Comparing Cats: A Discussion of Similarities & Differences

Options

~~Luipaard~~ Offline

Leopard enthusiast

1,161 Replies

1 Topics

Joined: Mar 2017

#338

03-10-2021, 01:53 PM

(03-07-2021, 10:11 AM)Balam Wrote: I wanted to make this post to clear up some misconceptions I've seen spread regarding the sexual dimorphism on jaguars and how it compares to other felids of the genus Panthera. There is an idea I've seen that claims jaguars have the least pronounced sexual dimorphism among the pantherine felids and this somehow translates to them being the worst fighters (??). I find this claim to be, to put it mildly, ridiculous and speaks to how easy it is for people to spread misinformation about a species they dislike when the data used is skewed and the public it is being presented to might not be the most versed on the subject to push back against it.

In terms of body size, jaguars present sexual size differentiations that fall in line with what is seen with other pantherine cats, with males being usually 30% larger than females, while the largest individuals of each sex having a very drastic sexual demarcation, with the heaviest male being almost 50% larger than the heaviest female on record (100-110 kg vs 148 kg, Troncha/Lopez). Sexual size differences and therefore dimorphism also varies across different jaguars populations, as described by Hoogestijn and Mondolfi in their paper BODY MASS AND SKULL MEASUREMENTS IN FOUR JAGUAR POPULATIONS AND OBSERVATIONS ON THEIR PREY BASE (1996). Here, by comparing the size differences among the two largest populations, Llanos and Pantanal, it became clear that Llanos jaguars showed more pronounced size differences among the sexes:

*This image is copyright of its original author

*This image is copyright of its original author

The aspect ratio in weight differences between Llanos jaguars was 1.1:0.67, for Pantanal jaguars it was 1:0.77. In the Llanos, according to this study, the females were 36%, whereas in the Pantanal the gap between the sexes was 23%. By contrast, if we compare these ratios to Persian leopards, as an example, from Patterns of sexual dimorphism in the Persian Leopard (Panthera pardus saxicolor) and implications for sex differentiation by Farhadinia et al. we get the following:

*This image is copyright of its original author

Aspect ratio 0.66:0.45, with males being roughly 32% larger than females. Therefore, jaguars from the Llanos would show an even greater gap in size than Persian leopards, while Pantanal jaguars would remain with the smaller gap size among the three populations.

These size gaps remain constant with skull measurements as well:

*This image is copyright of its original author

*This image is copyright of its original author

In skull length, the Pantanal male jaguars had a longer skull by 11,3%, whereas with Llanos jaguars the skulls of the males were longer by 16.2%.
When we compare the ratio differences between floodplain jaguars and their immediate interspecific size counterparts, the Sunda tigers, we get the following results from the tigers, using the data on the greatest skull length of Mazak and Grove from A taxonomic revision of the tigers (Panthera tigris) of Southeast Asia:

*This image is copyright of its original author

For the extant population of Sumatran tigers, male skulls were 12,51% longer than females, putting the size difference only slightly higher than Pantanal jaguars, but substantially lower than Llanos jaguars. So far, Llanos jaguars have shown the most drastic sexual dimorphism on weight craniometric measurements compared to three other populations of pantherines.

Here's 130 kg Ruxu mating with Jagua female, the size difference between these two could not be more obvious:

*This image is copyright of its original author

*This image is copyright of its original author

This discussion of marked sexual dimorphism is derived from a claim that jaguars having the least prominent secondary sexual differentiating traits somehow means that male jaguars are less equipped to fight in comparison to other pantherines, and the ones pushing for this idea focus on the dewlap in the leopard to make their points. What do actual scientists and biologists from reputable organizations have to say about the function of dewlaps in leopards? Johanna Taylor from Panthera released the following article on the subject:

"Mature male leopards are at least 60% larger than females, and broader, with larger chest girths and longer, bulkier heads. But there’s something else you may notice that sets males apart: Their thick necks can be adorned with a loose flap of skin hanging underneath. These skin folds are called dewlaps.

Dewlaps are observed in a variety of species throughout the animal kingdom, most notably in certain birds, lizards, and hoofed mammals. In mature male leopards, a well-developed dewlap is prominent and one of the best ways to determine age.
However, the function of leopard dewlaps remains unknown and largely unexplored. Since they are a sexually-dimorphic feature—meaning only one sex exhibits the trait—scientists speculate that this enigmatic ornament is linked to sexual selection or male fitness.

Of another conspicuous, sexually-dimorphic feature among cats—the mane of a male lion—Charles Darwin postulated: “[It] forms a good defense against the one danger to which he is liable, namely the attacks of rival lions.”
The idea behind this hypothesis is that adaptations such as body armor or weaponry, like antlers on male deer, increase the ability of males competing against other males. Most often the winner is the lucky male who gets to mate with the female and pass on his genetics.

On the other hand, results of more contemporary research indicate that injuries sustained during fights between lions don’t appear to differ between maned and non-maned sub-adult males or even females. This outcome suggests that the mane/neck area is not a high-target region during fights. Instead, observations find that the back and hindquarters seem to be the targeted areas during confrontations.

