Theoretical foundation for the use of Brown Bear females (Ursus arctos) as recipients for the reproduction of Polar Bear cubs (Ursus maritimus) in captivity.
A.V. Malyov, M.G. Mirolubov, V.S. Pazhetnov, S.E. Belikov, A.R. Moudarisov, Kazan Zoo
According to the International Pedigree Book on Polar Bear ( Linke, 1994), 199 of 304 polar bear cubs born in European zoos survived, making a survival rate of 65.5%. Those cubs that died were under 6 months of age, and the main reason for death in the first months of life could be considered breaches in the mother bear’s conduct in captivity.
Brown bears feel comfortable in captivity and give posterity. The experience of Russian zoos as well as those around the world shows that brown bears are not exacting about the conditions of their breeding. From 1987 until 1997, 311 (193, 97, 21) brown bear cubs (Ursus arctos arctos) were born in Russian zoos and 268 grew up, making a survival rate of 86.2 % (Malyov, 2000). Quite often, female brown bears rear up to 3 cubs simultaneously. One brown bear at the Western Berlin Zoo gave birth to 5 cubs. At the Leipzig Zoo a female brown bear gave birth to 6 cubs and all survived. Five were fed by the female while only one was fed artificially (Puschmann, 1983).
The data received in the Kazan Zoo from 1981-1993 (Malyov, Chispyakov, 1994) confirm that the brown bear and polar bear are very similar in their reproductive biology:
1.The beginning of coupling of brown and polar bears in the Kazan Zoo coincides, though the period of coupling of brown bears is longer, lasting until the beginning of July.
2.The average duration of coupling of polar bears is 7 to 12 days longer and lasts 14.5 days (n-6).
3.The average fecundity of the brown bear is 2 to 33 (n-9), and the polar-bear is 1 to 56 (n-9).
4.The survival of brown bear cubs is 2% higher and makes 81% (n-10).
5.The average duration of brown bear pregnancy is 4.4 days longer than that of the polar bear and lasts 246 days (n-14), which is considered unimportant.
After ovule fecundation both species have a latent period, when zygote in blastocist period does not implant into mucous membrane of the womb until late autumn. There have been reports of growing bear embryos – caught in November before the female bear begins bedding in den – but such occurrences are rare. According to American scientists, zygote implantation and cell division start at the bedding period of a male bear. So, the periods of coupling are not important while calculating the duration of embryos growing. For example, at the Kiev Zoo, estrus of a pair of Ursus arctos isabellinus within a number of years might last from the middle of March until the end of July or the beginning of August, but the cubs were always delivered between the 5th of November and 23rd of December (Kachan, 1987).
On the northeastern part of Greenland, Christian Weib found polar bear cubs with brown spots. Brown bears do not live in this region. Probably it was a case of genetic reversion to the founder type (greasily) (Taylor, 1995). In 1995 during an expedition to the northern part of New Land [sic. Newfoundland?], scientists found a female bear with cubs. Her body was dotted with dark spots that looked like herpes. She had slightly dark spots on her snout (Garner G., Belikov S.). The likeness of polar bears and brown bears is confirmed by the inter-types hybrids in the Lodze’s Zoo (Kawalska, 1965; Sosnowski, Kowalska, 1986).
The received experience of inter-breeding of polar and brown bears confirms that both types cross and breed. The hybrids (generation F2) also give fecund posterity and have practically unlimited ability to reproduce. Of 36 (16.19.1) bear cubs born here, 26 survived (13.13) and 10 died (3.6.1). The percentage of cub survival is 72.2%.
The international experience analysis from 1960 to 1996 (Malyov, 2000), according to International Zoo Yearbook, 1960-1996, demonstrated the following:
- During this period 100 bear-hybrids were born in 18 zoos worldwide.
- All hybrids had a brown bear parent.
- Hybrids are received between 4 bear species: Ursus arctos, Selenarctos thibetanus, Ursus americanus, Ursus maritimus.
- Different subspecies of brown bear are easily crossed.
The given information proves the fact that the zygote transplantation of one species to another is possible (theoretically). This fact moved us to begin scientific research into methods for transplanting embryos from polar bear females into brown bear females. Over twenty years at the Kazan Zoo, we have found parameters of polar and brown bears’ reproduction on one territory in captivity.
The process of transplanting polar bear embryos to female brown bears consists of 3 stages.
The 1st stage:
1.1 Stimulation of super-ovulation of female brown bear that has already had cubs.
1.2 Paring stimulated female bear.
1.3 Receiving zygotes from fecundated she-bear (donor) by the washout method and putting them into the unfecundated she-bear (recipient), with the aim of working out the method of getting bear-cubs with the help of transplantation method.
1.4 The birth of brown bear-cubs from recipient.
The 2nd stage:
2.1 Stimulation of super-ovulation of polar she-bear that has already had cubs.
2.2 Pairing stimulated fecundated bear-female by the washout method (donor), their evaluation and conservation.
2.3 Receiving of zygotes from fecundated she-bear (donor) by the washout method, their evaluation and preservation.
The 3d stage:
3.1 Stimulation of ovulation of brown bear (recipients).
3.2 Transplantation of zygotes from polar she-bear (donor) to brown she-bears (recipients) with the aim to get polar cubs by transplantation method.
3.3 The birth and raising of polar cubs by bear-females - the brown bear recipient.
The development of biology and new technologies nowadays allows for consideration of this possibility. We think that Russian scientists can contribute to realizing this possibility with sufficient funding.
The idea of getting bear-cubs through the implantation of fecund dates ovum is interesting from the scientific and cognitive point of view. With the necessary conditions provided we think that the survival of brown and polar cubs in zoos will not differ much and make no more than 2% (Malyov, Chispyakov, 1994). It’s quite logical to suppose that developing a polar bear embryo inside a female brown bear can have a positive influence on its future survival. Through the nourishment that the embryo receives (brown bear mother’s blood), protective properties for keeping polar bears in new surroundings might be transferred. The environment for survival in the Arctic is practically sterile.
Realizing this program might solve the problem of replenishing zoos by lengthening posterity of the polar bear, and will open the way for transplanting embryos of other bear species via female brown bears, along with their reproduction and preservation.
References:
1. Linke K. International studbook of the Polar Bear (Ursus maritimus). Rostok, 1994.
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