BIOL112 midterm test: Evolution

define biological evolution

changes in species over time, with or without formation of new species

what are the 2 main versions of evolution

how do these differ

macroevolution

• change in species over time (to form new ones) - at the scale of different forms of life

• associated with long time periods, slow changes, and evidence from fossils to show intermediates

microevolution

• change in gene pools over time (not nesecarily forming new species) - at the scale of differences between population members

• associated with shorter time periods, and very small changes in the genome with effects on the species

what is an alternate theory of life origin from evolutionary theory?

• special creation

• theorises that things were created as we see them, that species were created seperately, and do not change

• relies on the belief that earth, and life on it, is young

what is the theory of evolution

• theory that explains the diversity / history of life on Earth, through ‘descent with modification’ - the idea that species change with time, and derive from common ancestors, sucessively changing in a lineage, gradually deviating from ancestral species

• so suggesting modern life is a product of long past evolution

• relies on the belief that Earth, and life on it, is old

• can be tested based on evidence, so is backed by / based on, facts collected from the 19th century onwards (when the idea took off)

• leads to testable predictions about future changes of species

define Anagenesis & Cladogenesis

how do these differ

• these are two models of evolution proposed by evolutionary theory, to explain diversity of species seen today

• anagenesis is changes in one lineage, one species changing to another, through progressive change (modern species deviating more and more over time from ancestors)

• cladogenesis is splitting of an evolving lineage, one species developing into multiple distinct lineages (modern species lineages merge tracing back, until eventually one lineage - LUCA, common ancestry)

what are the levels of organisation that evolution can be looked at in

• DNA sequences, molecules, cells, organisms, populations, ecosystems

• no matter the level, underpinned by changes of genotype

• considered independently

define phenotype

provide an example

• the sum of an organism’s observable characterisitcs / specific characteristics

• influenced by both genotype AND environment (but mostly due to interactions between the two)

• e.g.human skin colour - influenced by genotype, but can change with UV light

define fitness in terms of evolution

• how good a particular genotype is at remaining in the next generation of offspring, relative to other genotypes

• so reproductive sucess and survival success of alleles and genotypes

define adaptation in terms of evolution

why is this idea important to the theory of evolution

• a trait of an organism, evolved over time via natural selection, due to this trait increasing the expected long-term reproductive success

• central to ‘descent with modification’ (it is the modification) - a key element of evolutionary theory

what is an example of current microevolution in a species

what is causing this

• climate change is causing microevolution in many species, as they adapt to the increasing temperature - this increases reproductive & survival success for different alleles than previously favored

  e.g. Eurasian Great Tits

• nesting time is temperature-dependent, to ensure hatching is timed with appearance of caterpillars (main food source for chicks)

• however, the caterpillars are more successful at tracking warmer temperatures due to climate change (have done microevolution to appear at their favorable temperature, which has changed now)

• the birds microevolution has been at a slower rate, so populations can nest too late, chicks starve / are underfed - as they miss the timing of caterpillar appearance

• however enough variability within populations so some survive, suggesting that microevolution can occur to ensure survival

who proposed the theory of evolution and when

what was the knowledge of the creation of life / earth, at that point in history?

• Charles Darwin, in 1859

• the knowledge accepted at the time was that the Earth was a few thousand years old

• they thought species were each created specifically and didnt change with time, and there was no known extinction of species

how old is the Earth now known to be?

what is known about the timing of life’s origin?

what evidence supports this?

• the Earth is now known to be ~4.54 billion years old

• the timing of life on Earth is supported by stromatolite fossils, and molecular clock (4.2 - 3.7BYA)

• stromatolites are fossilised layers of sand and microfossils (dated 3.7BYA), accumulated over time, created by cyanobacteria, as they photosynthesised to oxygenate the atmosphere, which required them to grow towards the sun, forming these layers upon older generations as they died off

• the molecular clock (dated 4.2BYA) is the idea that genomes are constantly changing at fixed rates (differ between organisms has been disocvered, so newer methods consider this too) - so looking at the level of mutation between the same gene in 2 different organisms, provides a time estimate of the last common ancestor, due to the amount of differences accumulated (can also calibrate along fossils) - doing so for all organisms provides an estimate of LUCA

• fossils can be looked at, but have limitations as soft tissue doesnt preserve well (the older, the lest preserved)

what are the implications of the origin of life on Earth, for evolutionary theory?

• once life appeared, it diverged from the Last Universal Common Ancestor (LUCA), and took a variety of forms over time

what does the timing of Earth’s origin vs life’s origin, tell us about how life may have come to be

• since there was at least 1 billion years difference between Earth’s origin and life’s origin, it suggests the early conditions musn’t have been suitable for life

• however, they provided the ingredients for life, which eventually resulted in life forming and adapting to thrive on Earth - changing Earth in the process, resulting in the diversity of life today

what did Carl Linnaeus propose

when?

what did he believe at the time about evolution (science at this point in history)?

how may this have influenced Darwin

• 1707-1778

• he developed the idea of arranging living forms in increasing complexity / specificity

• this led to the development of the binomial naming system for species

• and also hierarchical classification based on physical similarity of species (taxonomy) - the idea of grouping things that looked similar (however didnt consider other factors like species in different countries would have different origins)

• however, he believed in stability of species, and didnt consider the fact that species can change with evolution (not known at this point in history)

• shows Darwin ideas about different species, sharing similarities despite unrealtion - must be related in some way

what did James Hutton propose

when?

how may this have influenced Darwin

• 1726 - 1797

• he proposed the idea of gradualism with rocks, that the landscapes / geographic formation seen now, is the result of cumulative slow but continuous process

