Ancient DNA and osteological analyses of a unique paleo-archive reveal Early Holocene faunal expansion into the Scandinavian Arctic.

Paleo-archives are essential for our understanding of species responses to climate warming, yet such archives are extremely rare in the Arctic. Here, we combine morphological analyses and bulk-bone metabarcoding to investigate a unique chronology of bone deposits sealed in the high-latitude Storsteinhola cave system (68°50' N 16°22' E) in Norway. This deposit dates to a period of climate warming from the end of the Late Glacial [~13 thousand calibrated years before the present (ka cal B.P.)] to the Holocene thermal maximum (~5.6 ka cal B.P.). Paleogenetic analyses allow us to exploit the 1000s of morphologically unidentifiable bone fragments resulting in a high-resolution sequence with 40 different taxa, including species not previously found here. Our record reveals borealization in both the marine and terrestrial environments above the Arctic Circle as a naturally recurring phenomenon in past periods of warming, providing fundamental insights into the ecosystem-wide responses that are ongoing today.

Defining Coral Bleaching as a Microbial Dysbiosis within the Coral Holobiont.

Coral microbiomes are critical to holobiont health and functioning, but the stability of host-microbial interactions is fragile, easily shifting from eubiosis to dysbiosis. The heat-induced breakdown of the symbiosis between the host and its dinoflagellate algae (that is, "bleaching"), is one of the most devastating outcomes for reef ecosystems. Yet, bleaching tolerance has been observed in some coral species. This review provides an overview of the holobiont's diversity, explores coral thermal tolerance in relation to their associated microorganisms, discusses the hypothesis of adaptive dysbiosis as a mechanism of environmental adaptation, mentions potential solutions to mitigate bleaching, and suggests new research avenues. More specifically, we define coral bleaching as the succession of three holobiont stages, where the microbiota can (i) maintain essential functions for holobiont homeostasis during stress and/or (ii) act as a buffer to mitigate bleaching by favoring the recruitment of thermally tolerant Symbiodiniaceae species (adaptive dysbiosis), and where (iii) environmental stressors exceed the buffering capacity of both microbial and dinoflagellate partners leading to coral death.