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Tsavo Lions Unusual Social Behavior Related to their Manelessness
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Tsavo Lions Unusual Social Behavior Related to their Manelessness

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Tsavo Lions Unusual Social Behavior Related to their Manelessness Tsavo Lions Unusual Social Behavior Related to their Manelessness Document Transcript

  • Tsavo Lions Unusual Social Behavior Related to their Manelessness JESYKA MELÉNDEZ, RISE program UPR Cayey P.R. Grant number 5 R25 GM059429 _________________________________ Abstract Lions are the only felines with manes, although there are exceptions such as the Tsavo Lions. Manes are believed to play an important role in various social behaviors. The Tsavo lion’s manelessness sets them apart when it comes to social structure and hostility. Their manelessness has been a mystery resulting in the creation of numerous theories by scientists in search of a justification to such change in hair distribution. Some scientists have speculated that this change results because of lower sexual selection, predation efficiency, environmental circumstances and testosterone levels. Introduction Lions are the largest felines known. There are various sub species of lions. The subspecies are identified by the geographic region they inhabit. Amongst them are the well known Panthera leo senegalensis (west African or Senegalese lions), P. l. azandica (north east Congo lions), P. l. bleyenberghi (Katanga, Angolan, or south Congo lions). persica, uncontested. (O'Brien et al., 1987; Urban and West, 2002). The first felines appeared on earth approximately twenty five million years ago and were distributed all over Europe, Asia, Africa, and North America. One of
  • the first inhabitants was the saber toothed tiger. African lions known as Panthera leo inhabit most of the sub-Saharan Africa. They live in plains and savanna based habitats where they are the largest predator. They have a fully carnivorous diet consisting of small or medium sized animals such as antelopes and zebras. They have highly developed senses that contribute to their efficiency in being a predator; eyes developed to see at distances and with a special reflective layer behind the retina that allows them to see in the presence of poor light. Taste and smell senses are strictly connected providing them with a mechanism with which to discard unlikely meals. Felines also have very acute hearing and whiskers that have a sensory function. Lions are the only felines with manes, although there are exceptions such as the Tsavo Lions. These lions inhabit the Tsavo National Park in Kenya. They were infamous for their behavior during the building of a British railroad in Kenya during the year 1898 when two maneless fully grown males attacked and killed an estimated 135 workers during a period of 9 months (Patterson 1898-1899). Their manelessness is attributed to various factors such as the temperature, altitude, environment surroundings in general and testosterone levels. Their manelessness also sets them apart when it comes to social structure and hostility. Panthera leo General Behavior The Panther Leo is the largest feline in existence, measuring a mass 126 to 272 kg and a length of 2.40 to 3.30 m. They have short sand colored hair covering the larger part of their body, tails with a black tuft at the end and (in fully developed males) a mane. The Panthera Leo’s behavior is very particular from the rest of its feline relatives. Unlike smaller related cats, lions are social and establish family groups known as prides. There are various reasons why lions form prides. It is done in order to achieve greater hunting efficiency and because of the need for cooperation when it comes to defending territory. Prides usually consist of a ratio of 2-11
  • breeding females that are courted by 2-4 males (Kays and Patterson, 2002). Female lions constitute the base of the pride structure; they are the cub bearers and hunters. Males are solely dependent on the females for survival. Even though it is highly unlikely, male lions may occasionally form small temporary prides. This can result in conflictive situations, but is done in order to survive through adverse situations. One of the most frequent reasons for male departure from their family group is the search for more receptive females in order to mate. It may also occur that a male lion is cast out from its pride by a challenger in which case the lion has to retort to scavenging. If the outcast is an old male, he will leave the pride dying shortly after. The usual Panthera leo has a large and visible mane which may constitute various functions. The common mane consists of hair on the shoulder, upper-neck, forehead, belly, throat and elbows. It plays an important role when mating and it is very likely that females will choose their mate based on the condition of their mane. Manes are also useful when warning potential threats; the larger and sometimes darker the mane is results in creating a more threatening image. Manes are an important symbol of masculinity when it comes to the protection of their belongings. Male lions are particularly territorial, constantly protecting and watching over their land. They spray urine on their territory, rub glandular secretions on objects as territorial markings and roar to warn possible threats. Smaller prides seem to be more hostile when it comes to defending their territorial range. But, even though they are territorial animals, they are shy creatures never leaving their comfort zone unless really threatened or in order to hunt.
