Biology – Preliminary – Evolution of Australian Biota



Biology – Preliminary – Evolution of Australian Biota

1. Evidence for the rearrangement of crustal plates and continental drift indicates that Australia was once part of an ancient super continent

identify and describe evidence that supports the assertion that Australia was once part of a landmass called Gondwana, including:

▪ − matching continental margins

▪ − position of mid-ocean ridges

▪ − spreading zones between continental plates

▪ − fossils in common on Gondwanan continents, including Glossopteris and Gangamopteris flora, and marsupials

▪ − similarities between present-day organisms on Gondwanan continents

Plate tectonics is the study of the movement of crustal plates. The lithosphere consists of the crust and the upper mantle and is divided into several major plates. Plate tectonics provides the evidence that Australia was once part of an ancient super continent.

Alfred Wegner proposed that the continents had once the continents had been united in one large land mass known as Pangaea. He suggested that pangaea broke apart and the continents drifted apart into their present positions. For this reason his hypothesis was called the continental drift hypothesis. Wegner however, was not the first person to suggest the continents had once been joined especially since many scientists noticed the maps of Africa and South America suggested the two continents were once joined together.

There was much opposition to Wegner’s hypothesis but it was later hypothesized by Arthur Holmes that convention currents in the upper mantle moved the continents. However it was not until WWII when scientists began to investigate the topography of the ocean floor that the theory of continental drift became prominent.

Matching Continental Margins

The continental margin is the zone between the ocean basin and the mass of the continent. The continental shelf is the area underwater from the shore to the continental margin. If the continental margins of the continents in the southern hemisphere are aligned like a jigsaw, you can reconstruct the great southern landmass Gondwana, which formed when Pangaea split around 150 mya. Gondwana consisted of the present day continents South America, Australia, Africa, India and Antarctica. When the continental margins are aligned, it is important that rock types and rock structures also align.

Position of Mid-ocean ridges + Spreading zones between continental plates

Mid-ocean ridges are the sites where two crustal plates meet or move apart. The theory of continental drift suggests that as the continents drift apart magma wells up through the spreading floor and new crust is formed.

There is scientific evidence using radiometric dating that the rocks towards the edges of these mid-ocean ridges are younger than those further in from the margins, supporting the idea that rock near the edges of spreading zones are newly laid down.

Mid-ocean ridges where plates collide are the sites where most volcanoes and earthquakes occur

At subduction zones, where plates collide and fold, or one plate slides beneath the other, the formation of mountains and the continued movement of present-day continents provides evidence to support the theory of plate tectonics.

The Himalayan mountain range is at a subduction point where India is sliding under the Asian plate. Evidence is provided by the fact that the Himalayan mountains are still slowly rising, supporting the theory of continental drift. Australia is still moving northwards at a rate of approximately 7 cm per year.

Common Fossils of Flora and Fauna

A fossil is any trace or remains of past life. A study of the fossil evidence from the different continents that once made up Gondwana shows great similarities that are hard to explain unless the continents were once connected.

The Glossopterids are an order of plant that lived during the Permian period and were deciduous woody trees and shrubs They are hard to classify as most fossils are leaf impressions. Fossils have been found in Australia, India, South America, Africa and Antarctica – all the continents that made up Gondwana.

The Glossopterids is a genus of seed ferns with several hundred species. Since the mature seeds were believed to be several millimeters in length, it is probable to conclude that the seeds were too big to be dispersed by wind across oceans. Hence the presence of the plant on the Southern Continents during the Permian is strong evidence to show that Gondwana existed in that time frame. Gangamopteris is a similar fern but has slightly different leaf structure but is also evidence for the existence of Gondwana.

The distribution of mammals, especially the marsupials provides evidence for plate tectonics and the past existence of Gondwana. When Australia and Antarctica separated from Africa around 150 million years ago, mammals were still primitive with monotremes, marsupials and only a few placentals. Australia became isolated and the marsupials evolved and diverse species flourished. In the rest of the world, placental mammals flourished while monotremes became extinct and except for the South American possum, marsupials also became extinct. When Australia crashed with Asia many placental mammals were able to island hop to Australia. The main point here is that the isolation of monotremes in Australia and marsupials in Australia and South Africa, provide information that Gondwana existed and due to its separation isolated certain types.

Present day Gondwanan organisms.

Many present day plants and animals that are found on the continents of the Southern Hemisphere show Gondwanan Ancestry.

1 – Ratites – The Flightless Birds

The large flightless birds, the ratites are found only on the Southern continents. These include the Australian emus, the African Ostrich, New Zealand Kiwi and South American Rhea. Ratites do not have a keel on their breastbone which is where the flight muscles are attached for birds that can fly. Thus they are called flat-chested. It is believed that ratites evolved in the Cretaceous period and then divergent evolution occurred when the groups were separated.

2 – Southern Beach Tree – Nothofagus

This is found in Australia, New Guinea, New Zealand and South America and its presence on the southern continents led scientists to believe that these continents had once been joined. It evolved after Africa separated from Gondwana and it formed large rainforests. Fossil pollen of Nothofagus from Aus has been dated at 80 mya. As Aus became drier and hotter, the Eucalyptus evolved so that only certain species of Nothofagus remained. It is only present in Tasmania and Australia’s only deciduous tree.

3 – Proteaceae

The family Proteaceae includes many familiar Australian plants such as the Waratah and Banskia. They have low dispersal ability but many are found on the southern continents showing the ancient landmass of Gondwana once exited and enabled the spread of these plants. The drying of Aus has led to a division between the east coast species and west coast species and current research is being done with DNA sequences to trace evolutionary paths of the family.

Discuss current research into the evolutionary relationships between extinct species, including megafauna and extant Australian species

The geological history of Australia shows that the land area we identify as ‘Australia’ has experienced a vast variety of conditions and has been in many geographical locations from the equator to the south pole. Many species evolved and have become extinct. For example, Glossopterids appears in the fossil record of the Permian period but became extinct 245 mya. Extant species have living representatives. For example the Nothofagus is still distributed in Tasmania but appeared during the Cretaceous era.

The Megafauna are animals which are similar to present day organisms but are much bigger. For example the Australian megafauna included large kangaroos, wombats, the huge Diprotodon, giant running birds and a giant python.

