INVESTIGATIONS INTO THE ADAPTIVE POTENTIAL OF SOUTHERN OCEAN PHYTOPLANKTON

Le résumé fourni par la source

Southern Ocean (SO) phytoplankton are foundational to Antarctic marine food webs and global carbon and silica cycling. As polar ocean environments continue to rapidly evolve, it is important to assess the extent to which these communities can successfully respond. Adaptation to novel conditions will be particularly important here, as shifts in biogeography to track temperature preferences are unlikely where communities already inhabit the coldest surface waters in the Southern Hemisphere. This work employs high throughput physiological and genomic methods to better understand how three important attributes, thermal trait diversity, standing genetic diversity, and repetitive genomic elements, assessed at a multiple taxonomic scales (community, population and individual genomes), all help shape the adaptive potential of Southern Ocean phytoplankton. Physiological trait variability is crucial to successful and efficient adaptation to novel environmental conditions. As the SO warms, the degree to which traits related to temperature preference and tolerance vary inter- and intra-specifically will be particularly important. Given how poorly characterized traits such as optimal temperature for growth (Topt), maximum temperature for growth (Tmax) and maximum growth rate (μmax) are for cold-adapted phytoplankton (especially from SO), we applied a high throughput phenotyping method to determine growth rates for 43 SO diatom strains representing seven diverse lineages across eight ecologically relevant temperatures. We found these traits to meaningfully vary both among and within species, and that when applied to estimating species-specific thermal fundamental niches, intraspecific differences in observed Tmax values led to large differences (almost 2-fold greater for some taxa) in tolerable geographic range. Ultimately, standing genetic variation underpins the thermal trait variation observed in Chapter 2. Marine phytoplankton, especially diatoms, are well-documented as being genetically diverse and have exhibited a range of spatial population structures elsewhere in the global ocean. Yet, this is still poorly understood for SO phytoplankton, which in addition to their global relevance, are difficult to sample. To address this, we sequenced 31 recently collected isolates of the endemic SO diatom Actinocyclus actinochilus and assessed genetic diversity levels and population structure. We found that standing genetic diversity in this taxon is remarkably high, more so than for previously analyzed temperate phytoplankton. We also identified a complete lack of population subdivision among the sampled strains. These findings suggest the presence of genetically diverse, large panmictic phytoplankton populations in the productive high latitudes of the Southern Ocean. While phenotypic and genotypic diversity estimates are vital for any assessment or modeling of adaptive

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.