Fitness correlates of blubber oxidative stress and cellular defences in grey seals (Halichoerus grypus): support for the life-history-oxidative stress theory from an animal model of simultaneous lactation and fasting.

Life-history-oxidative stress theory predicts that elevated energy costs during reproduction reduce allocation to defences and increase cellular stress, with fitness consequences, particularly when resources are limited. As capital breeders, grey seals are a natural system in which to test this theory. We investigated oxidative damage (malondialdehyde (MDA) concentration) and cellular defences (relative mRNA abundance of heat shock proteins (Hsps) and redox enzymes (REs)) in blubber of wild female grey seals during the lactation fast (n = 17) and summer foraging (n = 13). Transcript abundance of Hsc70 increased, and Nox4, a pro-oxidant enzyme, decreased throughout lactation. Foraging females had higher mRNA abundance of some Hsps and lower RE transcript abundance and MDA concentrations, suggesting they experienced lower oxidative stress than lactating mothers, which diverted resources into pup rearing at the expense of blubber tissue damage. Lactation duration and maternal mass loss rate were both positively related to pup weaning mass. Pups whose mothers had higher blubber glutathione-S-transferase (GST) expression at early lactation gained mass more slowly. Higher glutathione peroxidase (GPx) and lower catalase (CAT) were associated with longer lactation but reduced maternal transfer efficiency and lower pup weaning mass. Cellular stress, and the ability to mount effective cellular defences, could proscribe lactation strategy in grey seal mothers and thus affect pup survival probability. These data support the life-history-oxidative stress hypothesis in a capital breeding mammal and suggest lactation is a period of heightened vulnerability to environmental factors that exacerbate cellular stress. Fitness consequences of stress may thus be accentuated during periods of rapid environmental change.

Changes in trace elements during lactation in a marine top predator, the grey seal.

Lactation in pinnipeds represents the most significant cost to mothers during the reproductive cycle. Dynamics of trace elements and their mobilization associated with energy reserves during such an intense physiological process remains poorly understood in marine mammals. The changes in tissue concentrations of 11 elements (Ca, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Se, V, and Zn) were investigated in a longitudinal study during the lactation period and during the post-weaning fast period. Blood, milk, blubber, and hair samples were collected sequentially from 21 mother-pup pairs of grey seals (Halichoerus grypus) from the Isle of May in Scotland. Maternal transfer through the milk was observed for all trace elements, except for Cd. As an indicator of the placental transfer, levels in pup lanugo (natal coat) revealed also the existence of maternal transfer and accumulation of all assayed trace elements during the foetal development. The placental and mammary barriers against non-essential metal transfer to offspring appear to be absent or weak in grey seals. Examining the contamination levels showed that this grey seal population seems more highly exposed to Pb than other phocid populations (2.2 mg/kg dw of grey seal hair). In contrast, blood and hair levels reflected a lower Hg exposure in grey seals from the Isle of May than in harbour seals from the southeastern North Sea. This study also showed that trace element concentrations in blood and blubber could change rapidly over the lactation period. Such physiological processes must be considered carefully during biomonitoring of trace elements, and potential impacts that rapid fluctuations in concentrations can exert on seal health should be further investigated.

Effects of polychlorobiphenyls, polybromodiphenylethers, organochlorine pesticides and their metabolites on vitamin A status in lactating grey seals.

Polychlorobiphenyls (PCBs), polybromodiphenylethers (PBDEs) and organochlorine pesticides (OCPs), such as dichlorodiphenyltrichloroethane (DDT) and hexachlorobenzene (HCB), are considered as endocrine disruptors in laboratory and wild animals. This study investigated whether these compounds and their hydroxylated metabolites (HO-PCBs and HO-PBDEs) may affect the homoeostasis of vitamin A, a dietary hormone, in the blubber and serum of twenty lactating grey seals sampled at early and late lactation on the Isle of May, Scotland. The effect of naturally produced compounds such as the methoxylated (MeO)-PBDEs was also examined. Vitamin A levels in inner blubber (37±9 µg/g wet weight (ww) and 92±32 µg/g ww at early and late lactation, respectively) and serum (408±143 and 390±98 ng/ml at early and late lactation, respectively) appeared to be positively related to ΣPCBs, ΣPBDEs and several individual PCB and PBDE congeners in inner blubber and serum. These findings may suggest enhanced mobilisation of hepatic retinoid stores and redistribution in the blubber, a storage site for vitamin A in marine mammals. We have also reported that serum concentrations of ΣHO-PCBs and 4-OH-CB107 tended to increase with circulating vitamin A levels. Although the direction of the relationships may sometimes differ from those reported in the literature, our results are in agreement with previous findings highlighting a disruption of vitamin A homoeostasis in the blubber and bloodstream following exposure to environmental pollutants. The fact that vitamin A and PCBs appeared to share common mechanisms of mobilisation and transfer during lactation in grey seals (Debier et al., 2004; Vanden Berghe et al., 2010) may also play a role in the different relationships observed between vitamin A and lipophilic pollutants.

