South American Lungfish: A Living Fossil with Giant Genome

Introduction and Evolutionary Significance

• The South American lungfish (Lepidosiren paradoxa) is considered a living fossil.
• Found in slow-moving and stagnant waters across South America.
• Closest living relative to the first land vertebrates.
• Resembles primordial ancestors from over 400 million years ago.
• Provides valuable insights into vertebrate evolution, especially the transition from aquatic to terrestrial life.

Record-Breaking Genome

• Possesses the largest genome of any animal on Earth.
• Genome is approximately 30 times larger than the human genome.
• Contains about 91 billion base pairs of DNA.
• If stretched out, the DNA in each cell would extend almost 200 feet (60 meters).
• 18 out of 19 chromosomes are individually larger than the entire human genome.
• Genome expanded massively over the past 100 million years.
• Added the equivalent of one human genome every 10 million years.

Genome Composition and Comparison

• About 90% of the genome consists of repetitive elements.
• Only 20,000 genes actually code for proteins.
• Genome expansion linked to reduced suppression of genomic repetition.
• Previously, the Australian lungfish held the record for the largest animal genome.
• Some plants, like the fork fern Tmesipteris oblanceolata, have even larger genomes.

Biological Characteristics and Adaptations

• Reaches up to 4 feet (1.25 meters) in length.
• Possesses both gills and lung-like organs for breathing.
• Can breathe air, adapting to oxygen-starved environments.
• Found in the Amazon and Parana-Paraguay River basins.
• Can survive prolonged droughts by burrowing in mud and entering aestivation.
• Has an elongated body with four limb-like fins, resembling amphibians.
• Diet mainly consists of invertebrates and detritus.