Abstract
Among marine phytoplankton, Mamiellales encompass several species from the genera Micromonas, Ostreococcus and Bathycoccus, which are important contributors to primary production. Previous studies based on single gene markers described their wide geographical distribution but led to discussion because of the uneven taxonomic resolution of the method. Here, we leverage genome sequences for six Mamiellales species, two from each genus Micromonas, Ostreococcus and Bathycoccus, to investigate their distribution across 133 stations sampled during the Tara Oceans expedition. Our study confirms the cosmopolitan distribution of Mamiellales and further suggests non-random distribution of species, with two triplets of co-occurring genomes associated with different temperatures: Ostreococcus lucimarinus, Bathycoccus prasinos and Micromonas pusilla were found in colder waters, whereas Ostreococcus spp. RCC809, Bathycoccus spp. TOSAG39-1 and Micromonas commoda were more abundant in warmer conditions. We also report the distribution of the two candidate mating-types of Ostreococcus for which the frequency of sexual reproduction was previously assumed to be very low. Indeed, both mating types were systematically detected together in agreement with either frequent sexual reproduction or the high prevalence of a diploid stage. Altogether, these analyses provide novel insights into Mamiellales’ biogeography and raise novel testable hypotheses about their life cycle and ecology.
Highlights
Mamiellales is an order of green algae (Chlorophyta) that contains some of the most ecologically important groups of photosynthetic picoeukaryotes in the marine environment [1,2,3]
This study focused on samples from the 0.8–5 μm organism-size fraction, corresponding to the cell size of Mamiellales, adding up to a total of 79 surface samples as well as 54 samples from the deep-chlorophyll maximum (DCM)
In order to gain a global view of their geographical distribution, we estimated the proportions of metagenomic reads from each of 133 Tara Oceans metagenomes that were recruited to six Mamiellales genomes (Figure 1)
Summary
Mamiellales is an order of green algae (Chlorophyta) that contains some of the most ecologically important groups of photosynthetic picoeukaryotes in the marine environment [1,2,3]. They are prevalent and abundant in coastal surface waters and throughout the oceanic euphotic zone [4,5,6,7]. Where populations can reach high densities up to 103 –105 cells per ml [8] This order is composed of two families. Ostreococcus and Bathycoccus, which are distributed across a range of marine environments [2,3,9].
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