• this was discovered from looking at rock layering sequences and stratification process, revealling the importance of processes like soil erosion

• previously, things like canyons were thought to have originated from sudden catastrophies

• may have been influencing to Darwin as this is adjacent to the idea of evolution, but for landscapes

what did Jean-Baptiste Lamarck propose

when?

how may this have influenced Darwin

• 1700s

• the idea that what an animal has aquired throughout its lifetime, is passed onto the next generation (e.g. long necked giraffe is due to stretching of its neck throughout its life, as it reached for branches to eat)

• we now know this isn’t true, but it does suggest the important idea that species can change with time- which may have influenced Darwin

what did Georges Cuvier propose

when?

how may this have influenced Darwin

• 1769 - 1832

• ‘father of palentology’ - a very good anatomist who could construct extinct animal structures with a few fossilised bones

• thus discovered the idea of extinction, as he found elephant fossils in Paris that looked unlike modern elephants (Mammoth fossils) - before then, extinction / catastrophic events weren’t beilieved (the belief that god wouldn’t make animals that then go extinct)

• he also found elephant bones in Italy even though they didnt live their currently - proposing that patterns of distribution ranges change with time

• thus influencing Darwin by showing change in species with time and the existance of extinct species

what did Charles Lyell propose

when?

how may this have influenced Darwin

• 1797 - 1875

• popularised the idea of Uniformitarianism, which was built off Hutton’s Gradualism, which suggests previous changes to Earth’s landscape (that led to the state today - mountains, valleys, sea level), are due to changes still operating today, but very slowly

• due to seeing 2000 year old Italian marble temples, that had bivalve marks 9 feet up, suggesting it was once submerged, but had changed over time (due to volcanic activity)

• influenced Darwin, as it also supports changes in the Earth with time - adjacent to evolution changes in species over time

what did Thomas Malthus propose

when?

how may this have influenced Darwin

• 1766 - 1834

• he theorised that with time, population growth would be exponential, and although productivity could increase, this would only be a linear increase, that wouldn’t be enough for the exponential population size

• suggesting eventually, there would be a time of crisis in resource availability, which shows the idea of competition limiting populations, there must be some factor preventing exponential population growth

• this was thought of at a time where life was improving as societies were developing, moving into towns and ‘utopias’, which Malthus struggled with the idea of - a political economist

• this may have influenced Darwin by showing that populations can undergo competition, which may limit the survival success of individuals - limiting population size, but who survives? is there a reason why certain members survive?

what was Darwin’s background / upbringing

• wealthy and well educated

• his father a doctor, so he decided to become one himself, so studied at Edinborough

• however he didnt have the stomach for medicine, so dropped out and enrolled to become a Church Minister, as it gave him lots of time to research his interests - Natural History

when did Darwin go on his voyage

why?

what did he know due to science at the time?

• 1831-1836 he set sail on the Beagle

• this was due to an opportunity given after he quit med school to study natural history

• he knew the world was very old, and species go extinct

• he also knew ideas of things changing over time

what did Darwin suspect before he went on his voyage

what were 2 locations he went to

what did he figure out here

• he suspected that species change with environments, and some of this was heritable

• he also knew of Lyell’s book - ideas of geology where landscapes changed slowly over time, due to constant processes

• (South America) he found fossils which were similar but different to live animals (not old fossils) - which revealled the thought that related species change with time

• (Galapogos Islands) he saw how animals changed noticably between the many islands here, helping formulate ideas of adaptations, so he collected evidence (differences between land / sea / finch bird species) - later realising they were all different species

• this showed him clear patterns that all organisms are related and share a common ancestor

what is the famous Galapogous finch x Darwin example

how does this support evolutionary theory

• long-beaked finches on islands with cactus (fed on cactus flowers), pointy-beaked finches on islands with insects (fed on insects), large/broad-beaked finches on islands with seeds (beak cracked them open)

• showed that species have adaptations to suit their environments, so suggesting they evolved from one common finch ancestor, which formed different species as they lived in seperate groups on seperate islands, with different environments

• thus supporting descent with modification

what were 2 conditions Darwin posed in his theory of evolution, which the theory was based on

• all life evolved from a single common ancestor (through descent with modification)

• modification is due to adaptation, which is due to natural selection (but noted there may be other mechanisms of evolution too)

what did Darwin do after his voyage ended?

• in terms of experimenting

• in terms of his theory

• he returned to England to think about the ideas / writings / data collected on the Beagle

• he further experimented, on Tumbler Pigeons, for artificial selection (to try show this descent with modification), selecting for behaviour and morphology (flipping behaviour) - originally for predator avoidance

• here he spent 20 years not publishing anything on his theory, as he tried to become an expert on classifications and everything to do with his theory

• he was also unsure of what the church / world would say

what did Darwin recognise was fundamental for evolutionary change, but he couldn’t figure out the means for (due to science at the time)

• he spent 8 years of the 20 after his voyage, studying variation within barnacle species, using worldwide collections - as he knew variation drove evolution

• variation among individuals, but only that heritable

• and some related individuals (e.g. parent and offspring) were more related than others (e.g. same species)

• due to Mendels ideas unknown - no knowledge on genes, mutations, DNA, mechanisms of inheritance

what realisations helped Darwin come up with his theory of Natural Selection

• Malthus’s idea of exponential population growth, but limited resources - made him realise some mechanism must limit population growth, or the world wouldn’t fit them all

