Theme 1

Question 1

What is the importance of understanding natural extinction rates?

Answer 1

Natural extinctions rates tell us what rate we should expect to see species disappearing. By comparing that with real data of how many are observed to be going extinct, or are at high risk of extinction, we can evaluate the effects which we are having on nature. Today, the extinction rate is around 20 times greater than the background extinction rate - this is indicative of a mass extinction event.

Question 2

What is the background rate of extinction? How does this compare to mass extinctions in the grand scheme?

Answer 2

The background rate of extinction is an estimation of the rate of species extinctions we would expect to see out with extinction events (i.e. under normal levels of environmental pressure). Natural rates of extinction are 0.1-1 extinction per million species per year. This background rate accounts for 95% of all extinctions, and the average species lasts 1-4 million years. Although the rate of extinction is much greater during mass extinction events, they only account for 5% of the total number of extinctions in biological history.

Question 3

How do mass extinctions drive adaptive radiations? Give an example of this.

Answer 3

The sudden loss of organismal diversity can provide “ecospace” for other organisms to diversify and occupy the newly available niches. For example, after the cretaceous-tertiary boundary event, around 70% of all species died out (most of them being dinosaurs). Where very large and competitive organisms were no longer outcompeting the smaller mammals at the time, and this resulted in the ecological release of mammals. A rapid expansion in disparity of mammals allowed them to occupy many newly available niches by virtue of this freed up ecospace.

Question 4

Explain the concept of local negative entropy, and how this is key to all life.

Answer 4

Entropy is a measure of how randomly energy is distributed in a system - net entropy of any reaction must always increase (2nd law of thermodynamics). This is not necessarily the entropy of the system, but is the entropy of the universe as a whole.
In order for organisms to survive, they must have highly organised systems, which is not consistent with increase in entropy. Therefore, they must create local negative entropy, whereby the biological system has a decrease in entropy (via processes such as chemical synthesis or mechanical work), but the entropy of the universe still increases due to the dissipation of energy from the biological system. This dissipation includes kinetic energy from mechanical work, excretion of bi-products, release of heat, etc.

Question 5

What are the requirements/tradeoffs for multicellular life?

Answer 5

The conditions for multicellular life to be viable are highly specific - there are many limiting factors such as sufficient nutrients, intracellular conflict, sufficient oxygen, etc.
They require adaptations such as cell-cell adhesion, cell specialisations, germ-soma separation, and most importantly, alternation of life cycles via a unicellular intermediate.

This unicellular intermediate (zygote) is vital in purging inter-cell variation, facilitating sexual recombination, restoration of telomere length, and mitigation of the impact of deleterious mutations in the somatic cell line.

Question 6

Discuss the differences in early embryonic development between protostomes and deuterostomes (and cindarians).

Answer 6

From an embryological perspective, all higher (bilateral) animals can be divided into two categories based on the development of their blastula - protostomes and deterostomes. Cnidarians are non-bilateral multicellular animals (such as jellyfish). The blastula is the hollow ball of cells which develops from a zygote. It gastrulates (invaginates) to give rise to the inner endoderm (central tract), and outer ectoderm (outer surfaces such as skin). There are two gastrulations which occur to form blastophores - one for the mouth and one for the anus. Bilateral animals also possess a third layer of tissue between these two - the mesoderm, which gives rise to musculature and internal organs between the digestive tract and skin.
In protostomes, the mouth blastophore invaginates first, but in deuterostomes, the anal blastophore invaginates first. Deuterostomes include echinodermata and chordata. Protostomes include all other bilateral life apart from cnidarians.

Question 7

What are HOX genes?

Answer 7

HOX genes are a subset of homeobox genes, and are responsible for determining the body plan of a multicelllar organism. They are extremely simple and conserved across all life. Very profound changes can be produced from very small changes to HOX genes. They are transcription factors.

Question 8

What is lagerstatten?

Answer 8

A good layer of sediment for fossilisation - shows fossil evidence which can be dated back hundreds of millions of years.