  • Tsavo Lions General Behavior Tsavo Lions is the name given to a particular group of Panther leo that inhabits the Tsavo East and Tsavo West National parks in Africa. Tsavo lions are infamous felines receiving their name from an incident that occurred in Kenya (1898) during the construction of a British railroad. There, 135 workers were killed by two fully grown maneless Tsavo male lions (Patterson 1898-1899). Tsavo Lions inhabit the arid and semi-arid savannas and bush. Here, large prey abundance is scarce which led scientists to believe that their social groups would be smaller in order to achieve better food management (this is an incorrect assumption discussed further on). These lions are very particular from the rest of the other lions both physically and behaviorally. These lions if not completely deprived of their manes when fully adult, only have small chest tufts, side burns, and dorsal crests. The average mane score is of 11.0 ± 9.1 for all males and 15.0 ± 7.8 when young adults (Kays and Patterson, 2002). The body measurements of the Tsavo lions remain constant with the rest of the Panthera leo. They have a different social structure that does not involve the grouping of numerous males per pride. Tsavo lion prides may have a grouping of an average of 7.4 females per one male; this is a very large pride population that defies the suppositions of scientists. It is peculiar how males are able to reproduce and exert dominance even without their mane (Kays and Pattersons, 2002.) This proves that manelessness does not result in social problems or inhibition of certain behaviors. They are highly territorial continuously spraying their land, as noted by Kays and Patterson during their research, investing more time than the average lion in protecting their land. This type of behavior justifies the British railroad incident back in 1898. It is believed that the absence of prey in the Tsavo savanna led to the attack of humans (Peterhans and Gnoske, 2001). But, even if so, it is evident that Tsavo lions are more territorial, dominant and hostile. Otherwise, one male lion would not
  • be able to preserve the large family structure displayed in its prides. It is impressive how one male alone can control a group of up to eight females and avoid coalition with other wondering males. Manelessness: The Theories. The manelessness of Tsavo lions has been a mystery resulting in the creation of numerous theories by scientists in search of a justification to such change in hair distribution. Some scientists have speculated that this change results because these lions have a lower sexual selection, meaning that there are less male lions leading to less male competition. Because of this, they have no need for their manes and therefore have eliminated it. As explained above, the lion mane plays an important role when in the mating process. This theory is proved unlikely by Kays and Patterson who noted normal reproductive behavior in the Tsavo lion pride just as it would take place in any other pride. Another theory establishes that it is not efficient to keep the mane in the environmental circumstances the lion inhabits. According to this theory, lions lose their manes due to the elevation; lions with the most buoyant manes inhabit the upper limit of the altitudinal range, and the ones that inhabit the lower and warmer range have scarce manes (Smee, 1833). This theory has sufficient loopholes in it to lead to its disqualification. The most important one of these is that the author (Smee, 1833) found other larger groups of Panthera leo living at the same altitude as the Tsavo lions that had developed large manes. This leads to believe that something else is impairing the production of manes. Supported by another study (Kays and Patterson, 2002) is the relation of their habitat surroundings to their mane loss. They speculate that because of the types of plants and short shrubs that grow in the Tsavo savanna, their efficiency when traveling and hunting may be impaired by having all sorts of seeds and twigs from these plants stuck to their manes This seems partially unlikely since studies have
  • failed to provide strong evidence to support all aspects of it. The most recent and likely theory is the one linking manelessness to levels of testosterone in the body. Studies relating levels of testosterone in the body and male androgenic alopecia have been conducted for years. They have exposed sufficient evidence to consider this a potential reason for the Tsavo lion’s manelessness. Studies on plasma testosterone, saliva testosterone and plasma sex hormone binding globulin (SHBG) levels in human males with androgenic alopecia (Cipriani, 1983 et al.) have exposed that indeed at least salivary testosterone levels where significantly higher in bald men. As explained by investigations conducted by Mitsuko (et al. 2008) “The use of saliva as a material for screening biomarkers has several advantages in the study of large research