Eurasian foxes adapted to Sahara by breeding with local species

An international team sequenced the genomes of 82 foxes, including widespread red foxes as well as three desert-dwelling fox species – Rueppell's foxes, fennecs, and pale foxes – to uncover the evolutionary processes and genomic changes behind animal adaptation to desert environments. 

Their findings show that red fox ancestors left their Eurasian populations and migrated to North Africa during a humid period of the Sahara Desert, around 78,000 years ago. They reached places that were previously inhospitable and bred with desert-adapted Rueppell’s foxes, which had already inhabited the Sahara for at least 400,000 years. 

The team found a significant sharing of genetic material between North African red foxes and Rueppell’s foxes relative to Eurasian red foxes, and also between Rueppell’s foxes and fennecs. In particular, they discovered a long genomic region, spanning 25 million base pairs, that was shared between Rueppell's foxes and fennecs, but absent in red foxes, despite Rueppell's and red foxes being phylogenetically more closely related. “While we were surprised by these findings, the notion of shared ancestral genomic variation persisting throughout speciation events, sometimes as far as 16 million years, is actually very well established, with a growing body of research showing this to be pervasive in nature,” says Joana L. Rocha of the University of California Berkeley, in the United State. This study was part of her PhD project at the University of Porto, Portugal.   

The long genomic region shared between Rueppell’s and fennec foxes includes genes associated with adaptation to arid environments. For example, the researchers found a gene that affects the hormone vasopressin and plays a role in the ability to concentrate urine and reduce its volume. This sheds light on why Rueppell’s foxes have more concentrated urine compared to red foxes from North Africa and Eurasia.

The genomic analysis also suggests that desert-dwelling foxes have unique traits related to tolerance of extreme temperatures, thyroid hormone metabolism, water retention and fur colour. For example, SLC12A2 – a gene that plays a vital role in the regulation of ion balance – is significantly less expressed in North African red foxes and Rueppell’s foxes, compared with Eurasian red fox. This may reduce water loss through panting. 

“The study showed how the newly desert-inhabitant species can adapt to arid conditions by the act of natural selection – an important phenomenon to be studied and considered in the light of increased desertification due to accelerated climate changes,” says ecologist, Ali Basuony of Al-Azhar University in Egypt, who was not involved in this study. 

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