Scaling (allometry) of organ mass in Felidae: how big cats are more - and less - than small cats

Please see

• the second photo in https://acylme.com/2015/11/19/the-lion-and-the-cat/, and
• https://www.dreamstime.com/stock-photo-cat-lion-shadow-wall-image43539657.

Also see https://academic.oup.com/jeb/article-abstract/28/8/1516/7381326?login=false.

Most of my Posts report some original observation, contribute terminologically, or make some original interpretation.

This Post is not original, because it merely rehashes material in the literature.

However, the topic is of such interest that it deserves to be aired again, more than six decades after the original publication by Davis (1962, https://www.semanticscholar.org/paper/ALLOMETRIC-RELATIONSHIPS-IN-LIONS-VS.-DOMESTIC-CATS-Davis/fcae1e3094e1b6d96bdabd1efabea516bdf6efcc).

Everyone knows that the lion (Panthera leo) is essentially a scaled-up version of the domestic cat (Felis catus).

However, it is also obvious that the eyes are proportionately far smaller in the former felid than in the latter felid.

Please compare

• https://www.gettyimages.com.au/detail/photo/portrait-of-lioness-royalty-free-image/534968126?phrase=female+lion+face&adppopup=true with
• https://www.dreamstime.com/fluffy-cat-fawn-color-lies-floor-portrait-good-natured-playful-young-kitten-image107470061.

https://www.pinterest.com.au/pin/manny-the-selfie-cat-and-his-selfiecat-security--777433954432445959/

This differential scaling, in which the various organs are not commensurate, is called allometry (https://en.wikipedia.org/wiki/Allometry).

More particularly, eyeballs exemplify negative allometry (= hypoallometry). Negative because, as we go from small-bodied spp. to large-bodied spp., the organ in question gets proportionately smaller.

So, how do the various other organs scale, in the small-cat-writ-large that is the genus Panthera?

Comparison of Felis catus with Panthera leo:

Values are percentages of adult body mass, based on Davis (1962). The first value is for F. catus, the second is for P. leo, and the third is the ratio.

https://www.mun.ca/biology/scarr/Allomteric_Equation.html

Eyeballs 0.4% 0.04% -10.0 (negative allometry)
Brain 1.1% 0.2% -5.5
Pancreas 0.25% 0.1% -2.5
Kidneys 0.7% 0.5% -1.4
Bladder and urethra 0.1% 0.07% -1.4
Liver 3.5% 3.0% -1.2
Gastrointestinal tract 5.0% 5.0% 1.0 (isometry)
Skeleton 13.5% 13.0% 1.0 (isometry)
Muscles 50.0% 59.0% +1.2
Heart 0.4% 0.6% +1.5
Adrenals 0.01% 0.02% +2.0
Spleen 0.25% 0.5% +2.0
Respiratory 1.0% 2.0% +2.0 (positive allometry)

We can fill in the comparison by looking at the leopard (Panthera pardus), as follows from different sources.

Body composition (percentages of adult body mass), and allometric exponent (https://www.researchgate.net/figure/The-allometric-scaling-exponent-b-ie-the-slope-describes-how-the-parameter-of_fig1_263705401#:~:text=Jim%20E%20Riviere-,The%20allometric%20scaling%20exponent%20b%20(i.e.%2C%20the%20slope)%20describes,%C3%82%20Wb%20as%20an%20example.).

The first value refers to Panthera leo, the second to Panthera pardus, and the third to Felis catus.

Please note that

• negative allometry means an exponent of <1,
• positive allometry (= hyperallometry) means an exponent >1, and
• proportional constancy (= isometry) means an exponent of 1.

Eyeballs 0.04% 0.07% 0.38% 0.43
Brain 0.21% 0.41% 1.1% 0.61
Liver 2.8% 3.7% 3.6% 0.89
Kidneys 0.55% 0.55% 0.71% 0.94
Gastrointestinal tract 4.8% 3.1% 4.85% 0.98
Skin 12% - 13.2% 0.99
Skeleton 13% 12.2% 13.6% 0.99
Muscles 59% - 50% 1.03
Heart 0.6% 0.5% 0.4% 1.03
Spleen 0.52% 0.26% 0.24% 1.14
Respiratory 2.2% 1.0% 1.1% 1.19

What emerges is that there is no organ in felids that is the positive counterpart of the negative allometry seen in eyeballs and brain.

Posted on May 23, 2024 12:25 AM by milewski