Question 9

What were the major drivers of the Cambrian explosion?

Answer 9

The Cambrian explosion was a huge explosion in abundance and diversity of multicellular life which occurred 490-540 MYA. Potential drivers for this explosion include expansion of the shallow seas alongside the break-up of the supercontinent Pangea, end of a recent ice age, and an increase in atmospheric oxygen. However, these processes may have been too gradual to explain the very rapid explosion in life. It is more likely because of the ecospace created by the Ediacaran mass extinction, and the emergence of predator-prey dynamics creating an arms race.

Question 10

How can modularity in body plans influence evolutionary radiations? Give an example of this.

Answer 10

Modularity is genetic independence between groups of phenotypic traits. Group of traits which interact with each other at a genetic level are known as modules, and whilst there is a lot of interplay between traits within modules, there is very little between traits of separate modules. This means that the evolution of one trait may avoid a cascading effect where it affects many other traits, helping an organism to avoid tradeoffs.

For example, domestic dogs show variations in their snouts/jaws which far exceeds the variation exhibited in wild dogs, wolves, and coyotes combined. This variation in facial structure has evolved extremely rapidly, with the help of selective breeding. This required a genetic predisposition to profound changes in jaw phenotype with negligible effects on cranial phenotype. Through experimentation, it was found to be true that domestic dogs have separate genetic modules for jaw and cranial shape.

Question 11

Explain how biologists can determine the genetic basis of particular phenotypes.

Answer 11

Once morphological variations have been quantified (e.g. by principal component analysis), GWAS can be used to determine which allelic changes correspond to specific morphological variations. This is used to inform researchers of likely candidate genes for the variation. Body plan genes are highly conserved across species, which means that model species can be appropriate for experimenting on if the species in question would raise ethical concerns. By interfering with transcription or translation pathways of a particular gene/gene product, causation of certain genotypes regarding their phenotypic influence can be inferred. Morpholinos are molecules which are designed to block the activity of certain genes, and these are commonly used to evaluate the outcomes.

Question 12

Outline the different geographical modes of speciation.

Answer 12

1) Allopatric speciation:
Occurs when a geographical barrier such a mountain or flowing water physically separates a population into two more groups, and different environmental pressures cause alternative adaptations until the populations, if/when re-introduced, ca no longer interbreed successfully. This requires a large amount of space and time for speciation to occur, and can occur under low or high levels of selection. Extrinsic barriers usually cause no gene flow at all between the divided groups. Allopatric speciation can be tested by measuring sexual isolation against geographic distance.
When the population is split into two or more roughly equally sized groups, this is known as vicariance. An example of this would be the different compliments of species on either side of the Amazon river.
When a small population separates from the main population and diverges this is known as peripatric speciation. These smaller populations will be subjected to a much stronger effect from genetic drift (due to bottlenosing). Evidence for peripatric speciation involves observing isolated, smaller populations having distinct genetic profiles. An example of peripatric speciation is Darwin’s Galapagos finches.

2) Parapatric speciation:
The population splits due to a lack of gene flow across a large area with abutting environmental differences. Restricted gene flow between populations (due to a cline or small geographical barrier) results in reproductive isolation. Space and time must be intermediate, and so must be selection pressure.
For example, water spring salamanders exist in a large extended body of water, but separate lineages develop in caves adjacent to the main body of water - gene flow is restricted to the interface between the cave and the surface.
It is difficult to infer this speciation mechanism, as many examples in nature can be explained as allopatric speciation and then re-introduction.

3) Sympatric speciation:
Reproductive isolation occurs without the influence of any geographical barrier. There is full potential for gene flow within the populations, but a high degree of selection against the mean trait value is imposed (disruptive selection). This means that intermediate phenotypes become a fitness valley, and extreme traits become fitness peaks. A mechanism of assortative mating gradually produces reproductive isolation.

Question 13

Outline the differences between ecological and genetic speciation paradigms.

