Proc. Indian Acad. Sei.. Vol. 88 B, Part I, Number 5, October 1979, pp. 311-323, printed in India.
Inbreeding in white tigers
A K R O Y C H O U D H U R Y and K S SANKHALA* Bose Institute, Calcutta 700 009 * Department of Agriculture, Government of India, New Delhi
MS received 14 June 1978
Abstract. One of the problems of breeding of endangered species in captivity is inbreeding, An exemplary illustration is the inbreeding in the white tigers of Rewa. Genealogies and other relevant information on white tigers were collected from four Zoological Parks to investigate whether matings between close relatives were res- ponsible for the reduction in litter size and increase in early mortality which has been observed. Inbreeding coefficients were calculated for different types of mating. It was generally found that tigers failed to survive, if their inbreeding coefficient attained a level of 0.4687 or higher. Regression analysis reveals a tendency for the average litter size to decrease and the early mortality rate to increase with an increase in the value of the inbreeding coefficient.
Keywords. Genealogy; inbreeding coefficient; linear regression; litter size; mortality rate; white tigers.
Inbreeding is known to increase the degree of homozygosity of gone pairs in a population. The closeness o f relationship between individuals mated determip.es the speed of attaining homozygosity. The deleterious recessive genes which are hidden in heterozygous forms are revealed when they become homozygous as a result of inbreeding. There is abundant evidence in guinea pigs, poultry, pigs and cattle that inbreeding is often accompanied by increased early mortality, decreased growth rate, reduction in litter size at birth and pronounced increase in sterility and ,.'n the freqttortcy of congenital malformations (Johansson and Rondel 1968).
To increase the number of animals with a rare character, matings are sometimes made between close relatives. Recently, there has been a sudden decrease in the number of white tigers in captivity, posing a threat to their survival. Reduced fertility and increased early mortality have become common occurrences. In the Zoological Parks of the world there are 30 white tigers of which Calcutta has eight, Delhi nine, Bristol and Washington DC have five each and Gauhati, Hyderabad and Lucknow in India have one each. In July 1970 Delhi and Bristol had 16 and 10 tigers respectively while in August 1974 Calcutta had 13. Between 1969 and 1970 seven cubs were born to one white tigress in Washington DC of which only one survived. It is, therefore, of interest to investigate whether matings between
312 A K Roychoudhury and K S Sankhala
close relatives practised in different zoos have had a role in causing the smaller size of litter and higher rate of mortality now observed.
2. Materials and method
All the white tigers found in zoos today are descendants of one white male, named Mohan, captured ia May 1951 from the forests of Rewa, Madhya Pradesh, India. They are not completely white. They have varying shades of white and cream colour with black or chocolate stripes and their eyes are icy blue. They are generally bigger in size than normal coloured tigers.
Mohan first mated with a normal ooloured tigress, named Begum, also captured from the forests of Rewa. She produced tea normal coloured cubs in three litters. Ia the second litter, one female cub named Radha, whoa grown, was mated to her father, Mohan. Ia her four litters Radha produced 14 cubs of which eleven were white and three yellow. The genealogy of the white tigers at Govindgarh Palace in Rewa is shown in figure 1. The dates of births and deaths of the tigers are indi- cated where available.
A short description of the history and propagation of the white tigers in the Delhi Zoological Park, Calcutta Zoological Garden, National Zoological Park, Washington DC, USA and Bristol Zoo, Bristol, England is given below:
2.1. Delhi Zoological Park, New Delhi
Radha in her first litter produced one male and throe female white cubs named, respectively Rain, Rani, Sukeshi and Mohini (figure 1). Raja and Rani were brought from Rewa to Delhi in 1963. Mated to each other they produced 20 white cubs in seven litters. There were thirteen deaths of which four were acci- dental. Rukko, a white female of the first litter died after being mauled by her mother. Two cubs of the second litter died within a day due to careless handling and neglect of their mother. Ravl, a white male in the third litter died due to sun stroke. The remaining nine deaths are non-accidental. Besides two stillborn cubs, five died at an early age, while two males, Bahadur and Jagl~ in the fourth and fifth litter died of congested lungs ar, d lumber paralysis respectively. Raja mated with his mother, Radha who gave birth to five and four cubs, respectively in her first and second litters and within seven months all the five cubs of her first litter died of pneumonia. Two cubs of her second litter died of starvation shortly after their birth. One white male named Roop was sent to Bristol Zoo in exchange for a white tigress, named Sceta. Rani was then mated to her son Dalip and she produced one white female cub who died of Parkimouse syndrome and pneumonia within nine days after birth. Hari and Ashima born to Rani and Raja in separate litters, had only one stillborn white male.
