A reductive evolution from a complex community of ancestors as a general trend in the evolution of life.

Meet the Pompeii Worm (Alvinella pompejana).

This little creature is famous among biologists because it is the most heat tolerant animal known to exist – it lives buried in the sides of hydrothermal vents and is thus regularly exposed to water temperatures up to 176 degrees Fahrenheit.  To survive in such an extreme environment, the worm lives in a close symbiotic relationship with thermophilic bacteria:

Scientists believe the bacteria on the worms’ backs act like firefighters’ blankets, shielding the worms from intermittent blasts of hot, metal-rich water.

http://news.nationalgeographic.com/news/2005/01/0117_050117_tubeworms.html

While this shows us another example of the way the global bacterial superorganism can facilitate the evolution and survival of other eukaryotic organisms, right now, let’s focus on the gene content of this worm, as a library of 15,858 unique cDNAs has just been described. [1]

The researchers found that several genes once considered specific to vertebrates, as they are missing in arthropods and nematodes, are alive and well in this polychaete worm.  For example:

the protein TERA08399 belongs to the superfamily of secreted cysteine rich factors and its N-terminal domain sequence exhibits the idiosyncratic features of the IGFBP (Insulin-Like Growth Factor Binding Protein) family reported to be vertebrate-specific.

Step back, and the larger picture is one that echoes themes I have highlighted on this blog: the gene content of the vertebrate genome looks more ancient than derived and  more like the genome of this worm than the genome of arthropods or nematodes.

As the authors of the study note:

The gene content of Alvinella reveals that an important pool of genes previously considered to be specific to Deuterostomes were in fact already present in the last common ancestor of the Bilaterian animals, but have been secondarily lost in model invertebrates. This pool is enriched in glycoproteins that play a key role in intercellular communication, hormonal regulation and immunity.

In fact, more startling is their summary conclusion:

Thus, the emerging picture of evolution is one of a complex ancestor of Metazoa, with a gene toolkit and a gene structure closer to those of extant Vertebrates and Annelids than to model Ecdysozoa. This contradicts the intuitive view of a linear evolution, from simple ancestral networks to more complex ones in Vertebrates, although it is in line with several studies suggesting a reductive evolution from a complex community of ancestors as a general trend in the evolution of life.

A complex metazoan ancestor that is followed by loss of genes in various lineages that emerged from it.  Yet the lineage that led to we brainy creatures has done a better job of retaining this ancient complexity.  This emerging picture fits comfortably within the perspective of front-loading, more so than the older “the intuitive view of a linear evolution.”

1. Gagniere N et al.  2010.  Insights into metazoan evolution from Alvinella pompejana cDNAs. BMC Genomics. 11(1):634.

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One response to “A reductive evolution from a complex community of ancestors as a general trend in the evolution of life.

  1. Just because Alvinella pompejana of today has genome X does not mean genome X is ancient. That is it doesn’t mean those “important pool of genes” were already present in some ancient common ancestor.

    In a software-driven front-loading scenario (targeted search) you do not need a host of genes to be present early on. So you have an intelligently designed genetic algorithm guided by epigenetic factors and resources.

    And the similarity in genes and proteins are just similar solutions to different problems- or better yet using similar tools to solve different problems.

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