Comparing Cats: A Discussion of Similarities & Differences

[Pckts]

The Cranial Morphology of Large Wild versus Captive Felids


http://caravel.sc.edu/2014/12/the-crania...ve-felids/
"RESULTS
Graphing the PCA showed that species was the first principle component, accounting for 21.28% of the variation, and visibly separating the groups into lions and tigers with almost zero overlap on the x-axis (See Figure 1 & Table 2). The second principle component clearly represented captivity status, accounting for 15.58% of the variance, and separating the wild and captive specimens across the y-axis. The third principle component represented the sex of the individuals, accounting for 7.97% of the variance. Figure 2 shows the second principle component, captivity status, plotted against the third, with females occupying mostly the lower extreme of the y-axis and males occupying the higher extreme.
Differences in morphology were evident at each extreme of the x-axis and y-axis of each PCA test (See Fig. 1 & 2). Among some of the differences were the length of the rostrum, mandibular angle, flexion of the mandibular angles relative to the mandibular symphysis, and the width of the skull. Rostral length differed across species, as tigers were shown to have shorter rostra than lions, which is a trait that has been described by Sunquist (2002) and Christiansen (2007). Christiansen also describes increased nasal height in tigers and differentiates between canine heights across lions and tigers. Mandibular angles also varied across the species, as tigers showed mandibles wider at the top (i.e., bi-coronal breadth) and lions showed the widest point at the base of the mandible (i.e., bi-angular breadth).
Different skull shapes and differences in width were also observable across captivity status. Mandibular angle and rostrum length varied across lion and tiger individuals (Figure 1). Captive individuals appeared to have flatter heads than the wild specimens against whom they were compared. The width of the skull across specimens was also noticeably different, as captives seemed to have wider skulls than wilds. Within both species, mandibular angle variation was also evident across males and females."

DISCUSSION
As expected, the first driving factor, PC1 (21.28%) separated the two species, as obvious phenotypic differences exist between tiger and lion individuals (Sunquist and Sunquist 2002). As you move further right on the x-axis of the graph shown on Figure 1, you can see that the frequency of tiger individuals declines and the frequency of lion individuals increase. Unexpectedly, the second most important source of variation (PC2) was most influenced by captive status (15.57%) and not sex (which emerged as the key factor in PC3). This means that, after species, captive status is the most discernable characteristic across this population. Previous studies on both captive tiger and lion individuals have yielded results supporting the idea that captivity status affects morphology. Geordie Duckler attributed malformations in the external occipital region of tiger skulls to phenotypic plasticity, judging that significant differences between the examined captive and wild specimens of the study were due to “reduced jaw activity” (Duckler 1998). A similar observation was made by O’Regan, examining the cranial thickness in captive lion individuals (O’Regan 2005).
Differences across species were evident upon examination of the wireframe renderings of the specimens in Morphologika. One difference is a shortened rostrum in the tiger specimens relative to the lion specimens, which is consistent with descriptions of tigers (Sunquist and Sunquist 2002). This is a possible topic for future research. Mandibular angles also varied across the species, as tigers exhibited wider bi-coronal breadths and lions exhibited wider bi-angular breadth. The results of the PCA output are encouraging, demonstrating the ability of statistical analysis to account for observable qualitative differences across specimens. Variation of skull width and in biangular-anterior mandibular angle, or dome shape was observed differences across captivity status. Wild specimens were found to have more robust domes, than captive (Figure 1). Relatedly, captive specimens had greater skull widths relative to length than wild.
The third principle component, observed to be sex, accounted for nearly eight percent of the variance across the sample population (7.97%, respectively.) The fact that sex was the third principle component, behind species and captivity status, suggests that it is easier to tell the difference between captive and wild felids than it is to tell the difference between the sexes of the two species. One explanation for this phenomenon is that behavioral differences between sexes that occur in the wild due to hunting do not occur in captivity and therefore do not contribute to sexual dimorphism in captivity. A further question comes up in the analysis of these data: are females and males affected by captivity to different extents?
The results of this study supported the captivity status hypothesis and statistically confirmed that observable differences in cranial morphology do exist across species. These results are especially significant because sexual dimorphism is a known characteristic of both lion and tiger species (Naples 2012, Mazaak 2004). Whether the differences that occur are actually due to mechanical diet is a persistent question. The strength of captivity status as a component of difference in the data also opens up a new line of inquiry about sexual dimorphism. There are two questions to consider: How much do the mechanical properties of food really affect felids? In what other ways captivity status affects morphology of captive felids?
A study to further investigate captivity’s impact on cranial morphology will include more species of large carnivores as well as a control group. A type of zoo animal such as Zalophus californicus, the California sea lion, with a diet primarily made up of fish in captivity and the wild should therefore exhibit little to no differences in cranial morphology across captivity status if the morphology is mostly influenced by the food’s mechanical properties. If there are differences in morphology across captivity status, regardless of diet, other possible factors contributing to the differences in cranial morphology across captivity statuses may include genetic issues, for example those stemming from inbreeding.
If further studies yield similar results to those of this analysis and continue to show a direct relationship between captive diet and changes in cranial morphology of carnivores, these studies could be a possible basis for handlers and animal dietitians to rethink their policies regarding the mechanical diets of captive carnivores. If a mechanical diet that requires further engagement of masticatory muscles, because nutrients alone are insufficient for the proper maturation and health of captive felids, zoos must take proper measures to assure the health of captive specimens."


Probably one of the main reasons why tigers are thought to have the strongest bite of big cats is their relatively shorter jaws compared to Lions
Statement from Adam Below:

Relative to weight, it’s the jaguar. Recent research by Adam Hartstone-Rose and colleagues at the University of South Carolina, who compared the bite forces of nine different cat species, reveals that jaguars have three-quarters the bite force of tigers.
However, given that jaguars are considerably smaller (the body mass of the individual in the study was only half that of the tiger), relatively speaking their bite is stronger.
“If you had to choose, you’d want to be bitten by a jaguar, not a lion or a tiger. But pound for pound, jaguars pack a stronger punch,” says Adam. “The strength of the jaguar’s bite is due to the arrangement of its jaw muscles, which, relative to weight, are slightly stronger than those of other cats. In addition – also relative to weight – its jaws are slightly shorter, which increases the leverage for biting.”

http://www.discoverwildlife.com/animals/...ngest-bite Reply