• this provided the idea of ‘survival of the fittest’ - some offspring don’t survive / contribute to the next generation, but this is not random - is due to certain variation providing better surival

• individuals that survive due to certain traits, have more offspring which have these traits too, so these lineages survive through evolutionary time

what are the 4 conditions of Darwin’s theory of Natural Selection

1. individuals within a species are variable

2. variation is heritable

3. every generation produces more individuals than will survive (resource limits)

4. survival is not random

= more favored forms of variation (better adapted traits) will survive and increase (reproduce)

what led Darwin to publish his theory of Evolution / Natural Selection

• he had been formulating, experimenting, studying, and sitting on research and observations for 20 years - collecting evidence to strengthen his case (unsure of how it would be recieved)

• his push was Alfred Russel Wallace - who independently came up with this idea too

• Wallace had formulated his ideas from a trip to South America (whose evidence (Samples / plants / animals / writings) had burnt in a fire on the ship), and a follow-up trip to Indonesia

• he didn’t have connections of wealth like Darwin, so mailed his ideas to him

• Darwin took notice, and they decided to share their ideas with the public / science community, together (back-to-back) which strengthened their cases

what are some important considerations of Natural Selection

• acts on individuals, but it is the population that evolves (Slowly changing over time) - not the individuals

• it does not think - not moving to a perfect state of adaptation (it simply happens depending on the situation of the time)

• it therefore also cannot produce perfect adaptations, it simply uses the variation that is there - producing new traits by modifying existing ones

• e.g. Panda thumb is a modified wrist bone that varies in the bear family

• so has constraints and cannot produce perfect adaptations that eventually lead to a perfect design - adaptations have compromises and trade offs (may provide fitness in one aspect, but a potential issue in another)

• e.g. frogs mating calls attract bat predators

• e.g. walking upright benefits humans, but provides disadvantages like back pain (not fully beneficial)

are humans still evolving? are species still evolving?

• yes

• for species, especially due to things like climate change, global temperature increases causing environmental changes that must be adapted to (Different traits favored for survival)

what was an issue of Darwin’s evolutionary theory at the time?

whos work / field of science, led to the modern understandings of evolution?

what did they call this

• Darwin had not come up with mechanisms to explain heredity, nor the mechanisms of which evolution occurred (only Natural Selection, but even this had unknowns to do with heredity)

• so encorporating genetics, provided this information - via the rediscovery of Mendel’s 1865 publishings, from the 1900s onwards (= the modern synthesis 1930s)

• this provides the mechanisms as to HOW evolution occurs (modern ideas)

• now we know these to be mutation, artificial selection, natural selection, etc. (note - with only natural selection causing adaptive evolution - change in organisms structure / function to enable survival)

define population genetics

what is this also known as

• aka microevolution

• genetic variation exists within and between populations, so population genetics looks at how this changes across generations / among populations

• this is done by looking at mechanisms that cause changes in allele frequencies

define population

• a localised group of individuals of the same species (capable of interbreeding to produce fertile offspring)

• one species may have many populations, but populations are just made up of one speces

• populations are different due to environmental factors / size etc, which changes the accumulation of variation (is amplified if more isolated)

what is a fixed allele

• a locus for a gene that is homozygous for the same allele, for all individuals in a population (the only option)

what does it mean if a locus for a gene is polymorphic

• individuals in the population have more than one different allele for this locus - the population has more than one option possible

define gene pool

• all the alleles for each loci of a gene, for all genes within a population

define genetic variation

• the variation in alleles for each gene within a population

define allele frequency

what is the equation to work this out

• the frequency / number of a certain allele for a gene, relative to the other alleles at that locus for the gene (for a specific gene) - in a population

allele frequency = number of copies of a particular allele / total number of all alleles for that gene

define genetic drift

what population size is it amplified for and why

• the change in allale frequency across generations, due to chance alone / random events (e.g. by chance only some individuals have offspring, individuals die by chance, indiscriminant killing)

• neutral to the benefits / disadvantages of the allele - no control over alleles lost / fixed

• amplified in small populations as there are less individuals and less alleles (less variability), so random changes have a larger effect

• reduces variation, can lead to alleles being lost or fixed

how does natural selection interact with allele frequencies for a population

• changes allele frequency considering the functionality and benefits of that allele - increasing its frequency if beneficial (if providing survival & reproductive success), and decreasing its frequency if opposite

what are the 4 mechanisms of evolution

• mutation

• genetic drift

• natural selection

• gene flow

define genotype frequency

what is the equation to find this

• the frequency of a particular genotype for a particular gene (combination of 2 alleles into homozygous / heterozygous), out of all the genotypes for that particular gene in a population

genotype frequency = number of copies of a particular genotype / total number of genotypes for that gene in the population

what is Hardy-Weinberg equilibrium

what conditions does this have

why is this important

• this is a model for a theoretical non-evolving population (no mutation, no natural selection, no gene flow, no genetic drift) - with absence of evolutionary influences

• this is important as it provides a null hypothesis for allele frequencies, so real populations can have their changes in allele frequencies compared to, to see if they are in fact changing in a statistically significant way

• therefore seeing if the population is evolving

what is the first Hardy-Weinberg equation

what does each symbol mean

what can this be used to find

p + q = 1

• p is the frequency of the dominant allele

• q is the frequency of the recessive allele

provides allele frequencies for generation 0

can be used to find missing allele frequencies

can be used in the second HW equation to predict changes in allele / genotype frequencies across generations

what is the second Hardy Weinberg equation

what does each symbol mean

what can this be used to find

p² + 2pq + q² = 1

• p is the frequency of the dominant allele, q is the frequency for the recessive allele in generation 0

• therefore each of these parts of the equation represent a genotype frequency (homozygous dominant / heterozygoes / homozygous recessive) - as it is modelled after a punnett square

• this provides the genotype frequencies for generation 1

• this can be worked backwards from, to find allele frequencies for generation 1 (therefore providing info about changes in allele frequencies across generations - evolution - in absence)

how do you use allele / genotype frequencies, to find the number of individuals with these genotypes in a population - and vice versa?

