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A Fish-feeding Laboratory Bioassay to Assess the Antipredatory Activity of Secondary Metabolites from the Tissues of Marine Organisms
Published on: January 11, 2015
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Sterol and genomic analyses validate the sponge biomarker hypothesis
David A Gold1, Jonathan Grabenstatter1, Alex de Mendoza2
1Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA 02139;
Summary
Molecular fossils like 24-isopropylcholestane suggest early animal life. This study found sponges, not algae, likely produced these biomarkers, pushing back animal evolution evidence to the Neoproterozoic era.
Area of Science:
- Paleontology
- Biogeochemistry
- Molecular Evolution
Background:
- Molecular fossils, such as steranes, are crucial for understanding early eukaryotic evolution, particularly animal origins.
- The sterane 24-isopropylcholestane, found in ancient rocks, has been proposed as a biomarker for sponges and potentially the earliest evidence of animal life.
- The sterol precursor, 24-isopropylcholesterol (24-ipc), is synthesized by modern sponges but also found in trace amounts in pelagophyte algae, creating ambiguity in biomarker interpretation.
Purpose of the Study:
- To investigate the biosynthesis of 24-isopropylcholesterol (24-ipc) in major animal outgroups to clarify the origin of 24-isopropylcholestane biomarkers.
- To determine whether sponges or algae are the more likely source of Neoproterozoic 24-isopropylcholestanes.
- To refine the timeline for the evolution of early animal life based on molecular fossil evidence.
Main Methods:
- Sterol analysis of four key animal outgroup taxa: Salpingoeca rosetta, Capsaspora owczarzaki, Sphaeroforma arctica, and Creolimax fragrantissima.
- Phylogenetic analysis of key enzymes involved in C30 sterol biosynthesis, focusing on carbon-24/28 sterol methyltransferase (SMT).
- Molecular clock dating of SMT gene duplication events in sponges and algae.
Main Results:
- All analyzed animal outgroups lack C30 sterols, including 24-ipc.
- Phylogenetic analysis identified clade-specific SMT duplications in sponges and pelagophyte algae, suggesting independent evolution of C30 sterol biosynthesis.
- Molecular clock data indicate the sponge SMT duplication predates the algal SMT duplication, aligning with the Neoproterozoic appearance of 24-isopropylcholestanes.
Conclusions:
- Pelagophyte algae and their relatives are unlikely sources of Neoproterozoic 24-isopropylcholestanes.
- The findings support sponges as the producers of 24-isopropylcholestanes, reinforcing their role as the oldest animal biomarkers.
- This evidence suggests sponges evolved significantly earlier than the Cambrian explosion, pushing back the timeline for animal life's origins.