Current Research into the evolutionary relationships between extinct and extant species revolves around the search for fossil evidence. Many sites are being excavated in search of these fossils. Once the fossils are found, similarities and differences with other known species, both living and extinct can be made so that relationships can be deduced. Radiometric dating provides dates for when these animals died and the study of a range of these animals gives clues about the climatic and environmental conditions of the time. Ancient temperatures can be calculated by studying fossil plants and by the oxygen isotope in fossil marine shells.

Wynyardia was a primitive marsupial that was a cross between a wombat and a kangaroo. It is one of the oldest fossil marsupials with a preserved skeleton and is believed to be the ancestor of Australia’s living diprotodont marsupials.

By about 20000 years ago most of the megafauna had become extinct. Some species survived eg. The large red and grey kangaroo, however their ancestors had been significantly larger. Some fossils found show these ancestors to be double the size of present day organisms.

• Illustrate the changing ideas of scientists in the last 200 years about individual species such as the platypus as new information and technologies became available.

The Platypus: Ornithorhynchus Anatinus

The platypus is quite an unusual species that baffled scientist for many years, until new information and technologies became available. The platypus was firstly described in 1799 along with the koala, kangaroo, wombat and the emu which were all curious creates to the scientific community of that era. There was significant debate on the classification by the platypus as little information about it was available and the technology of the time was unable to retrieve that information.

The platypus is one of the primitive mammals that are present on Australia, and it displays characteristics which make it unique when compared with other mammals. For example: some of these characteristics include the fact that it lays eggs, there is an absence of true teeth, there is also no mammary glands but despite this, it has special glands that are able to secrete milk. Additionally, it has fur like most other mammals, but it also has a horny beak similar to a bill of a duck. Unusually, it has webbed feet and a short tail like a beaver.

Dried platypus skin was sent to England in 1798, a year after the discovery of the unusual species, but the sample was rejected, with many claiming that the skin was a fake. For more than 80 years, there was uncertainty about how the platypus reproduced. Thus showing how lack of information and technology shaped the views of the scientists of that time, however, in 1884, as technology improved, scientists were able to unravel the mystery by capturing female eggs. This again altered the views of scientist as with new information, they needed to again re-understand the characteristics of this species.

Furthermore, now with technology supremely advanced to what it was 200 years ago, scientists are able to use modern technologies such as fibre optics to enable to them to televise and view female platypuses feeding and caring for their young.

Around 1904, as increasing information became available, a scientific journal was able to publish the fact that many mammals do not posses teeth when they are adults. This was a striking discovery as the platypus was one of these mammals but it was commonly believed that it was a rare kind.

For the next seventy-odd years, due to lack of technology and scientific information there was much uncertainty about how the platypus was able to regulate its body temperature like other mammals do. Only through recent research and advanced technology has it been discovered, how this operation works. Scientists have now understood how it regulates body temperature, but they believe that the mechanism is primitive or underdeveloped.

New fossils have helped scientists understand the evolution of the platypus, further showing how increasing information can shift the views of scientists. For example, some of the fossil findings as well as research based on the sequence of amino acid have led to changes in the scientific community in the way they interpret the origin and evolution of mammals and in particular the platypus.

Some of the important fossil finds that shaped the views that scientists currently hold on the evolution of the platypus include:

- 120 – 170 million year old fossil of an ancestor of monotremes (as the platypus is classified as a monotreme) were found in Australia and Madagascar.

- 100 million year old fossils of platypus ancestors were discovered in Lightning Ridge, New South Wales, Australia. (Scientific name of the ancestor: Steropoden Galmani).

- Relatively recent (50 million years ago) fossils were discovered of platypus-like creatures from Southern South-America.

As the number and type of fossils were found, the knowledge depth of the scientists increased vastly, thus allowing for a more accurate evolutionary path of the platypus to be determined.

Furthermore, increasing information, in the form of fossils, arrived from both hemispheres of the Earth showed evidence of certain molar teeth that were designed both to grind down food as well as slice through meat. This new information led scientists to the hypothesis that mammals (such as the platypus), might have had dual origins, thus further showing how scientists views have changed as increasing information became available due to the advancements in technology.

In recent years, the contribution of Australian scientists to this puzzle has been through the research of amino-acids. With advancing technology and faster machinery, scientist were able to observe trends between amino acid sequences of placentals and marsupials. This has changed the views of scientists who now understand that the two species are more closely related than what they were believed to be initially. Currently, scientists believe the monotremes diverged between 160 and 180 million years ago.

Note: A monotreme is a mammal, instead of giving birth to live young, lays eggs. So simply put, it is an egg laying mammal.

Evolution of the Platypus:

The platypus shows no obvious signs of evolution, its only change seems to be the loss of teeth and a distinct shrink in size. Thus, most evolutionary scientists are baffled about the unknown ancestry of this unique creature. The only significant information available to current day scientists a few fossils scattered all over Australia.

However, in 1984, a 110 year old fossil was found in NSW (Lightning Ridge as mentioned above). This increased knowledge depth, shifted the views of scientists as they had no record of any mammals present on Australia before about 20 million years ago.

However, the evolutionary mystery still remained a puzzle as the fossil that had been discovered showed a skull that was significantly bigger than current-day platypuses. This only showed the obvious degeneration in present day platypuses but this information was already inferred due to previous mega-fauna degeneration knowledge. This shows how lack of knowledge can shape the views of scientists despite the fact that there is more advanced technology.

Food Collecting:

Scientists were yet to unravel this puzzle until recently. Many scientists believed that the primitive (or dumb) platypus had not evolved to enough of an extent that it was able to be a food collector. Scientists believed that it simply swam along eating any food that came along.

However with increasing technology such as acute magnetic detectors as well as fibre optical vision and fast computers scientists have bee able to determine that the platypus has a highly tuned receptor that is able to pick up the weak electric fields of shrimps and worms. This sense is so acute that it is able to detect prey under mud and rocks. It has also been discovered that platypuses don’t stay under water for long periods of time to collect food.

Thus due to increasing technology, scientists have been able to discover much more information about the platypus. This has changed the way that they perceive the animal and their views have shifted as the depth of knowledge that they posses increases. Thus showing how the ideas of scientists changed in the last 200 years about individual species such as the platypus as new information and technologies became available.

