Departamento de Hidrobiología, Universidade Federal de São Carlos, São Carlos, Brazil.
Dipartimento Di Biologia E Biotecnologie "Charles Darwin", Università Di Roma La Sapienza, Rome, Italy.
Microbiome. 2024 Sep 4;12(1):162. doi: 10.1186/s40168-024-01874-1.
The backbone of the eukaryotic tree of life contains taxa only found in molecular surveys, of which we still have a limited understanding. Such is the case of Picozoa, an enigmatic lineage of heterotrophic picoeukaryotes within the supergroup Archaeplastida, which has emerged as a significant component of marine microbial planktonic communities. To enhance our understanding of the diversity, distribution, and ecology of Picozoa, we conduct a comprehensive assessment at different levels, from assemblages to taxa, employing phylogenetic analysis, species distribution modeling, and ecological niche characterization.
Picozoa was among the ten most abundant eukaryotic groups, found almost exclusively in marine environments. The phylum was represented by 179 Picozoa's OTU (pOTUs) placed in five phylogenetic clades. Picozoa community structure had a clear latitudinal pattern, with polar assemblages tending to cluster separately from non-polar ones. Based on the abundance and occupancy pattern, the pOTUs were classified into four categories: Low-abundant, Widespread, Polar, and Non-polar. We calculated the ecological niche of each of these categories. Notably, pOTUs sharing similar ecological niches were not closely related species, indicating a phylogenetic overdispersion in Picozoa communities. This could be attributed to competitive exclusion and the strong influence of the seasonal amplitude of variations in environmental factors, such as temperature, shaping physiological and ecological traits.
Overall, this work advances our understanding of uncharted protists' evolutionary dynamics and ecological strategies. Our results highlight the importance of understanding the species-level ecology of marine heteroflagellates like Picozoa. The observed phylogenetic overdispersion challenges the concept of phylogenetic niche conservatism in protist communities, suggesting that closely related species do not necessarily share similar ecological niches. Video Abstract.
真核生物树的主干包含仅在分子调查中发现的分类群，我们对这些分类群的了解仍然有限。真核生物超群古菌域内的异养微微体超微型真核生物门（Picozoa）就是一个神秘的谱系，它已成为海洋微生物浮游群落的重要组成部分。为了增强我们对 Picozoa 的多样性、分布和生态的理解，我们从类群到分类单元，在不同层次上进行综合评估，运用系统发育分析、物种分布模型和生态位特征描述。
Picozoa 是最丰富的十个真核生物组之一，几乎只存在于海洋环境中。该门由 179 个 Picozoa 的 OTU（pOTU）组成，分为五个系统发育分支。Picozoa 群落结构具有明显的纬度模式，极地类群倾向于与非极地类群分开聚类。根据丰度和占据模式，pOTU 分为四个类别：低丰度、广布、极地和非极地。我们计算了这些类别的生态位。值得注意的是，具有相似生态位的 pOTU 不是密切相关的物种，这表明 Picozoa 群落中存在系统发育离散。这可能归因于竞争排斥和环境因素（如温度）季节性幅度变化的强烈影响，这些因素塑造了生理和生态特征。
总的来说，这项工作推进了我们对未被探索的原生生物进化动态和生态策略的理解。我们的结果强调了了解海洋异养鞭毛虫（如 Picozoa）种水平生态的重要性。观察到的系统发育离散挑战了原生生物群落中系统发育生态位保守主义的概念，表明密切相关的物种不一定具有相似的生态位。
