Fundamental Concepts Of Genetic Variability Biology Essay

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Genetic variability is one of the fundamental concepts concerning speciation and the ability to produce viable and fit offspring who not only are able to adapt to their particular environment but avoid problems such as inbreeding. Genetic variability is dependent on population size; therefore, the greater the number of species who are able to reproduce and be found in a concentrated area the greater is the increase in fitness and adaptation of the species. According to William Amos and John Harwood, the presence of higher levels of variability, the greater the response and effectiveness is in reducing "disease, parasites, predators, and environmental changes" (177). Genetic variability can however be shrunk in bottlenecked populations in which the mean population is downsized through genetic drift. The consequences are reduction in long-term adaptability and the process of inbreeding becomes more prevalent due to the lack of variability in reproductive organisms as well as the basic choice for a mating partner. It is important to keep this notion in perspective that population size and genetic variability are not always as contingent upon each other or discussed in such a formulaic method, stating that this is how nature works every single time. This is often not the case, and therefore researching cheetahs and the many different theories of the causes for their genetic variability is important to understand and study in order to relate it to other species bottlenecks. It is quite possible that a population size can be large with minimal variability, whereas an "endangered species can have more or less variability comparatively to that large population" (Amos and Harwood 184). It is therefore suggested that instead of merely concentrating on the population size and the possibilities of each individual finding a mate, it is important to look at the environmental factors and social behaviors that may have significantly reduced the population size and therefore in the process affected the genetic variability.

I aim to discuss the reasons for the low levels of genetic variability in both wild and captive cheetah populations and investigate the effects this has on the species' ability to breed and produce fit and adaptable offspring in both zoos and in African preserves such as in Namibia as well as in the Serengeti. I pose the research question: What factors have caused the cheetah population to become a small gene pool, how has it affected the population sizes in both captivity and in the wild, and what kind of strategies are zoos and wildlife preserves taking to maintain the cheetah numbers at a minimum viable population size? It has been hypothesized that a significant bottleneck during the Pleistocene, 10,000 years ago, followed by high incidences of inbreeding caused low genetic variability in cheetahs; subsequently, inbreeding depression has in turn caused higher susceptibility for the cheetah population to become infertile, has reduced litter sizes, and harbored a greater vulnerability to disease. I, however, claim that the cheetah's low genetic variability is associated more with their behavioral adaptations, which has a direct effect on captive breeding and influences programs and strategies at the zoo. It also involves a high risk of predation in areas where cheetahs are in close proximity to the other felid order organisms such as lions and jaguars.

Cheetahs, referred to by their scientific name as Acinoyx jubatus, have not always been located on the African continent. In fact, over 18 million years ago, it has been suggested that cheetahs roamed across diverse ecosystems in throughout Africa, the Middle East, and Asia, as well as two species in North America which may have arrived by crossing the Bering Strait during the Pleistocene era (Etheridge 5). O'Brien suggested through DNA fingerprinting and mitochondrial DNA sequencing techniques (qtd. in Merola 964) that the cheetah population must have gone through several bottlenecks 10,000 years ago when large mammals went extinct throughout Asia and Africa (Nowell 14). The cheetah population in particular, experienced a genetic bottleneck resulting in the reduction of genetic diversity within its own species. The lack of genetic diversity caused a great percentage of inbreeding and resulted in birth defects and infertility (Etheridge 7). Many geneticists theorize that genetic variation is essential to maintain fitness in the species population and to be environmentally adaptable, however, it has been hypothesized that if cheetahs did in fact experience several severe bottlenecks thousands of years ago, they are "less vulnerable to future bottlenecks than other more genetically heterogeneous species because any lethal mutations [that might have existed before the previous bottleneck, may] have already been [eliminated]" (Nowell 15). The severe bottlenecks reduce the population sizes considerably and therefore inbreeding is practiced as there is less choice in potential mates.

