Exploring Cryptic Diversity and Distribution Patterns in the Mallomonas kalinae/rasilis Species Complex with a Description of a New Taxon—Mallomonas furtiva sp. nov.

Abstract

A complex of closely related Mallomonas taxa belonging to the section Papillosae, M. kalinaeRez a cov a and M. rasilis D€ urrschmidt, has been studied in detail by molecular and morphometric methods. Our investigations uncovered the existence of a new species found in water bodies in Vietnam, which we describe here as Mallomonas furtiva sp. nov. This taxon is morphologically very similar to M. kalinae, from which it differs by minute, but statistically significant morphological differences on the structure of silica scales. Indeed, the principal component analysis of morphological traits measured on silica scales significantly separates all three species in the complex. Mallomonas kalinae and M. furtiva differ by number of papillae on the shield and the dome, as well as by the scale sizes. Likewise, Mallomonas rasilis and M. furtiva are primarily differentiated by the absence of submarginal anterior ribs on silica scales of the former species. Phylogenetic analyses showed that Mallomonas furtiva is closely related to M. kalinae, with which it formed a highly supported lineage. Distribution patterns of all three studied taxa are further discussed.MALLOMONAS (Stramenopiles, Chrysophyceae, order Synurales) taxonomy is based on the ultrastructure of siliceous scales and bristles (Asmund and Kristiansen 1986;Siver 1991). The genus, which contains more than 180 taxa, is divided into 19 sections due to the large number of species and great variability of scale ultrastructure (Kristiansen and Preisig 2007). The main diagnostic characters of scales used to separate species into sections are the presence/absence of a V-rib and dome, the nature of secondary siliceous structures such as papillae, ribs, and reticulations, and the morphology and position of different scale types on the cell covering. Nine of the sections are rare and contain only one or two species each. The remaining 10 sections are more speciose, each with between 5 and over 40 taxa (Siver et al. 2015). Molecular studies, based on the analysis of several nuclear and plastid genes, corroborated most of the sections with a few exceptions (Jo et al. 2011(Jo et al. , 2013. According to the most recent multigene phylogeny of synuralean algae, the genus Mallomonas is divided into two large major lineages. The A1 lineage comprises species with scales possessing a V-rib, whereas the A2 lineage includes species lacking this structure (Siver et al. 2015). The clade A2 thus comprises only two Mallomonas sections (Planae and Heterospinae), whereas all the remaining ones belong in the clade A1. The section Papillosae was established by Asmund and Kristiansen (1986) to comprise taxa producing papillae on the scale surface, and having a shallow dome on all scale types. According to Kristiansen and Preisig (2007), the section Papillosae consists of 11 species and three varieties. Recently, four additional species were described from the tropics (Gusev 2013;Gusev et al. 2016; Pia z tek 2015). However, the genetic diversity as well as the relationship among the taxa ...

Diversity of Silica-Scaled Chrysophytes in Central Vietnam

“…Examples include taxa such as Mallomonas spinosa [79], M. fimbriata [81], M. pseudobronchartiana [86], and M. lusca [116]. Analysis of images illustrated earlier under the epithets of other species ("deviating" morphotypes or misidentified taxa) from different regions of the world [41,58,60,100] have helped clarify the distribution features of some recently described taxa, such as Mallomonas cattiensis [84], M. neoampla [82], M. furtiva [87], M. loricata [77], and M. siderea [78].…”

“…Examples of cryptic/pseudo-cryptic species have been found-for example, in the M. furtiva/M. kalinae Rezácova [87] and S. curtispina/S. longitubularis [114] complexes.…”

“…Information about diversity of algae from the order Synurales in the Northern Vietnam has also been published recently, including the description of two new species [76][77][78]. In addition, a number of new species for science have been described from individual regions of the country [71,[76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91]. However, Central Vietnam, except for certain areas of the Khanh Hoa province, has not yet been studied.…”

Studies on Algae from the Order Synurales (Chrysophyceae) in Northern Vietnam

“…These studies have revealed a very rich flora from the order Synurales, including 57 taxa from genera Mallomonas and Synura. Indeed, 19 new species from the genus Mallomonas [40,[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] and one Synura species [60] were described in these studies. However, the northern part of Vietnam, which differs in hydrology, climate, and anthropogenic impact from the Central and Southern provinces, is lacking sufficient descriptive studies.…”

Mallomonas minuscula sp. nov. (Synurales, Chrysophyceae), a new member in the section Torquatae from Vietnam

“…Intensive studies of the last decade with molecular and morphological approaches show that the real diversity of the genus is underestimated. Over last ten years, twenty new Mallomonas species have been described from different regions in Asia, including one from Russia (Gusev & Kulikovskiy 2013), two from China (Ma & Wei 2013;Němcová et al 2015), six from Korea (Kim & Kim 2008;Kim & Kim 2010;Jo et al 2013;Kim et al 2014), and eleven from Vietnam (Gusev 2012(Gusev , 2013(Gusev , 2015aGusev et al 2015Gusev et al , 2016Gusev et al , 2018. Two of these, Mallomonas elevata Han Soon Kim Dürrschmidt, and M. liturata K.H.…”