292-7 Population Structure, Growth, and Life History of Nucula proxima Along Holocene Spatiotemporal Environmental Gradients

Session: Life and Environments Through Time and Space: Multi-Record Approaches to Stratigraphic Paleobiology, Part II

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The oceans are rapidly warming as a result of greenhouse gas emissions, which have also reduced dissolved oxygen concentrations and increased ocean acidity. Here we use molecular, biophysical, and paleontological approaches to develop a synthetic understanding of the response of calcifying marine animals to climate change. Our work focuses on the northern Gulf of Mexico, a region where anthropogenic run-off contributes to gradients in primary productivity, dissolved oxygen, and pH, and where ocean temperatures are rising at twice the global average. By analyzing present-day geographic gradients, and live-collected and historical (dead-collected) samples that span the last ~3000 years, we assess variability in (i) population genetic structure, (ii) biomineralization, and (iii) life history in the bivalve mollusk Nucula proxima in response to near and long-term changes in environmental conditions in the late Holocene. Cytochrome c oxidase subunit I sequence data derived from N. proxima tissue revealed genetic differences among populations that occur in regions of the northern gulf that vary in the extent of fluvial influence. The elemental composition and microstructure of live and historical shells was analyzed using electron backscatter diffraction and x-ray photoemission electron microscopy. Preliminary results indicate minimal live-dead variation in composition and crystal misorientation within a given region, but differences among regions in misorientation. Live-collected shells from offshore larger watersheds exhibited greater crystal misorientation than those from offshore smaller watersheds, with no significant regional differences in elemental composition. Life history data were collected by measuring the diameter of the first stage of larval shell growth (PI) using scanning electron microscopy; PI diameter is positively correlated with egg size. Preliminary results reveal considerable variation among regions in life history, with smaller PI size observed in more productive waters offshore of larger watersheds. N. proxima exhibited little temporal variation in PI size within a given region, in contrast with other bivalve species in the northern gulf. Population-level variation in N. proxima microstructure and life history correspond to regional environmental differences which have also shaped gene flow and population differentiation. Ongoing work is focused on extending analyses of population genetic structure back through time using sequence data extracted from shell-bound organic matter, biomineralization analyses through consideration of other species, and life history analyses through comparisons between species that vary in larval mode.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9335

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