Hidden levels of phylodiversity in Antarctic green algae: further evidence for the existence of glacial refugia

Abstract

Recent data revealed that metazoans such as mites and springtails have persisted in Antarctica throughout several glacial -interglacial cycles, which contradicts the existing paradigm that terrestrial life was wiped out by successive glacial events and that the current inhabitants are recent colonizers. We used molecular phylogenetic techniques to study Antarctic microchlorophyte strains isolated from lacustrine habitats from maritime and continental Antarctica. The 14 distinct chlorophycean and trebouxiophycean lineages observed point to a wide phylogenetic diversity of apparently endemic Antarctic lineages at different taxonomic levels. This supports the hypothesis that long-term survival took place in glacial refugia, resulting in a specific Antarctic flora. The majority of the lineages have estimated ages between 17 and 84 Ma and probably diverged from their closest relatives around the time of the opening of Drake Passage (30 -45 Ma), while some lineages with longer branch lengths have estimated ages that precede the break-up of Gondwana. The variation in branch length and estimated age points to several independent but rare colonization events.

Molecular and morphological diversity of Zygnema and Zygnemopsis (Zygnematophyceae, Streptophyta) from Svalbard (High Arctic)

“…For example, Antarctic and Arctic endemites are common within diatom species complexes (Souffreau et al ., 2013; Kociolek et al ., 2017; Pinseel et al ., 2017). Antarctic microchlorophytes (De Wever et al ., 2009) or Prasiola (Moniz et al ., 2012) also possess endemic lineages. Typically, different species within a single protist genus may exhibit contrasting distribution patterns (Heesch et al ., 2016; Ryšánek et al ., 2016).…”

Leptochlorella corticola gen. et sp. nov. and Kalinella apyrenoidosa sp. nov.: two novel Chlorella-like green microalgae (Trebouxiophyceae, Chlorophyta) from subaerial habitats

“…Aboal & Werner, 2011;Neustupa et al, 2011). Furthermore, broad sampling of the 18S rRNA gene among various members of the class makes this marker extremely useful for identification of new, previously unknown lineages (De Wever et al, 2009;Horath & Bachofen, 2009). The rbcL gene has gradually become the standard second choice among various molecular markers in the Trebouxiophyceae and it has recently been used in several taxonomic and diversity studies (Novis et al, 2008;Thüs et al, 2011;Novis & Visnovsky, 2012), providing relatively broad sampling of individual lineages within the class.…”

“…De Wever et al (2009) reported the FJ946881 sequence from the summer phytobenthos of a lake in the Schirmacher Oasis, Antarctica. This 18S rRNA gene sequence was detected three times in a single locality, a possible indication that this alga frequently occurred in the phytobenthos of the lake.…”

“…This overview of studies describing different, often widely unrelated taxa of the morphologically rather uniform Chlorella-like microalgae illustrates that the real taxonomic diversity of these organisms is probably only starting to emerge as result of the extended sampling and molecular phylogenetic investigation of various phototrophic microbial communities. Indeed, several studies on the molecular diversity of microbial eukaryotes in various extreme microhabitats, such as desert soil crusts (Lewis & Lewis, 2005), Antarctic lake epipelon (De Wever et al, 2009), endolithic (Horath & Bachofen, 2009) or hypolithic biofilms (Wong et al, 2010), have revealed unique environmental sequences of additional, so far undescribed, lineages within the Chlorophyceae and Trebouxiophyceae. One of these lineages, which was originally known only from environmental sequencing of an endolithic microbial community thriving in alpine dolomite rocks in Switzerland (Horath & Bachofen, 2009), was recently morphologically characterized and taxonomically described as a new chlorophycean genus, Jenufa, typified by Chlorella-like morphology (Němcová et al, 2011).…”

Geothermal activity helps life survive glacial cycles

“…We used this dataset and spatial modeling approaches to assess diversity patterns in Antarctica in relation to the locations of geothermal areas. Postglacial population expansion away from LGM refugia is typically marked by a distinct reduction in diversity in recolonized vs. refugial regions (36)(37)(38)(39) [including intraspecific genetic diversity (15,31,32)]. Under a hypothesis that geothermal refugia allowed persistence of Antarctic species throughout recent glacial periods, species richness is predicted to be highest close to geothermally active areas and lower in nonactive regions, with significant nestedness (40) of taxa from high-to low-richness areas, consistent with postglacial recolonization of more distant sites by a subset of the refugial taxa.…”