Neural responses in parietal and occipital areas in response to visual events are modulated by prior multisensory stimuli

The effect of multi-modal vs uni-modal prior stimuli on the subsequent processing of a simple flash stimulus was studied in the context of the audio-visual 'flash-beep' illusion, in which the number of flashes a person sees is influenced by accompanying beep stimuli. EEG recordings were made while combinations of simple visual and audio-visual stimuli were presented. The experiments found that the electric field strength related to a flash stimulus was stronger when it was preceded by a multi-modal flash/beep stimulus, compared to when it was preceded by another uni-modal flash stimulus. This difference was found to be significant in two distinct timeframes--an early timeframe, from 130-160 ms, and a late timeframe, from 300-320 ms. Source localisation analysis found that the increased activity in the early interval was localised to an area centred on the inferior and superior parietal lobes, whereas the later increase was associated with stronger activity in an area centred on primary and secondary visual cortex, in the occipital lobe. The results suggest that processing of a visual stimulus can be affected by the presence of an immediately prior multisensory event. Relatively long-lasting interactions generated by the initial auditory and visual stimuli altered the processing of a subsequent visual stimulus.status: publishe

Who’s there? A comprehensive eDNA metabarcoding survey of gelatinous zooplankton biodiversity in the Fram Strait

The Arctic is warming two times faster than the global mean, and a phenomenon known as the ‘Atlantification of the Arctic’ via the Fram Strait is having growing influences on both physical and biological processes in the region. Changes to community composition and function are already underway and these environmental changes will continue to rapidly alter ecosystems in the Arctic and its marginal seas. Greater understanding of how these changes impact local marine biodiversity is crucial for future management and mitigation decisions as well as accurately predicting future Arctic marine ecosystems. Gelatinous zooplankton (GZP) is a highly diverse group of taxa, including cnidarians, ctenophores and tunicates. Very little is currently known about GZP ecology, particularly in the Arctic Ocean, and even less about how they are being impacted by climate-related changes. Not only are they often actively left out of zooplankton surveys, but GZP are notoriously difficult to catch in good condition because their fragile bodies are easily destroyed by traditional sampling methods. GZP are there for regularly underestimated in biodiversity, distribution and abundance, which contributes to the lack of reliable and comprehensive baseline data available. The aim of this study is to a) genetically barcode net-caught Arctic GZP specimens to supplement existing reference datasets and utilize these to b) apply non-invasive environmental DNA (eDNA) metabarcoding methods to investigate GZP biodiversity across the Fram Strait. COI mitochondrial amplicons from water samples will be sequenced with Next Generation Sequencing (NGS) and validated with net catch data from the same locality and period. Oceanographic data will then be incorporated in order to form a holistic baseline dataset of summer GZP biodiversity across the region. Such data would be a valuable contribution to future research into the deviations in Arctic GZP biodiversity and community composition, as a result of on-going environmental changes

Arctic vs sub-Arctic pelagic amphipods: DNA reveals a different history and a different future in the face of climate change

The Arctic is experiencing climate change-related warming at a faster rate than any other region. This is inducing unprecedented reductions in sea ice cover, increasing freshwater inflow and rising ocean temperatures. These environmental changes are already having drastic impacts on the marine ecosystem; affecting species composition, distribution and food web structure in the Arctic Ocean. Pelagic Themisto amphipods are an important link between secondary producers and marine vertebrates at higher trophic levels. Two co-existing species dominate the Arctic region: Themisto libellula, considered a genuine Arctic species and Themisto abyssorum, considered a sub-Arctic, boreal species. Both prey on mesoplankton but are thought to occupy different niches. T. libellula is larger, feeds on herbivorous copepods and is a key prey item for seabirds, key Arctic fish species and certain marine mammals. Whereas T. abyssorum is smaller, feeds on omnivorous and carnivorous zooplankton and is considered an indicator species of warmer water masses. Both species have exhibited recent changes in abundance and range shifts, likely as a result of the Atlantification of the Arctic. Many aspects of the ecology and genetic structure of these two species are not well studied, despite their importance in the food web and biogeochemical cycles. Further understanding of the phylogeography and distributional patterns of these key zooplankton species is crucial to understanding how they will be affected by climate change and how this will impact the ecosystem. This study focuses on the genetic structure and connectivity of both Themisto species as well as their association with Arctic and Atlantic water masses. We do this by analysing and comparing mitochondrial cytochrome oxidase I gene sequences according to the geographic populations. These data reveal a contrasting genetic structure, predicting T. libellula will be less able to cope with environmental changes than T. abyssorum. Distributional data of both species and their abundances are statistically analysed in relation to hydrographic data. Individuals were collected between 2016 and 2020 on a number of international campaigns, from a broad geographic distribution including Svalbard fjord systems, the Fram Strait and Southern Greenland

