Is the pronghorn (Antilocapra americana) inferior to like-size bovid ruminants, in braininess?

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For an index to my Posts on Antilocapra americana (https://www.inaturalist.org/taxa/42429-Antilocapra-americana), please see https://www.inaturalist.org/journal/milewski/93100-an-index-to-my-posts-about-the-pronghorn-antilocapra-americana#.

AIMS

In this Post, I assess the size of the brain, relative to body size, in a peculiar species of ruminant (https://en.wikipedia.org/wiki/Ruminant), namely Antilocapra americana.

BODY MASS OF ADULTS

O'Gara (1978, https://www.science.smith.edu/departments/Biology/VHAYSSEN/msi/pdf/i0076-3519-090-01-0001.pdf) gives body masses as follows:

Alberta: adult females, mean 50 kg, range 47-56 kg
Alberta: adult males, mean 57 kg, range 47-70 kg
New Mexico: adult females, mean about 40 kg

Wikipedia (https://en.wikipedia.org/wiki/Pronghorn) states that adult females weigh 34-48 kg, and adult males weigh 40-65 kg.

My commentary:

Antilocapra americana seems to conform to Bergmann's rule (https://en.wikipedia.org/wiki/Biological_rules#:~:text=Bergmann%27s%20rule%20states%20that%20within,to%20many%20mammals%20and%20birds.).

DATA ON BRAIN MASS IN BEAR et al. (1973, Colorado Game, Fish and Parks Dept internal report: also see first comment below for individual measurements)

Adult females: brain mass mean 108 g (n=19) at body mass mean 46.4 kg
Adult males: brain mass mean 114 g (n=12) at body mass mean 50.4 kg

Yearling females: brain mass mean 107 g (n=8) at body mass mean 42.9 kg
Yearling males: brain mass mean 108 (n=7) at body mass mean 41.8 kg

My commentary:

The above data seem reliable.

DATA ON BRAIN MASS IN KOPPERUD (2017)

Kopperud (2017, https://www.duo.uio.no/handle/10852/59351) contains the following data for various wild ruminants.

Brain mass (g)/body mass (kg), in decreasing order of body mass (*cervids are asterisked):

Addax nasomaculatus 200 g/113.5 kg
Kobus leche 208.5 g/105.0 kg
*Rangifer tarandus 290 g/96.0 kg
*Rucervus eldi 198 g/88.0 kg
*Cervus nippon 109 g/73.0 kg
Damaliscus pygargus 305 g/70.0 kg
*Odocoileus hemionus 191g /68.0 kg
*Axis axis 134 g/67.5 kg
*Odocoileus virginianus 166 g/67.0 kg
*Rusa timorensis 169 g/62.0 kg
Nanger dama 150g/59.3 kg
Redunca arundinum 143 g/58.1 kg
Aepyceros melampus 178 g/55.3 kg
*Dama dama 194 g/54.7 kg
ANTILOCAPRA AMERICANA 114 g/53.1 kg
Nanger granti 151 g/50.0 kg
Tragelaphus spekii 156 g/48.1 kg
*Axis porcinus 156 g/43.9 kg
Tragelaphus scriptus 167 g/42.2 kg
Antilope cervicapra 138 g/37.4 kg
Saiga tatarica 111 g/38.6 kg
*Ozotoceros bezoarticus 92 g/38.2 kg
Rupicapra rupicapra 123 g/37.4 kg
Capricornis crispus 136 g/37.1 kg
Antidorcas marsupialis 136 g/36.0 kg
Litocranius walleri 134 g/34.5 kg
Rupicapra pyrenaica 114 g/33.9 kg

My commentary:

Among bovids:

An alcelaphin (Damaliscus pygargus) is brainy; see comment below https://www.inaturalist.org/posts/96029-is-the-pronghorn-antilocapra-americana-inferior-to-like-size-bovid-ruminants-in-braininess#activity_comment_a6a0b6b5-bb1c-4a64-9c8d-8ec382e49a45

However, caprins (Rupicapra spp.) and a saigin (Saiga tatarica, https://www.inaturalist.org/taxa/42378-Saiga-tatarica) seem somewhat below-par in braininess.