Answer 13

The ecological and genetic speciation paradigms consider mechanisms for reproductive isolation from an ecological or genetic perspective rather than from a geographical perspective.
Ecological speciation is the process by which barriers to gene flow evolve between populations as a result of ecologically-based divergent selection.
Contrary to this genetic modes of speciation are where fundamental genetic differences result in divergence (bottlenecks/founder effects, genetic drift hybridisation, etc). These can be slow (e.g. genetic drift), or rapid (e.g. polyploidy).
An example of an instantaneous, non-ecological speciation is observed in frogs. One species is diploid, and another is tetraploid - they may be able to produce a triploid hybrid with intermediate characteristics.

Question 14

Describe pre and postzygotic incompatibility.

Answer 14

pre/postzygotic incompatibility are types of reproductive isolation, caused by the evolution of genetic differences due to natural selection. Prezygotic incompatibility means that the two genetically distinct organisms will choose not to mate with each other, whereas postzygotic incompatibility means that if/when they do mate, the resulting zygote will not be viable, and no fertile offspring will be produced.
In nature, prezygotic incompatibility is usually observed before postzygotic, meaning that as organisms speciate, they will usually choose not to mate before they become genetically incompatible.

Question 15

Describe pre and postzygotic incompatibility.

Answer 15

pre/postzygotic incompatibility are types of reproductive isolation, caused by the evolution of genetic differences due to natural selection. Prezygotic incompatibility means that the two genetically distinct organisms will choose not to mate with each other, whereas postzygotic incompatibility means that if/when they do mate, the resulting zygote will not be viable, and no fertile offspring will be produced.
In nature, prezygotic incompatibility is usually observed before postzygotic, meaning that as organisms speciate, they will usually choose not to mate before they become genetically incompatible.
In sympatric pairs of Drosophila, prezygotic isolation occurs at lower genetic distances than in allopatric pairs, due to reinforcement.

Question 16

Outline the differences between adaptive and evolutionary radiations.

Answer 16

Adaptive radiations are associated with ecological differences and particular geographic conditions, whilst evolutionary radiations are associated without much ecological partitioning or sexual selection. Adaptive radiations have a particular adaptive diversification component, but evolutionary radiations generate extreme levels of species richness over much longer time-scales (finer differences).
Adaptive traits are tested for using comparative methods, which involve comparing historical and contemporary similarities and differences of the trait across different lineages. We can also test whether a trait is adaptive based on its fitness consequences which can be done through experimentation. Convergent evolution among different lineages is good evidence of an adaptive trait.

Question 17

Describe the origin and key adaptations of mammals.

Answer 17

The oldest mammalian fossils are around 220 million years old. Mammals are considered air-breathing vertebrates with no larval form. They possess hair, have a large, four-chambered heart and high metabolic rate, expanded hard and soft palates, specialised teeth and jaw musculature, and are usually viviparous (embryos are nourished by a vascular placenta). Limbs are typically held under the body for rapid and efficient locomotion, requiring endothermy. They excrete urea rather than uric acid. Mammals also typically have three middle ear bones, mammary glands, and highly developed sense of smell, as well as RBCs with no nuclei.
Mammals also possess a two-layered skin, the outer layer (epidermis) contains a protective cornified keratin-layer, and the inner contains hair follicles, glands, and more.
Hair is produced by keratin, and can be modified in many ways (hooves, horns claws, etc) for a huge variety of uses.
Mammals have 5 main types of glands - sweat glands, eccrine glands, apocrine glands (pheromones and reproduction), scent glands, and sebaceous glands. Mammary glands are a particular type of apocrine gland which excrete milk to nourish offspring. They are believed to have first evolved to confer innate and adaptive immune protection to offspring. They first produce colostrum, a thick milk which contains immune and growth factors, antibodies, nutreints, a gut microbiome, and endocrine competence, as well as a laxative.

Mammals evolved from synapsid reptiles. The evolution of lactation is believed to predate the appearance of mammals - synapsid reptiles first evolved into cynodontia, then mammaliaformes, then mammalia, and these pre-mammal lineages were able to secrete a primitive form of milk fro their cutaneous glands.

