The Liquid Earth

Evolution is the result of the tendency for some organisms to have better reproductive success than others with changes in gene frequency in a population from one generation to the next. Evolution helps us to understand the history of life.

Fig.1 Salt water Crocodile (Crocodylus porosus)

Mutation is a copying error in the replication of DNA , it can give a rise to variation in an organisms phenotype and if this new phenotype is beneficial to survival and reproductive success it will be naturally selected against the immediate environment , then if this selected organism leaves many descendants with the same beneficial traits then the populations gene pool will change in allele frequency and you have Evolution. However, mutations brings about variation which is the basis of evolution and the two types of variation are heritable and non-heritable. In this sense, mutations which need to be in the line to be heritable serve up variations in organisms that are subject to natural selection and selected organisms leave more decadents that have a higher genetic representation in the population gene pool; and so evolution had occurred yet again.

The relationship between mutations and genetic variations are that mutations are random changes in DNA; genetic recombinations are a new arrangement of genetic material, as a result of sexual reproduction. Together they are the ‘fuel’ that powers evolution, as the direction of which is determined by natural selection. Although some mutations can be very successful in some organisms as mutations play a role in evolution by natural selection. They provide the allele variation that natural selection selects from. In a similar way the significance of genetic variation towards natural selection and evolution as natural selections ‘selects’ individuals within a population whom have traits that increase the organism’s ability to reproduce. If no genetic variation was present, then all individuals would be identical and equally fit in their environment.

In reference to the saltwater crocodile (Crocodylus porosus), Earth’s largest living crocodilian and some say the animal most likely to eat a human. Still today display such a prehistoric looking appreance, from which they did evolve from the dinosaur age. With average size males reaching 17 feet and up to 450 kilograms, but specimens 23 feet long and weighing 2,200 pounds (1,000 kilograms) are not uncommon.

Kingdom     Animalia
Phylum       Chordata
Class           Reptilia
Order          Crocodylia
Family        Crocodylidae
Genus        Crocodylus
Species     C. porosus

Fig.2 Countries where organism inhabits

Saltwater crocs, or “salties,” as Australians affectionately refer to them, have an enormous range, populating the brackish and freshwater regions of eastern India, Southeast Asia, and northern Australia. They are excellent swimmers and have often been spotted far out at sea.

The saltwater crocodile can live in fresh water, salt water or brackish (mixed) water. If it is living in salty water, its kidneys and tongue allows the excretions of salt. It has eyes and nostrils high up on its head and a broad tail with webbed feet for swimming. Three eyelids, a leathery two for protection and one clear lid suited for any hunting situation, an advantage it has over its prey.It feeds on almost any meat it can get. Animals that live in the water and near the water may or will become food for the saltwater crocs – even people! A hunting tactic that it has developed over years of evolution includes the art of camouflage, where it stealthily moves underwater with only its nostrils above the surface. Besides the saltwater crocodile’s art of stalking its prey, it also has its elusive death roll that it uses in order to tear flesh which gives an instantaneous death when clamped between both jaws. The crocodiles behavioural adaption comes from that they are the apex predators of their habitats. Because of their lethargic nature, saltwater crocodiles spend the majority of their day lying in the water, waiting for their prey. When an animal enters its killing field, they are caught as the monster lunges out of the water. This element of surprise allows the crocodiles to hunt animals that could easily outrun it. This adaptation is necessary for its environment, as the main diet of the crocodiles has the potential to swim or run faster. The primary behaviour to distinguish the saltwater crocodile from other crocodiles is its tendency to occupy salt water. The salt water crocodile has evolved in such a way that they have salt glands which enable them to survive in saltwater, a trait which alligators do not possess, most other species do not venture out to sea except during extreme conditions. This has enabled them to venture into a whole bigger territory to reproduce and thrive as there is less competition with other species of crocodile.

Fig.3 Size scale of saltwater crocodile to 6 foot man

From just looking at modern day crocodiles possess a property that makes them ancient river monsters and there is proof of evidence from evolution of the crocodile as archaeologists have discovered fossil skulls and partial skeletons in Niger from a 110 million year old crocodile that grew to the size of a school bus and weighed as much as a whale.

Figure.4 Evolution of the Salt water Crocodile

Reproduction of this organism is promising, as the females lay between 40-60 eggs on average, but can lay as many as 90 at one time. She places her eggs and buries them in nests of vegetation and mud which are elevated to avoid loss from flooding during the rainy season. This shows this organism’s evolved intelligence from previous loss of eggs that may have drowned or been washed away in high tides. Females protect their nests until the eggs are hatched in 90 days depending on nest temperature. Once the female hears the newborn call, she digs up the nest and carries her offspring back to the water in her mouth watching them until they learn to swim.

It’s population estimates range from 200,000 to 300,000 worldwide, and they are considered at low risk for extinction. But saltwater croc hides are valued above all other crocodilians, and illegal hunting, habitat loss, and antipathy toward the species because of its reputation as a man-eater continue to putting selection pressures on its population. With being hunted for its meat and eggs, the saltwater crocodile has the most commercially valuable skin of any crocodilian; and unregulated hunting during the 20th century caused a dramatic decline in the species throughout its range, with the population in northern Australia reduced 95% by 1971.

In addition, habitat loss continues to be a major problem. In northern Australia, much of the nesting habitat of the saltwater crocodile is susceptible to trampling by feral water buffalo, although buffalo eradication programs have now reduced this problem considerably.

