Little Neptune Grass (Cymodocea nodosa).
Photo: Thorsten Reusch, GEOMAR
Sea grasses are the only flowering plants to become fully submerged, having evolved from three independent lineages some 100 million years ago in fresh water and transitioned into marine plants. This appears to have been facilitated some 86 million years ago by a whole genome tripling, which created plenty of spare DNA which could mutate harmlessly to create new genetic information - something deemed 'impossible' by creationist dogma. Since then, they have undergone further evolutionary adaptation by gene loss - something else that creationist dogma says is impossible.
Now an international group of 38 researchers coordinated by Professor Dr. Yves Van de Peer, Ghent University, Belgium, Professor Dr. Jeanine Olsen, University of Groningen, Netherlands, Professor Dr. Thorsten Reusch, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany, Dr. Gabriele Procaccini, Stazione Zoologica Anton Dohrn of Napoli, Italy, and the Joint Genome Institute, Berkeley, California, United States of America, sequenced and analyzed the genomes of three of the most important seagrass species – the iconic Mediterranean endemic Neptune grass (Posidonia oceanica), the broadly distributed Little Neptune grass (Cymodocea nodosa) and the Caribbean endemic Turtlegrass (Thalassia testudinum), to discover what evolutionary changes had enabled this transition.
Anyone who has holidayed on the Mediterranean coast may be familiar with the 'Poseidon balls' that wash up on beaches. These example of emergence of order from chaos are the result of the fibrous remains of Poseidon grass leaves being rolled along the seabed at the tidal interface to form long rolls which then break up and get rolled further into balls, as I relate here.
But the question the team addressed was not how the Poseidon balls form but how did the sea grasses evolve? This is the subject of their paper in Nature Plants and a press release from GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany:
Gene analyses revealing the capacity of marine flowering plants to exist under changing environmental conditions provide clues for the conservation and sustainable use of important ecosystemsFrom the team's paper in Nature Plants which regrettably is behind an expensive paywall:
Seagrasses provide the foundation of one of the most highly biodiverse, yet vulnerable, coastal marine ecosystems globally. They arose in three independent lineages from their freshwater ancestors some 100 million years ago and are the only fully submerged, marine flowering plants. Moving to such a radically different environment is a rare evolutionary event and definitely not easy. How did they do it? New reference quality genomes provide important clues with relevance to their conservation and biotechnological application.
[…]
The researchers first examined genome structure and then compared gene families and pathways associated with structural and physiological adaptations, between the seagrasses and their related freshwater relatives. Their findings are presented today in a peer-reviewed publication in the scientific journal Nature Plants, entitled “Seagrass genomes reveal ancient polyploidy and adaptations to the marine environment”.
Seagrass-based ecosystems provide multiple functions and services – for instance as protection against erosion that preserves coastal seascapes, as biodiversity hotspots for associated animals and algae and as a nature-based solution for climate mitigation owing to their carbon storage capacity in belowground biomass. Both conservation and restoration are areas of intensive research because seagrasses are being lost, as are coral reefs, to climate warming and other human impacts.
As the saying goes, “Many hands/brains make the work light”: To begin, the research consortium took a deep evolutionary look at the structure of the genomes themselves, followed by a comparative analysis of their more than 20,000 genes and relevant pathways that have evolved into the specific marine adaptations. Next, the 23 collaborating research teams each focused on different complementary structural or functional gene sets including their physiological functions. A key question was whether genomic adaptations came about in parallel, or whether they arose independently and maybe even involved different gene sets.
One major result was that seagrasses were able to jump-start radical adaptation via genome duplication, which is often associated with severe environmental stress.Seagrasses underwent an extremely rare set of adaptations. Whereas re-adaptation to freshwater environments has occurred more than 200 times in flowering plant evolutionary history – involving hundreds of lineages and thousands of species – seagrasses evolved from their freshwater ancestors only three times – involving 84 species. To do this required specialized ecological tolerance to, for example, high salinity, lower light, a wide range of temperature tolerances, underwater carbon capture for photosynthesis, different pathogen defense, structural flexibility and an underwater pollination.
Professor Jeanine L. Olsen, co-corresponding author.
Groningen Institute for Evolutionary Life Sciences
University of Groningen, Groningen, the Netherlands.