The occurrences of recessive alleles in the homozygous organisms in the population of mammals may also become adaptive to inbreeding. This suggests that inbreeding can in some instances be beneficial to the natural selection of the population by removing any deleterious recessive alleles from the gene pool (Lacy 324). This is not to disregard the ideas that inbreeding is no longer able to cause any severe complications in areas such as greater susceptibility to disease that has the potentiality to wipe out an entire species due to the homozygosity in the alleles and genes, because it definitely does. However, it demonstrates also that the lack of gene variation might not be such a detrimental issue as it has been made out. There might be other issues rather than just genetics that have affected cheetah inbreeding and lack of genetic variability. In fact, it is not uncommon for many large mammals to exhibit less genetic variability than other mammals. Lacy discusses that the loss of genetic variation is not unusual among the cat family because they are solitary hunters in which their survival and ability to procreate largely depends on the health and subsistence of the environment (327). The occurrences of the members of the cat family are greatly influenced by "the fragmentation and loss of habitat than species with greater population densities" (Lacy 327). Cheetahs demonstrate "39 times less average genetic heterozygosity than the four other African felines such as the lion, leopard, serval, and caracal" (Nowell 23) and therefore are placed into the lower half of the genetic variability spectrum in the Felidae order. Merola provides statistics of the proportions of polymorphism and heterozygosity in cheetah populations and demonstrates that the "cheetah populations have 0.02 percent polymorphism and 0.0004 heterozygosity in comparison to the leopard (Panthera parldus) whose heterozygosity level is 0.029 and the ocelot (Leopardus parldalus) is 0.072" (963-964). However, Merola also discusses that this should not characterize cheetahs as less fit than the other cats because they are still able to maintain a viable population (964). Demographic estimates conducted in 1996 state that a range of 200 to a possible 2,000 cheetahs are still found in the wild (Amos and Harwood 178), in which the population density is less than one animal per six kilometers due to their solitary behavior (O'Brien 1428). Despite still retaining relatively sufficient numbers in an effective population size, the cheetah has still "lost approximately 90-99% of its allozyme variability" and it would have needed "[through] genetic drift alone, approximately 16 generations" for this to occur (Amos and Harwood 178). It is therefore imperative to research the social behavior of cheetahs in the wild as well as the loss of their habitats through human encroachment and habitat fragmentation to understand why, with the population size remaining relatively acceptable, the genetic variations are so low. It is then important to extract this information and better relate it to the organisms found in zoos to find comparisons between both wild and captive cheetahs' lack of genetic variability and the reasons for this to be found specifically in captive cheetahs.

The two locations in which wild cheetah populations were observed and what will be discussed here are from Namibia and the Serengeti. According to Marker-Kraus and Grisham, Namibia retains the largest wild cheetah population in the world to date accommodating approximately 2,500 of them (6). However, Marker-Kraus and Grisham continues to state that "95% of this population lives on farmland outside of conservation areas where they are in direct conflict with livestock and game farmers" (6). This suggests that since most of the cheetahs live outside of the borders of the conservation areas that they and their environment are not protected from poachers and habitat degradation. The conservation areas essentially hold no jurisdiction over these animals and cannot implement policies to protect them. Since the cheetahs' spatial distribution lies outside of the park's borders, it appears to be a direct cause for their low genetic variability because it is a constant battle for the cheetahs to survive when their habitat becomes constantly marginalized and they themselves are prolific for poachers to sell their extremely valuable hides on the black market. The decrease in their population in effect creates a less diverse gene pool and therefore loss in genetic variability (Marker-Kraus and Grisham 6). Another reason for free-range cheetahs to contain low genetic variation in context to their environment is due to predation. Predation is a major cause of juvenile mortality and is directly relatable to the concentration of lions and cheetahs living in close proximity of each other. Cheetahs try to avoid areas in which there is a high concentration of other carnivores because it also invites a higher risk of predation and cub morality (Durant, Kelly, and Caro 20). Through observation and research it is has been recorded that cheetahs prefer to live in environments in which there is a low gazelle density because that instigates a smaller possibility of encountering a lion and its pride (Durant, Kelly, and Caro 20). Therefore, reproductive success and longer lifespan for females and greater tendency for male coalition recruitment have been recorded for these specific areas. Another interesting issue that Durant, Kelly, and Caro discuss is that rainfall significantly characterizes where animals congregate: ideally close to watering holes. Cheetahs are less dependent on water than lions are which suggests that during years with little rainfall, cheetahs can avoid their predators and subsequently cub mortality is also in decline (20). Caro states that 95% of female cheetahs in the Serengeti were able to reproduce large litters with viable offspring (Caro 20) which suggests that genetics is not so much an issue as extrinsic factors are in regards to genetic invariability because essentially the genes are good enough to carry on the next generation. It has therefore been suggested that captive breeding programs are responsible for the poor gene pool.

