liger
,
offspring
of a male
lion
and a female
tiger
. The liger is a
zoo
-bred
hybrid
, as is the
tigon
, which is the result of mating a male tiger with a female lion. The liger and the tigon possess features of both parents, in variable proportions, but are generally larger than either. It is thought that most, if not all, male ligers and tigons are sterile. The females, however, on occasion, may be able to produce young. The terms
liger
and
tigon
are
portmanteaus
of the words
lion
and
tiger
.
liger
A liger, the result of a mating between a male lion and a female tiger in a captive environment. In nature, interbreeding between these separate species is prevented by prezygotic reproductive isolating mechanisms (RIMs), such as differences in behaviour, and by nonbiological factors, such as differences in range. Most, if not all, male ligers and many female ligers that arise by accident or intent do not develop functional sex cells. Such hybrid sterility is a postzygotic RIM.
Ligers tend to be larger and heavier than members of their parent
species
. Biologists suggest that the liger’s large size, or “
growth dysplasia,” results from the absence of certain growth-limiting
genes
. Female lions mate with several male lions throughout their lives, so the genes of a male lion are adapted to maximize the growth of his offspring, since his offspring may be required to compete with those of other males produced by the same lioness. The genes of female lions, however, are adapted to cancel or dampen the effects of the growth-maximizing genes of male lions, so lions remain within a given size range. Tigers, on the other hand, have no such competitive mating strategy, and many biologists argue that tigresses do not possess the growth-limiting
adaptations
of their lioness counterparts. As a result, the influence of the growth-maximizing adaptations provided by male lions is greater, which allows ligers to become larger than their parents. However, for tigons, growth-limiting genes are found in both male tigers and female lions, so their offspring possess an abundance of these genes, which accounts for their smaller size.
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The largest ligers often grow to lengths of more than 3.3 metres (10.8 feet) and weigh more than 400 kg (900 pounds); however, there are reports of some individuals weighing more than 1,000 kg (1 metric ton [about 2,200 pounds]). Tigons, in contrast, tend to be the same size or smaller than their parents, because the growth-limiting genes are carried by both parents.
ligers and tigons
Diagram showing how different combinations of tigers (
Panthera tigris
) and lions (
P. leo
) produce ligers and tigons.
Although lions and tigers may mate in the wild, they are separated by geography and behaviour, and thus all known ligers stem from accidental mating between lions and tigers as well as from directed breeding efforts that have occurred while in captivity. The first known breeding of a lion and a tigress in captivity likely occurred sometime during the late 1700s. Roughly 100 ligers and fewer than 100 tigons are thought to exist. Many national governments and
animal-rights
organizations view the practice of breeding lions and tigers as unethical, because ligers often acquire birth defects that result in death shortly after birth and are prone to
obesity
and abnormal growth that places stress on their internal organs. In addition, ligers and tigons have problems interacting with members of their parent species because their behavioral traits often
manifest
as a mix of the habits of both species rather than either one or the other (
see also
animal social behaviour
). Other opponents of liger breeding point out that ligers often take up valuable space in zoos that could be better used as
habitat
for
endangered species
.