Australian lungfish wins gold (for genome size)

There’s been some big lungfish news this week! A project led by Axel Meyer, Siegfried Schloissnig, Paolo Franchini, Kang Du, Joost Woltering and almost 15 others in their team, have published the full genome* for the Australian lungfish (Neoceratodus forsteri) in the high profile journal, Nature.

*A ‘genome’ is all of the genetic material of an organism and consists of DNA, while ‘genetics’ is concerned with the study of particular ‘genes’ and not necessarily the entire genome.

The genome of the Australian lungfish is absolutely huge at roughly 14 times the size of the human version, and is now the largest known in any animal. Previously the African lungfish, Protopterus, and then more recently the axolotl (salamander Ambystoma mexicanum), have been considered the record holders for this grand title.

This work by Meyer and team confirms the hypothesis that lungfish are the closest living lineage to the tetrapods (all amphibians, reptiles, birds and mammals), rather than the other group of living “lobe-finned fish”, the coelacanths. I like to say that in this way we can consider lungfish as our distant fishy cousins.

Figure 1 from the paper by Meyer et al. (2021) published in Nature showing the position of the lungfish (Neoceratodus) to tetrapods (https://www.nature.com/articles/s41586-021-03198-8)

For a time, the advent of molecular biology failed to definitively clarify this (known as the phylogenetic relationship) despite research on it spanning almost 30 years. The main issue was that the coelacanth, lungfish and tetrapod lineages are thought to have diverged from each other so long ago (about 420 million years ago!) which made piecing together their independent evolutionary molecular histories incredibly problematic. This is where palaeontology is absolutely invaluable for elucidating the relationships even between living animals when molecular methods may have their own limitations. Naturally I believe the best approach is to combine data from both lines of evidence to help us properly understand all life on earth today.

It was found that the lungfish had genes related to limb-like development in their fins, as well as some involved in air-breathing (lung surfactants and odour receptors) which were likely ‘preadaptations’ to living on land. The authors consider than these novelties found in lungfish -but not other fishes-, must have predisposed this group (sarcopterygians, the “lobe-fins”) to have been able to make that first foray onto land all those millions of years ago.

My photograph of a live animal, and 3D model of the Australian lungfish

These are just some of the reasons that I study lungfish in my own research, they are absolutely fascinating and hold the unique position as our closest fishy relatives (lungfish are more closely related to us than they are to a salmon or shark, for example). They are one of the best living representatives for helping us to understand what obstacles our distant tetrapod ancestors had to overcome to make their way from the water onto land almost 400 million years ago.

My own work researching lungfish has covered their air-breathing (Clement et al. 2016b; Clement & Long 2010a), muscles (Ziermann et al. 2017), brains (Challands et al. 2020; Clement et al. 2016a; Clement et al. 2016c; Clement et al. 2015; Clement & Ahlberg 2014), as well as fossils and the early evolution of the group (Gess & Clement 2019; Clement 2012; Clement & Long 2010b; Clement 2009; Long & Clement 2009). If you ever want to talk about lungfish, about these topics or otherwise, and specifically the Australian lungfish, then please get in touch! I have several ongoing projects also on these fabulous fishies.

Always excited to see these adorable fish at the Melbourne Museum

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