Further, the researchers found that the retention and expansions of some gene families could still be traced back through retained syntenic blocks to these early duplication events, for example flavonoids to provide protection against ultraviolet radiation and fungi, while stimulating recruitment of nitrogen-fixing bacteria; expanded cysteine oxidases for coping with hypoxic sediments and genes associated with circadian clocks. The results also showed that “jumping genes” – transposable elements – played a major role in creating new genetic variation for selection to act upon. This applied particularly to the large genomes of Thalassia testudinum and Posidonia oceanica.Comparison of the three independent seagrass lineages, including freshwater sister lineages, revealed a shared ancient whole genome triplication at about 86 million years. This was quite exciting because large parts of the ocean were oxygen-free at that time and it’s also a uniting event involving the three lineages.
Professor Yves Van de Peer, co-corresponding author.
Department of Plant Biotechnology and Bioinformatics
Ghent University, Ghent, Belgium
The team also found several adaptations to be the result of convergence. This applied mainly to traits that became redundant or detrimental in a submerged, highly saline, marine environment. Loss of genes for stomata – the tiny holes in the leaf surface providing gas exchange with the atmosphere – loss of genes for volatiles and signaling to defend against pathogens and tolerate marine heat waves, notably heat shock factors, are compelling examples of “use it or lose it”.
It’s clear that fine-tuning of supportive pathways has played the dominant role, rather than genes taking on major new functions. Salt-tolerance is a good example in which a higher efficiency of multiple processes has occurred to regulate sodium, chlorine and potassium. Evolutionary changes have also provided different species with the ability to withstand different environments.
Dr. Gabriele Procaccini, co-corresponding author
Department of Integrative Marine Ecology
Stazione Zoologica Anton Dohrn, Naples, Italy.The new genomic resources will accelerate experimental and functional studies that are especially relevant to transformative management and restoration of seagrass ecosystems. They are a formidable resource for the research community.Most ecologically important functions are complex traits, involving the interaction of many genes through flexible pathways. With genomic tools now developed for key seagrasses, we can begin to experimentally test and manipulate them. This is especially important for restoration under climate change scenarios involving many of the conditions discussed here.
Professor Thorsten B. H. Reusch, co-corresponding author
Marine Evolutionary Ecology, GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel, Kiel, Germany
AbstractThere is so much for creationists to cope with here, that it's doubtful any will even try:
We present chromosome-level genome assemblies from representative species of three independently evolved seagrass lineages: Posidonia oceanica, Cymodocea nodosa, Thalassia testudinum and Zostera marina. We also include a draft genome of Potamogeton acutifolius, belonging to a freshwater sister lineage to Zosteraceae. All seagrass species share an ancient whole-genome triplication, while additional whole-genome duplications were uncovered for C. nodosa, Z. marina and P. acutifolius. Comparative analysis of selected gene families suggests that the transition from submerged-freshwater to submerged-marine environments mainly involved fine-tuning of multiple processes (such as osmoregulation, salinity, light capture, carbon acquisition and temperature) that all had to happen in parallel, probably explaining why adaptation to a marine lifestyle has been exceedingly rare. Major gene losses related to stomata, volatiles, defence and lignification are probably a consequence of the return to the sea rather than the cause of it. These new genomes will accelerate functional studies and solutions, as continuing losses of the ‘savannahs of the sea’ are of major concern in times of climate change and loss of biodiversity.
Ma, X., Vanneste, S., Chang, J. et al.
Seagrass genomes reveal ancient polyploidy and adaptations to the marine environment. Nat. Plants (2024). https://doi.org/10.1038/s41477-023-01608-5
© 2024 Springer Nature Ltd.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
- Firstly, there is the fact that these evolutionary changes mostly happened in the long period of Earth's pre-'Creation Week' history before creationists believe Earth existed.
- Then there is the evidence of new genetic information being created multiple times with one incidence of genome triplication and a couple of genome duplication events in some lines.
- Further adaptation to salt water by gene loss, losing the genes for the stomata - the pores in terrestrial plant leaves that allow gas exchange and water transpiration, and those associated with volatile scent signals.
- Evidence of common descent in the synteny in the genomes of distantly-related species.
- Evidence of unintelligent design, in that no sane, half-competent designer would use the same method for reproduction including flowers and pollen that was clearly 'designed' for terrestrial reproduction, especially when there were perfectly good systems for reproduction in other marine plants, but then only a mindless idiot would design a flowering plant and then put it under water to live in the first place then have to come up with some half-baked, Heath Robinson machine to overcome its lack of foresight.
- Lack of any doubt on the part of the biologists who did the research that what they were seeing was the result, not of supernatural magic, but of the mindless, god-free, natural process of evolution.
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