Squeezed off the branch

New find­ings say sponges are not the old­est branch of an­i­mal fam­ily tree.

The Star Malaysia - Star2 - - SCIENCE -

SORRY, Mis­ter SquarePants. Sponges are get­ting squeezed out of a dis­tinc­tive role in evo­lu­tion. A new study says they don’t rep­re­sent the old­est branch of the an­i­mal fam­ily tree af­ter all.

The DNA re­search gives the spot in­stead to comb jel­lies, a group of gelati­nous ma­rine an­i­mals with names like the sea wal­nut and the sea goose­berry.

All an­i­mals evolved from a sin­gle an­ces­tor and sci­en­tists want to know more about how that hap­pened.

More than half a bil­lion years ago, long be­fore hu­mans ap­peared, the first split in the tree sep­a­rated one lineage from all other an­i­mals. Tra­di­tion­ally, sci­en­tists have thought it was sponges.

The ev­i­dence in favour of comb jel­lies comes from de­ci­pher­ing the first com­plete ge­netic code from a mem­ber of this group. Sci­en­tists were fi­nally able to com­pare the full DNA codes from all the ear­li­est branches.

The genome of a sea wal­nut, a plank­ton-eat­ing crea­ture na­tive to the western At­lantic Ocean, was re­ported last Thurs­day in the jour­nal Sci­ence by An­dreas Bax­e­va­nis of the Na­tional Hu­man Genome Re­search In­sti­tute with co-au­thors there and else­where. The work supports some ear­lier indi­ca­tions that comb jel­lies were the first to branch off.

Sort­ing out the early branch­ing of the tree could help sci­en­tists learn what the an­ces­tor of all an­i­mals was like.

But de­spite decades of study and the tra­di­tional view favour­ing sponges, there is plenty of dis­agree­ment about which early branch came first.

The ques­tion is “dev­il­ishly dif­fi­cult” to an­swer, and the new pa­per is prob­a­bly not the last word, said An­to­nis Rokas of Van­der­bilt Univer­sity, who did not par­tic­i­pate in it.

“The re­sults need to be taken se­ri­ously,” he said, but “I’m pretty sure there will be other stud­ies that sug­gest some­thing else.” – AP

Very early an­i­mals: a mne­miop­sis lei­dyi, a species of comb jelly known as a sea wal­nut. This group of gelati­nous ma­rine an­i­mals rep­re­sents the old­est branch of the an­i­mal fam­ily tree. — aP Photo

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