Repeated evolution of uniparental reproduction in <i>Sellaphora</i> (Bacillariophyceae)

<div><p>Diatoms possess a remarkable life cycle in which cell size decreases slowly during vegetative cell division and then increases rapidly via special expanding cells called ‘auxospores’, which are usually formed as a result of biparental sexual reproduction. However, auxospores are sometimes produced by single unpaired cells, i.e. uniparentally. We examined the nature of uniparental auxosporulation in <i>Sellaphora</i> and used a two-gene dataset to study phylogenetic relationships between uniparental and biparental <i>Sellaphora</i> demes and species; we tested whether uniparental reproduction has evolved once or repeatedly in the genus. In at least two of the uniparental demes auxosporulation occurred through autogamy (i.e. intra-tetrad mating within an undivided cell). Maximum likelihood phylogenies indicated four lineages of uniparental <i>Sellaphora</i> and significance tests of alternative topologies, in which combinations of uniparental <i>Sellaphora</i> were constrained to be monophyletic, coupled with likelihood reconstruction of ancestral character states, led to rejection of the hypothesis that uniparental auxosporulation evolved only once in the genus. Uniparentally reproducing lineages appear to arise not infrequently in diatoms but do not persist. Two small extranuclear bodies, apparently containing DNA and lying outside the chloroplast (one close to each pole of the cell), were revealed by DAPI staining.</p></div

BI_consensus_phylogeny_cox1_Sellaphora_capitata

Tree file of Sellaphora Bayesian Inference phylogeny based on partial cox1 sequences (Fig. S2)

Alignment_complete_rbcL_Eunotia

Alignment of complete rbcL sequences of the Eunotia bilunaris/flexuosa complex used for phylogeny reconstruction (Fig. S1)

MLG_data_Sellaphora_capitata

Microsatellite allelic composition of Sellaphora capitata strains

MLG_data_Ebilunaris_robust

Microsatellite allelic composition of Eunotia bilunaris "robust" strains

Isolation_by_distance

Matrices of pairwise standardized Fst values and (log-transformed) geographic distances between sampling locations of Eunotia bilunaris "robust" and Sellaphora capitata respectively, for assessment of isolation-by-distance patterns (Fig. 3)

Alignment_cox1_Sellaphora_capitata

Alignment of partial cox1 sequences of Sellaphora used for phylogeny reconstruction (Fig. S2)

Alignment_partial_rbcL_Eunotia

Partial rbcL sequences of Eunotia bilunaris "robust" strains used for phylogeography of the species in Western Europe (Fig. 2)