Many biologists believe that a male lion’s mane serves as an indicator of sexual fitness. Studies using life-sized toy lions sporting contrasting mane colors and lengths found that male lions were more likely to approach the imposters with lighter, shorter manes, while female lions were drawn more to models with darker manes. These results suggest that males with shorter, blonder manes are less intimidating to rival males, and thus perceived to have lower overall fitness.

We can apply this theory to hypothesize about the functions of a dewlap on a male leopard. However, fights between elusive male leopards are rarely observed and documented by scientists. This makes it difficult to confirm if the leopard’s dewlap has any defensive functions. Likewise, it’s hard to determine if it serves a similar purpose to that of a large, dark mane in sexual selection, as an indicator of fitness and longevity.

Another speculation about the dewlap is that it simply makes mature leopard males appear larger and more intimidating to rivals. Typically, as a male leopard ages, his dewlap enlarges. Mature males hold wider territories and have more opportunity to mate with females.

This also means that there are more opportunities to come into conflict with other males seeking the same territory and females. It would be ideal to avoid physical confrontation, and potential injury, by being able to display fighting capability and fitness, thus deterring potential rivals without physically engaging them. Fighting with other males has potential to lead to injury or death. Even the smallest injuries can fester and inhibit hunting abilities, leading to a decline in body condition that could result in death.

Younger and smaller males may be dissuaded from engaging in a fight with a larger male sporting a more pronounced dewlap. Alternatively, estrous females may select a male with a larger dewlap, perceiving him to have greater fitness than his peers. As of yet, no studies have been conducted to determine if dewlap size correlates with testosterone levels or is linked to reproductive success as an indicator of longevity."

The claims stated above by Dr. Taylor are very clear in that the function of the dewlap in leopards as a sort of protection for males during territorial fights has little to no scientific standing and is not widely supported by biologists and researchers. Instead, much like many other species of animals, by making the neck of the leopard appears larger, males are able to avoid direct confrontation by intimidating smaller males who might not want to risk injury in the case of a fight that could prove fatal down the line.

It is also claimed that among 4 of the 5 pantherines in this discussion the jaguar shows the lesser external dimorphic traits and that besides the dewlap in leopards and the manes in lions, male tigers have ruffs around their heads which females, according to them, do not, and therefore that trait symbolizes that tigers have more frequent confrontations than jaguars. How exactly is a short patch of hair around the jaws supposed to defend a tiger from 10 cm canines is beyond me, but that is their claim.

This is of course not true, the ruff in tigers is present in both sexes and it not always consistent in size or occurrence at all. Here's a captive Sumatran couple mating, the female just like the male possesses a large ruff of hair around her head:

*This image is copyright of its original author

Here's a wild female displaying a small ruff as well:

*This image is copyright of its original author

By contrast, the very famous Umarpani male who is renowned for defending his territory and even going as far as to kill larger opponents in fights does not have ay ruff around his head:

*This image is copyright of its original author

According to the "hypothesis" of the external sexual dimorphic traits and their link to fighting abilities, one would expect a dominant male tiger such as Umarpai to show a very marked and distinct ruff around his head, but this is not the case. The lack of ruffs around the face can also be appreciated with Sundarbans tigers, female and male for comparison:

*This image is copyright of its original author

*This image is copyright of its original author

To further expand on the interspecific fights among jaguars and how they compare with other felids, jaguars in areas where resources are scarcer such as the Cerrado have shown to be particularly aggressive with each other. Last year we documented the case of a very large melanistic male named Tiago that was killed in a territorial dispute with a different male, and his adversary managed to get a grip of his nape which allowed him to tore it apart, killing the huge 117 kg jaguar.
Jaguars in the Pantanal too have been recorded killing each other through the perforation of the skull, although in some areas jaguars may be more tolerant of each other and males may share territories in relative peace since the prey abundance of the area allows them to share resources, but this is not the universal case for jaguars.

With all of this being said, it's very clear that the idea that jaguars are somehow outliers among its cousin in terms of sexual dimorphism is a lie, there is no hard science to back up those assertions, just the conjectures of people with an agenda who need to hype up their favorite cat by spreading misinformation about another one they dislike. It's important to show hard data when participating in these discussions because otherwise the uninformed opinions of certain people may be confused for facts and quickly spread around among more easily impressionable minds.

I don't know where this statement comes from (i.e. having the least sexual dimorphism resulting in being worse fighters) nor do I believe it, but skull-wise jaguars do have the least sexual dimorphism.

Compared to females, adult male skulls from Central America were 13.2% larger, from the Amazon 10.8% larger, from the Pantanal 12.8% larger, and from the Llanos 19.3% larger:

*This image is copyright of its original author

The following tables from Pocock and Allen show skull measurements for leopards from the Congo Basin forest and the adjacent forest/savanna mosaic habitat. The average skull length for 22 adult males was 254.2mm and for 18 females 193.4mm, a difference of 31.4%.

*This image is copyright of its original author

For lions, we have average skull length for a total of 130 adult male and 126 adult female lion skulls from all over Africa, with male skulls being 21.2% larger.

*This image is copyright of its original author

From the same paper, skull lengths of Kruger lions specifically and Bengal tigers. Kruger lions show a difference of 21% while Bengal tigers show 19.8%.