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AGU2025 Abstract #1967252 

Climatic changes have decreased the stability of the Gulf Stream (GS), increasing the frequency at which its meanders interact with the Mid-Atlantic Bight (MAB) continental shelf and slope region. These intrusions are thought to suppress biological productivity by transporting low-nutrient water to the otherwise productive shelf edge region. Here we present evidence of widespread, anomalously intense subsurface diatom hotspots in the MAB slope sea that likely resulted from a GS intrusion in July 2019. The hotspots (at ∼50 m) were associated with water mass properties characteristic of GS water (∼100 m); it is probable that the hotspots resulted from the upwelling of GS water during its transport into the slope sea, likely by a GS meander directly intruding onto the continental slope east of where the hotspots were observed. Further work is required to unravel how increasingly frequent direct GS intrusions could influence MAB marine ecosystems. 

ABSTRACT Physiological systems often have emergent properties but the effects of genetic variation on physiology are often unknown, which presents a major challenge to understanding the mechanisms of phenotypic evolution. We investigated whether genetic variants in haemoglobin (Hb) that contribute to high-altitude adaptation in deer mice (Peromyscus maniculatus) are associated with evolved changes in the control of breathing. We created F2 inter-population hybrids of highland and lowland deer mice to test for phenotypic associations of α- and β-globin variants on a mixed genetic background. Hb genotype had expected effects on Hb–O2 affinity that were associated with differences in arterial O2 saturation in hypoxia. However, high-altitude genotypes were also associated with breathing phenotypes that should contribute to enhancing O2 uptake in hypoxia. Mice with highland α-globin exhibited a more effective breathing pattern, with highland homozygotes breathing deeper but less frequently across a range of inspired O2, and this difference was comparable to the evolved changes in breathing pattern in deer mouse populations native to high altitude. The ventilatory response to hypoxia was augmented in mice that were homozygous for highland β-globin. The association of globin variants with variation in breathing phenotypes could not be recapitulated by acute manipulation of Hb–O2 affinity, because treatment with efaproxiral (a synthetic drug that acutely reduces Hb–O2 affinity) had no effect on breathing in normoxia or hypoxia. Therefore, adaptive variation in Hb may have unexpected effects on physiology in addition to the canonical function of this protein in circulatory O2 transport. 

Animals native to the hypoxic and cold environment at high altitude provide an excellent opportunity to elucidate the integrative mechanisms underlying the adaptive evolution and plasticity of complex traits. The capacity for aerobic thermogenesis can be a critical determinant of survival for small mammals at high altitude, but the physiological mechanisms underlying the evolution of this performance trait remain unresolved. We examined this issue by comparing high-altitude deer mice ( Peromyscus maniculatus ) with low-altitude deer mice and white-footed mice ( P. leucopus ). Mice were bred in captivity and adults were acclimated to each of four treatments: warm (25°C) normoxia, warm hypoxia (12 kPa O 2 ), cold (5°C) normoxia or cold hypoxia. Acclimation to hypoxia and/or cold increased thermogenic capacity in deer mice, but hypoxia acclimation led to much greater increases in thermogenic capacity in highlanders than in lowlanders. The high thermogenic capacity of highlanders was associated with increases in pulmonary O 2 extraction, arterial O 2 saturation, cardiac output and arterial–venous O 2 difference. Mechanisms underlying the evolution of enhanced thermogenic capacity in highlanders were partially distinct from those underlying the ancestral acclimation responses of lowlanders. Environmental adaptation has thus enhanced phenotypic plasticity and expanded the physiological toolkit for coping with the challenges at high altitude.