Arctic vs sub-Arctic pelagic amphipods: DNA reveals a different history and a different future in the face of climate change

Rapid warming in the Arctic is drastically impacting marine ecosystems, affecting species diversity, distribution, and food web structure. Pelagic Themisto amphipods are dominant in the Arctic zooplankton community and represent a key link between secondary producers and higher trophic levels. Two co-existing species dominate in the region: Themisto libellula, considered a true Arctic species and Themisto abyssorum, a sub-Arctic, boreal species. Many aspects of the ecology and genetic structure of these two species are not well studied, despite their high biomass, importance in the food web and the fact that they are already being affected by rapid climate change. We tested both species for levels of genetic diversity, patterns of spatial genetic structure and demographic history in the Greenland shelf, Fram Strait, and Svalbard. This was achieved using variation on the mitochondrial cytochrome c oxidase subunit 1 gene (mtCOI). These data revealed strikingly different levels of mtCOI diversity: low levels in T. libellula contrasted with higher diversity in T. abyssorum. No spatial genetic structure was found, and high levels of connectivity and evidence of historic demographic expansion were exhibited by both species. The diversity and demographic signatures are likely explained by glaciation events impacting population sizes during the last glacial maximum. High population connectivity is likely due to current-induced mixing among Themisto populations. The observed low genetic diversity, in combination with its cold adaptions, could cause T. libellula to be more susceptible to the Atlantification of the Arctic. In contrast, high diversity likely increases adaptive potential in T. abyssorum which, combined with its Atlantic affinity, could lead to it benefitting from warming trends. This study provides new data on the phylogeography of two ecologically important species, which can contribute to predicting how zooplankton communities, species interactions and food web structure will manifest in the Arctic as a result of climate change

Range expansions of scyphozoan jellyfish – the case study of Periphylla periphylla and Cyanea capillata

Jellyfish abundances have been reported to increase significantly in different aquatic ecosystems. Particularly in areas of rapid change such as the warming Arctic waters, jellyfish blooms might occur more frequently and cause problems for local fisheries. However, until today jellyfish remain an understudied part of zooplankton due to their fragility and historically proposed irrelevance in marine food webs. This study aims to investigate the genetic diversity of the two species Periphylla periphylla and Cyanea capillata using a set of molecular methods. To monitor future range expansions, we aim to validate eDNA as a viable detection method for jellyfish. The analysis consists of three parts: first, the intraspecific genetic diversity of the two species is investigated using DNA barcoding. Second, to characterize the status quo of high-Arctic jellyfish species diversity, we apply eDNA metabarcoding of sediment samples around Svalbard. Lastly, species-specific primers are developed and tested, with the aim to optimize quantitative real-time PCR as a cost-effective, accurate monitoring. A high intraspecific genetic diversity has been shown in the studied area for both species. For C. capillata three divergent species-level lineages were uncovered. Genetic structure according to geographic region was lacking for both species. The metabarcoding analyses of the Svalbard sediment samples did not represent the pelagic community well, compared to net catches from the same stations. Many of the zooplankton and especially jellyfish species caught with nets were not represented in the eDNA. However, differences in pelagic species composition could be observed between North and West Svalbard fjords. In the Arctic-influenced fjords, consistently more jellyfish species were found. The design of a species-specific primer was successful for C. capillata. This study shows how important it is to investigate jellyfish with modern molecular tools, which may help to inform us on their potential range expansions or populations increases in the future

Genetic connectivity of the widespread hydrozoan Aglantha digitale from temperate to central Arctic regions

Climate change proceeding at unprecedented pace is currently redistributing life on Earth. In the Arctic region, climate change is acting more rapidly than elsewhere on this planet, and has dramatically altered sea ice thickness and extent. However, for many Arctic taxa, the distribution ranges and population connectivity have remained undocumented. This is particularly so for Arctic gelatinous zooplankton, of which the diversity, abundances and role in the food web are understudied. The hydromedusa Aglantha digitale is highly abundant in the Arctic Ocean, and characterized by a widespread distribution, ranging from temperate waters to the central Arctic. Its distribution in the water column has been linked to the presence of Atlantic water masses, which renders it a likely candidate to benefit from the ongoing “Atlantification” of the Arctic. Despite its ubiquity and abundance, its genetic diversity remains unknown, and it is unclear whether this species is composed of different geographic lineages throughout its distribution range. To compare the genetic diversity and assess the phylogeography of A. digitale, we collected samples from several recent international cruises. Geographic populations from temperate waters, sub-Arctic Greenland, Svalbard and the central Arctic are compared based on sequences of the mitochondrial cytochrome c oxidase subunit I (COI). A better understanding of the distribution and connectivity will help to predict potential range shifts of A. digitale in an “Atlantified” Arctic