Post Speciation Admixture in Big Cats

12 million years of evolution separate the domestic housecat from the African lion.  A recent study used the genome of the housecat as an outgroup in their examination of the evolutionary relationships between big cats in the Panthera genus which includes the lion (Panthera leo), jaguar (P. onca), leopard (P. pardus), snow leopard (P. uncia), and tiger (P. tigris).  The ancestor of all species in the Panthera genus diverged from its now extinct relatives 4.58 million years ago.  The common ancestor of lions, leopards, and jaguars diverged from this early lineage 3.65 million years ago.  The common ancestor of tigers and snow leopards diverged from the rest of the Panthera lineage 3.47 million years ago.  Leopards and lions diverged from each other 2.57 million years ago.  (The chart below simplifies this history.)  However, genetic evidence suggests after these species diverged from each other and became separate species they occasionally interbred with each other.   Lions interbred the most because they had the widest geographical range and overlapped with more species.  Lions formerly lived from the southern tip of Africa across Eurasia and to the east coast of North America, and they came into contact with more species.  Jaguars originally evolved in Eurasia and were common there during the late Pliocene/early Pleistocene.  After jaguars crossed the Bering Land Bridge and colonized the Americas they became extinct in Eurasia.  Jaguars periodically interbred with lions during the early Pleistocene.  Snow leopards and tigers also interbred with each other during the early Pleistocene.

Chart showing speciation divergence within the Panthera genus and later hybridization events resulting in admixtures of certain genes that were positively selected for survival of the species. From the below reference.

Leopon (male leopard & female lion hybrid) - Apparently a leopard ...

Lion/leopard hybrid.  Lions and leopards diverged over 2 million years ago, but rarely did hybridize in the wild following this divergence.  Lions interbreed with tigers, jaguars, and leopards in captivity, but currently are not known to do so in the wild.  

Genetic evidence indicates some of the hybridization events benefitted the descendants and were a positive force in naturally selecting characteristics that helped the species survive.  The trait that gives jaguars a large skull and powerful bite originated from when a jaguar mated with a lion.  This characteristic later helped jaguars survive the megafauna extinction event because they could prey on heavily armored caimans and turtles as a substitute.  Interbreeding between snow leopards and tigers was also important.  The characteristic that helps snow leopards thrive at high altitudes originated from the pairing of a snow leopard and a tiger.  Populations of cats in the Panthera genus fluctuated during the Pleistocene and the authors of the below study believe hybridization events facilitated the survival of these species.

Reference:

Figueiro, H. etl al.

“Genome-wide Signatures of Complex Introgression and Adaptive Evolution in the Big Cats”

Science Advances July 2017

https://advances.sciencemag.org/content/3/7/e1700299

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