• if given allele frequency, find genotype frequency, then multiply this by the number of individuals within a population

• if given number of individuals within a population with each genotype, can put this in a fraction over the total number of individuals within a population, to provide a genotype frequency

does each mechanism of evolution either increase or decrease genetic variation

• within a population

• between populations

• (increase variation within) = mutations / gene flow / certain types of natural selection

• (decrease variation within) = gene flow / types of natural selection / genetic drift

• (increase variation between) = mutations / types of natural selection / genetic drift

• (decrease varaitaion between) = types of natural selection / genetic drift / gene flow

what is a population bottleneck

provide a real life example

• an extreme example of genetic drift

• this is where a population has variability, until a severe event indiscriminately kills individuals (not based on fitness), resulting in a small population with greatly reduced variability

• even with recovery, devastating effects remain as the resulting population often must inbreed to keep it alive - reducing variation as they originate from a single female / male

• e.g. due to human action / hunting / habitat fragmentation / weather events / geographic change / predator introduced

• e.g. North American Bison (30-60 million in 1875, indiscrimnately killed by European coloniser hunters, until only 300 remained 120 years later) - now recovered partially to ~500,000 individuals

• e.g. Florida Panthers (historic range in many states around Florida, now confined to a small area of Florida, due to habitat loss and fragmentation induced by humans - resulting in inbreeding, harming them as they recovered)

what is founder effect

provide a real world example

• an extreme example of genetic drift

• this is where a few individuals are isolated from their larger population, and begin a new population (founder population)

• the allele frequencies / variatbility can be different in this founder population, due to chance of which individuals left (it is random who the founders were) - but all together likely reducing genetic diversity greatly

• can often result in inbreeding which limits genetic diversity in the long term

• e.g. moving NZ native birds to small conservation islands to form new (protected) populations, can subsequently bring birds from original mainland populations to increase diversity later (As they are isolated populations) - Takahe, South island Saddlebacks (Tieke)

define natural selection

what is a current real life example

• ‘survival of the fittest’ - increase in allele frequencies for alleles that benefit survival and reproduction, as those with these alleles are likelier to survive → reproduce → pass on these alleles to offspring

• results in adaptive evolution, as allele frequencies change to better suit their environment (evolving to survive better in the environment)

• selecting agents are the factors that favor certain alleles, may be biotic or abiotic

• usually acts on traits controlled by many genes (quantitative genes), so these have continuous variation (e.g. human height involving 180 genes)

• e.g. happening currently in many species due to climate change (global warming temperature changes = changing adaptations to daylight / temperature levels, as these change, so different alleles are favored)

• e.g. Wyeomyia smithii (Mosquito species) - as global temperature increased, populations at 50N lattitude evolved to wait 9 days later to go dormant (hotter temperature favors later dormancy)

compare qualitative and quantitative genes / traits

• (quantitative) controlled by many genes, have variation over a continuum (e.g. height, hair colour)

• (qualitative) clearly categoriesed, one or the other - no inbetween (e.g. blood type)

name the 3 types of natural selection

what type of traits can be influenced by these

• stabilising selection

• directional selection

• disruptive selection

influences traits with continuous variation (quantitative) as these can be modelled with a normal distribution (by default, for the variation of the trait in a population)

regardless of the type, acts upon traits that benefit survival

describe stabilising selection

provide a real life example

• favors the average / median trait, and selects against variation on either end of the extreme

• narrows the width of the default normal distribution for the variation of the trait

• e.g. human birth weight, favors the median optimal birth weight, and selects against the two extremes of too small / too large weights (both disadvantageous to survival, those who do this are less likelier to survive and pass on this trait)

describe directional selection

provide a real life example

• favors one extreme, selects against the opposite extreme

• shifts the distribution to the left / right (doesn’t affect the width)

• e.g. Texas Longhorn Cow, taken from South America → Texas, which had new selection pressures (predators) that favored the horn length extreme of long horns (for defense), resulting in directional selection for long horns

• e.g. Soay Sheep, introduced to an island with dark and light morphs, which originally favored dark (absorb heat to aid thermoregulation and survive cold winters), but climate change resulted in selection pressures that favored white wool (cooling body in warmer temperatures), resulting in directional selection (white wool more prominent now)

describe disruptive selection

provide a real life example

• favors two extremes of the trait, and selects against the median

• results in a bimodal distribution

• e.g. African Black-bellied Seed-cracker Finch, relies on 2 seed species (small hard seeds & large soft seeds), so birds with small bills & large bills can feed effectively on the respective seeds, while medium bills cannot on either (Selecting against the median, less likely to survive due to starvation)

define gene flow

provide a real life example

• movement of alleles between populations, via migration

• can increase or decrease diversity within populations, but reduces variation between populations

• can disrupt local environmental adaptations

• e.g. Erie Water Snake, two different morphs at either side of Lake Erie (limestone beaches & islands = light coloured, no bands VS forested areas = darker coloured, banded), but gene flow via migration has placed some banded and some unbanded individuals in the irrespective areas (disrupting adaptation)

what is the main factor that leads to variation between populations

describe this

• geographic variation - variation due to different environmental conditions in the different areas of the population, due to different selecting agents - therefore different phenotypes favored for survival

what is clinal variation

give a real example

• change in trait along a georgaphic gradient

• is adaptive variation, fuelled by adaptations (not random)

