Variation and Evolution of the Salt Water Crocodile

October 27, 2014 in Uncategorized

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.

salt water croc

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

far at sea

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.

size

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.

prehistoric

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.

hand

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/

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