Jaagichlorella, Reisigl, 1964

Darienko, Tatyana & Pröschold, Thomas, 2019, The genus Jaagichlorella Reisigl (Trebouxiophyceae, Chlorophyta) and its close relatives: an evolutionary puzzle, Phytotaxa 388 (1), pp. 47-68 : 59-62

Jaagichlorella , Heterochlorella , Heveochlorella and Kalinella : an evolutionary puzzle

As shown in the figures and tables, all investigated strains showed a Chlorella luteoviridis morphology. These algae have little phenotypic plasticity, but were characterized by very high genetic variability reflected in the high evolutionary rates among the members of the Watanabea clade ( Trebouxiophyceae). As a result of phylogenetic analyses, taxa with similar morphology were described as new genera and species among this clade: Kalinella with its two species, K. bambusicola and K. apyrenoidosa ( Neustupa et al. 2009, 2013), and Heveochlorella , with H. hainangensis and H. roystonensis ( Zhang et al. 2008, Ma et al. 2013). In addition, the new generic name Heterochlorella was proposed for Chlorella luteoviridis ( Neustupa et al. 2009) . The phylogenetic analyses of the new sequences presented in this study shined a new light on the generic concept of closely related taxa. The two species of Heveochlorella belonged to two different groups (C and D of the Jaagichlorella subclade; Fig. 1 ). Both groups are closely related to the groups A ( Heterochlorella ) and B (new lineage, described below as Jaagichlorella africana ). The group D contains beside Heveochlorella hainangensis , Chlorella sphaerica and a strain, which could be clearly identified as Jaagichlorella geometrica . As a consequence of our findings, which are highly supported in all bootstrap and Bayesian analyses and the probability tests of user-defined trees, the three genera Jaagichlorella , Heterochlorella and Heveochlorella need to be revised (see proposal below). As shown in Figs 1–2 , the strains belonging to the Jaagichlorella subclade represent six species of one genus. According to the International Code for Nomenclature (ICN), the oldest generic name has priority, in our case Jaagichlorella , which was described by Reisigl (1964). Both other genera are therefore later synonyms (proposals see below). The only alternative scenario, the recognition of each group (A-D) as separated genera, was rejected by approximately unbiased tests presented in Table 2. The other argument against the establishment of new generic names for these groups is that the genetic biodiversity among the Watanabea clade has not fully been discovered. For example, Sanders et al. (2016) showed that different lichen species contained new undescribed taxa of Heveochlorella , which also belong to the Jaagichlorella subclade and therefore to the genus Jaagichlorella . Unfortunately, only partial SSU rDNA sequences without any documented morphology are available, but the combination with our data in this study showed that new lineages can still be discovered ( Fig. 8 ). We cannot decipher if these new lineages represent new species because no ITS rDNA sequences of these specimens are available in GenBank.

Using traditional identification keys such as Komárek & Fott (1983) or Ettl & Gärtner (2014), most of the investigated strains were identified as Chlorella luteoviridis .This included the strains, which were described as Kalinella bambusicola and K. apyrenoidosa . Our analyses revealed that both species are the sister group of Jaagichlorella . We cannot decide at this stage if the genus Kalinella should also be synonymized, this needs further investigations especially by including of more strains. Therefore, we kept Kalinella as a separate genus despite its close affiliation to Jaagichlorella . Summarizing, both genera were characterized by morphology (spherical cells, unequal size of autospores, and chloroplast saucer- or cup-shaped, presence of pyrenoid with/without starch layers) and molecular phylogeny (SSU and ITS rDNA sequences including their secondary structures). As demonstrated in this study, genera should be characterized using an integrative approach, recognizable by different features (morphology, reproduction, and molecular signatures), which includes the study of old literature to avoid double descriptions of species and genera as demonstrated here for Heterochlorella and Heveochlorella .

Figures

FIGURE 1. Molecular phylogeny of representatives belonging to the Watanabea clade based on SSU rDNA sequence comparisons. The phylogenetic tree shown was inferred using the maximum likelihood method based on the data set (29 taxa: 1787 aligned positions for SSU) using PAUP 4.0b10. For the analyses the best model was calculated by Modeltest 3.7. The setting of the best model was given as follows: TIM+I+G (base frequencies: A 0.2413, C 0.2367, G 0.2935, T 0.2285; rate matrix A-C 1.0000, A-G 2.1970, A-U 1.2024, C-G 1.2024, C-U 5.128, G-U 1.0000) with the proportion of invariable sites (I = 0.4935) and gamma shape parameter (G = 0.6539); The branches in bold are highly supported in all analyses (Bayesian values> 0.95 calculated with PHASE and MrBayes; bootstrap values> 90% calculated with PAUP using maximum likelihood, neighbor-joining, maximum parsimony and RAxML using maximum likelihood). The authentic strains of species are marked with an asterisk.

FIGURE 2. Molecular phylogeny of Jaagichlorella and Kalinella based on SSU and ITS rDNA sequence comparisons. The phylogenetic tree shown was inferred using the maximum likelihood method based on the data set (2655 aligned positions of 23 taxa) using PAUP 4.0b10. For the analyses the best model was calculated by Modeltest 3.7. The setting of the best model was given as follows: GTR+I+G (base frequencies:A 0.2324, C 0.2449, G 0.2794, T 0.2433; rate matrix A-C 1.5591, A-G 2.0795, A-U 1.4741, C-G 0.5739, C-U 4.8359, G-U 1.0000) with the proportion of invariable sites (I = 0.3875) and gamma shape parameter (G = 0.4780). The branches in bold are highly supported in all analyses (Bayesian values 1.00 calculated with PHASE and MrBayes; bootstrap values 100% calculated with PAUP using maximum likelihood, neighbor-joining, maximum parsimony and RAxML using maximum likelihood).

FIGURE 8. Molecular phylogeny of Jaagichlorella and Kalinella based on partial SSU rDNA sequence comparisons. The phylogenetic tree shown were inferred using the neighbor-joining method based on the data set (346 aligned positions of 24 taxa) using PAUP 4.0b10. The accession numbers of the partial sequences found in GenBank is given after the names of the isolates/clones. The letters after each sequence indicates their origin (A = aquatic; E = epiphytic; P = photobiont of lichen; S = epilithic on rocks or artificial hard substrates; U = unknown).