Among *cervids:

The data for Cervus nippon, Axis axis, and Ozotoceros bezoarticus presumably refer to mature males, whereas that for Rangifer tarandus may refer to adult females.

All these spp. are sexually dimorphic in body mass. The apparently greater braininess of R. tarandus than of C. nippon, A. axis, and O. bezoarticus may possibly be owing to the brawniness of mature males. The brain may cease to grow when adulthood is reached, despite body mass continuing to increase for several more years, in males (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10371095/ and https://link.springer.com/article/10.1007/s00265-023-03424-5).

Also see https://www.inaturalist.org/posts/96248-individual-variation-in-brain-size-in-the-rocky-mountain-mule-deer-odocoileus-hemionus-hemionus#activity_comment_78209f65-1479-46ba-b7c0-9077763d7f7c.

However, this caveat does not seem to apply to Axis porcinus (https://pestsmart.org.au/toolkit-resource/identifying-hog-deer-cervus-axis-porcinus/).

DATA ON BRAIN MASS IN RAICHLEN AND GORDON (2011, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3120765/)

These authors give brain mass and body mass for A. americana as 145.8g and 35.4 kg.

My commentary:

The value for body mass is puzzlingly small, indicating that juveniles, not adults, were sampled. However, the value for brain mass is anomalously great, relative to the above two references.

DISCUSSION

Two caveats are that

• the data presented by Raichlen and Gordon (2011) seem anomalous, in that the value for brain mass is as great as in like-size bovids, and
• the data for cervids (in Kopperud 2017) are ambivalent, owing to the complications of sexual dimorphism.

However,

• two of the three references seem congruent, and
• there seems to be no sexual dimorphism in the mass of the brain, relative to body mass, in A. americana.

According to the interspecific allometry of brain mass to body mass in wild bovids, the brain mass of Antilocapra americana is predicted to be about 165 g, at body mass about 53 kg.

The real brain mass of A. americana has a mean no greater than 114 g.

This means that the brain of A. americana, relative to that of bovids,

• shows a shortfall of at least 50 g, and
• is no more than 70% of the mass predicted.

Based on gazelles, Aepyceros melampus, and Tragelaphus spp. in Kopperud (2017), we would predict the brain mass of Antilocapra americana to be at least 150 g. In reality, the value is 114 g or less, viz. 75% or less of the predicted value.

Even Rupicapra (https://www.inaturalist.org/observations?place_id=any&subview=map&taxon_id=42345&view=species), at body mass of only 34 kg, has the same brain mass (114 g) as A. americana of body mass 53 kg.

CONCLUSIONS

The results suggest that Antilocapra americana is less brainy than are like-size bovids, with a noteworthy exception in Saiga tatarica (https://pubmed.ncbi.nlm.nih.gov/30963347/).

This shortfall is surprising, because A. americana is

• the only ecological counterpart for antelopes on plains in North America, and
• notorious for its curiosity (https://www.youtube.com/watch?app=desktop&v=EMncnjX7vcU and https://albertashistoricplaces.com/2018/07/18/pronghorn-traps-on-the-northern-plains-of-alberta/ and https://tpwd.texas.gov/huntwild/wild/species/prong/#:~:text=An%20interesting%20trait%20of%20Pronghorns,one%20that%20is%20in%20motion.), which would seem to imply intelligence (https://onlinelibrary.wiley.com/doi/full/10.1111/brv.13054 and https://ieeexplore.ieee.org/document/683171 and https://www.researchgate.net/publication/264422629_Curiosity_and_Information_Seeking_in_Animal_and_Human_Behavior).

Posted on 22 June, 2024 15:14 by milewski