populations. Since testosterone is not bound to protein in saliva, salivary testosterone determination provides an excellent approach for the evaluation of serum bio available or free testosterone”. According to this, by measuring salivary testosterone levels we are able to record highly accurate measurements of the testosterone (“free”) that is actually influencing in the androgenic alopecia. Levels of Testosterone and Aggressiveness As proved in aggressiveness studies (Olweus and Mattson, 1988), circulating testosterone levels tend to make human males impatient and irritable. This results in a higher probability of them to engage in destructive behavior. Furthermore, it was proved that the primary reasons for an aggressive attack would be the exposure to unfair treatment and anything that could possibly be considered a threat. The same applies to the Tsavo lion’s behavior. Panthera leo testosterone levels may be measured by the amount of intraocular pressure. This pressure, when studied in lions, was much higher in males than females. This is the result of the fluctuation of sex hormones (testosterone) in the male lions (Ofri, et.al 1999). Tsavo lions, as a result of their higher levels of testosterone, tend to be easily irritated. This occurs especially when threatened or
  • when their personal space is invaded. They show no fear towards humans responding curiously by approaching (Kays and Patterson 2002). The raised testosterone levels circulating in the Tsavo lions play an important role in the development of their social behavior. It would cause them to express more hostility and less patience towards intruders justifying then the unfortunate events of 1898. Discussion Lions are natural born predators, they hunt in order to survive but seldom hunt humans. So why then did the male Tsavo lions engage in such a hunting feast? What is even more astonishing is that it is not common for male lions to go out into the hunt. “Males refrain more and pursue less than females” (Scheel and Packer, 1991). Females do all the work, or at least most of the time. This well known standard was evidently defied but the male Tsavo lion duo back in 1898. Both lions went out for the biggest kill ever recorded. This has lead to numerous controversies. It is evident that both biological and ecological factors may influence such uncommon behavior to take place. One thing is clear; Tsvao lions are definitely different from the rest of their cousin felines. They defy lion standards both physically and behaviorally. Both their manelessness and 1898 attack have interested scientists for years. These two factors are evidently connected, for one is the consequence of the other. The elevated levels of testosterone in Tsavo lions leads both to their elevated hostility and the loss of their manes, which gives them their characteristic maneless look. Manelessness is not the cause of the Tsavo lion’s behavior, but, is in fact the visual consequence of the hormonal differences.
  • Acknowledgements I wish to extend a special thanks to the RISE program and its entire staff for their always enthusiastic support and guidance. Eneida Díaz Ph.D., Robert Ross Ph.D., Nelson Vicente Ph.D., and Chantelle Macphee Ph.D.
  • LITERATURE CITED Cipriani R., Ruzza G., Foresta C., Veller Fornasa C., Perserico A. 1983 Sex hormone-binding globulin and saliva testosterone levels in men with androgenetic alopecia British Journal of Dermatology 109: 249-252, Harrington, E. and Myers P. 2004. "Panthera leo" (On-line), Animal Diversity Web. Accessed October 12, 2008 at http://animaldiversity.ummz.umich.edu/site/accounts/information/ Panthera_leo.html. Kays R.W., Patterson B.D., 2002. Mane Variation in African lions and its social correlates Canadian Journal of Zoology. 80: 471-478. Mitsuko Y. , Seijiro H , Kumiko F, Takashi Y, Yutaka K, Hisamitsu I, Satoru M, Shigeo H 2008 Diagnostic significance of salivary testosterone measurement revisited : using liquid chromatography/mass spectrometry and enzyme-linked immunosorbent assay Journal of Men’s Health 5: 56-63 Ofri R., Shore L., Kass P., Horowitz I. 1999. The Effect of Elevated Progesterone levels on intraocular pressure in lions (Panther leo) Reasearch Veterinary Science. 67(2): 121-123 Olweus D., Mattson A., Schalling D. and Low H., 1988. Circulating Testosterone Levels and Aggression in Adolescent Males: A Causal Analysis. Psychosomatic Medicine, 50 (3): 261-272. Patterson, J.H. 1898-1899. Personal Journals, Bodelian Library, Oxford University, Oxford. Peterhans J C., Gnoske T.P., 2001 .The science of ‘Man-eating’* among lions (Panthera leo) with a reconstruction of the natural history of the “Man-eaters of Tsavo” Journal of East African Natural History 90 (1&2): 1-40 Scheel D., Parker C. 1991 Group Hunting Behaviour of Lions: a Search for Cooperation. Department of Ecology, Animal Behavior 41(4): 697-709 Smee, Capt. W. 1833 "On the maneless lion of Gujerat," Proceedings of the Zoological Society of London; part 1:140