Enter the Dragon: The Dynamic and Multifunctional Evolution of Anguimorpha Lizard Venoms
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This would greatly complicate matters, as oral secretions e. This confusion stems from the use of the two terms interchangeably in papers concerning Toxicofera going back at least as far as [ 23 ]. In making a selectable contribution to the subjugation of prey, it is not necessary for a venom to be capable of rapidly killing or incapacitating the prey item.
Venoms do not necessarily function as stand-alone prey subjugation mechanisms—they may be used in concert with physical means of subjugation. This does not constitute a strong argument against the lizard being venomous, instead it only serves to illustrate the fact that venom systems exist in myriad states of development within Toxicofera, as they do within the advanced snakes themselves [ 39 ]. Criticisms of some variants of the Toxicofera hypothesis of venom evolution notwithstanding, it is clear that a core set of toxins are present in the venoms of all anguimorph lizards studied to date including CRiSP, kallikrein, B-type natriuretic peptides and type III phospholipase A2 PLA2 [ 2324252728293031323334 ].BA303 Module B Compounding & Discounting
It is an important point that the presence of a particular species of protein within a secretion does not demonstrate the function of that secretion, which is why the evolution of venom must be studied by considering the venom system as a whole—functional assays should be deployed, as well as considerations of associated anatomy i. Some of the previously listed toxins are responsible for the hypotensive effect of intravenous injection of crude venom in rats [ 223233 ], such as aortic smooth muscle relaxation by natriuretic peptides equipotent to forms recovered from venomous snakes [ 44 ].
In addition, kinin release from kininogen by kallikrein enzymes is another source of hypotensive effects resulting from lizard venoms [ 45 ]. In addition, it has also been previously noted that injection of rodents and birds with V.
Reports of human envenomation by monitor lizards have been noted both in the literature and anecdotally. A bite report documented effects for a V. Additional reports of V. In all the above V. Vikrant and Verma reported a lethal bite by the related V. The actual culprit responsible for this bite has been questioned by clinical toxinologists, who considered it more likely to be a venomous snakebite [ 50 ].
However, it must be noted that this dissenting opinion by people who were not involved in the case did not provide any new and contradictory evidence. In contrast, a local wildlife officer who was present at the event confirmed the identity of the monitor lizard and the attending physicians documented the bite wounds as being inconsistent with the puncture wounds characteristic of bites by venomous snakes but rather consistent with the lacerations produced by monitor lizard bites Vikrant personal communication.
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Thus, while this case is extraordinary, the possibility of dangerous bites from varanid lizards to humans, under exceptional circumstances, should not be discounted. Another case report described a bite by a juvenile V.
- Key Differences Between Compounding and Discounting
- Associated Data
- Content: Present Value Vs Future Value
The authors attributed these effects to a vasovagal reaction despite noting themselves the similarity to reported in vitro effects of V. Anecdotally, a great many varanid lizard bites to biologists, zookeepers and amateur reptile enthusiasts have resulted in little that could be attributed to the action of toxins; however, some bite victims do report burning sensations, prolonged bleeding and inflammation disproportionate to the mechanical damage inflicted [ 10 ].
In addition to published cases, BGF has been contacted by keepers of varanid species who had symptomatic cases, sometimes with taxon-specific effects: These effects are consistent with the characterised venom chemistry of anguimorph lizards [ 23293233 ].
When compared with helodermatid lizard bites, which have received far more research attention than those of their varanoid cousins, a key point becomes evident: Typically, a helodermatid lizard will stay attached, chewing more venom into the bite site, while a monitor lizard is less likely to hold onto something that is not a food item but in some cases may hold on for up to a half hour when defensively biting. This likely leads to differences in the amount of oral fluids inoculated to the victim, with symptomatic human bites typically being those in which the varanid lizard chewed for a prolonged period of time.
Interestingly, while feeding on large prey items, varanid lizards seem to have a tendency to shake it violently and chew vigorously until it is subdued, which may facilitate venom delivery as well as potentiating mechanical damage [ 52 ].
Varanoid lizards are characterised by a refined mandibular venom gland that is homologous with that of the helodermatid lizards [ 23252729323353 ]. Both lineages derived their compartmentalised venom glands from the ancestral anguimorph lizard condition of an enlarged, mixed sero-mucous gland in which the protein- and mucous-secreting regions are not segregated into distinct glandular structures.
In both cases, sophisticated structures with separated protein and mucous regions, a structured lumen for storing liquid venom, and a thick membranous cover, have evolved. Further to this, morphological as well as molecular evolutionary studies have indicated that these glands are homologous with the venom glands of snakes [ 23252729323353 ]. The fact that varanid lizards possess highly developed dental glands suggests that those glands in one way or another play an important role in their life.
It has been shown with venomous snakes which switch to eggs or constriction as an alternate form of prey capture rapidly lose the functionality of their venom glands, with atrophying occurring in short periods of evolutionary time [ 25295455 ].
Compounding and Discounting
The evolution of a complex venom system is likely only possible under certain contingent circumstances—i. In addition, when a species evolves an alternative method of subduing prey that renders the venom system redundant, or switches to a diet with no need for subjugation e. The cost of venom production is presumably high enough to justify the presence of active secretory and delivery apparatuses only when it confers an evolutionary advantage [ 56 ].
While the venom glands of Varanus species have been compared transcriptomically, the only proteomic comparisons to-date were limited to SELDI mass spectrometry [ 233233 ].
Difference Between Compounding and Discounting
However a diversity of components have been functionally characterised from helodermatid and varanid venoms Table 1and since studies have demonstrated the complexity and medicinal potential of Heloderma venom [ 2758596061626364 ] it is of interest to study the venom system of varanoid lizards in detail.
Table 1 Toxins from anguimorph lizard venoms with characterised activities. Print Compounding In order to compare different alternatives in an economic evaluation, they should have the same base equivalent base. Compound interest is a method that can help applying the time value of money. Then, you will put the dollars in the bank again for another year.
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