• e.g. human skin colour varies with latitude

what is phenotype plasticity

how is this related to heritability

give an example

• phenotypic variation / specific changes (behaviour, morphology, physiology) in response to variation in environmental conditions (e.g. temperature and light - vary with time of year)

• these variations in phenotype are controlled by the same one genotype - not changes in the actual genotype, just changes in switching on / off the phenotype expressed (e.g. controlling protein production)

• e.g. Caterpillars, switch on different phenotypes of the same gene, to appear different at different times of he year (like foliage vs like branch, to camoflague), to aid survival in varying environmental conditions (trees with foliage vs trees naked)

what is epigenetics

explain how this works

• this is the study of heritable phenotype plasticity (phenotype changes driven by environmental factors, while the genotype stays the same - not involving alterations in DNA sequence)

• so despite the fact these changes dont change DNA, they can be passed onto offspring (heritable) via changes in DNA expression machinery

• these ‘flip different switches’, or activate different epigenetic tags which instruct cells how to act / what DNA sequences specifically to follow - a ‘switch on/off’ can be inherited

• e.g. Mice - recieved shocks when orange scents were released, creating fear alongside the scent - learned behaviour, which was found to be passed down generations despite no change in DNA (the ‘switch on’ / epigenetic tag for fear associated with this smell, was passed on in Mice sperm cells)

what things can you consider when thinking about genetic variation betwee species

• populations are full of variation

• distribution of alleles - are most widely distributed, or confined to specific areas of the world

• alleles and geography - do geographic regions have distinctive alleles, to distinguish individiuals in different populations

• difference - on average how different are two individuals from the same population vs two individuals chosen randomly from any two populations

distinguish between

• facts

• hypotheses

• theories

• (Facts) indisputable observations of natural phenomenom seen directly

• (hypotheses) proposed explanations for the phenomenom, must be testable if scientific

• (theories) carefully constructed explanations of observed phenomenom, drawing together many facts and hypotheses (strength increases as they explain more)

what are 3 important, evidence-backed (at the time of Darwin), points that evolutionary theory is based on

1. Earth is very old (~4.55byo)

2. Organisms have lived on Earth for most of this time

3. All organisms alive today, originated from earlier simpler life forms, via evolution

what is the estimated age of Earth

what is the evidence for this (point 1 of Evo Theory)

• estimated as 4.55 byo (± 50 million years)

• this is based on rock radiometric dating

• this looks at isotopes of radioactive elements in rock, which decay (into more stable daughter atoms) at a predictable rate - half the atoms presesnt to begin with, will decay over its ‘half-life’ - a known amount of time

• so the ratio of parent:daughter atoms can be used to calculate its age

• most commonly Uranium-238 which decays into Lead

• since Earth’s surface has eroded, meteorites leftover from Earth & the Solar System’s formation are dated

what evidence suggests organisms have inhabited Earth for most of its history (point 2 of Evo Theory)

stromatolites

• dated 3.7byo, via rock radiometry, looking at Carbon-14 isotopes, as these are replenished in living systems until death, where they decay into Nitrogen-14 at a predictable rate, so the ratio and its known half-life can be used to date it (if younger than ~50,000 years old)

strata

• also evidenced by layering of rock on rock faces (Forming strata), which can also be dated based on radioactive decay of elements (or the fossils themselves can be dated if new enough) - to suggest when the organisms were alive

• oldest fossils found at the bottom, providing a record of Earth’s past life, show change over time of organisms, as the fossils gradually change throughout the rock layers (evidence for change, evolution, speciation, extinction)

• rock layers also provide evidence for timings of mass extinctions, when fossils found change drastically with layers

• note - geology of the area is important as some layering may not be exactly consecutive if close together

list the things that evidence all organisms found today, evolving from previous simpler life forms (point 3 of Evo Theory)

• fossil record

• homologous structures (physical, molecular, physiological)

• biogeography (geographic distribution of species)

• artificial selection

• vestigial structures

what are vestigial structures

provide a real example

• evidence for today’s life evolving from previous forms

• structures in species, that have no purpose, due to having importance in ancestral species which is no longer needed

• they remain despite this, as they have no reason to be adapted against

• this shows that species have changed over time, as they have required different adaptations

• e.g. human goosebumps - important ancestrally as Apes to puff up our hair to seem larger, or serve as insulation in the cold / hot - which we no longer need

• e.g. human tendon

• e.g. human tailbone, a site for a tail which had importance in ancestors, but now does not form

• e.g. human embryos, resemble many other animals and have a tail, whos cells die off before formation (but continue to form tails in other organisms)

define artificial selection

provide a real example

how does this provide evidence of today’s life evolving from previous ones

• selection based on human selecting agents, traits favored by humans, that may not be environmentalyl beneficial (Selected for by natural selection), but are made more common as individuals with this trait are used to breed

• e.g. dog breeds, all originated from wolves, which have been selectively bred for characters found appealing by human, into massive diversity

• e.g. agriculturally important vegetables, wild mustard being bred to form broccoli & cabbage & brussel sprouts - due to selecting characters idea for human consumption, and breeding these

• is evidence for evolution due to showing how species can change with time - these changes didnt just happen randomly to what we wanted, they happened due to humans acting as selecting agents

how does biogeography / geographic distribution of species provide evidence that today’s life evolved from previous lifeforms

provide a real example

• differences in distribution for current species, vs where fossils of their ancestors were found, suggests evolution to live in new areas