Question 18

Describe the three main subgroups of mammals.

Answer 18

Mammals are divided into three subgroups - prototheria, eutheria, and and theria.
Prototheria are considered the most primitive mammals, and are oviparous monotremes. They are only found in Australia and New Guinea, and there are 5 living species (Platypus and echidna x4). Their urinary, defaecatory, and reproductive systes all open into a single duct (cloaca). They lack nipples (milk secreted into depression in mother’s belly), have many “reptilian” characteristics, adults lack teeth. They have 10 sex chromosomes, lower body temperatures and metabolic rates than other mammals. They lay cleidoic, amniotic eggs.

Theria are marsupials. They are believed to have evolved in South America and crossed antarctica to what is now Australia, reaching here around 50 MYA (eutheria disappeared from here around 55 MYA). They give birth to highly altricial young. Male penises have no urinary function, and females have two lateral vaginas with separate uteri, both of which open externally to a cloaca. They lack a corpus callosum between their brain hemispheres (as do prototherians). The embryo develops within an embryonic capsule, which it then hatches from and crawls to the nipple. They then exhibit rapid forelimb and facial development, but slow hind limb and brain development. Nipples can be found in the marsupium or open to the environment.

Eutheria are placenta mammals. The oldest eutherian fossil was found to be 160 million years old. They have highly developed allantoic placentae, as well as complex milk and prolonged parental care. They show a huge diversity of dietary and ecological specialisations and body forms. Most are homeothermic, endothermic, but some are poikilothermic (hibernate or torpor). They have the absence of epipubic bones found in all other mammals (possible that these bones are harmful in pregnant placentals.

Question 19

What are the four main clades of eutherians? How did they come to be?

Answer 19

Eutherians can be subdivided into laurasiatherians, euarchontoglires, xenarthrae, and afrotherians.
Laurasiatherians evolved on the supercontinent Laurasia, after it split from Gondwana when Pangea broke up.
Euarchontoglires probably split from the Laurasiatherians 85-95 MYA, developing in the Laurasian island group which later became Europe.
Xenarthrae were restricted to South America until the great American interchange. All Xenarthan megafauna died out in the Pleistocene.
Afrotheria evolved on Africa when it separated 105 MYA, and is a sister taxon of Xenartha.

Question 20

Explain what a key innovation is, and give examples.

Answer 20

Key innovations are evolved traits which allow a rapid increase in the rate of speciation and success of a lineage.

One example of a key innovation is amniotic eggs - these eggs have a membrane surrounding the fetus, which allows them to be laid on land or held within the mother (resulted in the evolutionary success of terrestrial reptiles, birds, and mammals).

Question 21

Describe the three main groups of amphibians.

Answer 21

1) Caecilians are legless amphibians with dermal scales, a blunt head for digging, vestigial eyes, and have retractable sensory tentacles. The earliest fossils to have been found date back to the early Jurassic. There are roughly 160 species, most found near the equator, and they exhibit both internal and external fertilisation.
2) Caudata (salamanders and newts) have reduced skulls well developed tails, cylindrical bodies, and some species are lungless. They are long-lived and have a slow rate of development. They have a slightly more temperature distribution than caecilians (mostly on the northern hemisphere), and have been traced back to the middle Jurassic. They exhibit both internal and external fertilisation, and there are over 400 known species.
3) Anura (frogs and toads) have a short/no tail as adults, long muscular hind limbs, and shortened vertebral column. They are very widespread, found in almost every global habitat. There are over 6775 species, and they exhibit mostly external fertilisation. There are believed to be so many anura species due to radiation during the tertiary period (following the K/T mass extinction). There are two major subgroups of anura - archaeobatrachia and neobatrachia. 88% of all neobatrachian species emergences coincide with the K/T event (for example, arboreal frog species emerged at this time, and massively diversified).

