"Trashfish" AKA the Ultimate ‘Living Fossils’ may Advance Human Medicine.

If you could hop into a time machine and travel back 150 million years, the world would have looked very different. The supercontinent Pangaea was just beginning to break up, stegosaurus roamed the Earth, and ichthyosaurs dominated the seas- but if you stuck your head into a stream, you might have spotted a familiar face from our modern age...Gars.






In 1859 Charles Darwin coined the term “living fossil” to describe lineages that have looked the same for tens of millions of years, such as the coelacanth, sturgeon, and horseshoe crab. The term captured the popular imagination, but scientists have struggled to understand whether such species just resemble their long-ago ancestors or have truly evolved little over the eons.

Gars, often dismissed as "trash fish," are toothy, torpedo-shaped fish that have remained relatively unchanged throughout time. These fish are 'living fossils' - among the most primitive animals on Earth for 150 million years. Over this whole time these fish have mostly stayed the same, a rare consistency not even seen in sharks. A new study says that at the molecular level, gars are the most living fossil-y out of all living fossils- and it’s not even close.

Of 481 vertebrate species, researchers—led by Chase Brownstein and Thomas Near of Yale University and Dan MacGuigan of the University of Buffalo—found that gars have the slowest rate of molecular evolution known to science. The team also proposes a mechanism to explain gars’ timelessness to be superb DNA repair machinery. They suggest gars are extremely efficient at repairing DNA after mutations or damage, keeping the animals from evolving even as the continents have shifted around them. This repairing ability has likely kept gar genomes so stable that species and even genera whose last common ancestor lived more than 100 million years ago have diverged very little, and some can still hybridize today to produce viable offspring.

A similar hypothesis has previously been proposed by other researchers for sturgeon, which had the second-lowest substitution rates among vertebrates in the study

The scientists believe this genetic quirk could lead to advances in human medicine- which I find fascinating.

“If we can isolate what that is—and we’ve got some ideas as to what gene that might be—we can then take it to the next step of thinking about implications for human medicine and disease,” says Solomon David, an aquatic ecologist at the University of Minnesota and co-author of the study.David believes that if whatever is correcting those mutations can be replicated in human bodies, it could potentially prevent or counteract diseases such as cancer, the result of shortcomings in DNA repair and cell growth run amok.




Sources:

https://www.nationalgeographic.com/animals/article/living-fossils-gars-fish-evolution

https://www.science.org/content/article/these-gars-are-ultimate-living-fossils

Living fossil Genome Unveiled

This article presents the genome sequence of Ginkgo biloba, the oldest extant tree species. The research was carried out by a team of scientists at BGI, Zheijiang University and the Chinese Academy of Sciences, who tackled and analyzed an exceptionally large genome, totalling more than 10 billion DNA "letters." Ginkgo is considered a "living fossil," meaning its form and structure have changed very little in the 270 million years since it first came into existence. Given its longevity as a species and unique position in the evolutionary tree of life, the ginkgo genome will provide an extensive resource for studies concerning plant defenses against insects and pathogens, and research investigating early events in tree evolution and in evolution overall.

To study the ginkgo's extraordinary biology at a genetic and molecular level, sequencing its genome was high up on the wish list of plant biologists. However, because of its size as well as the presence of an enormous number of repeat sequences, assembling the whole genome sequence would be a difficult task. The ginkgo genome stretches over more than 10 Gb, which is 80 times larger than the "model plant" Arabidopsis thaliana genome. The tree's genome is also larger than other plant species known for extremely big genomes, such as maize or orchids. The great interest in the history and biology of gingko, however, made the work of sequencing and assembling the genome a challenge the researchers from China felt worth taking, and one they succeeded in accomplishing.
Wenbin Chen from BGI explains some of the difficulties that they had to overcome: "A huge amount of raw data (~2 TB) was generated, and the computing capability for genome assembly was challenged by both the huge data and the remarkably high proportion of repetitive sequences. So an incredible amount of memory was required." He went on to highlight several genome features: "The large genome of ginkgo may have resulted from whole genome duplication and insertion of a remarkably high proportion of repetitive sequences, at least 76.58%, and the longest introns among all sequenced species due to insertions of transposable elements."

Meeting the sequencing challenge was worth it for a variety of reasons. One certainly relates to its status as a "living fossil," at title shared by few other species, including the horseshoe crab and the nautilus. As the only surviving representative of a highly unusual group of non-flowering plants that appeared at least 270 million years ago, the ginkgo has retained traits over millions of years, such as the emblematic fan-shaped leaves, that are not seen in any other surviving plant species surviving. It further holds a very unique position in the plant evolutionary tree.

Professor Yunpeng Zhao, one of the authors from Zhejiang University, explains how this evolutionary placement is of great interest to researchers: "Ginkgo represents one of the five living groups of seed plants, and has no living relatives. Such a genome fills a major phylogenetic gap of land plants, and provides key genetic resources to address evolutionary questions like phylogenetic relationships of gymnosperm lineages, evolution of genome and genes in land plants, innovation of developmental traits, evolution of sex as well as history of demography and distribution, resistance and conservation of ginkgo."

Researchers are also fascinated by the ginkgo's resilience under adverse conditions -- it is worth noting that ginkgo trees were one of the few living things to survive the blast of the atomic bombing of Hiroshima. This hardiness likely helped the ginkgo survive periods of glaciation in China that killed many other species, and may also promote the longevity of individual trees, some living up to several thousand years, according to reports. The ginkgo is also able to defend itself against a wide range of attackers, employing an arsenal of chemical weapons against insects, bacteria and fungi.
To better understand the ginkgo's defensive systems, the authors analysed the repertoire of genes present in the genome that are known to play a role in fending off attackers. An initial analysis of the tree's more than 40,000 predicted genes showed extensive expansion of gene families that provide for a variety of defensive mechanisms.

Genes that enable resistance against pathogens are often duplicated. Additionally, ginkgo has a double-knockout punch in its fight against insects by synthesizing chemicals that directly fight insects and by releasing volatile organic compounds that specifically attract enemies of plant-eating insects. These findings indicated that having multiple mechanisms -- the expansion of gene families, higher doses of specific genes, and versatility in its defence genes -- might be linked to the ginkgo's extraordinary resilience. This information may then be useful to aid in understanding plant defence system with an eye to improving food security.