• also if transitional species were found in the same area of a current species, it suggests evolution has occurred to form this

• e.g. continental drift, life’s contients used to be one supercontinent, which seperated - evidenced by fossils found on connecting parts of this theorised continent, but today on different continents seperated by large water bodies, that would be unrealistic to have been crossed by them

define convergent evolution / analogy

what is this evidence for

what is this NOT evidence for

provide a real example

• where two species that do NOT share a recent common ancestor, independently evolve similarly, to have similar features (analagous features)

• due to facing similar selecting agents (e.g. if in same environment)

• is not evidence for relation / ancestral connection / recent common ancestors

• is evidence for natural selection acting to fuel adaptations

• e.g. Sugar Gliders & Flying Squirrels - only distantly related, living on different continents (Australia vs America / Asia), have faced similar environmental selecting agents, resulting in similar flappy skin to fly

• e.g. Birds & Insects - very distantly related, but share wing structures, due to the benefits these provide for their lifestyles

what are molecular homologies

what do these provide evidence for

provide an example

• homolgous features (things shared by species due to sharing of a common ancestor which had these species) at the molecular level

• like in DNA sequence, and proteins coded for, so species sharing specific DNA base sequences and proteins coded for, likely have a common ancestor

• e.g. all organisms have the same genetic code - the same base sequences code for the same amino acids - the only plausible explanation is due to a shared common ancestor for all of life

• e.g. humans have ~99% shared DNA with Chimpanzees, suggesting relation and that we share a common ancestor

• e.g. human cell division gene was placed in Yeast, and was able to carry out cell divison (suggesting we are similar enough, only explained by having shared a common ancestor - suggesting animal x bacteria relation)

• e.g. Cytochrome C Oxidase Gene - seen in most organisms, so provides a good marker to look at a molecular clock for (rate of mutations which are consent) - suggesting closer related organisms will have less base differences in the gene, which was tested to suggest evolutionary patterns (human>pig>duck>snake>tuna>moth>yeast)

how does the fossil record suggest today’s life originated from previous forms

provide a real example

• the fossil record does this by documenting transitions between previous species, to todays ones

• done by showing transitional life forms with traits intermediate between old and new species, and gradual change in traits

• also done by looking at shared features between fossils and current species (homologous structures) due to being present in their common ancestor (Suggesting relation, thus evolution)

• e.g. Pakicetus (50myo pre-whale, 4 legs / tail / long mouth / land mammal) linked to today’s whales (suggesting it was how whales had originated) due to their sharing of a particular inner-ear bone structure (homologous feature)

• e.g. Peregocetus pacificus (43myo pre-whale, same features as above, but had semi-aquatic features, suggesting land & aquatic use, similarity physically with other early whales) - this suggests it was an intermediate closer to whales, between the land-dwelling Pakicetus and current whales

what are homologous structures

what do they provide evidence for

give a real example

• similarities in structures between species, due to common ancestry, which resulted in them sharing the same structures

• may be adapted for different uses, due to differences in selection pressures

• provide evidence that today’s life originated from previous species, as completely different species may share homologous structures, suggesting they are related, originating from past species

• e.g. similarities in tetrapod (4 limbed) forelimbs (human / cat / whale / bat), suggesting they shared a common ancestor, then had this feature tweaked by natural selection as they evolved further apart, due to different lifestyles

• e.g. similarities in Astralagus (type of ankle bone) between early Cetaceans (marine mammals - whales / dolphins - seen through ancestor Pakicetus) and even-toed Ungulates (pigs / deer / cows / hippos) - more similar (double humps on both ends) than to most mammals (double hump on one side) - suggesting Cetaceans arose from Ungulate land mammals (closer relation than to other mammals like dogs)

what is the problem with defining ‘species’

what are 3 main types of definitions

what is the most commonly accepted

• scientists cannot agree - ~24 concepts, none ideal

• due to species looking similar, different, etc, hard to compartmentalise (e.g. Western vs Eastern Meadowlark - morphologically identical, but only respond to respective species male mating calls)

• 3 main types: morphological species concept / phylogenetic species concept / biological species concept

• the biological species concept is most commonly accepted

what is the morphological species concept

who thought of this

how relevant is it

• grouping individuals into species, based on physical appearance (descrbing things based on what they looked like)

• came from Karl Lineaus

• still used today, important for things like fossils, where biological species concept is harder to apply - all we have is physical structures

what is the phylogenetic species concept

who proposed this

• grouping species based on monophyletic groups that share an ancestor back in time (a single common ancestor, and all of its descendents)

• based on morphological features that link ancestry

• proposed by Willi Hennig

what is the biological species concept

who proposed this and when

how relevant is this

• first proposed by Ernst Mayr - 1942

• grouping species as populations capable of interbreeding to produce fertile offspring (dont have to do this currently, just be capable)

• most commonly accepted definition, but does have limitations where other definitions may be better

what are the limitations of the biological species concepts

provide a real example

• cannot apply this definition to fossils, so must determine fossil species based on a morphological species concept or other methods

• cannot apply to organisms who reproduce asexually, as they cannot interbreed technically, but are still a species - gene flow still occurs based on reproduction just in a different sense

• is hard to test, like if individuals are in different areas of the world but count potentially interbreed

• doesn’t apply to all cases, some different species may be able to interbeed to produce hybrids, but still be different species morphologically / technically

• e.g. Mallard Ducks (N hemisphere) & Grey Ducks (native to NZ), different species based on geographic isolation, however when brought together they could interbreed to produce hybrids (species or not?)