2. The changes in Australian flora and fauna over millions of years have happened through evolution.

Discuss examples of variations between members of a species

A species is a group of organisms that can interbreed and produce fertile offspring. Within a species there is variations – i.e. differences between individuals.

Variations occur due to genetic mutations or environmental adaptations.

Examples of Variations:

- In humans – eye colour, skin colour, height, build, etc are all variations that make each individual different from another

- In dogs (Canis familaris), the are great differences in size, colour, hair length etc.

- The Epacris Impressa is the ‘common heath’. It has flowers that are tubular or bell-shaped. It is only found in Australiasia and belongs the family Epacridaceae. It is found in the dry sclerophyll forest and coastal heaths of Tasmania, and the East coast. It is a very polymorphic species. Those that are found in Victoria are most distinguishable with large flowers and grayish leaves covered in hairs. The soils in this region are more fertile compared to ‘normal’ land in Australia. The ‘Bega’ from of the heath as bright red flowers and some can have white flowers and may be located in the same population.

Identify the relationship between variation within a species and the chances of survival of that species when environmental change occurs

Variations in a species are important in a changing environment. A particular adaptation may provide an advantage (eg as protection against a predator or too find food or attract a mate).

The variation in the gene pool of a population is important in determining the chances of survival of that population. If there is a sudden change in the environment, those individuals in the population that randomly possess a variation that is of advantage are more likely to survive the changed conditions. Individuals that do not possess that variation may be unable to compete and survive. Those that survive are more likely to reach an age where they can reproduce and pass their favourable characteristic on to their offspring. Individuals with less favourable variations will eventually be eliminated from the population as they are out-competed.

If individuals within the population become so different that they can no longer interbreed with individuals from the original population to produce fertile offspring, then the population is considered to be a new species. Therefore variation in a population is extremely important, because it gives the population a better chance of surviving a sudden environmental change.

Variation can arise is several ways. In both sexually and asexually reproducing organisms mutations can change the genetic code and hence change the characteristics of the individual. A mutation that occurs in the body cell of a multicellular organism will be lost when that individual dies. A mutation that occurs in a sex cell (such as sperm) it will be passed on to the next generation.

In sexually reproducing organisms variation is also caused by random segregation of chromosomes during meiosis, crossing over during meiosis and the fact that sexual reproduction involves the union of two gametes which means half the characteristics come from one parent and the other half from the other and thus the offspring is not identical to either parent.

Heredity is the transfer of similar characteristics from parents to offspring.

Heredity and variation are both essential for evolution to occur.

Darwin Wallace Theory of Natural Selection:

In 1858, based on their independent studies and observation of flora and fauna over many years, both Charles Darwin and Alfred Wallace proposed the same mechanism for evolution— the mechanism of natural selection. Their theory of evolution by natural selection is based on four main points:

1. Variation—individuals within a population that reproduce sexually, show variations that can be passed from one generation to the next

2. natural selection—selective pressure (e.g. change in the environment) puts constraints on organisms (e.g. resources become limited). These constraints are called selective pressures and determine which individuals are best suited to the prevailing conditions

THE EVOLUTION OF AUSTRALIAN FLORA AND FAUNA

3. survival of the fittest—more individuals are produced within a population than can survive; those individuals with favourable variations have a greater chance of survival because they out-compete those with less favourable variations. Organisms that do survive to reproduce will pass their genetic variations on to their offspring

4. isolation—if a population is isolated from the original population, interbreeding will be prevented over a period of time. This is necessary for evolution of a new species to occur.

Darwin and Wallace’s two main ideas

■ Natural selection and isolation are the mechanisms by means of which organisms evolve: the environment selects individuals, based on variations that favour their suitability. When resources in the environment become limited, these individuals survive, reproduce and pass on their characteristics.

■ Speciation, the formation of a new species, occurs when a population becomes isolated from the original group of organisms. Only those individuals that have variations that favour their survival under the changed conditions will reproduce and pass on their characteristics to the next generation. Eventually, the population becomes so different from the original population that they are no longer able to interbreed and produce fertile offspring. A new species has been formed.

Identify and describe evidence of changing environments in Australia over millions of years.

The main evidence that shows changing environments in Australia over millions of years comes from the rock types and fossils present in the rocks. Although we cannot be totally precise about the environmental tolerances of extinct plant species, paleoclimates can be determined by comparing the extinct species with closely related extant species and looking at a range of fossils found at one site.

Evidence showing changing environments:

1) Evidence of Glaciation:

Glaciers leave a permanent mark on the landscape. As the ice river grinds over the land it polishes the rocks making them quite smooth. It also picks up debris to carry along and the debris scratches the rocks in an almost parallel manner. These rocks show that Australia had glaciers when Australia was Near the south pole.

2) Evidence of Swamps:

As the temperatures rose, going from cold to cool and the ice melted, sea levels began to rise. Many coastal areas around the east coast became swamps. Evidence for this change is shown in plant fossils. For example the Glossopteris lived in cold boggy swamps and this plant is the basis for our coal deposits.

3) Evidence of a Warmer Climate

After the cold Permian era, the climates warmed in the Triassic and the changing plant life shows this change as the Glossopterids disappeared and new seed ferns and conifers that were better adapted appeared.

4) Evidence of Rainforests in Central Australia

Fossils of Nothofagus the southern beech tree which grows in humid rainforests have been found in rocks in central Australia dated 20-30 million years ago. This shows that rainforests once existed in central Australia. Some of the fossil beds form a stratigraphic layers showing the sequence of events over a long period of time. The Law of Superposition can be used to reconstruct a history of the area. There were climate fluctuations related to ice age periods and this is the reason that Nothofagus disappeared from that area.

5) Evidence that Australia was becoming Drier

Tertiary fossils from central Australia show the presence of several permanent freshwater lakes surrounded by rainforest. Fossils include marsupial lions, flamingos, crocodiles, dolphins. As Australia began to dry out the fossils tell as story of the rainforests being replaced by more open vegetation and the arboreal animals were being replaced by ground dwellers.

