Abstract
Lion (Panthera leo) populations have dramatically decreased worldwide with a surviving population estimated at 32,000 across the African savannah. Lions have been kept in captivity for centuries and, although they reproduce well, high rates of stillbirths as well as morbidity and mortality of neonate and young lions are reported. Many of these cases are associated with bone malformations, including foramen magnum (FM) stenosis and thickened tentorium cerebelli. The precise causes of these malformations and whether they are unique to captive lions remain unclear. To test whether captivity is associated with FM stenosis, we evaluated 575 lion skulls of wild (N = 512) and captive (N = 63) origin. Tiger skulls (N = 276; 56 captive, 220 wild) were measured for comparison. While no differences were found between males and females or between subadults and adults in FM height (FMH), FMH of captive lions (17.36±3.20 mm) was significantly smaller and with greater variability when compared to that in wild lions (19.77±2.11 mm). There was no difference between wild (18.47±1.26 mm) and captive (18.56±1.64 mm) tigers in FMH. Birth origin (wild vs. captive) as a factor for FMH remained significant in lions even after controlling for age and sex. Whereas only 20/473 wild lions (4.2%) had FMH equal to or smaller than the 5th percentile of the wild population (16.60 mm), this was evident in 40.4% (23/57) of captive lion skulls. Similar comparison for tigers found no differences between the captive and wild populations. Lions with FMH equal to or smaller than the 5th percentile had wider skulls with smaller cranial volume. Cranial volume remained smaller in both male and female captive lions when controlled for skull size. These findings suggest species- and captivity-related predisposition for the pathology in lions.
Highlights
The lion (Panthera leo) once ranged across large parts of Africa, Europe, the Middle East and Asia
A total of 851 skulls of known captive or wild status at death were included in this study
The lion specimens consisted of 63 skulls of captive animals and 512 of wild ones whilst for tigers there were 56 and 220 skulls of captive and wild origin, respectively
Summary
The lion (Panthera leo) once ranged across large parts of Africa, Europe, the Middle East and Asia. Of the 126 captive born lions with known outcome listed in the 2002 North American studbook, 51 (40.5%) died before the age of two years (age of sexual maturity) Of these deaths, eight (15.7%) resulted from infanticide; five (9.8%) were registered as stillbirth; 37 (74.5%) were of unknown cause, and one animal was euthanized for unknown reason [5]. Skull abnormalities have been reported over the years in lions from zoological gardens in Europe [17], South Africa [11], Australia [8], the United States [10,18], and Asia [19] Whether these malformations occur in wild lions and whether they are caused by environmental or genetic factors, or a combination of both, has yet to be determined. It is important to note that such morphological abnormalities have not been reported to date from wild lion populations and have only been rarely described in non-lion large felids in captivity (cheetah, Acinonyx jubatus [20]; tiger, P. tigris [21])
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