• e.g. Giraffes were considered one species, in 4 non-overlapping populations across Africa, but DNA analysis (multi-locus analysis) & genome studies, revealed them to be 4 different species (despite evidence of interbreeding) - biological definition says 1 species, morphological definition says 4 species

• e.g. Elk (America) & Red Deer (Europe / Asia), seemed to be 1 species morphologically, and can possibly interbreed - but DNA evidence eventually revealed them to be 2 species

distinguish between Anagenesis & Cladogenesis

Anagenesis

• a new species replacing an old species over time, evolutionary changes within one lineage

• doesn’t increase diversity

Cladogenesis

• one species becoming two species over time, evolutionary changes splitting a lineage into two, where they then evolve differently (due to some sort of isolation)

• increases diversity

define speciation

• one genetically cohesive population, splitting into two or more reproductively-isolated populations

• results in gradual diversion between populations, as they face different selection pressures, until they cannot interbreed to produce fertile offspring

• thus forming two seperate species

• requires disruption / barrier to gene flow, then evolution of RIMS

what is a hybrid zone in speciation

what are the 3 possible outcomes

• a point during speciation where individuals of the two seperating populations, can still possibly interbreed

  1. (reinforcement) may strengthen the reproductive barrier, and hybrids gradually stop forming, as hybrids are less fit and natural selection strengthens RIMS

  2. (fusion) may weaken the reproductive barrier, as the two populations converge again to form one, as gene flow increasingly occurs to decrease variation between their gene pools

  3. (stability) the species continue to diverge and seperate, but the hybrid zone continues so hybrids continue to be formed, while the species are also seperate, both are favored / neutral by natural selection

• e.g. Wilderbeasts (blue / black / regular) have gene flow between species in overlapping ranges, but are still different species

what are RIMS

distinguish between the two types

• a collection of mechanisms / behaviours / physiological processes / morphologies, that prevent individuals from different species mating / producing offspring / producing fertile offspring

• (prezygotic) before the zygote forms / the mating itself - no energy wasted in mating

• (postzygotic) after the zygote forms / the mating has occurred - something prevents offspring from surviving / being fertile

list and distinguish the 5 prezygotic RIMS

• (habitat isolation) species in different habitats / areas so wont meet to mate

• e.g. snakes - land vs water

• (temporal isolation) species have different reproductive timing

• e.g. Western vs Eastern, spotted skunks

• e.g. Celmisia species in the Southern Alps Craigieburn range, rely on the same pollenators but have differently timed life events, flowering at different times

• (behavioural isolation) species provide different essential cues to mating

• e.g. Blue Footed Boobies

• (mechanical isolation) species have different structures which make mating physically impossible

• e.g. Snails

• (gametic isolation) species have specific gamete proteins which cannot be fused by opposite gametes of different species (so the zygote cannot form)

• e.g. Sea Urchins

list and distinguish the 3 postzygotic RIMS

provide an example for each

• (reduced hybrid viability) the hybrid is born but development is impared, so they don’t survive

• e.g. Salamanders

• (reduced hybrid fertility) the hybrid is born and survive, but is not fertile and cannot continue to reproduce to form more of this species

• e.g. Horse + Mule → Donkey (infertile)

• (hybrid breakdown) the first generation hybrid survives and can interbreed, but the second generation is infertile

• e.g. cultivated rice

define Allopatric Speciation

what are the potential outcomes

provide an example

• speciation occurring due to geographic seperation of populations

• this prevents gene flow, resulting in RIMS accumulating until two distinct species are formed

• (successful) can become sympatric again and not interbreed, so two species have formed

• (unsuccessful) can become sympatric again and interbreed, so no new species has formed - the populations fuse again into one

  e.g. Bahamas Mosquito Fish

• water levels lowered, seperating populations into two areas of their pond, where they faced different selection pressures - one exposed to predators (developed rapid movements via streamlined bodies) and one not (different body shape to favor long & steady swimming)

• when put sympatric, RIMS were arising, selection acting via females choosing streamlined bodies in predatory ponds

what are two real life examples of evidence for Allopatric Speciation

Diane Dodd

• did experiments on fruit flies in the lab, isolating an initial sample into two groups, which were fed different foods (Starch vs maltose medium)

• after several generations, the isolated groups were reintroduced, and had mating preference within their groups (RIMS beginning to prevent interbreeding)

• this suggests that isolating populations in different environments, can lead to the beginning of reproductive isolation (and of new species forming)

• also suggests that geographic isolation is an important step in speciation

Dusky Salamanders

• geographically closer populations were hypothesised to better reproduce

• experiment found this to be true, further apart populations having higher isolation values - showing a clear trend of reproductive isolation increasing with increased distance

define Sympatric Speciation

is this more common in plants or animals? - what are the mechanisms for each

• a subset of a population forms a new species, without geographic seperation - in the same location as the parent population / species, so they remain in contact throughout the process

• more common in plants

• (plants) occurs via polyploidy - common in plants, resulting in instant speciation as gametes have different chromosome counts so are incompatible (RIM)

• (animals) polyploidy is much less common, so sympatric speciation is also much less common, however can occur through sexual selection, and habitat differentiation (e.g. parasite host shifts)

provide a real example of Sympatric Speciation in animals

(habitat differentiation) - e.g. USA Hawthorne Maggot Flies

• laid eggs on Hawthorne fruits, but when Apples (similar) were introduced to US, some flies developed a preference for laying eggs on apple trees

