Final Report Summary - POLAREXPRESS (TEMPERATURE DRIVES EVOLUTION: IN SEARCH OF GENE EXPRESSION DIFFERENCES BETWEEN EURYTHERM AND POLAR STENOTHERM FISHES)
Among the scientific priorities identified by Antarctic research community is the need to “forecast responses to environmental change” and “to learn how past events have driven diversifications and extinctions”. To this aim, we have to investigate “the genomic, molecular and cellular bases of adaptation” and “rates of evolution in the Antarctic in comparison with elsewhere.” This would enable scientists and stakeholders to fix “irreversible environmental thresholds” and to focus on “which species respond first”.
Climate change is causing an increase in temperatures for most regions of the Southern Ocean and is predicted to affect Antarctic marine species through increased physiological stress, reduction of suitable habitats and connectivity, demographic decline of phytoplankton, krill and fish populations, crucial for local food webs, and arrival of invasive species.
The aims of the “Polarexpress” project are grounded on this background and focus on the integrative, multidisciplinary study of a hot target for conservation: Notothenioids, Perciform fish living in the freezing Antarctic waters. These fish are highly stenotherm organisms, which means they are capable of living within a very narrow temperature range. They offer a truly unique opportunity to study the evolution of temperature preference from a genetic point of view. Moreover, their genetic variability can be compared to other notothenioid species with a lower sensitivity to temperature changes (this fish are called eurytherms). These eurytherm notothenioids are usually referred to as sub-Antarctic notothenioids.
This project seeks to answer two general questions: 1) what is indeed the adaptation potential of Antarctic notothenioids to temperature increase? 2) do sub-Antarctic species from different thermal habitats respond to temperature changes in the same way? These investigations have been conducted at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI).
In this study, I have incubated two Antarctic notothenioid species at four different temperatures and extracted RNA (the messenger nucleic acid, the molecules informing us about expressed genes) from several different tissues. I performed a high throughput sequencing via Illumina RNA-seq of one tissue per species. In parallel, I have sequenced a partial genome of a sub-Antarctic species. From these very big datasets, I proceeded by identifying the function of each gene found in the three species. I and the bioinformaticians of the AWI are now comparing these genes among species to identify over- and under-represented functions, sequence differences and signatures of natural selection. These genes might be involved in the temperature adaptation. I have also isolated several molecular markers (from nuclear and mitochondrial origin) for population genetics of Antarctic species, which means monitoring the changes in the frequency of each variant observed at these markers. Any change and in particular any reduction in the variability should be considered cautiously especially in the light of environmental changes. These markers can also be used to identify correctly the species for future experiments and during sampling campaigns. In fact, climate changes can determine contacts between species previously geographically isolated, triggering processes of competition and hybridization and leading to unexpected impacts at the level of populations, species and communities. These processes have important implications for biodiversity conservation.
Running such exploratory studies, as “Polarexpress”, has the long-term perspective to be applied to forecast possible changes in the distribution area of important marine species which are not only threatened by fishery exploitation (e.g. sub-Antarctic species) but also by reduction in suitable areas (and temperatures) for their biological cycles (Antarctic notothenioids).
Climate change is causing an increase in temperatures for most regions of the Southern Ocean and is predicted to affect Antarctic marine species through increased physiological stress, reduction of suitable habitats and connectivity, demographic decline of phytoplankton, krill and fish populations, crucial for local food webs, and arrival of invasive species.
The aims of the “Polarexpress” project are grounded on this background and focus on the integrative, multidisciplinary study of a hot target for conservation: Notothenioids, Perciform fish living in the freezing Antarctic waters. These fish are highly stenotherm organisms, which means they are capable of living within a very narrow temperature range. They offer a truly unique opportunity to study the evolution of temperature preference from a genetic point of view. Moreover, their genetic variability can be compared to other notothenioid species with a lower sensitivity to temperature changes (this fish are called eurytherms). These eurytherm notothenioids are usually referred to as sub-Antarctic notothenioids.
This project seeks to answer two general questions: 1) what is indeed the adaptation potential of Antarctic notothenioids to temperature increase? 2) do sub-Antarctic species from different thermal habitats respond to temperature changes in the same way? These investigations have been conducted at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI).
In this study, I have incubated two Antarctic notothenioid species at four different temperatures and extracted RNA (the messenger nucleic acid, the molecules informing us about expressed genes) from several different tissues. I performed a high throughput sequencing via Illumina RNA-seq of one tissue per species. In parallel, I have sequenced a partial genome of a sub-Antarctic species. From these very big datasets, I proceeded by identifying the function of each gene found in the three species. I and the bioinformaticians of the AWI are now comparing these genes among species to identify over- and under-represented functions, sequence differences and signatures of natural selection. These genes might be involved in the temperature adaptation. I have also isolated several molecular markers (from nuclear and mitochondrial origin) for population genetics of Antarctic species, which means monitoring the changes in the frequency of each variant observed at these markers. Any change and in particular any reduction in the variability should be considered cautiously especially in the light of environmental changes. These markers can also be used to identify correctly the species for future experiments and during sampling campaigns. In fact, climate changes can determine contacts between species previously geographically isolated, triggering processes of competition and hybridization and leading to unexpected impacts at the level of populations, species and communities. These processes have important implications for biodiversity conservation.
Running such exploratory studies, as “Polarexpress”, has the long-term perspective to be applied to forecast possible changes in the distribution area of important marine species which are not only threatened by fishery exploitation (e.g. sub-Antarctic species) but also by reduction in suitable areas (and temperatures) for their biological cycles (Antarctic notothenioids).
