The Slow Evolution Of Crocodiles

Three papers shed light on the unusually slow evolution of the crocodilian genome, paving the way for better selective breeding.

AsianScientist (Dec. 18, 2014) – Crocodilians, including the Australian saltwater crocodile, mutate at about a quarter of the rate of birds, new research has revealed. The study, published in Science, is part of a special edition on birds, which are the crocodilians closest living biological grouping.

The discovery is the result of genome sequencing three crocodilian species—the Australian saltwater crocodile, the American alligator and the Indian gharial—by an international collaboration of scientists, including six from the University of Sydney’s Faculty of Veterinary Science.

“The research shows that compared to bird genomes, crocodilians evolved approximately four times more slowly than birds,” said Associate Professor Jaime Gongora from the University’s Faculty of Veterinary Science and a team leader on the project.

“It challenges us to solve the mystery of how the crocodilians have maintained their genetic diversity and survived for hundreds of millions of years—given this slow mutation rate.”

The findings are crucial to providing a comprehensive understanding of the genomic underpinnings of the diversity, natural history, immunity and biology of crocodilians and will certainly open new frontiers in crocodile research.

“We can use these genome resources to investigate the diversity of captive and wild saltwater crocodile populations to better understand their disease resistance, and their susceptibility and specific adaptations to their environments,” Gongora said.

Related findings by Associate Professor Gongora and his team are being published simultaneously in companion papers in the journals Retrovirology and PLOS ONE.

The two papers identify new lineages of viruses within the crocodilian genomes, some of which have captured crocodilian genes. They reveal that genes of adaptive immunity have diversified in crocodilians and shown a different organisational pattern from that in birds and other reptiles, which may provide some advantage to fight microbes.

Dr. Sally Isberg from the Center for Crocodile Research and Honorary Associate in the Faculty of Veterinary Science, coauthored these papers and was the main crocodile industry driver behind the project: “While bridging the gap in evolutionary studies, this knowledge will also help crocodile producers by enhancing the genetic regulation of the immune and endocrine systems, maximizing growth and ensuring skin quality.”

“Crocodile farming is a conservation success story but understanding the underlying genomic differences will enhance our ability to farm crocodiles ethically, efficiently and effectively,” she said.

“The work does not end here. We are now in the process of identifying an enormous number of sites in the DNA that show variation so that crocodile producers can select breeding crocodiles in the same way they select dairy cattle,” said University of Sydney Emeritus Professor Christopher Moran, co-author of the Science paper.

The articles can be found at:
Green et al. (2014) Three Crocodilian Genomes Reveal Ancestral Patterns of Evolution Among Crchosaurs.
Jaratlerdsiri et al. (2014) Comparative Genome Analyses Reveal Distinct Structure in the Saltwater Crocodile MHC.
Chong et al. (2014) Evolution and Gene Capture in Ancient Endogenous Retroviruses – Insights from the Crocodilian Genomes.


Source: University of Sydney; Photo: jean-louis Zimmerman/Flickr/CC.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Asian Scientist Magazine is an award-winning science and technology magazine that highlights R&D news stories from Asia to a global audience. The magazine is published by Singapore-headquartered Wildtype Media Group.

Related Stories from Asian Scientist