Question 22

Describe key innovations of modern amphibians

Answer 22

A wide variety of reproductive strategies have resulted in high rates of cladogenesis (emergence of new lineages), potentially due to reduced gene flow with other frog lineages, and increased potential for spatial segregation and speciation. For example, Darwin’s frog incubates its young the mamle’s vocal sacs (rather than in a water-pool). Another example, seen in Pristimantis frogs, is direct development - here, eggs are laid on land, and they hatch as “froglets” rather than tadpoles.

Another key innovation of many amphibians are defensive toxins, which allow them to avoid predation. Different species produce a range of toxins in different ways - for example, poison dart frogs produce their toxins by processing their prey after they consume them. Some species of salamander are highly toxic, and produce their poison endogenously.

Question 23

Describe the possible drivers and consequences of the End Ordovician mass extinction event.

Answer 23

The End Ordovician extinction was believed to be due to intense glaciation (ice age). This extinction event occured over a period of around 30 million years, ending around 434 MYA. During the Ordovician period, ocean invertebrates were diversifying - cephalopods emerged, predatory sea scorpions and giant orthocones, as well as coral, molluscs, trilobites, and the first vertebrate fish all emerged (as well as terrestrial plants). The continents were all located in the southern hemisphere, and Antarctica, Australia, and Africa formed the supercontinent Gondwana. A major ice cap developed over most of the continental area and into the sea.
One theory as to the cause of this global cooling was a major drop in atmospheric CO2 due to the weathering of silicate rocks (forming calcium carbonate), and volcanism. The sea level dropped due to the increased ice, and many coastal organisms died out. Next, subsequent global warming took place, CO2 was released, and biodegradation by marine organisms caused anoxia.

Question 24

Describe the possible drivers and consequences of the Late Devonian mass extinction event.

Answer 24

Devonian period lasted around 60 million years, and ended roughly 354 MYA - it was known as “a greenhouse age” and “an age of fish” due to its wetness and warmth, and marine life, respectively. Lobe-finned fish emerged at this time (later became amphibians), reef ecosystems dominated by coral and sponges developed, as well as diversification of cephalopods, the first terrestrial vertebrates emerged, as well as many invertebrates (possibly flying insects), and lush forest developed with vascular plants and deep roots. An abrupt drop in average temperature from global cooling, as well as oceanic volcanism, and the potential contribution of two meteorites resulted in lowering of sea levels and ocean anoxia. It is also possible that cosmopolitan species started to expand, pushing others out of their niches, and reducing the overall speciation rate.
Another theory is that the forests’ roots broke through rock substrates, creating nutrient-rich soils. When these were weathered, the nutrients moved to downstream aquatic ecosystems, resulting in huge algal blooms which eventually disintegrated through aerobic decomposition, causing anoxia. The extinction event is split into two spikes - the Hangenberg extinction spike and the Kellwasser extinction event. 70-80% of ocean species went extinct, mostly in the tropics (reef communities suffered most)

Question 25

Describe the possible drivers and consequences of the End Permian mass extinction event.

Answer 25

Also known as “the great dying”, this was the largest of all extinction vents in history. During this time, all continents merged to form Pangea - there was glacial ice in the south extreme seasonal changes in the north, and lots of hotness and dryness in the middle. The period lasted just over 50 million years, and ended around 251 MYA.
Terrestrial reptiles developed large webbed spines to disseminate heat. Amniotic eggs emerged at this time, therapsids diversified into ancestral groups of mammals, turtles, lepidosaurs, and archosaurs (which then diversified into dinosaurs). Bony fish began replaced lobe-finned fish.
There is poor fossil evidence for this period, resulting in many contradictory theories for the cause of the extinction. Ocean acidification is considered the most likely candidate (as there is evidence of significant pH drop in oceans during the second phase of the extinction) - this is attributed to the eruption of the Siberian traps, which resulted in sulphur dioxide emission, darkening the sky (limiting photosynthesis), and causing acid rain (as well as CO2 emission, causing ocean anoxia and acidificaiton). Around 96% of marine species, and 70% of terrestrial species went extinct. Shallow, warm-water marine invertebrates were the most affected (trilobites, corals, sea scorpions, etc).

