Culture of Platypus Fibroblast - Paper Example

Introduction

A few figures would be good, e.g. a photograph of the Duck-billed platypus and a phylogenetic tree Ornithorhynchids anaticus (the duck-billed platypus) reveals clues of a synapsid origin of mammalian species that occupy an evolutionary position (Unusual creatures, 2006). These cues, morphologically, include the cloaca and oviparous reproduction. Also, the duck-billed platypus structure has electro-receptors and mechanoreceptors (Unusual creatures, 2006). The hind limbs of the males have spurs that emit venom. At the genomic level, these mammalian and non-mammalian characteristics are reiterated. It possesses a camera eye like all other vertebrates and is thus able to detect light using pigments that are highly conserved. It has carnivorous, crepuscular, and semi-aquatic habits (Unusual creatures, 2006). While hunting underwater, it entirely uses its bill with its eyes fully closed. The features noted above shall be used extensively in this essay to compare with other Monotremes, the evolving mammalian species, the echidna, eutherian mammals and later the marsupials (Unusual creatures, 2006).

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Classification and Characteristics

The Duck-billed platypus through designation belongs to the Phylum Chordata Bateson, Order Monotremata Bonaparte, and species Ornithorhynchus anatinus Shaw. The species is, however, commonly referred to as the Duck-billed platypus, or in short, the "Platypus." It is notable that the Duck-billed platypus has no other living species that have been discovered yet noting that it is part of the five extant species of the Monotremes (Lightner, 2012). The Duck-billed platypus is bilaterally symmetrical and is a homoeothermic mammal that primarily lives in semi-aquatic environments. Their front feet are entirely webbed, whilst their back feet are partially webbed. This characteristic is not present in any other Monotremes. The wholly webbed and the partially webbed feet can be explained to be the adaptation that they underwent to enable the Duck-billed platypus to swim comfortably in water, and to move quickly when in dirty environments.

The Duck-billed platypus characteristically is a mammal, yet it lays its eggs and hence does not give birth to young ones. The young ones suckle on their mother for a few months feeding only on the milk that is produced by their mothers. The male Duck-billed platypus, through their spurs, can produce venom that protects them from dangerous animals. From their hind legs, the males can produce venom that cannot affect large animals, yet it can kill smaller animals that may pose a danger (Werth and Shear, 2014). When reviewing the Duck-billed platypus, it is seen that they are susceptible to the surrounding as they have within their body (not sure what you are saying here). The sensitivity is brought about by the mechanoreceptors and the electroreceptors that detect stimuli when they are looking for food. The platypuses when they are young have teeth but as they grow up the teeth are lost, and the adults grow a keratinized grinding pad that allows them to smash their food (Cree, 2014).

In this regard, the duckbilled platypus is a semi-aquatic mammal of the order montremata and is the only remaining member of the family Ornithorhynchidae, and the genus ornithorhynchus. A 'living fossil' is an organism that over the years has remained unchanged essentially throughout its existence in various geological periods (Khamsi, 2004). Close relatives of such organisms do not exist anymore, and examples include the Horse-shoe crab and the ginko tree. Many biologists and scientists have dubbed it a "living fossil" due to its longevity and recognizable species in the fossil record. It has retained a lot of the archaic features of the earlier living organisms in its lineal ancestry, most of whom existed over 40 million years ago. It is worth noting that the term "living fossil" is used to describe extant taxa that display minimal morphological divergences from its ancestors of the distant past. Usually, such organisms remain recognizable in the fossil record over a greater timeline (The boldened text would be better in the information).

According to the numerous studies undertaken, the duck-billed mammal has a lot of similarity to members in the classes' reptilia and aves. This places it as one of the earliest offshoots of the mammal family (Grutzner et al., 2004). The platypus along with echidna, a mammal with which it shares lots of similarities, comprises the group called monotremes. This group is estimated to have diverged from other mammals very early on the evolutional scale, at over 160 million years ago (Grutzner et al., 2004). Platypus possesses genes that enable the formation of egg proteins that have only been found in the class Reptilia, and among various fish species. This is apparently a manifestation of the primitive trait that has been preserved in its DNA for millions of years, and which is inherited from earlier members that had reptilian traits (Grutzner et al., 2004).

Reproduction among the platypus provides rich insight(s) into its unusual evolutionary past. The female possesses two ovaries like most mammals, but only the left one provides functionality. Eggs are laid, and incubation takes place at around 32 degrees Celsius, which is the average body temperature of the platypus (Grutzner et al., 2004). Incubation has been found to last for about ten days, and the offspring are then carried by the mother (how are they carried) as the platypus bears no pouch or any similar structure. Genomes that are responsible for lactation and yielding milk are also present in this DNA, and the young ones are suckled for 3-4 months. However, females lack teats and secrete the milk through pores in the skin at the region around the lower abdomen (Grutzner et al., 2004).

