Paleoclimate-induced stress on polar forested ecosystems prior to the Permian–Triassic mass extinction

The end Permian extinction (EPE) has been considered to be contemporaneous on land and in the oceans. However, re-examined floristic records and new radiometric ages from Gondwana indicate a nuanced terrestrial ecosystem response to EPE global change. Paleosol geochemistry and climate simulations indicate paleoclimate change likely caused the demise of the widespread glossopterid ecosystems on Gondwana. Here, we evaluate the climate response of plants to the EPE via dendrochronology to produce annual-resolution records of tree ring growth for a succession of Late Permian and early Middle Triassic fossil forests from Antarctica. Paleosol geochemistry provides a broader context paleoclimate history. The plant responses to this paleoclimate change were accompanied by enhanced stress during the latest Permian. These results suggest that paleoclimate change during the Late Permian exerted significant stress on high-latitude forests, consistent with the hypothesis that climate change was likely the primary driver of the extinction of the glossopterid ecosystems.

Supplemental Material: High-precision U-Pb age constraints on the Permian floral turnovers, paleoclimate change, and tectonics of the North China block

Stratigraphy of the study sections, previous geochronology, U-Pb analytical procedures, age results, and Bayesian age modeling.<br>

Supplemental Material: High-precision U-Pb age constraints on the Permian floral turnovers, paleoclimate change, and tectonics of the North China block

Stratigraphy of the study sections, previous geochronology, U-Pb analytical procedures, age results, and Bayesian age modeling.<br>

Developmental constraint shaped genome evolution and erythrocyte loss in Antarctic fishes following paleoclimate change

In the frigid, oxygen-rich Southern Ocean (SO), Antarctic icefishes (Channichthyidae; Notothenioidei) evolved the ability to survive without producing erythrocytes and hemoglobin, the oxygen-transport system of virtually all vertebrates. Here, we integrate paleoclimate records with an extensive phylogenomic dataset of notothenioid fishes to understand the evolution of trait loss associated with climate change. In contrast to buoyancy adaptations in this clade, we find relaxed selection on the genetic regions controlling erythropoiesis evolved only after sustained cooling in the SO. This pattern is seen not only within icefishes but also occurred independently in other high-latitude notothenioids. We show that one species of the red-blooded dragonfish clade evolved a spherocytic anemia that phenocopies human patients with this disease via orthologous mutations. The genomic imprint of SO climate change is biased toward erythrocyte-associated conserved noncoding elements (CNEs) rather than to coding regions, which are largely preserved through pleiotropy. The drift in CNEs is specifically enriched near genes that are preferentially expressed late in erythropoiesis. Furthermore, we find that the hematopoietic marrow of icefish species retained proerythroblasts, which indicates that early erythroid development remains intact. Our results provide a framework for understanding the interactions between development and the genome in shaping the response of species to climate change.