A comparison of organ sizes between the common warthog (Phacochoerus africanus) and the domestic pig (Sus scrofa)

INTRODUCTION

The common warthog (Phacochoerus africanus, https://www.inaturalist.org/taxa/42122-Phacochoerus-africanus) is extreme, among Suidae (https://en.wikipedia.org/wiki/Suidae), for its adaptation to African savannas.

This is based on a combination of

• specialisation on a staple diet of grass,
• dependence on burrows for refuge and shelter, and
• diurnal, not nocturnal, activity.

The most obvious morphological adaptation in the common warthog is in dentition (https://www.instagram.com/p/y7u1rDsXp6/ and https://www.vin.com/apputil/content/defaultadv1.aspx?pId=26439&catId=159991&id=10047368&ind=32&objTypeID=17#:~:text=The%20premolars%20and%20molars%20are,tubules%20may%20have%20single%20roots.).

The teeth are extremely modified for grinding fibrous and gritty items, mainly the rhizomes of grasses.

I was, therefore, curious to see how the internal organs of the common warthog differ in proportional size from those of the domestic pig (Sus scrofa, https://www.inaturalist.org/observations?taxon_id=324492).

METHODS

Sources:

Common warthog: data collected in Uganda by H P Ledger and N S Smith (authors of https://www.jstor.org/stable/3798800 and https://www.semanticscholar.org/paper/The-Carcass-and-Body-Composition-of-the-Uganda-Kob-Ledger-Smith/c891d40fecc1cb23ead94a137421e929870c1df3 and https://kalrorepository.kalro.org/items/eab259a5-ccd3-44ab-8e84-872dc179970d) for

• n = 10 adult females, and
• n = 11 adult males.

Domestic pig: various references (all referring to sexually mature subadults of both sexes that have not yet attained full body mass), including https://www.scielo.cl/scielo.php?pid=S0718-16202009000200002&script=sci_arttext and https://www.jstage.jst.go.jp/article/jvms/60/5/60_5_545/_pdf and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9863662/ and https://www.perplexity.ai/search/Give-lengths-of-7EadhvLkRVyTwb1r31OJPg.

RESULTS (all values are means)

Body masses:
Common warthog 71 kg, domestic pig 112 kg.

This indicates a two-fold difference in full maturity, probably owing partly to the mass of adipose tissues in the domestic pig.

The contents of the large intestine, including the caecum, are much more massive, relative to body mass, in the common warthog (10.3%) than in the domestic pig (2.2%).

The small intestine is remarkably short, both absolutely and relatively to body mass, in the common warthog (7.2 m) compared to the domestic pig (17.0 m).

The following are absolutely similar between the two spp.:

• mass of empty stomach,
• length of large intestine (5.1 m for common warthog, 4.8 m for domestic pig),
• mass of heart, and
• mass of spleen.

The following are similar in mass, relative to body mass:

• empty stomach (common warthog 0.53% of body mass, domestic pig 0.48%),
• empty small intestine (common warthog 0.78%, domestic pig 0.93%)
• liver (common warthog 1.35%, domestic pig 1.07%).

The following organs are somewhat more massive, relative to body mass, in the common warthog than in the domestic pig:

• empty large intestine, including caecum (common warthog 2.0%, domestic pig 1.15%)
• mass of heart (common warthog 0.38%, domestic pig 0.26%),
• mass of lungs (common warthog 0.87% including trachea, domestic pig 0.24%)
• mass of spleen (common warthog 0.2%, domestic pig 0.12%).

The following are nebulously/slightly more massive in the common warthog than in the domestic pig, relative to body mass:

• stomach (0.53% cf 0.48%), and
• liver (1.35% cf 1.07%).

DISCUSSION

The comparison is complicated by the differences

• in mature in body masses between the two spp., and
• the different ontogenetic stages of the individuals sampled for each species.

Slight differences in the relative sizes of certain organs may possibly be explained by the domestic pig having been selectively bred for fattiness.

However, the most striking difference is that the large intestine (including the caecum) of the common warthog is clearly more filled - absolutely as well as relatively - than that of the domestic pig. Consistent with this is that the small intestine of the common warthog is shorter than that of the domestic pig.

These salient differences may be explained by the fibrous diet of mainly grass of the common warthog, compared to the omnivory of the domestic pig.

The main differences between the common warthog and the domestic pig relate to gastrointestinal fermentation (in the hindgut). Any differences relating to cursoriality (heart and lungs) are minor.

Perhaps the crucial difference in this whole comparison is that - in conjunction with modification of the dentition - the contents of the large intestine are far more massive than those of the domestic pig.

This reflects the grazing specialisation of the common warthog, and its dependence on volatile fatty acids generated by microbes in the colon and caecum. In this way, the common warthog is somewhat convergent with Equidae.

Note: The small intestine of the common warthog happens to be absolutely similar in length to that of the coexisting ostrich (Struthio camelus). I plan to Post on this topic soon...

Posted on May 14, 2024 02:42 PM by milewski