• these are now known as North American Maggot Flies

• these are not two species yet (not TECHNICALLY speciation), but two ‘tribes’ preferring different hosts - so RIMS are beginning to form (but gene flow is still occurring, and interbreeding is possible)

(sexual selection) - e.g. Lake Victoria Cichild Fish

• many species arising from a few colonising species of the lake

• hypothesised to have occurred as they adapted to different food sources, but also due to mate selection developed by females

• this is where females selected males based on appearance, physical coloration (evidenced by a lab experiment where under normal light they selected, under a coloured light it was random) - which is a RIM that keeps species seperate

• this resulted in speciation, as this is a RIM preventing interbreeding

what are the different types of Polyploidy

provide a real example for each

what type of speciation can this lead to and why

• can lead to sympatric speciation - as changing chromosome number means their gametes are then incompatible with those of the parent species

• thus this is a RIM that forms a new species, this individual can reproduce with other ploids of the same count, or self fertilise with another ploid gamete / asexually reproduce / form vegetation that then produces ploid gametes, to continue the species

• (autopolyploidy) ploid individual formed within the same plant / species, cell divison error results in chromosome doubling

• e.g. formed Potato species, and many other agriculturally important crops

• (allopolyploidy) polyploidy occurring in a sterile hybrid between two species, enabling fertility, thus forming a new species (biological definition)

• this is if this ploidy results in an even number of each species of the hybrid’s chromosome sets, so they have homologous pairs to line up with in meiosis, and form subsequent gametes (be fertile)

• e.g. Wheat species used for bread, originated from allopolyploidy

define taxonomy

why is this important

who created this and when

• the ordered division / compartmentalising, and naming, of organisms

• provides an organised structure, and removes confusion from common names (e.g. jellyfish vs crayfish vs silverfish, all different groups, and none are fish)

• based on shared physical characteristics, is not organised based on ancestral relatedness

• based on different levels of grouping - largest / least specific is the domain level, smallest / most specific is the species level

• created by Carl Linneaus, 18th Century

how are species named

who created this model

• via Binomial Nomenclature - a two part species scientific name

• all in italics, first word capatilised, second word lowercase

• created by Carl Linnaeus (assigned humans our Homo sapiens name)

• now the international code informs the international commision of approving new species names

• note - can disrupt already named species, if they are found to be new species (e.g. Acacia trees originally in both Australia and Africa, found to be different species, now only the Australian ones can be known as Acacias)

define Phylogenetics

distinguish it from Linneaus Classification

what field of Science is it involved with

• an alternative organisation of species to taxonomy, based on evolutionary relatedness / ancestry / patterns of descent (whearas Taxonomy is organised based on shared physical characteristics - Phylogeny doesnt consider)

• it generally corresponds with the systematics of Taxonomy however - branches aligned with names in the order of classification

• thought of as a hypothesis for relation, so can be changed based on new information (e.g. new fossil evidence)

• is the context of evolutionary biology, as it looks at connections between all organisms via ancestor / descendant relationships, so can trace any two back to a common ancestor

• a graphical summary is the Phylogenetic Tree - places all life on a family tree, then can look at smaller phylogenetic trees for relation between fewer species

• developed by Systematisists - related to the field of Systematics

define Systematics

• a branch of Biology that deals with classification, and naming, of species

• therefore encompasses Taxonomy, Binomial Nomenclature, and Taxonomy

• also looks at the relationships among living organisms, through time and evolutionary history - visualised via phylogenetic trees

how do Phylogenetic Trees work

• time can be on the X or Y axis, showing evolutionary history

• starts with one line which is the common ancestor, which branches off at nodes to represent new species / lineages forming, which branch off at nodes into more lineages

• each node represents a common ancestor, which is the key to evolutionary relationships, as these result in shared characteristics due to relation, for descendants

• the branches represent change over evolutionary time, but NOT how much change occurred or when species evolved

• the closeness of tips of lineages dont represent closeness of relation, it is just the way of representation

• and the longest branches (less nodes and branchings) arent the most rudimentary species, it doesnt suggest they haven’t been evolving either

• note - show patterns of descent, NOT phenotypic similarity

what is Cladistics?

• the area of Phylogenetics to do with constructing Phylogenetic Trees (=Cladograms)

• uses common ancestry / homologous characters (arising from these ancestors), to classify organisms, and depict their relationships with other descendants

• based on identifying clades / monophyletic groups (all descendents from a common ancestor)

name and define the three types of descendant groups in Cladistics

• (clades / monophyletic groups) a common ancestor and ALL descendants

• (grades / paraphyletic groups) a common ancestor and SOME descendants

• (polyphyletic groups) does NOT include the most recent common ancestor of the species

define Character

distinguish between…

• Analagous & Homologous Characters

• Ancestral & Derived Characters

• any observable trait of an organism, both aquired and inherited

• (analagous) responses to the environment, adaptations via Natural Selection

• (homologous) produced by genes transmitted from parent to offspring, shared among taxa descending from a common ancestor

• (ancestral) traits inherited from the ancestor, so are shared between ancestor and descendant species

• (derived) traits arising after a lineage splits from its ancestor, not being shared between ancestor and descendant species

how would you go about creating a Cladogram for a group of organisms

what would this show

• can use this to show relatedness of organisms, based on the sharing of common ancestors OR common (homologous) traits

• must determine the clade where each unique derived character first appeared

  1. organise a set of characters they share, but are lacked one by one for the species across the tree

  2. this is where they split off from the tree, allowing the structure to be drawn