Little lasting impact of the Paleocene-Eocene Thermal Maximum on shallow marine molluscan faunas

Global warming, acidification, and oxygen stress at the Paleocene-Eocene Thermal Maximum (PETM) are associated with severe extinction in the deep sea and major biogeographic and ecologic changes in planktonic and terrestrial ecosystems, yet impacts on shallow marine macrofaunas are obscured by the incompleteness of shelf sections. We analyze mollusk assemblages bracketing (but not including) the PETM and find few notable lasting impacts on diversity, turnover, functional ecology, body size, or life history of important clades. Infaunal and chemosymbiotic taxa become more common, and body size and abundance drop in one clade, consistent with hypoxia-driven selection, but within-clade changes are not generalizable across taxa. While an unrecorded transient response is still possible, the long-term evolutionary impact is minimal. Adaptation to already-warm conditions and slow release of CO₂ relative to the time scale of ocean mixing likely buffered the impact of PETM climate change on shelf faunas.

Evidence of horizontal transmission of the cancer-associated Steamer retrotransposon among ecological cohort bivalve species

Bivalve specimens from legacy frozen tissue collections, and others freshly obtained, were surveyed for the presence of the Steamer long terminal repeat (LTR)-retrotransposon associated with disseminated hemic neoplasia of the soft-shelled clam Mya areneria. Of 22 species investigated using primers for the pol region, only Atlantic M. arenaria, Atlantic and North Sea razor clams Ensis directus, and Baltic clams Macoma balthica from the North Sea were found to possess copies of Steamer in their genomes. Notably, close relatives like Mya truncata and Siliqua patula did not exhibit evidence of Steamer. Amplified Steamer sequences were uniformly identical in all M. areneria specimens, and were highly variable across specimens of E. directus. Variation in the latter included nucleotide polymorphisms among and within individuals as well as length variation in 2 specimens corresponding to the deletion of a predicted stable hairpin structure. Results implicate Atlantic razor clams as the proximal source for horizontal transmission of Steamer among ecologically similar yet markedly distantly related bivalves. The consequences of cross-species transmission of the Steamer retrotransposon are unknown, and the finding of Steamer in 3 bivalve species suggests that further spread is possible.

Nannoplankton extinction and origination across the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM, approximately 55 million years ago) was an interval of global warming and ocean acidification attributed to rapid release and oxidation of buried carbon. We show that the onset of the PETM coincided with a prominent increase in the origination and extinction of calcareous phytoplankton. Yet major perturbation of the surface-water saturation state across the PETM was not detrimental to the survival of most calcareous nannoplankton taxa and did not impart a calcification or ecological bias to the pattern of evolutionary turnover. Instead, the rate of environmental change appears to have driven turnover, preferentially affecting rare taxa living close to their viable limits.