Evolution: convergence or divergence (Introduction)

by David Turell @, Tuesday, January 12, 2021, 19:15 (12 days ago) @ David Turell

The platypus is divergence:


"The platypus and four echidna species, all native to Australia, are the world’s only living monotremes — a group perhaps best known for their unique reproductive strategy, which involves laying eggs and then nursing their young once they’ve hatched.


"But because the monotremes diverged from other mammals so early — about 187 million years ago — they are also “very important for understanding mammalian evolution,” he said. Indeed, some monotreme traits that seem so strange to us may have actually been present in the ancestor we all share.


"Having such a comprehensive map enables comparisons among the genomes of different species, and helps fill gaps in the step-by-step story of how mammals appeared and then diverged. For instance, many birds and insects have multiple copies of a gene called vitellogenin, which is involved in the production of egg yolks.

"Most mammals don’t have the vitellogenin gene, said Dr. Zhang. But the new genomes reveal that platypuses and echidnas have one copy of it, helping to explain their anomalous egg-laying — and suggesting that this gene (and perhaps the reproductive strategy itself) may have been something the rest of us lost, rather than an innovation of the monotremes. Meanwhile, they also have milk-producing genes similar to ours and those of other mammals, allowing them to nourish their young.

"Other traits took other paths. The new genome reveals that monotremes, which are toothless, have lost multiple genes associated with dental development that are present in other mammals. Platypuses also have venom-producing genes that other mammals lack, but that are similar to those found in some reptiles, perhaps explaining their toxic foot spikes.

"Less visible, but equally perplexing, is the fact that while other mammals generally have one pair of sex chromosomes, monotremes have five pairs. The structure of the newly revealed genomes suggests that these sex chromosomes were once in a ring formation, and then broke into pieces — although more research is needed to figure out how that happened."

Comment: Looks like a Rube Goldberg machine with bits and pieces of several types of evolutionary stages. Their econiche is in steam in Australia, like the ones I have seen.

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