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Meiofauna is a group of heterotrophic organisms smaller than macroinvertebrates but larger than microfauna and characterized by groups such as testate amoebae, ciliates, and nematodes. They are a link between bacteria and resources and macroinvertebrates. However, tropical meiofauna is poorly studied; thus, our goal was to characterize meiofaunal community composition and abundance and assess potential environmental variables controlling these community dynamics. Monthly samplings of meiofauna were conducted for eight months in Quebrada Prieta, El Yunque National Forest, Puerto Rico. Sampling was made in 12 pools, and data on discharge, sediment characteristics, and biotic variables were also collected. A total of 62 meiofaunal morphospecies were identified, with nematodes dominating the community, followed by testate amoebae. Bacterivores and detritivores taxa dominated the community. Meiofaunal abundance was negatively related to discharge and positively to the percentage of coarse sand, nitrate, and macroinvertebrate abundance. The composition of meiofauna in Quebrada Prieta is like the composition reported for temperate streams, at least in major meiofaunal groups present. However, the community in Quebrada Prieta was dominated by testate amoebae. In contrast, temperate streams are often dominated by rotifers and nematodes. Both abiotic and biotic variables are important for meiofaunal communities in the headwater streams in Puerto Rico.
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Amoebozoan testate amoebae illuminate the diversity of heterotrophs and the complexity of ecosystems throughout geological time
Heterotrophic protists are vital in Earth’s ecosystems, influencing carbon and nutrient cycles and occupying key positions in food webs as microbial predators. Fossils and molecular data suggest the emergence of predatory microeukaryotes and the transition to a eukaryote-rich marine environment by 800 million years ago (Ma). Neoproterozoic vase-shaped microfossils (VSMs) linked to Arcellinida testate amoebae represent the oldest evidence of heterotrophic microeukaryotes. This study explores the phylogenetic relationship and divergence times of modern Arcellinida and related taxa using a relaxed molecular clock approach. We estimate the origin of nodes leading to extant members of the Arcellinida Order to have happened during the latest Mesoproterozoic and Neoproterozoic (1054 to 661 Ma), while the divergence of extant infraorders postdates the Silurian. Our results demonstrate that at least one major heterotrophic eukaryote lineage originated during the Neoproterozoic. A putative radiation of eukaryotic groups (e.g., Arcellinida) during the early-Neoproterozoic sustained by favorable ecological and environmental conditions may have contributed to eukaryotic life endurance during the Cryogenian severe ice ages. Moreover, we infer that Arcellinida most likely already inhabited terrestrial habitats during the Neoproterozoic, coexisting with terrestrial Fungi and green algae, before land plant radiation. The most recent extant Arcellinida groups diverged during the Silurian Period, alongside other taxa within Fungi and flowering plants. These findings shed light on heterotrophic microeukaryotes’ evolutionary history and ecological significance in Earth’s ecosystems, using testate amoebae as a proxy.
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- Award ID(s):
- 2100888
- PAR ID:
- 10574805
- Publisher / Repository:
- National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 121
- Issue:
- 30
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2319628121