The saltwater crocodile has a fierce reputation for being a man-eater and so this also puts pressure on its population as they are seen as a threat and a danger to the human population, which should not be a problem as this organism has been intelligent and strong enough to evolve and still be competing in the world today just as humans have.

Fig.7 Saltwater crocodile living up to its fierce reputation

Information References

1. http://science.howstuffworks.com/life/evolution/natural-selection1.htm

2. http://animals.nationalgeographic.com/animals/reptiles/saltwater-crocodile/

3. http://specialist16.blogspot.co.uk/

Image Refernces

1. figure 1 – http://animals.nationalgeographic.com/animals/reptiles/saltwater-crocodile/

2. Figure 2 – http://thomsonn-croc.wikispaces.com/The+Saltwater+Crocodile

3. Figure 3 – http://commons.wikimedia.org/wiki/File:Saltwater_Crocodile_vs_Bengal_Tiger.jpg

4. Figure 4 – http://eol.org/pages/454963/details

5. Figure 5 – http://specialist16.blogspot.co.uk/

With sizes ranging up to 2 metres long, the Leatherback turtle Dermochelys coriacea, is the largest of any turtle, and one of the largest living reptiles in the world. They come from the family Dermochelyidae, which roots trace back over 100 millions years, and are said to be the last of the family.

Fig.1 Clearly defined characteristics
http://www1.qoloq.com/baby-leatherback-sea-turtles.html

As seen in fig. 1 the Dermochelys coriacea differs from other turtles due to the characteristics of their shell, flippers and mouth. Whereas most shells are a bony and hard shell, the Leatherback turtle has a more flexible shell, and feels rubbery due to the carapace. Their carapace is made from a leathery skin type material holding together dermal bones, the dermal bones also create the ridges of the shell and come together at a blunt point at the bottom of the shell. These ridges on the carapace allow the turtle to be more hydrodynamic. They do not have claws and scales on their front flippers, unlike the other 6 species of sea turtle, and are also much greater in length. The last distinctive characteristic is their mouth. They possess “pointed tooth-like cusps and sharp-edged jaws” as well as spines in the mouth and throat that point backwards, which allow them to consume their prey of jellyfish, salps and other invertebrate creatures in the open water.

The Leatherback turtle is also adapted to conserve, as well as generate heat, allowing them to survive in both temperate and tropical waters. Their global distribution is the widest of any reptile. This is because the species is known, due to tagged individuals, to travel thousands of miles in order to return to their birth place for breeding season, with the biggest nesting grounds being found in West Africa and Northern South America. They were found in every ocean, excluding the Arctic and Antarctica, however these numbers have heavily declined (over 90% in the last two decades), and the turtle, as well as the other 6 species, has now been classed as endangered and put under the U.S. Endangered Species Act. The global population decline is mainly due to fisheries, coastal development and egg harvesting. Temperature change has also had a small affect on the population. As they can create mass damage to trawler netting, when accidently caught up in the catch, they are often killed and sold on for meat and decoration within illegal trades in order for fisherman to afford the costs of either new netting, or for materials to repair their original net. In order to protect these turtles from extinction a joint conservation effort is needed between countries, especially in the U.S, due to the vast distances they travel when migrating. To stop the turtles being mistakenly caught by fisheries within the U.S, modifications to netting and equipment, and changing times and locations of fishing has been implemented by the NOAA, National Oceanic and Atmospheric Administration. This and many other organisations work individually to their area, as well as together, in order to enrich the life of both aquatic and non aquatic life, to create a sustainable environment. The use of TEDs, turtle excluder devices, which are placed within the fishing nets, have also lowered the death rates of the Leatherback. As well as working with fisheries to increase the population, conservation and protection organisations also work with communities that are close to nesting grounds and turtle habitats, discouraging poaching and providing new opportunities for their livelihood. Management plans is crucial in the protection of the Leatherback turtle.

Fig.2 Leatherback mother laying her eggs
http://www.saveourleatherbacks.org/leatherbackseaturtle.html

Nesting occurs 2-3 times a year, like most turtles this occurs in the same area as each turtle was hatched, however the Leatherback turtle is different to other sea turtles as it is not always on the same beach. Nesting occurs during breeding season after mating at sea. Nests are produced in the sand where approximately 80 fertilised eggs and 30 unfertilised eggs are buried in a deep hole. The unfertilised eggs are placed on top of the fertilised ones to increase the likelihood of hatching, as they were less likely to be eaten by predators, and the temperature is optimum. Around the nest, the female turtle will disturb the sand in order to blend the nest in with the surrounding area, so predators are less likely to find the nest and hatchling survival rates increase. With all this protection put in place, it could be said that the number of hatchlings must be great, wrong, only 1/1000 are said to survive to adulthood, mainly due to the removal of eggs for human consumption. The gender of the hatchlings is not due to chromosomes, but due to the temperature of the nest. Around 29.5 degrees Celsius is the temperature that produces both genders. The higher the temperature, then gender becomes female, the lower the temperature, the hatchlings will be male.

References

National Geographic – http://animals.nationalgeographic.com/animals/reptiles/leatherback-sea-turtle/

NOAA Fisheries – http://www.nmfs.noaa.gov/pr/species/turtles/leatherback.htm

Wildlife Conservation Society – http://www.wcs.org/saving-wildlife/ocean-giants/leatherback-sea-turtle.aspx

Sea Turtle Conservancy – http://www.conserveturtles.org/seaturtleinformation.php?page=leatherback