In order to reform the captive breeding programs in North America it was important to understand the social behavior in the relations between both males and females in the wild. Females generally live alone in the wild, while males live in groups (Caro 21). Young females are more likely to congregate in territories held by males found in coalitions and therefore males that are highly territorial will have a greater number of females to possibly reproduce with (Caro 21). It has also been described that adolescent cheetah groups have higher rates of survival when forming coalitions and are therefore more at an advantage in fitness passing their genes on to the next generation. Males have also been observed to rely highly on a sister to do almost all of their hunting (Durant, Kelly, and Caro 21). In order for zoos to be more efficient in their captive breeding programs it would be beneficial for them to set up cheetah enclosures in the same social design observed in free-range cheetahs. Some zoos have already begun to recognize the importance of social interaction between cheetahs and have placed two or three males together in the same enclosures. Caro discusses that the "affiliative behavior is normally shown by sibling males cohabiting since cub hood or by unrelated males provided they were introduced when one was less than 20 months old" (27). It is important to put males that have known each other essentially in their first 3 years of life together because the bond that these males construct connects them for a lifetime. This might also lessen the external stress that is exhibited in a captive environment and might decrease the abnormal sperm production, which will be discussed later. Caro has observed that successful mating generally occurs in the presence of male coalitions consisting of 2 males and one female, and has cited this observation as something that should be integrated in zoo breeding programs (28). Since cheetahs are a highly specialized species and vulnerable due to its history of bottlenecks and genetic invariability leading to other complications such as risks of contradicting diseases, captive breeding programs need to have very regimented and highly managed systems in order to safely and effectively breed cheetahs and increase its population and potentially gain more gene variation. Many breeding programs imported cheetahs from the wild and began breeding a select few males and females to increase their populations. This was not only effective in increasing their numbers in zoos, but led to inbreeding, abnormal spermatozoa, and unavoidable stress. The abnormal sperm count however does not seem so relevant because according to the statistics given by Marker-Kraus and Grisham, between the years 1871 and 1986, 470 free-range imported cheetahs were able to produce 417 captive births and 566 deaths (7). By 1991, "the breeding populations increased by 86% and the number of proven breeders alive at the end of 1991 was 66% higher than at the end of 1986" (Marker-Kraus and Grisham 7) which is a huge accomplishment for the various North American zoos. Marker-Kraus and Grisham continue to provide evidence for the cheetah breeding successes in that "13 of the 36 zoological facilities in North America maintaining cheetahs from 1987 to 1991" (9) demonstrated that for sustainability and management of these organisms to breed effectively it depended on husbandry and the continuous learning of social and behavioral characteristics demonstrated in the wild reaffirmed in the zoo's setting. Laurenson, Wielebnowski, and Caro point out that if the small presence of genetic variations were the key factor in the species' inability to breed in large sustainable numbers successfully then there would not be any evidence in improvements of those captively bred cheetah records (1330) as shown in some particular breeding facilities in North America. However, this does not counteract the notion that these cheetahs are still highly susceptible to diseases due to their genetics being so similar and from stress by the zoo environment. Other issues presented causing an increase in captive cheetahs' mortality is due to the stress from abnormal maternal behavior. Female cheetahs as noted before are solitary hunters while males form coalition groups. Caused by continuous stress and external factors at the zoo females are more likely to neglect their newborns or even kill them due to its disturbance (Laurenson, Wielebnowski, and Caro 1330). Laurenson, Wielebnowski, and Caro state that from the analysis of three breeding stations in North America approximately 78.8% of cheetah cubs' deaths have been due to external factors comparatively to 3.8% caused by genetic defects (1330). The fact, that cheetahs are able to breed and produce offspring, is a positive reality in the overall conservation of the species. It places great emphasis on zoological programs to create more uniform breeding strategies and obligations in order that every program is instituting similar techniques so that birth and death rates can also be consistent. In order to accomplish this, zoos should no longer randomly pair cheetahs together encouraging them to mate until a successful mating occurs, but instead they should observe each of the individual cheetah's behavior and interactions with each other and consider their genetics to avoid more inbreeding (Wildt and Grisham 3).