Aridity increased and the forests were replaced by woodlands. This is shown by the change in plants to Eucalyptus and then to wattle and saltbush. Around 20000 years ago the ice sheet in Antarctica spread to its greatest extent enhancing aridity in Australia and causing a 100 m drop in sea level. This evidence is shown by the formation of large gypsum dunes at Lake Eyre.

Identify areas within Australian that experience significant variations in temperature and water availability

Australia has great variations in temperature and water availability. It is the driest continent on Earth with a mean rainfall that varies from 0.15 metres in central Australia to more than 3.6 meters in the tropics and Tasmania. Droughts can last for several years and this affects plant and animal life. Areas north of the Tropic of Capricorn have year round high temperatures with a wet season in summer and a long, dry season through winter. The temperate areas south of the tropic of Capricorn have rainfall all year round with hot summers and mild to cool winters with only the high mountain areas receiving snow.

Inland Australia shows the greatest variation in daily temperatures as the heat of the day heats the land and the temperatures can easily reach 40 degrees but the heat is rapidly lost at night due to the clear skies and lack of cloud cover.

The water availability in inland Australia can also be highly variable as rainfall is unreliable with floods following long periods of drought.

Identify the changes in the distribution of Australian species, as rainforests contracted and sclerophyll communities and grasslands spread, as indicated by fossil evidence.

Changing Flora and Fauna

65 mya: Moist climates supported rainforests which formed the dominant vegetation type. Rainforests had replaced towering conifer forests. The climate was wet and warm and there was a large variety of flora and fauna.

45 mya: As Australia separated from Antarctica and began drifting north, the climate dried out and the Australian rainforests contracted, remaining mainly in the coastal regions in Australia. The inland areas had more open forests and woodlands. Evidence of this includes fossils show that inland forests dried up and the vegetation changed from forest to woodlands. Some living plants such as the Nothofagus remnants of the time Australia’s climate was much more tropical.

The climate then went from wet to dry and the pattern of forests, grasslands and deserts kept changing. This resulted in the abundance of megafauna

Indigenous people arrived and used fire to clear vegetation. Evidence of this is in fossils that have an increase in the incidence of carbon deposits which coincided with the arrival of humans.

Australia continued to become drier and the drier climate meant that there was lightning that resulted in fires, thus fire resistant species began to flourish. This resulted in the replacement of rainforest by fire resistant plants like eucalyptus.

In the interior of Australia, grasslands developed. As sea levels have risen and fallen, Australia has experienced a lot of erosion and so nutrients have leached from the soil resulting in soils which are nutrient poor.

Australia’s unique flora

Plants which are able to withstand fire and grow in soils lacking nutrients are now characteristic of Australia. Dry sclerophyll plants and grasses typically grow in nutrient poor soils on rough terrain, such as the slopes of mountains.

discuss current theories that provide a model to account for these changes

Several reasons have been put forward to account for the changing distribution of plants and animals in Australia as the vegetation changed from rainforest to sclerophyll forest to grassland. There was also a corresponding change in animal life as most of the megafauna became extinct around 40000 years ago.

Climate Change (Increasing Aridity and frequency of fires)

As Australia drifted north into warmer latitudes, combined with glacial periods and their corresponding times of high aridity, there was contraction of the rainforests containing Nothofagus. Some areas were replaced with dry rainforests while other areas were replaced with sclerophyll forests.

Sclerophyll plants are adapted to dry conditions and poor soils. The increased carbon in fossils shows an increase in fires from around 130 000 years ago. The fires could have been caused by lightning strikes and combined with dry conditions were more devastating than before. Fires were also used by Aboriginals as a hunting means and a form of land management. Plants that are fire tolerant have a natural advantage under this new selective pressure. Thus, this favoured the eucalyptus which are able to regrow from buds below the bark, while the other species such as Mulga are wiped out.

Arguments supporting climate change:

Large animals such as megafauna, which were dependent on an ample supply of water, would have died out when water became scarce. They may also have died out because they could not manage the sudden change in temperature, their breeding seasons may have been affected and possibly the plants that they ate became less freely available and/or less palatable.

Arguments against climate change:

The last ice age was probably similar to previous ice ages. If so, why would be the last one have had such an immense effect, when there is no evidence that the previous ice ages had a similar result? Also, the earlier extinctions seem to have occurred before the peak of the last ice age.

Impact of humans

Aborigines arrived in Australia about 40 000 years ago, probably having ‘island-hopped’ from the north. They were extremely successful predators.

E EVOLUTION OF AUSTRALIAN FLORA AND FAUNA

They used fire to burn back the bush— ‘fire-stick’ farming techniques involved burning the bush to regenerate grasses for the animals and for themselves, since increasing an abundance of animals meant that there would be more available for hunting. Humans hunted the megafauna and, because the larger animals were slower, they were the ones that were killed.

The smaller, faster animals that escaped survived to pass their genes on and so the species evolved to become smaller. It appears that the original indigenous people killed off most of the Australian terrestrial animals that were larger than they were. The introduction of the dingo may have also led to a decrease in the diversity of carnivore predators—it is possible that the dingoes drove the thylacine and Tasmanian devil to extinction on the mainland.

Arguments against the arrival of humans:

There is no fossil evidence of kill sites and very little evidence of humans and megafauna coexisting. If you consider the size of the animals, there is an overlap in the size of the smallest extinct species and that of the largest present-day species.

Arguments supporting the arrival of humans:

Main evidence for the theory of the arrival of the humans at the same time as the increase in fires is that the increase in carbon deposits in fossils coincides with the time of the arrival of humans (40 000 years ago). The smaller species of megafauna which became extinct had short limbs which would have made them slow; the largest surviving of our present-day species are also among the fastest (e.g. red and grey kangaroos).

discuss Darwin’s observations of Australian flora and fauna and relate these to his theory of evolution

Darwin tried to explain the similarities and differences (variations) that he observed in the Australian flora and fauna. He believed that, rather than similar creatures being created independently, they could arise from a common ancestor, accounting for basically similar organisms changing to become different (divergent evolution). He also suggested that organisms that started off distantly related, but were subjected to similar environments could evolve similar features (convergent evolution).

Darwin had made numerous observations including these examples of the fact that similar environments in completely different parts of the world seemed to be inhabited by animals having similar adaptations, but obviously belonging to different species. His curiosity drove him to think about possible reasons for the resemblance.

