Friday, 9 September 2011

Mystery behind dwindling number of tigers: The big cats in India are highly fertile but their low population in the forests make it difficult for them to find the mate for breeding

By Syed Akbar
Hyderabad, Sept 1: The big cats in India are highly fertile but their
low population in the forests make it difficult for them to find the
mate for breeding. The fast dwindling numbers is not due to fertility
or inbreeding problems but related to the loss of the habitat.

According to city researchers, the ratio between the male and the
female tigers and other big cats is roughly 3:7. For breeding to take
place, the animals should meet one another and during the encounter,
the female animal should be in heat or ovulation. The loss of habitat
and consequent fall in the number of big cats has made such encounters
difficult, and thus there's no remarkable increase in their population.

CCMB scientists, who conducted research on Asiatic lions and Indian
tigers, found that "majority of the animals exhibited good spermatozoa
number, high percentage of motile spermatozoa and low incidence of
abnormal spermatozoa". They also found that there's no "inbreeding
depression" as yet in big cats. "The high fertilising ability of the
semen samples and the high levels of serum testosterone further
support the view that the Asiatic lions and Indian tigers are not
completely inbred," a study by the CCMB team revealed.

In case of the Gir forests where lions are in sufficient number, the
population growth rate is relatively higher. But in tiger reserves
like Nagarjunasagar, which extends over a vast expanse of area in
Guntur, Nalgonda, Mahboobnagar, Prakasam and Kurnool districts, big
cats do not quite often meet and this explains why more cubs are not
born despite the high fecundity rate.

"The Asiatic lions exhibit a moderate genetic variability of around 26
per cent. The Indian tigers also exhibit similar levels of genetic
variation. There's also no significant difference in the incidence of
sperm abnormalities and circulating testosterone levels as compared to
other wild animals," according to a Central Zoo Authority report.

Scientists analysed the skin samples of tigers as old as 125 years and
compared the data with the present generation of big cats. They did
not find any significant difference between the old generation and the
present generation tigers, implying that the low genetic variability
is an inherent feature in these animals.

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