International Team Unravels the Genome of the World’s Largest Reptile

Crocodile farm owners, palaeontologists, cladistics specialists and geneticists hope to reap the benefits of the research into Saltwater Crocodile genes after a team of international scientists completed the genome sequence of this, the largest extant species of reptile.

The Saltwater, or Estuarine Crocodile (Crocodylus porosus) is found throughout S.E. Asia, with a geographical distribution from Sri Lanka to northern Australia, this species is the mainstay of the crocodile farming industry in Asia and it is hoped that a better understanding of the genome sequence will help improve commercial crocodile breeding techniques.  In Australia alone, the crocodile industry is estimated to be worth some $8.8 million AUD in exports.

Professor Chris Moran (Sydney University’s Faculty of Veterinary Science), one of the researchers working on this genome project stated:

“We had previously completed a genome map for the Saltwater crocodile but this is a huge leap forward.  Genome sequencing is the next step.  The difference between genome mapping and genome sequencing is the difference between having a map of Australia on a single page and a detailed street directory.”

Advances in DNA sequencing technology, so-called next generation or “nextgen” sequencing, have provided between one thousand and a ten thousand-fold reduction in cost, along with comparable increases in the speed with which whole genome sequences can be generated.  The scientists estimate that a complete genome for a complex vertebrate such as a crocodile can be mapped out for a few thousand dollars, at the start of this century, to undertake such a project would have cost millions of dollars.

Saltwater Crocodile Genome is Sequenced

Genome for the Estuarine Crocodile has been Sequenced

Picture Credit: Associated Press

One of the immediate benefits to commercial crocodile farm owners is that this sequenced genome will help them to identify individual animals for breeding programmes.  Crocodiles do not become mature and able to breed until they are seven years old, which means that, currently, breeders have to wait that long before they can choose suitable breeding stock.  The genome sequencing methodology permits selection for breeding programmes at a much earlier age.  DNA samples can be taken as soon as the animals hatched and once analysed the information in the genes can be used to determine which animals will be suitable for breeding.

Professor Moran explained how the process works:

“This is possible because the genome sequence identifies genetic ‘markers’ which provide information on the likely health and breeding quality of an animal.”

Professor Moran worked on the genome sequence with his University of Sydney colleague Dr Jaime Gongora, along with PhD students Amanda Chong and Pauline Dalzell together with research affiliates Dr. Sally Isberg and Dr. Lee Miles.

The research team have been working on the genetics and genomics of farmed Saltwater Crocodiles since 2001 with funding from the Rural Industries Research and Development Corporation.

Other outcomes of the genome sequencing work include a better understanding of the evolutionary relationships among crocodilians, especially between the alligator family and crocodile family.  It also will have implications for palaeontologists as they strive to obtain a greater  understanding of crocodilians’ relationships to other reptiles, including their closest living relatives, the birds.  The research papers were published in the scientific journal “Genome Biology”.

In unrelated research, a number of scientists have been studying the anti-bacterial properties of crocodilian blood.  An improved understanding of crocodile genomes may indirectly help speed up the development of new, anti-bacterial agents.

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