Biology subjects

Piredda, R.

Publications and source records attributed to Piredda, R..

3 recordsLinked to original sources

bioRxiv2022

Insight into diatoms diversity at two European coastal sites (LTER-MC in the Mediterranean Sea and SOMLIT-Astan in the Western English Channel) using a DNA metabarcoding approach

Diatoms are among the most successful marine eukaryotic phytoplankton groups. Their diversity has been investigated in the worlds oceans through expeditions and observations carried out from the equator to the poles. Traditionally, diatom species have been distinguished based on morphological characters of their frustules, but high-throughput sequencing offers new, high-resolution data that can be used to re-examine spatial and/or temporal patterns of diversity. Here we investigated diatoms genetic diversity using metabarcoding (18S V4 rRNA gene) obtained along the years 2011 to 2013 at two coastal time series stations (SOMLIT-Astan and LTER-MareChiara) installed respectively off Roscoff in the Western English Channel and in the Gulf of Naples in the Mediterranean Sea. Diatom species pools detected were different, which fitted with previous observations and with our expectations, since these stations are installed in two contrasted pelagic habitats (permanently-mixed versus stratified in summer). However, this analysis also shows a pool of common ASVs among which some are persistent and dominant in both sites. The observed synchronous variations in relative read abundances of shared ASVs assigned to Chaetoceros socialis, C. tenuissimus, Cyclotella, Mediolabrus comicus and Leptocylindrus aporus at the two geographically distant sites could indicate that internal controls of growth rate and sexual reproduction, rather that external environmental parameters are at work.

ecology↗

bioRxiv2021

Phenological segregation suggests speciation by time in the planktonic diatom Pseudo-nitzschia allochrona sp. nov.

The emergence of new species is poorly understood in marine plankton, where the lack of physical barriers and homogeneous environmental conditions limit spatial and ecological segregation. Here we combine molecular and ecological information from a long term time series and propose Pseudo-nitzschia allochrona, a new cryptic diatom, as a possible case of speciation by temporal segregation. The new species differs in several genetic markers (18S, LSU and ITS rDNA fragments and rbcL) and is reproductively isolated from its closest relative, which is morphologically identical. Data from a long term plankton time series show Pseudo-nitzschia allochrona invariably occurring in summer-autumn in the Gulf of Naples, where its sister species are instead found in winter-spring. Temperature and nutrients are the main factors associated with the occurrence of P. allochrona, which could have evolved in sympatry by switching its phenology and occupying a new ecological niche. This case of possible speciation by time shows the relevance of combining ecological time series with molecular information to shed light on the eco-evolutionary dynamics of marine microorganisms.

evolutionary biology↗

bioRxiv2021

High-Throughput Sequencing of 5S-IGS rDNA in Fagus L. (Fagaceae) reveals complex evolutionary patterns and hybrid origin of modern species

Standard models of plant speciation assume strictly dichotomous genealogies in which a species, the ancestor, is replaced by two offspring species. The reality in wind-pollinated trees with long evolutionary histories is more complex: species evolve from other species through isolation when genetic drift exceeds gene flow; lineage mixing can give rise to new species (hybrid taxa such as nothospecies and allopolyploids). The multi-copy, potentially multi-locus 5S rDNA is one of few gene regions conserving signal from dichotomous and reticulate evolutionary processes down to the level of intra-genomic recombination. Therefore, it can provide unique insights into the dynamic speciation processes of lineages that diversified tens of millions of years ago. Here, we provide the first high-throughput sequencing (HTS) of the 5S intergenic spacers (5S-IGS) for a lineage of wind-pollinated subtropical to temperate trees, the Fagus crenata - F. sylvatica s.l. lineage, and its distant relative F. japonica. The observed 4,963 unique 5S-IGS variants reflect a complex history of hybrid origins, lineage sorting, mixing via secondary gene flow, and intra-genomic competition between two or more paralogous-homoeologous 5S rDNA lineages. We show that modern species are genetic mosaics and represent a striking case of ongoing reticulate evolution during the past 55 million years. Significance statementThe evolution of extra-tropical wind-pollinated tree genera involves dynamic speciation processes. High-throughput sequencing of the multi-copy, potentially multi-locus 5S rDNA reveals a complex history of hybrid origins, lineage sorting and mixing, and intra-genomic competition between paralogous-homeologous loci in the core group of Eurasian beech trees (genus Fagus) and their distant relative, F. japonica. The modern species are genetic mosaics and represent a striking case of at least 55 million years of ongoing reticulate evolution.

evolutionary biology↗