Phocid Seal Leptin: Tertiary Structure and Hydrophobic Receptor Binding Site Preservation during Distinct Leptin Gene Evolution

The cytokine hormone leptin is a key signalling molecule in many pathways that control physiological functions. Although leptin demonstrates structural conservation in mammals, there is evidence of positive selection in primates, lagomorphs and chiropterans. We previously reported that the leptin genes of the grey and harbour seals (phocids) have significantly diverged from other mammals. Therefore we further investigated the diversification of leptin in phocids, other marine mammals and terrestrial taxa by sequencing the leptin genes of representative species. Phylogenetic reconstruction revealed that leptin diversification was pronounced within the phocid seals with a high dN/dS ratio of 2.8, indicating positive selection. We found significant evidence of positive selection along the branch leading to the phocids, within the phocid clade, but not over the dataset as a whole. Structural predictions indicate that the individual residues under selection are away from the leptin receptor (LEPR) binding site. Predictions of the surface electrostatic potential indicate that phocid seal leptin is notably different to other mammalian leptins, including the otariids. Cloning the grey seal leptin binding domain of LEPR confirmed that this was structurally conserved. These data, viewed in toto, support a hypothesis that phocid leptin divergence is unlikely to have arisen by random mutation. Based upon these phylogenetic and structural assessments, and considering the comparative physiology and varying life histories among species, we postulate that the unique phocid diving behaviour has produced this selection pressure. The Phocidae includes some of the deepest diving species, yet have the least modified lung structure to cope with pressure and volume changes experienced at depth. Therefore, greater surfactant production is required to facilitate rapid lung re-inflation upon surfacing, while maintaining patent airways. We suggest that this additional surfactant requirement is met by the leptin pulmonary surfactant production pathway which normally appears only to function in the mammalian foetus

Predicting climate change impacts on polar bear litter size

Predicting the ecological impacts of climate warming is critical for species conservation. Incorporating future warming into population models, however, is challenging because reproduction and survival cannot be measured for yet unobserved environmental conditions. In this study, we use mechanistic energy budget models and data obtainable under current conditions to predict polar bear litter size under future conditions. In western Hudson Bay, we predict climate warming-induced litter size declines that jeopardize population viability: ∼28% of pregnant females failed to reproduce for energetic reasons during the early 1990s, but 40–73% could fail if spring sea ice break-up occurs 1 month earlier than during the 1990s, and 55–100% if break-up occurs 2 months earlier. Simultaneously, mean litter size would decrease by 22–67% and 44–100%, respectively. The expected timeline for these declines varies with climate-model-specific sea ice predictions. Similar litter size declines may occur in over one-third of the global polar bear population

PUP PRODUCTION OF HARP SEALS, PHOCA-GROENLANDICA, IN THE NORTHWEST ATLANTIC

Northwest Atlantic harp seal, Phoca groenlandica, pup production was estimated from aerial surveys flown off eastern Newfoundland (''Front'') and in the Gulf of St. Lawrence (''Gulf'') during March 1990. One visual and two independent photographic estimates were obtained at the Front; a single photographic estimate was obtained in the Gulf. Photographic estimates were corrected form is identified pups by comparing black-and-white photographs with ultraviolet imagery. Estimates were also corrected for pups absent from the ice at the time of the survey using distinct age-related developmental stages. Stage durations in the Gulf appeared consistent with previous studies but were increased by 30\% to improve the fit to staging data collected at the Front. The best estimate of pup production at the Front was obtained from the visual surveys. A total of 467 000 (SE = 31 000) pups were born in three whelping concentrations. The photographic estimates were comparable. Pup production estimates for the southern (Magdalen Island) and northern (Mecatina) Gulf whelping patches were 106 000 (SE = 23 000) and 4 400 (SE = 1300), respectively. Thus, total pup production was estimated to be 578 000 (SE = 39 000)

Investigating annual diving behaviour by Hooded seals (Cystophora cristata) within the Northwest Atlantic Ocean

This work was funded through the Atlantic Seal Research Programme, International Governance Programme (DFO), the Greenland Institute of Natural Resources, and a CFI grant to YFW. The authors also acknowledge the support of the Marine Alliance for Science and Technology for Scotland (MASTS) pooling initiative in the completion of this study. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.With the exception of relatively brief periods when they reproduce and moult, hooded seals, Cystophora cristata, spend most of the year in the open ocean where they undergo feeding migrations to either recover or prepare for the next fasting period. Valuable insights into habitat use and diving behaviour during these periods have been obtained by attaching Satellite Relay Data Loggers (SRDLs) to 51 Northwest (NW) Atlantic hooded seals (33 females and 18 males) during ice-bound fasting periods (2004−2008). Using General Additive Models (GAMs) we describe habitat use in terms of First Passage Time (FPT) and analyse how bathymetry, seasonality and FPT influence the hooded seals’ diving behaviour described by maximum dive depth, dive duration and surface duration. Adult NW Atlantic hooded seals exhibit a change in diving activity in areas where they spend >20 h by increasing maximum dive depth, dive duration and surface duration, indicating a restricted search behaviour. We found that male and female hooded seals are spatially segregated and that diving behaviour varies between sexes in relation to habitat properties and seasonality. Migration periods are described by increased dive duration for both sexes with a peak in May, October and January. Males demonstrated an increase in dive depth and dive duration towards May (post-breeding/pre-moult) and August–October (post-moult/pre-breeding) but did not show any pronounced increase in surface duration. Females dived deepest and had the highest surface duration between December and January (post-moult/pre-breeding). Our results suggest that the smaller females may have a greater need to recover from dives than that of the larger males. Horizontal segregation could have evolved as a result of a resource partitioning strategy to avoid sexual competition or that the energy requirements of males and females are different due to different energy expenditure during fasting periods.Publisher PDFPeer reviewe

The effect of prey quality and ice conditions on the nutritional status of Baltic gray seals of different age groups

Abstract We analyzed a long-term data set of the body condition of Baltic gray seals (Halichoerus grypus) over time and investigated how average subcutaneous blubber thickness of different age groups of seals corresponds to environmental factors. Blubber thickness of pups declined until 2010. The decreasing weight of 5–6-year-old herring (Clupea harengus),the main prey fish for Baltic gray seals, explained well the decline. In the Gulf of Finland, the blubber thickness of pups declined also in recent years (2011–2015) with declining number of days with permanent ice cover. In other regions, the blubber thickness of pups increased during recent years with increasing weight of herring. The blubber thickness of subadults in Baltic Proper and that of hunted adult females in the Bothnian Bay also increased during recent years, and the weight of age 6+ or 7-year-old herring best explained the increase. The blubber thickness of all age groups of seals was thinnest in the Bothnian Bay where also herring weight was lowest. There was a negative correlation between blubber thickness of seals and herring catch size (an index of herring abundance) suggesting that herring quality, not the quantity, is important for the nutritional status of Baltic gray seals. Nutritional status of gray seals may thus reveal changes in the marine food web which affect herring quality. Marine food web, in turn, may be affected, e.g., by climate change. The warming climate also has an impact on ice cover and thus body condition of seal pups