Even though behavioral characteristics are important in constructing theories as to why there is such a high mortality rate in captive breeding programs and in the wild due to environmental and predation factors, the notion that genetics and great similarities within the cheetah population still causes concern centered upon the cheetahs' high susceptibility to different kinds of diseases and acts as a factor towards cheetah inbreeding and lack of genetic variation. Cheetahs' high susceptibility to disease has been listed as a cause due to low genetic variability. Through the well-known example at the Wildlife Safari in Oregon, in 1983 more than 60% of the cheetah population perished due to a disease called feline infectious peritonitis (FIP) (Etheridge 7). FIP is common in all felines, however, "it has never been fatal to more than 10% of domestic cats" (Etheridge 7) FIP produces lesions in tissues and organs such as the brain and the liver and causes infection to the immune system due to T-cell ineffectiveness (Groot-Mijnes 1036). Etheridge discusses that there are some arguments which describe that the profound number of cheetahs who perished in the Oregon breeding location was not only due to the interaction between the owner's domestic cat and the cheetahs but that the cheetah population did not have enough " 'genetic tools' to fight off the disease" (7). This can be counterattacked with the idea that if the cheetah population did not have the genetic tools to eliminate the disease, then the entire population would have perished, not only 60% due to the cheetah population having low genetic variability. With low genetic variability all the cheetahs would have essentially reacted the same way and not only some. Therefore, it can be hypothesized that something more than just the genetic issue was a factor in the Oregon case study.

The other counterargument to the cause of low genetic variability and its effect of inbreeding is the notion that cheetahs have really "bad sperm". Harwood and Amos actually state that all felids have relatively high quantities of nonfunctional sperm (183), however, cheetahs have by far the highest. The sperm's inadequate functionality means that it has the ability to impede reproduction. However, even though cheetahs do have low genetic variability, their populations are still able to effectively reproduce, which has already been experienced in the captive breeding programs. According to Don Lindburg in the ANBI 132 lecture, cheetahs do have poor quality sperm and over 70.6% is accounted as abnormal spermatozoa (7 May 2010). He states that this percentage would definitely make humans infertile, however, during his research at the Wild Animal Park in San Diego where they experienced 20 different pregnancies only 2 did not take which is a very reasonable number. Don Lindberg therefore asserts that the cheetahs' bad sperm is good enough.

In conclusion I believe cheetahs are very important animals to study because they have are a perfect representation for the consequences of inbreeding and the effects that humans have on the organism's high mortality rate due to the degradation of environment for their own utilitarian purposes. Humans are exploiting the environment for their own profit in their agricultural practices and also in the black market trade for prolific cheetah hides. By researching and studying cheetah populations we gain an insight not only about their genetic profiles but also learn more about the importance of conservation of a specific species and their habitat. Cheetahs can therefore be regarded as a type of animal ambassador for environmental conservation. Through the analysis of statistics derived from captive breeding programs in the North American zoos it has been demonstrated that the cause of low genetic variability is not necessarily completely dependent on low genetic variation and abnormal spermatozoa. This notion is derived from evidence that cheetahs, even though breeding them is rather difficult because of the stressful environment of the zoos and its aesthetics, they are still able to produce viable offspring. This suggests that the conservation issues should not be entirely focused on the captive breeding programs but instead on developing policies for the protection of cheetahs in their natural habitat. The cheetah populations have been located outside of the protected areas both in Namibia and Serengeti. Therefore in order to preserve these organisms and reduce chances of juvenile mortality, educating local villages about the importance of conservation of the environment as well as obtaining the perspective that these species are not nuisances to the local's agricultural fields can be one of the most effective ways in allowing the cheetah to be a survivalist. By educating the locals about these issues, the information might have more success and susceptibility for other African nations to engage in the protection of areas where cheetahs are found, allowing cheetah populations to once again increase and therefore possibly reintroduce genetic variability.