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Giralt, S.

Publications and source records attributed to Giralt, S..

3 recordsLinked to original sources

The Muskox Way: Humans, plants and animals in northeast Greenland through the Holocene

The Muskox Way hypothesis suggests that the first humans entering northeast Greenland from Arctic Canada followed and hunted muskox. Yet whether muskox arrived before people remains debated, as only two bones predate the Independence culture (4500-3900 cal BP). More broadly, the arrival of plants and animals, and how the three periods of human settlement related to ecosystem changes, remain poorly understood. We analysed sedimentary ancient DNA from lakes in Wandel Dal (Late Sommersoe and Midsommersoe) and Zackenberg, identifying 121 native plants and nine animal taxa. In Wandel Dal, the plant assemblage indicates a warmer climate than today about 8200-3900 years ago, followed by an abrupt change in flora and sedimentation rate at 3900 cal BP, especially at Midsommersoe. Muskox DNA is present continuously at Midsommersoe from 7400 cal BP, about three millennia before humans arrived. The Zackenberg record dates to 12,200 cal BP, with arctic forbs, grasses, ferns and crowberry in the earliest layers, willow from 8200 cal BP and birch from 7200 cal BP, but muskox only in the last 2500 years, the latter period coinciding with Greenlandic Dorset culture. The arrival of the Thule culture in 1400 CE coincides with a slight increase in plant richness at Wandel Dal and an increase in mammal detections. Reindeer occurred only in samples older than 6000 years, consistent with their absence from archaeological bone records. Overall, humans arrived long after the first megafauna and appear to have had limited impact on their populations, although cultural periods coincided with environmental changes.

ecology↗

Individual natal assignment in highly migratory species: the genomic baseline and its application in loggerhead turtles

O_LIEffective conservation of highly migratory species requires understanding genetic structure across breeding populations and access high{square}resolution markers capable of assigning individuals from mixed aggregates (e.g. bycatch or new nesting sites) to their natal origins. Genomic approaches provide unprecedented resolution but add methodological challenges; thus, it is essential to first build a genomic baseline from known breeding areas and then evaluate strategies for assigning unknown individuals. C_LIO_LITo address this, we used 2b-RAD sequencing, a genomic reduction technique useful for degraded DNA, and loggerhead turtles as a case study. This species shows philopatric breeding, while juveniles and adults form mixed aggregations in foraging grounds. C_LIO_LIOur results highlight the importance of building baselines that include all potential source populations contributing to mixed aggregations. We detected hierarchical genetic differentiation and high resolution and successfully assigned the natal origin of 124 unknown individuals from four Mediterranean foraging grounds. These grounds showed distinct source contributions, and comparisons with previous studies suggest possible temporal shifts in stock composition. C_LIO_LIWe provide a comprehensive genomic baseline for individual assignment of Altanto-Mediterranean loggerhead turtles of unknown natal origin and a general framework for identifying population-specific threats in highly migratory species. C_LI

evolutionary biology↗

Accelerated single cell seeding in relapsed multiple myeloma

The malignant progression of multiple myeloma is characterized by the seeding of cancer cells in different anatomic sites followed by their clonal expansion. It has been demonstrated that this spatial evolution at varying anatomic sites is characterized by genomic heterogeneity. However, it is unclear whether each anatomic site at relapse reflects the expansion of pre-existing but previously undetected disease or secondary seeding from other sites. Furthermore, genomic evolution over time at spatially distinct sites of disease has not been investigated in a systematic manner. To address this, we interrogated 25 samples, by whole genome sequencing, collected at autopsy from 4 patients with relapsed multiple myeloma and demonstrated that each site had a unique evolutionary trajectory characterized by distinct single and complex structural variants and copy number changes. By analyzing the landscape of mutational signatures at these sites and for an additional set of 125 published whole exomes collected from 51 patients, we demonstrate the profound mutagenic effect of melphalan and platinum in relapsed multiple myeloma. Chemotherapy-related mutagenic processes are known to introduce hundreds of unique mutations in each surviving cancer cell. These mutations can be detectable by bulk sequencing only in cases of clonal expansion of a single cancer cell bearing the mutational signature linked to chemotherapy exposure thus representing a unique single-cell genomic barcode linked to a discrete time window in each patients life. We leveraged this concept to show that multiple myeloma systemic seeding is accelerated at clinical relapse and appears to be driven by the survival and subsequent expansion of a single myeloma cell following treatment with high dose melphalan therapy and autologous stem cell transplant.

cancer biology↗