Observation forced him to discard the idea of fixed, unchanging species and so Darwin set out to try to find an explanation for his observations. He made many observations, both before and after his visit to Australia. Some of his most famous work included the study of finches and other birds, where he found that island populations may differ noticeably from mainland birds as a result of isolation and genetic drift.

How Darwin’s Observations related to his theory

Darwin’s observations of birds, marsupials and monotremes mammals in Australia revealed similarities with mammals in Europe which lived in similar environments. This led him to the idea that organisms could evolve to become similar (convergent evolution). If organisms live in similar habitats, similar variations that they possess would be favoured by natural selection to enable them to survive and breed in those conditions. These favourable variations would then be passed on to the next generation.

Darwin was puzzled over the variety of organisms he saw, and the adaptive nature of this variety. He began to question the theory of special creation. He tried to explain the similarity between the animals on the Galapagos Islands and South America, similarities between living forms and fossils and similarities between adjacent species. Due to this be became convinced that new species can develop from an ancestral type.

The Darwin-Wallace Theory of evolution by Natural Selection

In 1858, both Charles Darwin and Alfred Wallace proposed the same mechanism for evolution. The mechanism of natural selection. Their theory of evolution by natural selection is based on four main points.

Variation: Individuals within a population that reproduce sexually, show variations that can be passed on from one generation to the next.

Natural Selection: Change in the environment puts constraints on organisms (eg. Resources become limited). Those constraints are called selective pressures and determine which individuals are best suited to the prevailing conditions.

Survival of the fittest: More individuals are produced within a population that can survive; those individuals with favourable variations have a greater chance of surviving because they out compete those with less favourable variations (there is a struggle for survival).

Organisms that do survive to reproduce will pass on their genetic variations onto their offspring.

Isolation: If a population is isolated from the original population, interbreeding will be prevented over a period of time. This is necessary for evolution of a new species to occur.

Darwin and Wallace’s two main points:

Natural selection and isolation are the mechanisms by means of which organisms evolve: the environment selects individuals based on variations that favour their suitability. When resources become limited in the environment, these individuals survive, reproduce and pass on their characteristics.

Speciation: The formation of a new species occurs when a population becomes isolated from the orginal group of organisms. Only those individuals that have variations that favour their survival under the changed conditions will reproduce and pass on their characteristics to the next generation. Eventually the population becomes so different from the original that they are no longer able to interbreed and produce fertile offspring. A new species has been formed.

Present information from secondary sources to discuss the Huxley– Wilberforce debate on Darwin’s theory of evolution

Darwin's Theory of Evolution is the notion that all life is related and has descended from a singular common ancestor. Thus concludes that all species are related. Darwin's theory assumes that the development of life occurred from a non-living resource and exaggerates that the evolution that occurred was purely natural. I.e. complex creatures evolve from more simple ancestors naturally over time. Simply put, as genetic mutations (which are random) occur within an organism's genetic code, the beneficial mutations are preserved because they aid survival this is known as natural selection.

The Huxley – Wilberforce debate on Darwin’s theory of evolution is noted as one of the greatest encounters between science and religion. Samuel Wilberforce, bishop of Oxford, fuelled by his undying belief of Christianity attempted to show that Darwin’s Origin of Species, was false. T.H. Huxley, a scientific man who supported Darwin’s theory of evolution debated against Wilberforce at the British Association of Oxford on June 30th 1860. The debate was attended by numerous high ranked officials, all of which had their own points of view.

The exact recounts of the Debate are unavailable but letters and certain transcripts suggest that the debate was a heated one. Many of Britain’s current insults are believed to have originated through that debate. Furthermore, the overall belief is that T.H. Huxley was able to defeat Wilberforce in the debate, through the use of simplistic scientific principals and facts. "Sam was shut up—had not one word to say in reply, and the meeting was dissolved forthwith”

Many different perspectives and theories are present about the exact nature of the debate, thus making the information we have currently biased. Overall, it is still unclear who said what, or how the debate was finalised, but the encounter will be remembered for its legendary status.

Retort: Wilberofrce supposedly asked Huxely if he was descended from an ape on his grandmother’s side or his grandfather’s side. To which Huxely replied that he would rather be the offspring of two apes than a man who uses his intelligence to bring ridicule to a grave scientific discussion.

Sec 3: Continuation of species has resulted in part, from the reproductive adaptations that have evolved in Australian plants and animals.

Distinguish between the processes if meiosis and mitosis in terms of the daughter cells produced.

Meiosis is a type of cell division that produces gametes. Gametes are sex cells and have half the normal number of chromosomes. Mitosis is the process in which the cell nucleus divides into two.

There are some similarities between meisos and mitosis. However meisois involeces two cell divisions and produces 4 haploid daughter cells (called tetrads) while mitosis involves one cell divison and produces two identical daughter cells. Mitosis occurs in all living things while meisosis occurs only in organisms that sexually reproduce.

In mutlicellular organisms mitosis occurs in body cells (stomatic cells) and is needed for growth, repair and maintenance while meiosis occurs in the gonads (testes and ovaries) and is needed for sexual reproduction.

Note: Humans have 46 chromosomes and this is known as the diploid number. (23 pairs of chromosomes). Each haploid cell produced by meisois has 23 chromosomes.

How variation occurs during Meisois:

Crossing over occurs—arms of homologous chromosomes exchange genetic material (this introduces genetic variation).

Each pair of chromosomes separates so that one entire chromosome of each pair

moves into a daughter cell. This not only halves the chromosome number in gametes, but it also leads to genetic variation, depending on which chromosome (paternal or maternal) of each pair ends up in which daughter cell. This is termed independent assortment of chromosomes and produces different combinations of genes in different gametes.

Fertilisation—there are many combinations of chromosomes possible in gametes as a result meiosis, resulting in a variety gametes forming. Variation dependent upon which gametes fuse during fertilisation.

Compare and contrast internal and external fertilisation

Fertilisation is the bringing together of haploid gametes.