Question 26

Describe the possible drivers and consequences of the End Triassic mass extinction event, as well as the key evidence for this.

Answer 26

The Triassic period lasted for around 45 million years, and ended 205 MYA. The conditions of extreme heat from the Permian were carried over into the Triassic and were further exacerbated. Along the equator of Pangea, reptiles which lived there were expelled and had to move outwards to escape the heat and dryness. Conifer trees emerged at this time (advantageous because they rely on less water) and many ferns went extinct. The first dinosaurs appeared at this time, as well as the first Mammaliaformes. There is substantial evidence for the mass extinction due to good sedimentation at the time, so it is widely accepted that this extinction was caused by massive volcanic acticity in the central Atlantic magmatic province (CAMP), which is now a volcanic mountain range at the bottom of the Atlantic ocean. This resulted in huge climatic changes due to released CO2 and SO2, which in turn caused ocean acidification, anoxia, and sea levels rising. All Triassic archosaurs (apart from pterosaurs and crocodiles) went extinct, resulting in the opening of ecospace for the dinosaurs to take over in the Jurassic era.

Question 27

Describe the possible drivers and consequences of the End Ordovician mass extinction event, as well as the key evidence for this.

Answer 27

The Cretaceous/Tertiary (K/T, AKA Cretaceous-Paleogene, K/Pg) was the most recent mass extinction event. The cretaceous period lasted just under 80 million years, ending around 65 MYA. This era saw massive diversification of dinosaurs, including sauropods, theropods, and pteropods. The first flowering plants also emerged during this time.

Sediment from around this time is very well preserved in a layer called the K/Pg boundary. Two noteworthy elements have been found in this layer of sediment which give substantial evidence to the causes of the extinction:
1) Iridium - this element is found almost exclusively from extraterrestrial bodies, and is found in abundance in the K/Pg boundary. This suggests that a large asteroid collided with earth during this time and broke into many pieces which were preserved in sediment. Consistent with this is the Chicxulub asteroid crater located in the Gulf of Mexico - a massive crater which is estimated to have been created by the impact of an asteroid around the same time as the iridium was preserved in sediment. The location of the impact was key, as it struck directly onto an area with lots of sulphur-rich rocks, releasing sulphur dioxide into the atmosphere, causing severe global cooling, resulting in lowering of the sea level.
2) Mercury - this element suggests that there was a lot of volcanic activity occurring around the same time as the mass extinction event. It has been proposed that the Deccan traps (a large range of supervolcanos) erupted within quick succession of one another, releasing carbon dioxide and sulphur dioxide into the atmosphere, resulting in ocean acidification, anoxia, global warming, and sea level rising.
The asteroid impact is generally considered to be the cause of the K/T mass extinction due to its cooling effect (as opposed to the warming effect that the eruptions would have caused).

Question 28

Discuss the theories regarding the evolution of powered flight in birds.

Answer 28

The two main theories of how powered flight evolved in birds are the Cursorial theory (evolved flight from the ground, up), and the Arboreal theory (evolved from the trees, down).

One suggestion of the cursorial theory is that bipedal predators jumped into the air in pursuit of their prey, and that elongated forelimbs were useful as stabilisers. The main criticism to this theory is that it fails to explain how forelimb feathers would be advantageous. A proposed explanation to this is that these feathers adapted for an alternative purpose (such as insect trapping or display), and later became used in flight. Other criticism of this theory is that it does not seem biomechanically feasible as an explanation - working against the pull of gravity in this way would be very expensive energetically, and also would not explain the evolution of wing flapping (flight stroke). Another cursorial suggestion is wing-assisted incline running (WAIR), where extended forelimbs, with feathers, would be a selective advantage for running up steep slopes, a technique which is observed in modern-day birds. However, it has been argued that early birds’ shoulder joints would not be mechanically adapted for this.

