evolution: symbiosis and reproduction (Introduction)

by David Turell , Wednesday, May 18, 2022, 15:58 (703 days ago) @ David Turell

In certain seafloor organisms:

https://www.sciencedaily.com/releases/2022/05/220517210412.htm

"Most bottom-dwelling marine invertebrate animals, such as sponges, corals, worms and oysters, produce tiny larvae that swim in the ocean prior to attaching to the seafloor and transforming into juveniles. A new study published in the Proceedings of the National Academy of Sciences (PNAS) and led by University of Hawai'i (UH) at Mānoa researchers revealed that a large, complex molecule, called lipopolysaccharide, produced by bacteria is responsible for inducing larval marine tubeworms, Hydroides elegans, to settle to the seafloor and begin the complex processes of metamorphosis.

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"Most invertebrate larvae are capable of staying in the larval stage for extended periods of time until they find a right spot. In the study, led by Marnie Freckelton, a postdoctoral researcher at the Kewalo Marine Lab, a unit of the Pacific Biosciences Research Center (PBRC) in SOEST, the research team asked the question: how do 'right spots' cue larvae to settle and metamorphose?

"Metamorphosis is a profound change in the animal's form -- from a small swimming larva to an animal with a very different anatomy anchored to the seafloor. Although researchers have known that biofilms, thin layers comprised of bacteria, diatoms and small algae that blanket submerged surfaces, induce metamorphosis of a wide range of marine invertebrate larvae, the mechanism of induction remained poorly understood.

"In laboratory experiments with larval tubeworms, the team found that they would not settle on clean surfaces. They required a cue from a surface biofilm.

"The team isolated a single bacterial species, Cellulophaga lytica, that could, when formed into surface biofilm, induce the worm larvae to settle, and then we asked: what is it about that particular bacterium that causes the larvae to settle and metamorphose?" said Freckelton.

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"'In fact, we have different strains of the same bacterial species obtained from Kaneʻohe Bay and Pearl Harbor, and the Hydroides larvae settle only in response to the one from Pearl Harbor," said Hadfield, who has been a researcher at the Kewalo Marine Lab in PBRC since 1968. "Furthermore, we found in our lab that larvae of the coral Pocillopora damicornis, which is abundant in Kaneʻohe Bay, will settle only in response to the Kaneʻohe Bay strain of the bacterium. This is a breakthrough, because it tells us about the specificity of certain bacteria that guide and maintain a community of animals where they occur.'"

Comment: not only is metamorphosis itself unexplained by Darwinism, but this also apparently necessary triggering mechanism is not explained either. The specificity of the trigger, a complex molecule, must be designed to work as it does.