Ardissonea crystallina has a type of sexual reproduction that is unusual for centric diatoms

Abstract

Molecular phylogenetic analyses place Ardissonea crystallina (C. Agardh) Grunow and all Toxariids among the bi- and multipolar centric diatoms, almost always recovered as a derived lineage sister to Lampriscus. In all centrics where sexual reproduction has been documented, oogamy, with larger immobile eggs and smaller flagellated sperm has been observed. We were able to initiate both homothallic and heterothallic reproduction in A. crystallina. The heterothallic reproduction turned out to be non-oogamous; gametes were more or less equal in size but no flagellated cells were detected. At the same time, two mating types (“male” and “female”) were recognized by the distinct morphology and behaviour of the gametes. While no flagella were observed, periodically thin cytoplasmic projections arose on the surface of the “male” gametes. These projections similar to those found in some pennate diatoms facilitated contact with the “female” cells. In each gametangial cell, regardless of the mating type, only one gamete was formed. Thus, the Toxariids may represent a unique evolutionary group, at least in respect to their reproductive biology. The hypothesis discussed is that non-oogamous mode of reproduction could have evolved in Ardissonea (and possibly in other Toxariids) independently of the pennate lineage of diatoms.

Accelerated diversification is related to life history and locomotion in a hyperdiverse lineage of microbial eukaryotes (Diatoms, Bacillariophyta)

“…The frequency of sexual reproduction and the rates of selfing or outcrossing in natural populations of diatoms are unknown and difficult to estimate. However, in culture, the majority of surveyed pennate diatoms are heterothallic, with mating occurring only between genetically compatible clones (Chepurnov & Mann, 2004; Chepurnov et al ., 2004; but see, e.g., Davidovich et al ., 2010, 2017). This led to the hypothesis that heterothally is the ancestral condition in pennates (Chepurnov et al ., 2004).…”

“…Oogamy is thought to be advantageous because a species can maximize the number of gametes and, as a result, successful copulation encounters by producing many small and highly motile male gametes, as well as zygote survivorship by producing one or a few large (and immobile) female gametes (Parker et al, 1972;Maynard Smith, 1978;Matsuda & Abrams, 1999;Bulmer & Parker, 2002;Togashi et al, 2012). In pennate diatoms, however, the flagellum of male gametes was lost, and dimorphism between gametes diminished, such that gametes in a copulation pair converged towards a similar, intermediate size (reviewed in Kaczmarska et al, 2013), but differed in their behavior (Drebes, 1977), with male gametes that moved by pseudopodia to search for a nonmotile female gamete (Davidovich et al, 2010(Davidovich et al, , 2017Sato et al, 2011;Kaczmarska et al, 2017). The evolution of the raphe and active motility in vegetative cells enabled gametangia, rather than gametes, to search for mating partners, promoting further reduction in sexual dimorphism and gamete mobility.…”

“…Diatoms are thought to be ancestrally planktonic and oogamous, with nonmotile vegetative cells suspended in a dilute environment, necessitating motile flagellated gametes to reproduce successfully (Drebes, 1977; Round et al ., 1990; Chepurnov et al ., 2004). However, flagellated male gametes were lost at least twice: once in the common ancestor of the pennate diatoms – a large clade of predominantly benthic species whose gametes are behaviorally dimorphic and move via pseudopodia (Davidovich et al ., 2010; Sato et al ., 2011; Kaczmarska et al ., 2017), and once in Ardissonea crystallina – a member of a benthic marine clade referred to as toxariids (Davidovich et al ., 2017). Active, directed motility in vegetative cells evolved subsequently in a clade nested within pennate diatoms (raphid pennate diatoms; Harper, 1977; Round et al ., 1990).…”

Mitotic recombination between homologous chromosomes drives genomic diversity in diatoms

“…The period necessary to reach this threshold can last months to years. 3,[6][7][8] So how do diatoms generate novel genetic variation that is required for adaptive evolution?…”

Оценка Неоднородности Распределения Клеток При Токсикологических Экспериментах С Клоновыми Культурами Бентосных Диатомовых Водорослей

“…По результатам молекулярно-генетических исследований и экспериментов по половому воспроизведению, систематическое положение вида A. crystallina, ранее перемещённого из класса Fragilariophyceae в класс Coscinodiscophycea, поставлено под сомнение. Высказано предположение, что Ardissonea (и иные представители Toxariales) могут представлять уникальную эволюционную группу, обособленную от пеннатных диатомовых водорослей [22]. Учитывая то обстоятельство, что по форме панциря и способности к образованию пучковидных колоний, прикреплённых к субстрату, данный вид более схож с представителями Fragilariophyceae (к которым он и относился до недавнего времени), в целях нашего эксперимента мы рассматриваем A. crystallina именно в составе этого класса.…”