External Ferilisation takes place outside the body. Gametes are shed directly into the water, fertilisaiton occurs, and the fertilised eggs develop into adults. Many millions of gametes are usually released to ensure that some will successfully meet and feritlisation will occur. The requirement of water ensurs that the eggs and sperm do not dry out. Since the gametes and developing young are exposed to elements such as water currents, light, temperature changes, predators, a huge amount of eggs are released to increase chance that some will survive.

There is no contol over the gametes meeting, but their chances of doing so are increased by:

- cyclical reproductive behaviours

- synchronised timing of gamete reproduction and release

- the development of courtship and mating behaviours in animals.

This form of fertilisation is successful in an aquatic environment, enabling the gametes and young produced after fertilisation to spread out and colonise large bodies of water.

Internal Fertilisation occurs inside the body of the female in animals or in the female part of the plant in sexually reproducing plants. It is a characteristic of most land orgnaisms due to the fact that after fertilisation further development of the new organism requires water.

Direct transfer of gametes greatly increases the chance of successful fertilisation (copultion). Males still produce large numbers of sperm but females produce far fewer eggs. The reproductive strategies involved include bringiing the sexes together with mating behaviours and having a method of gamete transfer.

Organisms on land have developed many mechanisms to ensure successful transfer of the male gametes to the female. The female provides a moist environment for the sperm to swim to the egg. Without the need for external water for fertilisation, even the driest environments could be successfully colonised.

In flowering plants the male gamete is the polle and once the pollen lands on the stigma in the female part of the plant, thje pollen tube grows down to the ovary and the male gamete is transferred and the ovum is fertilised. This means that fertilisation occurs inside the plant, dessication is prevented and the mechanism is an adaptation for plants to live on land.

Note: Dessication is the process of the gametes drying out.

|External |Internal |

| Differences |

|Large numbers of Gametes produced |Large number of male gametes but limted female |

|Occurs in open water environments |Occurs inside female (terrestrial organisms) |

|Simulateanous spawning (release) |Male must copulate |

|Low chance of fertilisation |High chance of ferilisation |

|Young is vunerable to external conditions |Protected and Safe within female body |

|More frequent reproduction |Less frequent reproduction |

| Similarites |

|Both male and female gametes required for fertilisation |

|Gametes are provided with a watery environment where fertilisation will occur. |

|All possible fertilisations will grow to form zygotes |

|If male and female gametes are in close proximity, fertilisation will occur. |

Discuss the relative success of these forms of fertilisation in relation to the colonisation of terrestrial and aquatic organisms

Organisms in aquatic environments are successful in their reproduction and survival as they have adaptations suited to reproducing in this type of environment; however, this also means that they are completely dependent and reliant upon their environment providing the water required for successful external fertilisation. Water protects the gametes from desiccation and possible heat stress. However, in order to survive on land, organisms needed to overcome the dependence on aquatic environments for fertilisation by providing their own enclosed moist environment within the female reproductive tract, protected from the dry terrestrial environment. Flowering plants have colonized the land by fertilising internally and avoiding gamete desiccation. Reptiles have also colonised the land successfully by producing adaptations to the dry environment by carrying out internal fertilisation and allowing their young to develop inside a waterproof egg to protect from desiccation. Even further, mammals allow internal development of their young after internal fertilisation has occurred. This ensures successful reproduction and survival of the respective species in colonising the land.

External fertilisation

In an aquatic environment

Organisms attempting to carry out external fertilisation in an aquatic environment are usually highly

successful. In this environment gametes do not dry out, or dehydrate; however, organisms must produce very large numbers of gametes to compensate for the losses from predation, disease and dispersal to unsuitable environments.

In a terrestrial environment

Organisms attempting to carry out external fertilisation on land are not successful at all due to their complete reliance upon a water environment for fertilisation and the transfer of gametes.

Internal fertilisation

In an aquatic environment

Internal fertilisation is not a necessary adaptation for most aquatic species; however, it is a successful method of fertilisation in this environment. Fewer gametes are required because of the higher chance of the gametes uniting.

In a terrestrial environment

Internal fertilisation has only been possible on land because of overcoming the need for water for fertilisation. This method of fertilisation is very successful as the mechanism for direct transfer of gametes avoids dehydration and loss by dispersal, so fewer female gametes are required. The success of this form of fertilisation is very high as the environment is enclosed in a confined space protecting from predation and disease. Even the driest environments can be colonised successfully by using this method.

describe some mechanisms found in Australian flora for:

▪ pollination

▪ seed dispersal

▪ asexual reproduction

with reference to local examples

Pollination

Pollintion is the transfer of pollen from an anther to a stigma in flowering plants (angiosperms) and from make to female cones in conifers (gymnosperms).

Parts of a Flower:

There are two types of pollination:

- Self pollination

- Cross pollination

Self Pollination:

In some Australian plants the pollen matures and the anthers split open releasing the pollen which is usually depositited on its own stigma. This is self-pollination. In many species the stigma and anthers of a flower mature at different stages to prevent self pollination as it is underisable for evolution.

Example: Daisy and Sun orchids self pollinate

Cross Pollination:

When pollen from a flower’s anther pollinates a flower’s sitgma from a different plant, the process is called cross-pollination.

Gymnosperms have only one method of cross pollination and that is wind. Wind pollination occurs in these plants when the anther which is usually long released the very light pollen. They usually lack nectar and scent and the large stigma’s are well exposed inorder to catch the airborne pollen. Example: Native pines and grasses use wind pollination.

Some angosperms use wind pollination but many have evolved to use differing methods of

cross-pollination

Insect Pollination

Most flowering plants are pollinated by insects especially bees. In many cases, the insect and the plant are dependant on each other – the plant needs a pollinator and the insect needs food. To attract the insects the flowers have a scent, colour and specific arrangement of petals. The petals often have marks called “honey guides” to guide the insect to the stigma where they depost pollen from the last flower they visited and then to the stamen to collect new pollen and then to the nectar for the reward. The filaments holding the anther are short and stiff so that pollen can be transferred when the insect brushes past.

Example of an insect pollination plant is the bottle brush or the eucalyptus.

Bird Pollination

Birds usually pollinate red flowers. Many flowers are long and thin and only the beaks of honeyeaters can reach the nectar. The pollen can be sticky or powdery and large amounts of nectar are produced.