The arboreal theory is more widely accepted. It suggests that the ancestors of birds lived high in the trees, and would jump from tree to tree. Initially, the forelimbs would be advantageous for balance, and eventually gliding (where forelimb feathers would yield an aerodynamic advantage). Over time, these gliders would eventually become fliers. This theory is generally accepted for two reasons: 1) It suggests a single selective pressure to which both elongated forelimbs and forelimb feathers would be an adaptive advantage, and 2) There is fossil evidence that certain organisms, believed to be early ancestors of birds, exhibited extended forearms and keen vision, and lived in an arboreal habitat. The main criticisms to the arboreal theory are that it appears in the fossil record that down feathers (for thermal insulation) evolved prior to flight feathers, and that large, feathered wings would pose a selective advantage for brooding (a behaviour which has also been observed in the fossil record), and not just flight (a potential contender for a single, continuous selective advantage).

Question 29

Discuss the origins of birds - naming a few examples of early ancestors and their characteristics.

Answer 29

Birds evolved from diapsid reptiles - these ancestors existed in the Triassic era (beginning around 225 MYA).
Archaeopteryx is an early dinosaur which existed around 150 MYA, and had some characteristics of modern day birds, such as feathers and non-pneumatised bones. It is believed archaeopteryx could fly or glide to some extent. It did not have a keel on the sternum or a pygostyle, and had claws and teeth, as well as a long tail and reptilian skull.

Sinosauropteryx and conficiusornis are two species which are believed to have existed around 125 MYA. The former was the first known organism to exhibit flight feathers, and the latter was the first to have both a toothless beak and a pygostyle.

Deinonychus was a dinosaur which existed in the early Cretaceous period, and had a small, sleek body with horizontal posture, enlarged raptorial claws, and ratite-like spine suggested it was an agile predator (also opened debate on whether dinosaurs were warm-blooded).

Bambiraptor was a late velociraptor species which existed around 75 MYA. Although there were no feathers on fossils, cladistic analysis places this organism in the “feathered” group. It also possessed a wish-bone and an ossified sternum. It had an enlarged cerebellum, large optic lobes, and had very similar proportions to modern running birds.

Question 30

Discuss the criteria for eusociality, and describe some of the half-way points.

Answer 30

There are four criteria for eusociality: Cooperative care of juveniles; adults living in groups (common nest site); overlap in generations; and reproductive division of labour (not all individuals reproduce - one queen or breeding pair).

Solitary animals have none of the above criteria.

Communal/subsocial animals have a common nest site, but no other criteria.

Quasisocial animals have common nest sites and cooperative brood care, but no reproductive castes or generational overlap.

Semisocial animals have a common nest site, cooperative brood care, and reproductive castes, but no generational overlap.

Question 31

Explain Hamilton’s law of kin selection.

Answer 31

Hamilton’s law of kin selection states that if the product of the relatedness of an altruist to its recipient, and the benefit to that recipient, is greater than the cost to the altruist, then altruism will occur (and thus, eusociality can emerge) - can be expressed as rB>C.

This relies on the concept of inclusive fitness - the net fitness of an individual as well as their relatives (or the total number of genes which are passed to the next generation).
Direct fitness is a measure of an organism’s reproductive output, and indirect fitness is the amount of genetic output passed on to the next generation by an individual’s relatives with their contribution.

Question 32

Explain how honeybees exhibit kin selection. How does this compare to termites?

Answer 32

Honeybees are polyandrous, meaning that there are multiple males mating with one female (queen) when she is in heat. They also exhibit haplodiploidy, meaning that male drones (who mate with the queen) are haploid, whereas the queen herself is diploid. Every daughter therefore inherits 100% of their father’s genes, and 50% of their mother’s (the queen’s), meaning that sister drones are actually 75% related to one another, and only 25% related to their half-sisters.
Full sisters within the colony will be more closely related to each other than they will be to the queen which is vital for maintaining altruistic cohesion between siblings in the hive. When full sisters support one another, they will maximise their inclusive fitness, as well as the genetic integrity of the colony.

Termites, by contrast, are all full brothers and sisters to one another. There is one mating pair which gives rise to every termite worker within the colony. Pheromone production and sensing is fundamental to both the honeybees and the termites.