Collaborative Research: The role of maternal iron transfer in the development of heme stores and aerobic diving capacity in grey seal pups

A fundamental question in animal ecology is when and why physiology limits how animals behave, how often they reproduce, and how likely they are to survive. Marine mammals are particularly suited for these studies because their ability to forage underwater is constrained by the size of their tissue heme and O2 stores, and pups are born with very low hemoglobin (Hb) and myoglobin (Mb) levels that can limit breathold ability. Iron is an essential micronutrient for the biosynthesis of Hb and Mb, and maternal iron status and milk iron content strongly influences early development of heme stores in many species. This project will study grey seals (Halichoerus grypus) at Sable Island, Nova Scotia to determine how maternal and offspring dietary iron dynamics impact heme maturation and subsequent foraging activities. The team will first determine maternal diet, iron stores, milk iron content and milk transfer rates. Then, researchers will provide supplemental iron to half of the study animals to determine if iron intake limits pup physiological development. Finally, the impact of heme stores on the diving behavior and movement patterns of weaned pups will be evaluated. Understanding the interplay between iron intake, physiological development and foraging behavior, may reveal how ongoing changes in grey seal diet and ecosystem structure could influence pup survival and population trajectories. This work will provide training opportunities to graduate and undergraduate students at HSI and Alaska Native serving institutions and provide outreach through a diverse suite of activities in Texas, Alaska, Canada, and Massachusetts. This study will elucidate the underlying ecological and cellular mechanisms that facilitate or constrain the ontogeny of heme and O2 stores in grey seal pups (12 pups/year/3yrs). Bulk and compound specific stable isotope analysis will be used to identify maternal diet and iron intake, while milk iron and milk transfer rates will be quantified using hydrogen isotope dynamics to determine pup iron intake. The pup’s ability to utilize milk iron will be assessed by measuring the expression of iron transporters (Divalent metal transporter 1, Ferroportin) and serum hepcidin, transferrin, and ferritin concentrations. Age-related changes in blood and muscle heme stores, iron-containing enzymes, and endocrine factors known to regulate heme protein synthesis (i.e., Erythropoietin, Hypoxia-inducible-factor-1) will be measured. Providing half the study pups with supplemental iron at the start and end of the lactation period will reveal if maternal iron transfer rates are a significant influence on pup physiological development. At the end of the post-weaning fast, pups will be outfitted with a satellite-linked dive recorder to monitor foraging patterns and locations. Behavioral comparisons between iron-supplemented and control groups will reveal whether maternal effects as mediated through micronutrient limitations influence pup foraging capacity, or if behavioral plasticity can compensate for phenotypic constraints. Studies integrating across multiple physiological and behavioral scales in juvenile marine mammals remain rare, yet understanding these linkages becomes increasingly important as climate change and human activities are causing significant shifts in the functioning of marine ecosystems across the globe. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.