Characterization of the organellar genomes of Mazzaella laminarioides and Mazaella membranacea (Gigartinaceae, Rhodophyta).

Mazzaella, a genus with no genomic resources available, has extensive distribution in the cold waters of the Pacific, where they represent ecologically and economically important species. In this study, we aimed to sequence, assemble, and annotate the complete mitochondrial and chloroplast genomes from two Mazzaella spp. and characterize the intraspecific variation among them. We report for the first time seven whole organellar genomes (mitochondria: OR915856, OR947465, OR947466, OR947467, OR947468, OR947469, OR947470; chloroplast: OR881974, OR909680, OR909681, OR909682, OR909683, OR909684, OR909685) obtained through high-throughput sequencing for six M. laminarioides sampled from three Chilean regions and one M. membranacea. Sequenced Mazzaella mitogenomes have identical gene number, gene order, and genome structure. The same results were observed for assembled plastomes. A total of 52 genes were identified in mitogenomes, and a total of 235 genes were identified in plastomes. Although the M. membranacea plastome included a full-length pbsA gene, in all M. laminarioides samples, the pbsA gene was split in three open reading frames (ORFs). Within M. laminarioides, we observed important plastome lineage-specific variations, such as the pseudogenization of the two hypothetical protein-coding genes, ycf23 and ycf45. Nonsense mutations in the ycf23 and ycf45 genes were only detected in the northern lineage. These results are consistent with phylogenetic reconstructions and divergence time estimation using concatenated coding sequences that not only support the monophyly of M. laminarioides but also underscore that the three M. laminarioides lineages are in an advanced stage of divergence. These new results open the question of the existence of still undisclosed species in M. laminarioides.

Impact of persistent barrier to gene flow and catastrophic events on red algae evolutionary history along the Chilean coast.

Historical vicariance events, linked to the existence of stable physical barriers to gene flow, generate concordant genetic breaks in co-distributed species while stochastic processes (e.g., costal uplift) could cause species-specific genetic breaks as a result of local strong demographic bottlenecks or extinction. In Chile, previous studies show that the area of the 30°S-33°S could correspond to a stable barrier to gene flow that have affected the genetic structure of various algae and marine invertebrates. Here we sequenced two organellar genes (COI and rbcL) in four taxonomically accepted co-distributed red seaweeds species characterized by a low dispersal potential: Mazzaella laminarioides, M. membranacea, Asterfilopsis disciplinalis, and Ahnfeltiopsis vermicularis. Our results revealed the existence of ten strongly differentiated linages in the taxa studied. Strong genetic breaks, concordant in both space and time (divergence estimated to have occurred some 2.9-12.4 million years ago), were observed between taxa distributed across the 33°S. Conversely, in the Central/South part of the Chilean coast, the localization of the genetic breaks/sub-structure observed varied widely (36°S, 38°S, 39°S, and 40°S). These results suggest that a major historical vicariance event has modeled the genetic structure of several Chilean marine organisms in the north of the Chilean coast during the mid-Miocene, while more recent stochastic events and genetic drift could be the driving forces of genetic divergence/structuration in the central-southern part of the coast.

The impact of Pleistocene glaciations and environmental gradients on the genetic structure of Embothrium coccineum.

The South American temperate forests were subjected to drastic topographic and climatic changes during the Pliocene-Pleistocene as a consequence of the Andean orogeny and glacial cycles. Such changes are common drivers of genetic structure and adaptation. Embothrium coccineum (Proteaceae) is an emblematic tree of the South American temperate forest (around 20°S of latitude) that has strongly been affected by topographic and climatic events. Previous studies have shown a marked genetic structure in this species, and distinct ecotypes have been described. Yet, little is known about their adaptive genetic responses. The main goal of this study was to investigate the effects of historical and contemporary landscape features affecting the genetic diversity and connectivity of E. coccineum throughout its current natural distribution. Using over 2000 single nucleotide polymorphisms (SNPs), we identified two genetic groups (a Northern and a Central-Southern group) that diverged around 2.8 million years ago. The level of genetic structure was higher among populations within the Northern genetic group than within the Central-Southern group. We propose that these differences in genetic structure may be due to differences in the assemblages of pollinators and in the evolutionary histories of the two genetic groups. Moreover, the data displayed a strong pattern of isolation by the environment in E. coccineum, suggesting that selection could have led to adaptive divergence among localities. We propose that in the Chilean temperate forest, the patterns of genetic variation in E. coccineum reflect both a Quaternary phylogenetic imprint and signatures of selection as a consequence of a strong environmental gradient.