'In other line, Mohan mated with his grand daughter, Sukeshi, who produced five litters of two cubs each. Out of ten cubs, only two survived. Two cubs of th0 first litter died because they were not cared by their mother. The death of Gautam, a white male of the third litter, was accidental. At the age of 8 years, V|rat, a tiger of the fifth litter, died after a prolonged illness. The remaining four deaths including one stillborn are considered to be non-accidental. Gautam and Heron, the son and daughter of Sakeshi and Mohan had two whim male cabs in
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314 A K Roychoudhury and K S Sankhala
one litter but both died of pernicious anaemia shortly after their birth. Homa when mated to Tippu, the son of Rav.i and Raja, produced four cubs in two litters and all of them died of uv.known causes within a few days after their birth. All the white tigers born in Delhi Zoological Park are shown in figure 2. The main causes of early mortality in Delhi have been pneumonia, trauma of the abdomen, conges- tion of the lungs, feline entritis and negligence of the mother.
2.2. Calcutta Zoological Garden, Calcutta
Radha in her second litter, produced two male white cubs (Neeladri and Himadri) and a normal coloured female cub (Malini) (figure 1). All the cubs were brought from Rewa in 1963. They are the progenitors of the white tigers in Calcutta. Malini was mated to Neeladri and she produced seven litters comprising 14 cubs of which seven were normal coloured and the rest white. A male cub of her third litter was put to sleep because he was suffering from gangrene. A female cub (Kiranmala) of her fourth litter was killed by the cub's brother, Barun. Chandni, a white tigress of Malini's first litter, was mated to Himadri and she pro- duced 20 white cubs in six litters. All the six cubs in the first two litters and three cubs in the third litter died in infancy; they were not v.ursed by their mother. Two yellow heterozygotes, Ravi and Sushi, the son av.d daughter of Malini and Neeladri, produced three white and ten normal coloured cubs in three li~ters but all of them died of unknown causes within five days after birth. The majority of deaths in the Calcutta Zoo have been due to feline entritis but a few animals were victims of trypanosomiasis. The genealogy of the white tigers at Calcutta Zoological Garden is shown in figure 3.
2.3. National Zoological Park, Washington DC, USA
Mohini, the daughter of Radha and Mohan in the first litter was brought from Rewa in December 1960 (figure 1). Later she was mated to Radha's normal coloured brother, Samson. In her first litter she had one white male, Rajkumar, one normal coloured male, Ramana, and one normal coloured female, Ramani. All of them con- tracted art acute form of feline distemper. Rajkumar and Ramani died but Ramana recovered. Mohini was pregnant again by Samson and produced two normal colourod female cuba, one of which was stillborn. The normal coloured cub that survived was named Kesari. After the death of Samson, Mohini was mated to her sort, Ramana and she produced two litters. In her first litter a normal coloured male and a white female cubs were born. The male died shortly after birth but the female named Rewati survived. She had crossed eyes and short legs. The male that died had shortened t0ndons cf the forelegs which precluded the arfimal from a normal "treading action " during nursing. In the second litter, there were five cubs consisting of two white males, two normal coloured females and one normal coloured stillborn female. Mohini inadvertently crushed three of her tiny cubs to death. There is a supposition that the cubs were too weak to survive even if they were not crushed. The remaining one, a white male named Moni, died whoR he was 16 months old. His death was attributed to a neurological pheno- menon of the brain (persorml communication). When heterozygous normal coloured Kesari and Ramana mated, they had three, white and one normal coloured cubs. All the white tigers in the National Zoological Park are shown in figure 4.
