Journal
AMERICAN JOURNAL OF BOTANY
Volume 99, Issue 1, Pages 130-144Publisher
WILEY
DOI: 10.3732/ajb.1100245
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Funding
- National Science Foundation [DBI-0923448]
- NASA Exobiology [NNX07AU79G]
- American Chemical Society
- Direccion de Investigacion de la Universidad del Bio-Bio and Proyecto [DIUBB 020507 3/R]
- Direct For Biological Sciences
- Div Of Biological Infrastructure [0923448] Funding Source: National Science Foundation
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Premise of the study: The streptophyte water-to-land transition was a pivotal, but poorly understood event in Earth history. While some early-diverging modern streptophyte algae are aeroterrestrial (living in subaerial habitats), aeroterrestrial survival had not been tested for Coleochaete, widely regarded as obligately aquatic and one of the extant green algal genera most closely related to embryophytes. This relationship motivated a comparison of aeroterrestrial Coleochaete to lower Paleozoic microfossils whose relationships have been uncertain. Methods: We tested the ability of two species of the experimentally tractable, complex streptophyte algal genus Coleochaete Breb. to (1) grow and reproduce when cultivated under conditions that mimic humid subaerial habitats, (2) survive desiccation for some period of time, and (3) produce degradation-resistant remains comparable to enigmatic Cambrian microfossils. Key results: When grown on mineral agar media or on quartz sand, both species displayed bodies structurally distinct from those expressed in aquatic habitats. Aeroterrestrial Coleochaete occurred as hairless, multistratose, hemispherical bodies having unistratose lobes or irregular clusters of cells with thick, layered, and chemically resistant walls that resemble certain enigmatic lower Paleozoic microfossils. Whether grown under humid conditions or air-dried for a week, then exposed to liquid water, aeroterrestrial Coleochaete produced typical asexual zoospores and germlings. Cells that had been air-dried for periods up to several months maintained their integrity and green pigmentation. Conclusions: Features of modern aeroterrestrial Coleochaete suggest that ancient complex streptophyte algae could grow and reproduce in moist subaerial habitats, persist through periods of desiccation, and leave behind distinctive microfossil remains.
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