What gives the mighty mule its endurance? Researchers investigate

A mule named Juancito at work on the Mitre Peninsula, in Tierra del Fuego, Argentina. Photo: Dario u, public domain, via Wikimedia Commons

Mules are renowned worldwide for their outstanding muscular endurance, but what gives them this ability to outshine their horse and donkey parents?

Hybrid vigor has long been recognised and widely exploited in animal and plant breeding programs to enhance the productive traits of hybrid progeny from two breeds or species.

However, its underlying genetic mechanisms remain enigmatic.

Researchers from Northwest A&F University in Yangling, China, set out to understand more about the molecular mechanisms at work in mules that provide this superior muscular endurance.

Their genetic testing of samples from crosses between donkeys and horses mapped a total of 68 genes in the “muscle contraction” pathway, eight of which were found to be significantly enriched in mules.

In the hybrid individuals and their parents, one of these enriched genes, TNNC2, was mainly expressed in the fast skeletal muscle. Its expression level was found to be two times higher in the mule than in the horse.

They said their work, in which muscle, brain, and skin samples from mules, hinnies and their parents were tested, revealed significant differences between mules and hinnies, as well as differences between mules and both of their parents.

Apart from skeletal muscle tissue, which is the main difference which separates mules from hinnies and their parents, there are also clear differences between these animals in both the brain and skin.

The findings, they say, provide new insights into the genetic mechanism underlying hybrid vigor in mules.

The work could provide the basis for future studies of the genetic and molecular mechanism of hybrid vigor in donkeys and horses.

Gao, S.; Nanaei, H.A.; Wei, B.; Wang, Y.; Wang, X.; Li, Z.; Dai, X.; Wang, Z.; Jiang, Y.; Shao, J. Comparative Transcriptome Profiling Analysis Uncovers Novel Heterosis-Related Candidate Genes Associated with Muscular Endurance in Mules. Animals 2020, 10, 980.

The study, published under a Creative Commons License, can be read here


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2 thoughts on “What gives the mighty mule its endurance? Researchers investigate

  • June 10, 2020 at 9:59 am

    Excellent article! Finally, more studies are being done on mules and donkeys. This is great!

  • June 14, 2020 at 10:20 pm

    I find this fascinating love mules daughter has one. I have donkeys


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