Examlpe of a bird pollination plant is the Waratah. Waratah flowers are red, long, tubular and slightly curved; their rate of nectar production is relatively high and they are commonly visited by nectar-feeding honeyeaters.

Mammal Pollination

Mammals such as bats and tiny honey possums pollinate flowers. The possums move over the flowers.

For example: Banksias allow for the honey possum use their long thin snout to reach the nectar. The pollen sticks to their fur, which is then transferred to another plant.

Pollination by deceit

There are some orchids whose flower mimic the shape and colouring of female insects. The mimics are so realistic that the male insects will attempt to mate with the flowers, thereby pollinating them.

For example: The hammer orchids of Western Australia have a flower that resembles a wingless female wasp with shiny eyes, hairy thorax and a fat body. The flower is held outwards by a hinged arm. When the male wasp attempts to copulate with the flower. The hinged arm flings the wasp to the other end of the flower (the stigma), where the pollen is deposited. Pollen is located on the flower.

Seed Dispersal

After successful pollination and fertilisation of the flower, the seed develops. It is an advantage for a plant to spread or disperse its seeds over a wide distance. This prevents overcrowding from occurring within the same plant species and increases the chances of survival in situations of environmental change such as fire.

Seeds are dispersed by wind, Animal, fire, water or explosion.

Wind Dispersal

Some seeds are aerdynamically designed to be blown long distances by the wind. Very small seeds can be carried by the wind. If the seed has food reserves it can be heavier but still dispersed by the wind if it has wings or a parachute or some other form of buoyancy mechanism.

For example: Dandelions have feathery parachutes to catch the wind and float away and Hakea has a seed with wings.

Animal Dispersal

There are several mechanisms that are used in seed dispersal.

- Some seeds are hooks or burrs with bristles and spines to attach to fur and feathers. Eg. Bindii

- Other seeds are in fuits and berries which are eaten by the animal. The seed is protected by an indistestible layer which passes through the digestive system unharmed to be dropped onto the ground at some other point.

For example: Mistletoe berries are eaten by the mistletoe bird and farily quickly the sticky seed is expelled by the bird onto a tree branch, where the plant begins to grow. The deposit with feaces adds nutrients for the plant to grow.

Fire Dispersal

Several Native plants such as Eucalyptus only release their seeds after the occurance of a fire. After a fire, the eucalyptus is destroyed, exposing the capsules which release the seeds for dispersal usually by the wind. This provides a significant advantage as the seeds grow in a uncompetitive environment, allowing for them to flourish.

Water Dispersal

Some seeds rely of water dispesal, such as the water gum and mangrove. Seeds may float small or large distances from the parent plant along rivers and even across sees. The seeds are usually equipped with some sort of flotation device that allows for their protection.

Explosion

Some seeds are voilently propelled from the base of the fruit in an explosive dischanrge. Seeds are ejected from the pod at high speeds, caused by the drying and contraction of the pod. Some seeds such as the pea plant seeds can be hurled almost two metres in the air. This allows for greater dispersal of the seeds.

Asexual Reproduction

Asexual Reproduction is the making of a new individual without the use of sex cells or gametes. Only one parent is required for the mitotic cell divisions to occur.

Some types of asexual reproduction are:

- Binary Fission - Bacteria

- Budding – Coral and Yeast

- Spore formation – Fungi and moss

- Vegetative propagation – roses (plant cuttings regenerate)

- Fragmentation and Regeneration – Starfish

- Parthenogenesis – Honeybees and Gecko

Vegatative Propagation

In vegetative propagation parts of the parent detach and will grow into new individuals.

The advantage of VP is that less time and energy is needed to produce new individuals – the need for pollinators, pollination, fertilisation and the production of seeds + dispersal is removed.

The disadcabtage is the lack of genetic diversity. This is not a problem when the environment is stable but the lack of variation reduces survival chances for the evolution if the environment changes.

The new plant is simply regenerated out of one of four parts – stolons, tubers, rhizomes, and suckers.

Stolons or ‘runners’ are stems that grow along the sruface producing new roots and leaves at nodes. Spinefex grass or strawberry plants are an example of this

Tubers are swollen underground stems that store food and new plants can grow from the tuber. For example, a potato is a tuber and they eye of a potato are the buds which can each grow a new plant

Rhizomes are underground stems that give rise to new shoots at the nodes. Ginger and grasses employ this technique in order to reproduce.

Suckers are new shoots that arise from undergrouynd stems, often after fires. Certain types of pea plants or fan flowers are able to reproduce in this manner.

Parthenogenesis

This is the development of unfertilised effes into adults (esp honey bees). In honey bees every egg laid by the queen will develop whether or not they are fertilised. Most of the eggs are fertilised effs and develop into sterile worker females, while the few eggs which are not fertilised develop parthenogenetically into male drones.

In parthenogenesis the offspring are identical to the parent, which is an evolutionary disadvantage in a changing environment, but it allows the build up of a large population in a short space of time without the need to find a mate.

• describe some mechanisms found in Australian fauna to ensure:

o fertilisation

o survival of the embryo and of the young after birth

Many Australian animals have specific adaptations to ensure the survival of the embryo and the young after birth.

Internal fertilisation means that the sperm and the egg are protected in an enclosed space for fertilisation but once the zygote has formed it also needs protection from the elements, eg. From desiccation and from hungry predators. The shelled egg provides protection for the embryo

Eggs that are fertilised externally usually have little protection and little parental care. Eg fish or amphibian eggs.

Species where the young develop outside the female are oviparous while species where the female gives birth of live young are said to be viviparous.

The Shelled Egg

Reptiles, birds and monotreme mammals lay shelled eggs. The embryo develops in the egg which has a series of different membranes.

The yolk sac holds the yolk which the food for the developing embryo

The ammion is the inner membrane which surrounds the embryo allowing it to grow in a watery medium

The allantois receives and stores the embryo’s urinary wastes.

The chorion is the outer membrane surrounding all other membranes and embryo.

Care for Young

There is an inverse relationship between the number of eggs released and the amount of parental care

“As the number of eggs produced increases, the amount of care provided by the parent towards each offspring is reduced”

The freshwater crocodile shows the most care of all reptiles. After laying her eggs in a secure location, the mother comes back after 2 months (when they hatch), and takes them to the surface of the water body, where she protects them and provides food until they are able to support themselves.

