more closely related to each other than either is to anothe

taxon if they share a more recent common ancestor A group comprising an ancestor and all (and only) its descendants = monophyletic group or a clade



Phylogenetic systematics attempts to identify monophyletic groups/clades -> aka CLADISTICS



Branching diagrams illustrating this = CLADOGRAMS

Examples of Monophyletic Groups - MAMMALS: 

Primates



Amniota



Tetrapoda



Vertebrata



Animalia

 Paraphyletic Groups



Eukaryote A group comprising an ancestor and only some of its descendant = PARAPHYLETIC



Often indicated by inverted commas

Examples of Paraphyletic Groups – ‘REPTILES’: 

‘Reptilia’ would be monophyletic if birds are also ‘reptiles’, but this contradicts traditional usage

Traditional Vs Cladistic Classification

Polyphyletic Groups

A group that 

does not include its MRCA and all its descendants



includes descendants of several fidderent MRCASs

Are POLYPHYLETIC 

Usually comprise taxa that have convergently evolved similar adaptations

Examples of Polyphyletic groups – ‘EDENTATES’: 

Aardvark



Sloth



Anteater



Armadillo

What is a character

 Pangolin Any variation between individuals and taxa may be considered as characters to be

Characteristics

used in reconstructing phylogeny – morphological, behavioural, physiological, biochemical, genetic/molecular 

A character state (trait) is a particular version of that character o

Terminology for Traits

E.g. The character ‘horns’ may have the character state of ‘straight’,

‘curly’ Abomorphic

Character States



Different from ancestral state (derived)

Plesiomorphic 

Ancestral state

Homologous 

Similar traits with single evolutionary lineage

Homoplasy (analogous) 

Similar traits with more than one evolutionary path

Synapomorphy = shared derived trait 

Characterise monophyletic groups/clades



Are evidence of relationships

Some synapomorphies among vertebrates 

Vertebral column



Jaws



Four walking legs



Amniotic egg

 Distinguishing Derived



Traits

Hair Comparison with outgroup o



Outgroup branched off earlier so should have ancestral characters

Embryonic development o

Primitive state shown in development e.g. cartilage in fish, gill slits in humans



Fossil record o

Character Polarity



Distinguishing Derived

Ancestral states found in earilier forms and older rock

Only commonly used criterion today is the ‘outgroup criterion’: o

Traits

A character state that occurs in a taxon (outgroup) outside group of interest (ingroup) is plesiomorphic (‘primitive’)

The Out group Criterion in Action 

Eg. is egg laying (monotremes) or live births (marsupials and placentals) plesiomorphic for mammals o

Implications of

Outgroup = birds, crocodiles, turtles, lizards

o THUS eggs are plesiomorphic for mammals Cladistics can give ‘unexpected groupings’



Lungfish more closely related to cows than trout



Crocodiles more closely related to birds than skinks

 

Linnean ‘teptiles’ and ‘fish’ are not recognised Cladograms are hypotheses of evolutionary relationships



Constantly challenged and improved by new data

Cladistic approach

Considerations

o

New morphological analyses

o

New fossils

Fish 1

o New DNA analyses Jawless, Jaws and the Sharks

Phylum Chordata

Subphylum Cephalochordata 

Amphioxus

Subphylum Urochordata (Tunicata) 

Ascidians (sea squirts)



Thaliaceans (salps)



Larvaceans (larvaceans, appendicularians)

Agnathan Craniates (Subphylum Vertebrata) 

Lampreys and hagfish



Ostracoderms (extinct) and conodonts (extinct)

 Extant Agnathans



Armoured, jawless fish, wobbling over the sea floor Lampreys



Hagfish



Very different vertebrates



Separated a long time ago



No vertebrae (but necessary genes)

 

Very specialised (derived/evolved) from parasitic condition Parasites as adults



Ammocetes



In rivers



Filter-feeders

 

Step-up from Branchiostoma Not an eel due to lack of jaw



No paired fins



In deep oceans, lots of slime



Consume rotting flesh



Nevertheless clues to possible evolution of a jaw (mandible) from ‘gill arch’

Major step in



or pharynx Use the supports for the first gill slit as a mandible (‘mandible’ = lower jaw)

derivation of



‘mandibular arch’ = eupper and lower jaws