Inbreeding in white tigers 315
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2.4. Bristol zoo, Bristol, England
A pair of white tigers, namely Champak and Chameli, born to Radha and Mohan in the third litter was sold to the Bristol Zoo in 1963 (figure 1). Mated to each other they produced three litters comprising 14 cubs of which three still survive. All the four cubs of the first litter died within ten days after their birth. A cub in the second litter died and was devoured very shortly afterwards by the mother. Two cubs irt the third litter died in infancy. The artimals Champak, Akbar, Sarala, Shusrnita and Seem died from loss of appetite artd swelling of the abdomeI~.. Sumati was mat0d to Akbar; she produced one white male named Salim, whose kidney was not properly developed. H0 was put to sleep before he was two years old. The genealogy of the white tigers at Bristol Zoo is shown in figure 5.
The skirt colour of white tigers is known to be recessive, to the normal yellow. Thornton et al (1967) demonstrated that when a wild yellow tigress was mated to a white tiger, all their offspring were yellow. When these offspring were back- crossed with the white parent, their progeny segregated into yellow and white coloured cubs lit the ratio o f 1 : 1. Since the publication of the paper by Thornton et al (1967), a number of crossing betweorL heterozygous yellow and white tigers a~d betwoort two heterozygot~s yellow tigers have been made. They confirm the earlier findings. Pooled data show art expected segregation of yellow and white cubs ir~ ratio of 1 : 1 in the former and 3 : 1 in the latter type of crossings (table 1).
Table 1. Test for goodness of fit in two types of crosses.
Phenotypes of offspring Crosses Total
I. Between heterozygous yellow and white parents
Radha Mohan, Delhi Radha Raja, Delhi Malini Neeladri, Calcutta Mohini Samson, Washington, DC Mohini x Ramana, Washington, DC Observed Total Expected total (1 : 1)
3 11 14 5 4 9 7 7 14 4 1 5 4 3 7
23 26 49 24.5 24.5 49
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II. Between two heterogygou8 yellow parents
Sashi Ravi, Calcutta Kesari Ramana Washington, DC Observed total Expected total (3:1)
10 3 13 1 3 4
11 6 17 12"75 4"25 17
Z 2 0-960 d.f. = 1
318 A K Roychoudhury and K S Sankhala
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To examine the relationship between the degree of inbreeding, average litter sizo and non-accidental mortality rate, the inbreeding coefficients (F) for different types of mating wore determined following Wright's (1951) method. These values wore checked by another method given by Kudo (1962). The inbreeding coefficient is defiued as the probability that allelic genes in an individual are identi- cal by descent, i.e. both are descended from a single gone present in one of the ancestors common to both the parents. The values of the inbreeding coefficient for different rantings are shown in table 2.
Sometimes the cubs at the time of their birth wore devoured or neglected by their mothers and as a result all of them died. These accidental deaths have been excluded from the analysis. The non-accidental deaths include all stillbriths and deaths of cubs or tigers caused by known or unknown diseases at an early age. For each coupM, the non-accidental mortality rate was obtained by dividing the number of non-accidental deaths by the total number of cubs they produced. The average litter size and the mortality rate of the cubs for each couple are given in table 2. After pooling together the inbreeding coefficients of similar value and arranging them in ascending order, linear regressions of average litter size and mortality rate on the degree of inbreeding were calculated.
3. Results and discussion
One common feature observed is that the grandsons of Mohan and Radha when mated with their grand daughters have produced litters but no offspring have sur- vived. In all these matings the inbreeding coeificient of the offspring is 0.5000 (table 2). If an offspring is born whose inbreeding coefficient is higher than or equal to 0.5000, there is a great likelihood that it will not survive. There are also instances where offspring having inbreeding coefficients less than 0.5000 met with premature death. For example, all of the four cubs (F = 0.3750) of Homa and Tippu and one of the two cubs (F = 0-4687) of Homa and Gantam in D01hi died within a few days after birth (figure 2). An exception was found in the mating between Kesari and Ramana in Washington DC (Figure 4). All the four cubs ( F = 0.4062) they produc...