Asian Elephants (Elephas maximus) and Horses (Equus ferus caballus) Refused to Eat Pawpaws in a Controlled Experiment

Some scientists have hypothesized certain fruiting plants were dependent upon now extinct megafauna for distribution.  They believe the fruits were eaten and the still viable seeds were scattered across the landscape in beneficial piles of manure.  The extinction of large mammals that ate the fruits of pawpaw (Asimina triloba) and osage orange (Maclura pomifera) explains why these plant species today have such a patchy distribution.  They are considered anachronistic fruits.  Members of the Hendrix College Biology Department in Arkansas recently tested this hypothesis by feeding these fruits to species closely related to extinct Pleistocene megafauna.  They then planted the defecated seeds to determine viability.  Oddly enough, they also included persimmon (Diospyros virginiana) in their experiment. Persimmon is a common tree, not patchy in distribution, and the seeds are known to maintain viability after passing through a raccoon’s (Procyon lotor) alimentary tract.  I don’t consider persimmon an anachronistic fruit for those reasons.

Asian elephant.  In an experiment they readily ate persimmons and did try osage orange but absolutely refused to eat pawpaws.  This does not convince me that mastodons didn’t eat pawpaws.

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Horse eating osage orange.  The experiment suggests horses were not a distributor of osage orange seeds.  No viable seeds survived the horses digestive tract.

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Horses and elephants loved eating persimmons.  Viable seeds survived elephant digestive tracts but not the horse’s.

Pawpaw Fruit

Scientists were surprised that elephants and horses didn’t eat pawpaws, a nutritious sugary fruit.  This doesn’t mean mastodons didn’t eat pawpaws.  Mastodons were not the same species as the Asian elephant and evolved in the same region as this fruit. I believe they did eat them.

Asian elephants are closely related to extinct mammoths and distantly related to extinct mastodons (27 million years of evolution separate them from the latter proboscidean).  Modern horses are arguably the same animal as 1 of the species of North American horses of the Pleistocene.  The scientists involved in the study fed persimmons, osage orange, and pawpaws to Asian elephants and horses to gauge how effective they would be as seed dispersers.  Persimmons seeds sprouted and grew well in elephant dung but failed to survive horse digestion.  One elephant ate osage oranges but refused to retry them given a 2nd helping.  Some osage orange seeds sprouted and grew in elephant dung.  But again, none survived horse digestion, though horses really liked this fruit.  Elephants and horses surprisingly refused pawpaws.  At first the horses tasted them but spit them out and visibly grimaced (known as a Flehman response) as if they tasted bad.  Pawpaws are sweet and nutritious, so it is puzzling why neither species ate them.

The results of this study suggest mastodons and mammoths could have been effective dispersers of fruit seeds, while Pleistocene horses were not.  The study doesn’t prove mastodons didn’t eat pawpaws.  Though related, mastodons are not the same species as Asian elephants and likely had different tastes.  Mastodons evolved in North America for  millions of years alongside pawpaws, and I suspect some time during that span of time the species learned to like pawpaws. Persimmons grow in Asia but pawpaws do not.  Perhaps this explains why Asian elephants were so willing to eat persimmons but not pawpaws.  It is a fruit that occurs in the region from where they evolved.

The Hendrix College Biology Department should expand their study to include other close relatives of extinct Pleistocene megafauna such as tapirs, pigs, peccaries, llamas, and tree sloths.

Reference:

Boone, Madison; et. al.

“A Test of Potential Pleistocene Mammal Seed Dispersal in Anachronistic Fruits Using Extant Ecological and Physiological Analogs”

Southeastern Naturalist 14 (1) 2015

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One Response to “Asian Elephants (Elephas maximus) and Horses (Equus ferus caballus) Refused to Eat Pawpaws in a Controlled Experiment”

  1. Bodark Swamps | GeorgiaBeforePeople Says:

    […] orange seeds can survive transit through an elephant’s gut but not an horse’s.  (See:https://markgelbart.wordpress.com/2015/04/10/asian-elephants-elephas-maximus-and-horses-equus-ferus-&#8230😉  Horses and probably tapirs, a relative of the horse, consumed Osage orange, but this large fruit […]

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