Husain Fatima, Millar Jasmin L, Jungblut Anne D, Hawes Ian, Evans Thomas W, Summons Roger E
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK.
Nat Commun. 2025 Jun 19;16(1):5315. doi: 10.1038/s41467-025-60713-5.
The ephemeral, supraglacial meltwater ponds of the McMurdo Ice Shelf's undulating ice serve as analogues for refugia where eukaryotic organisms could have thrived during the Cryogenian period. The seafloor sediment and debris lined ponds support the growth of a diverse array of cyanobacterial mat communities and provide habitats for a variety of protists and meiofauna. Here, we show that these eukaryotic assemblages, assessed by steroid biomarker and 18S rRNA gene analyses, inform long-standing questions regarding the diversity of, and controls on, community composition in these environments. Sixteen photosynthetically active microbial mats from meltwater ponds, a 700-year-old relict microbial mat, and a microbial mat from the Bratina Lagoon were analysed for their sterol compositions. These sterols were subjected to simulated diagenesis via catalytic hydrogenation/hydrogenolysis affording their sterane hydrocarbon counterparts, facilitating comparisons with ancient settings. Pond salinity appeared to be a factor influencing the sterol distributions observed. Analyses of 18S rRNA gene sequences conducted on the modern mats independently confirm that the ponds host diverse eukaryotes, including many types of microalgae, protists, and an array of unclassifiable organisms. Our findings support the hypothesis that supraglacial meltwater ponds like those of the McMurdo ice are strong candidates for refugia that sheltered complex life during Snowball Earth episodes.
麦克默多冰架起伏冰层上短暂存在的冰上融水池塘，可作为避难所的类似物，在新元古代时期，真核生物可能曾在此繁衍生息。池塘底部衬有沉积物和碎屑，支持了各种各样蓝细菌席群落的生长，并为各种原生生物和小型动物提供了栖息地。在此，我们表明，通过类固醇生物标志物和18S rRNA基因分析评估的这些真核生物组合，为有关这些环境中群落组成的多样性及其控制因素的长期问题提供了信息。对来自融水池塘的16个光合活性微生物席、一个有700年历史的残留微生物席以及来自布拉蒂纳泻湖的一个微生物席进行了甾醇组成分析。这些甾醇通过催化氢化/氢解进行模拟成岩作用，生成其甾烷烃对应物，便于与古代环境进行比较。池塘盐度似乎是影响所观察到的甾醇分布的一个因素。对现代微生物席进行的18S rRNA基因序列分析独立证实，这些池塘中有多种真核生物，包括许多类型的微藻、原生生物以及一系列无法分类的生物。我们的研究结果支持这样一种假设，即像麦克默多冰架上的那些冰上融水池塘，是在雪球地球事件期间庇护复杂生命的避难所的有力候选者。