Birds have a larger level of degree of parental care than reptiles. Many birds have a muscular sac called a crop in their oesophagus which is able to store food, which is then regurgitated later to feed their young. Magpie Geese and Herons are two examples of birds that do this.

Mammals on the other hand have the highest level of degree of parental care. For example the joey of the Kangaroo does not become independent until 18 months old. This higher level of parental care enables the young to grow to a size where they are able to feed and support themselves and efficiently defend themselves against predators and thus increase the chances of survival.

• Explain how the evolution of these reproductive adaptations has increased the chanced of continuity of the species in the Australian Environment

Asexual reproduction

Organisms that reproduce asexually do not have to rely on another individual organism to provide gametes and are at an advantage when sudden or unexpectedly favourable conditions arise because they can quickly reproduce themselves (with offspring identical to the parent). This can become a competitive edge if the organism lives in an environment that is often disturbed, and they are particularly well suited to a certain environment or habitat. Asexual reproduction among plants is far more common in harsh environments where there is little margin for variation. The main disadvantage to asexual reproduction is if extremely harsh conditions arise, the whole group of species is particularly vulnerable to these conditions, or to disease, parasitism and predation.

Sexual reproduction

Sexual reproduction produces offspring that are genetically different and possibly better adapted to new and changing environmental conditions than their parents. This gives the species a better chance at surviving in ever-changing environments. However, sexual reproduction is often a more energetically expensive process, compared to asexual reproduction, and may be the first thing an organism abandons in times of hardship.

External fertilisation

The chances of successful external fertilisation are increased by the synchronisation of the release of gametes, reproductive cycles and the mating behaviours of each species. External fertilisation and development means that parents spend less time looking after the young, but more gametes have to be produced to ensure that some eggs get fertilised. The advantage of this method is the high dispersal of young. The gametes are thrown into the sea and fertilised eggs are carried away to settle in an area different to their parents. This reduces competition for food and living space for the parent generation, and allows quick recovery of populations away from damaged areas.

Internal fertilisation

Fewer gametes are produced because there is a much higher rate of fertilisation and survival. The move to internal fertilisation and development has demonstrated new adaptations for reproduction on land, which may have started with the ovules of flowers becoming enclosed in the ovary to provide adequate protection from desiccation.

Parental care

Many aquatic species simply abandon the fertilised eggs and leave them to risk development in the open sea. This means that less energy is put into caring for the young and the survival rate of the young is much lower; therefore, more eggs have to be produced to compensate. Mammals are generally viviparous, fish, birds, some reptiles and many invertebrates are oviparous (egg-laying). Oviparous animals will devote varying amounts of energy to caring for their eggs. Some oviparous animals brood their eggs until they hatch to increase the survival rate of their eggs, while others will stand guard over a nest of eggs until they hatch.

Plants

In plants, self-pollination expends less energy in the production of pollinator attractants and can grow in areas where the kinds of insects or other animals that might visit them are absent or very few. These plant species contain high proportions of individuals well-adapted to their particular habitats. In cross-pollinators, animal agents such as insects, birds and mammals have become a more effective way of transferring pollen to the stigma. As flowers become increasingly specialised, so do their relationships with particular groups of insects and other animals.

The transfer of pollen between flowers of separate plants ensures cross-pollination and may have been important in the early success of angiosperms. The various means of effective fruit dispersal that evolved in the group were also significant in the success of angiosperms. As early angiosperms evolved, all of these advantageous features became further elaborated and developed, and the pace of their diversification accelerated. In addition to insects, birds and mammals now assist in pollination and seed dispersal.

Adaptations for colonization and survival

Reproductive adaptations are needed for successful colonisation and survival in the Australian environment. Australia has many areas of harsh arid conditions, making it difficult for effective fertilisation and development. Reproducing offspring in times favourable to the organism— suitable climate and resources, available water and food supply— increases the chances of continuity of the species.

Species need to survive the harsh times and maintain their population numbers (without becoming extinct) until conditions improve, then utilise adaptations to rapidly increase species numbers afterwards (e.g. the kangaroo with its embryo on standby). Many Australian plants possess adaptations to harsh conditions like fire, for example hakeas have woody seed pods able to survive the high temperatures of fire. The pods do not usually open unless stimulated by the heat of fire, landing on soil enriched by ash from the fire. This means that the seed is not released and dispersed until environmental conditions are favourable for rapid increase and therefore continuity of the species. Hakeas also regenerate and ensure continuity of the species after fire by growing lignotubers from the fi re-damaged plant.

• Describe the conditions under which asexual reproduction is advantageous, with reference to specific Australian examples.

Only one parent is required so energy is not wasted on producing large numbers of gametes or on finding a mate.

This is advantageous:

• in arid conditions or where environmental conditions are not as favourable; for example, spinifex grass survives and reproduces successfully by sending out runners in harsh sand dune conditions such as high temperatures, high salinity and wind erosion

• when food supply may be short and there is a need to use less energy to reproduce.

• when there is a small mating population or time constraints on finding a mate.

• It is a relatively quick process and large numbers of offspring can be produced rapidly. This is an advantage when rapid recovery is needed after a decline in numbers (e.g. after a bushfire or drought). The colony wattle can send up shoots from the outer roots which grow into separate plants if the parent shrub dies. This allows for re-growth to occur quickly. It often forms colonies from root suckers.

• If there is no variation in the environment then the identical offspring will always be adapted to their surroundings and survive to reproduce successfully. Corals, such as the grooved brain coral reproduce by budding when conditions are favourable, however if the environment does change the entire species may rapidly decline and die out.

• Asexual reproduction is advantageous when environmental conditions are stable. In this situation the offspring of the parent plants are identical, having features that make them suited to the environment and likely to survive to reproduce themselves. This type of reproduction allows rapid colonisation after harsh conditions such as fire or drought which may decrease the species population numbers. Many Australian plants have adaptations for survival in this situation.

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Spindle forms on the equator the cell which is able to pull the chromosomes away

Chromosomes are attached via a centromere.

Spindle retracts after the chromosomes are in their desired location.

Spindle forms on the poles of the cell which is able to pull the chromatids away

Spindle retracts after the chromatids are in their desired location.

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