Του Γιώργου Λεκάκη
Οι επιστήμονες ανακάλυψαν ότι
τα κτενοφόρα / Ctenophores, που ονομάζονται και comb jellies, είναι η αδελφή
ομάδα όλων των νυν ζώντων ζώων.
Συνέκριναν το comb jelly
Bolinopsis microptera με σφουγγάρια – άλλον έναν υποψήφιο για το αρχαιότερο
πλάσμα στην Γη – μαζί με τρεις μονοκύτταρους συγγενείς ζώων.
Το μοτίβο των γονιδίων στα
χρωμοσώματα των jellies αποκάλυψε ότι αυτά εξελίχθηκαν πρώτα, πριν 600.000.000 –
700.000.000 χρόνια!
Αυτό σημαίνει ότι τα πρώιμα
ζώα ήταν εκπληκτικά πολύπλοκα: είχαν ένα καλά ανεπτυγμένο νευρικό σύστημα και
πιθανότατα μπορούσαν να κολυμβήσουν ελεύθερα!
«Πρέπει να ξανασκεφτούμε την
λειτουργία και την δομή του πρώιμου προγόνου των ζώων! Δεν ήταν σαν ένα απλό
σφουγγάρι», λέει η εξελικτική βιολόγος P. Cartwright.
ΠΗΓΗ: D. T. Schultz, κ.ά. «Ancient gene
linkages support ctenophores as sister to other animals», Nature, 17.5.2023. Και V. Callier «The Closest Living Relative of the First
Animal Has Finally Been Found – A debate has been settled over the earliest
animal ancestor—a free-swimming creature with a well-developed nervous system»,
17.5.2023. ΑΡΧΕΙΟΝ ΠΟΛΙΤΙΣΜΟΥ, 18.5.2023.
Abstract
A central question in evolutionary biology is whether sponges or
ctenophores (comb jellies) are the sister group to all other animals. These
alternative phylogenetic hypotheses imply different scenarios for the evolution
of complex neural systems and other animal-specific traits. Conventional
phylogenetic approaches based on morphological characters and increasingly
extensive gene sequence collections have not been able to definitively answer
this question. Here we develop chromosome-scale gene linkage, also known as
synteny, as a phylogenetic character for resolving this question12. We report
new chromosome-scale genomes for a ctenophore and two marine sponges, and for
three unicellular relatives of animals (a choanoflagellate, a filasterean
amoeba and an ichthyosporean) that serve as outgroups for phylogenetic
analysis. We find ancient syntenies that are conserved between animals and
their close unicellular relatives. Ctenophores and unicellular eukaryotes share
ancestral metazoan patterns, whereas sponges, bilaterians, and cnidarians share
derived chromosomal rearrangements. Conserved syntenic characters unite sponges
with bilaterians, cnidarians, and placozoans in a monophyletic clade to the
exclusion of ctenophores, placing ctenophores as the sister group to all other
animals. The patterns of synteny shared by sponges, bilaterians, and cnidarians
are the result of rare and irreversible chromosome fusion-and-mixing events
that provide robust and unambiguous phylogenetic support for the
ctenophore-sister hypothesis. These findings provide a new framework for
resolving deep, recalcitrant phylogenetic problems and have implications for
our understanding of animal evolution.
