第65回生態適応セミナー (Bセミナー)

     
 

日時:12月14日(水曜日)15:00 –

 
  場所:青葉山キャンパス 生物棟1階大会議室  
     

Télesphore SIME-NGANDO and Serena RASCONI(Génome et Environnement, Université Blaise Pascal)

     
  従属栄養鞭毛虫の正体、鞭毛菌類とその隠された機能
Heterotrophic flagellates and hidden putative functions from zoosporic fungi in pelagic ecosystems
 
     
 

海洋や陸水など、水界生態系では従属栄養鞭毛虫が細菌の捕食者として重要な役割をになっているが、それら分類群の位置づけは不明瞭であった。近年、環境DNA解析により分類学的検討を行ったところ、これら生物は従来の顕微鏡観察による知見とは異なり、多様な分類群に属しており、それらには細菌食ではなく寄生性や腐食性の微生物、例えば菌類などが多く含まれていることがわかった。これら事実は、従属栄養鞭毛虫とされていた生物は、細菌食者だけでなく、寄生や腐食など、従来無視されてきた機能をも担っており、水界微生物ループの概念について変更を迫るものである。本セミナーでは、これら近年の知見に加え、従来型の水界食物網にこれら生物(機能)を加えた場合、食物網の栄養連鎖が伸長する一方、システムが安定化することも紹介したい。
In aquatic ecosystems, heterotrophic flagellates have received particular attention as grazers, and have been regarded as a homogeneous group of bacterivorous protists. More recently, environmental rDNA surveys of small heterotrophic flagellates in the pelagic zone of freshwater ecosystems have revealed the following findings: (i) the dominant phyla found differed significantly from those known frommicroscope studies, (ii) the retrieved phylotypes generally belong to well-established eukaryotic clades but with very large diversity within clades and (iii) a substantial part of the retrieved sequences is not related to bacterivorous but to parasitic and saprophytic organisms, such as zoosporic fungi (chytrids), fungus-like organisms (oomycetes), or virulent alveolate parasites (Perkinsozoa). All these microorganisms are able to produce small flagellated zoospores to assure dispersal during their life-cycles. It is thus likely that previously overlooked functions, primarily parasitism and saprophytism, merit thorough attention (i) for an improved understanding of the roles of heterotrophic flagellates in pelagic ecosystems and, (ii) to transcend the concept of ‘the microbial loop’ in the context of modern pelagic microbial ecology. Finally, from the first assessment of the quantitative impact of parasitic chytrids on a carbon-based planktonic food web model, we conclude that, in particular conditions, chytrids increase the number of trophic links, leading to longer path lengths, which in general are considered as characteristics of stable ecosystems.