This also shows that giving birth and lactation developed and evolved independently of each other (Maybe another sentence explaining why). The duckbilled platypus along with few other egg-laying mammal species carried the trait on, even as divergence took place and most other animal species anchored and based their entire reproduction on either giving birth and suckling young ones, or laying eggs and the accompanying incubation (Grutzner et al., 2004). This possession of a mix of traits found in a very diverse range of animal species is what has led scientists to believe that the platypus could be a remnant of earlier species that existed during the period of the "split" that led to mammals separating from reptile (Grutzner et al., 2004).

Monotreme physiology has also been subject to many studies from as early as 1802, when Sir Everard Home discovered the trigeminal nerves in the platypus. This is an interconnected system of nerves that conduct sensory stimuli from the brain to the face. The bill of the platypus is a soft, leathery snout, and has emerged as the primary surface where electro-receptors and mechanoreceptors are very well established (While and Mcarthur, 2005). These sensory mechanisms provide the platypus with essential skills, necessary in hunting, and detecting the location of its prey since it closes its ears, eyes, and nostrils when under water. Electro-receptors detect electrical signals produced by other organisms as they move. The bill, unlike in some birds, is not part of the mouth in that its functionality is purely for hunting and the detection of its prey. It also uses its pads to chew, since its teeth are lost before the duckbilled platypus reaches adulthood (While and Mcarthur, 2005). This absence of teeth has been attributed and linked to the development of its sensory system, as described above.

Platypuses also possess spurs on their hind paws, but only males have venom. This venom is usually used against enemies but is also employed to deter male rivals. The alveolar, venom gland has also been known to spike and increases the secretion of venom in the breeding season (While and Mcarthur, 2005). Studies conducted on venom from the platypus and other animals have concluded that its manufacture is the product of alterations in the genes that had served other purposes before they evolved and mutated over time. This aspect has led to the proposition, by biologists, that platypuses have in fact existed for a longer time than previously thought (While and Mcarthur, 2005).

The skeletal anatomy of the platypus also provides great insight into its evolutionary past. The presence of procoracoid and interclavicle bones that connect the scapula to the sternum within the pectoral girdle points to its closeness to reptiles (Yamamoto et al., 2007). This goes to show how it has retained, and held onto ancient evolutionary traits not present in other mammalian creatures. However, it is worth noting that all present-day animals are a result of dissimilar evolutionary courses and no single species is singly representative of the ancestor in its original construction (Yamamoto et al., 2007). In effect, we must ascertain the ancestral nature of modern creatures by drawing analogies of multiple parentages. Data derived from analysis of the duck-billed platypus genome can, therefore, be of much assistance in unraveling what original characteristics arose throughout the 160 million-year-window on the eutherians and monotremes during and after the split (Yamamoto et al., 2007).

Visual Pigments and Retinal Anatomy in the Platypus

The platypus retinal architecture resembles that of mammals (Khamsi, 2004). However, there are some exceptions that include the presence of double cones, a comparatively thin outer nuclear layer, and cone oil droplets. In contrast to a majority of other mammals, the external nuclei layers have three rows of nuclei (Khamsi, 2004). Also present is one layer of ganglion cells which are sparsely distributed, but dense in the superior central retina. These characteristics cause a weak visual streak in the duck-billed platypus (Khamsi, 2004).

Monotremes have distinctive retention of some reptilian characters and some primitive characters. These characteristics has allowed them to be regarded as animals that represent a basal branch of mammals, the subclass Prototheria of Gill. Members of this subclass that have been deemed to be extinct include docodonta, tricodonta, and multituberculata. Extensive research has revealed that contrary to conventional beliefs, the monotremes have advanced features. The study has unearthed a species in Australia known as the steropodon galmani. The steropodon is believed to have had lower molars that have a similarity to the tribosphenic pattern which is characteristic of the living therians. Khamsi (2004) therefore concluded that "monotremes, one of the three groups of living mammals (the other two being marsupials and placentals) are phylogenetically close to the other groups of living mammals". Monotremes were believed to be non-therian mammals before the discovery of the steropodon.

Khamsi (2004) has recently supported the homology of trigonid cusps that exist among all living mammals. This study has placed monotremes within a group (Australosphenida) in which case the independent Gondwanan origin was proposed. Further investigation has led to more information that states that; "derived characters supporting the independent origin of a tribosphenic molar pattern in northern (boreosphenida) and southern (australosphenida) clades for mammals. Further, they expressed that; "they do not consider the toothed monotremes to have typical tribosphenic molars." This analysis shows a close relationship between the existing mammals and the duck-billed platypus.

Sequencing and assembly of the plat...