Selective transfer of persistent organic pollutants and their metabolites in grey seals during lactation.

Twenty grey seal (Halichoerus grypus) mother-pup pairs from the colony of the Isle of May (Scotland) were sampled at early and late lactation in order to study the transfer of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and their metabolites (HO-PCBs and HO-PBDEs) as well as organochlorine pesticides (OCPs), such as DDT and metabolites (DDXs) and hexachlorobenzene (HCB). The transfer of the naturally produced MeO-PBDEs was also investigated. Generally, concentrations (on a lipid weight basis) of the sum of PCBs, PBDEs and DDXs tended to be higher in all tissues at late lactation (for maternal outer blubber ΣPCBs=3860±2091 ng/g, ΣPBDEs=120±74 ng/g and ΣDDXs=559±207 ng/g; for maternal inner blubber ΣPCBs=4229±3274 ng/g, ΣPBDEs=148±118 ng/g and ΣDDXs=704±353 ng/g; for maternal serum ΣPCBs=1271±796 ng/g, ΣPBDEs=27±16 ng/g and ΣDDXs=242±125 ng/g; for milk ΣPCBs=1190±747 ng/g, ΣPBDEs=55±36 ng/g and ΣDDXs=357±160 ng/g; for pup serum ΣPCBs=1451±901 ng/g, ΣPBDEs=48±31 ng/g and ΣDDXs=395±201 ng/g). In all tissues, ΣMeO-PBDEs were found at very low levels or even undetected and their concentrations appeared to increase at late lactation only in maternal inner blubber (2.7±1.3 to 5.3±2.9 ng/g for early and late lactation, respectively) and milk (0.6±0.3 to 1.1±0.5 ng/g for early and late lactation, respectively). The transfer from inner blubber to maternal serum was selective and strongly depended on the log K(ow) value of the compounds, with less lipophilic compounds being more efficiently released. Only a limited amount of HO-PCBs was transferred during lactation as 4-HO-CB-107 was the only metabolite detected in milk (29 to 40 pg/g lw). On the contrary, most of HO-PCB metabolites found in maternal serum were also detected in pup serum. These findings suggest not only a transplacental transfer of HO-PCBs from mothers to pups but also the possibility of endogenous biotransformation in suckling pups or accumulation of undetectable low amounts from milk.

Effects of handling regime and sex on changes in cortisol, thyroid hormones and body mass in fasting grey seal pups.

Survival of seal pups may be affected by their ability to respond appropriately to stress. Chronic stress can adversely affect secretion of cortisol and thyroid hormones, which contribute to the control of fuel utilisation. Repeated handling could disrupt the endocrine response to stress and/or negatively impact upon mass changes during fasting. Here we investigated the effects of handling regime on cortisol and thyroid hormone levels, and body mass changes, in fasting male and female grey seal pups (Halichoerus grypus). Females had higher thyroid hormone levels than males throughout fasting and showed a reduction in cortisol midway through the fast that was not seen in males. This may reflect sex-specific fuel allocation or development. Neither handling frequency nor cumulative contact time affected plasma cortisol or thyroid hormone levels, the rate of increase in cortisol over the first five minutes of physical contact or the pattern of mass loss during fasting in either sex. The endocrine response to stress and the control of energy balance in grey seal pups appear to be robust to repeated, short periods of handling. Our results suggest that routine handling should have no additional impact on these animals than general disturbance caused by researchers moving around the colony.

Comparison of the 1988 and 2002 phocine distemper epizootics in British harbour seal Phoca vitulina populations.

In 1988 and 2002 dramatic and well-documented phocine distemper epizootics occurred in Europe. While their progression and impact were remarkably similar and consistent over much of Europe, mortality in the UK varied greatly between and within the 2 epizootics. We use antibody levels in blood samples to show that 51% (Bayesian 95% CI: 41 to 61%) of the individuals alive in 5 UK harbour seal populations at the end of the 1988 epizootic had been exposed to the virus, and that the equivalent figure after the 2002 outbreak was 22% (95% CI: 16 to 30%). Antibody prevalence was significantly higher in females than males after the 2002 epizootic. Combining these estimates with information on reductions in the numbers of animals observed hauled out during surveys of the Wash, Moray Firth, and Orkney populations and a simple epidemiological model, suggests that the differences between the 2 epizootics were primarily due to a 27% (95% CI: 8 to 43%) fall in R0, the basic reproductive rate of the virus. The large geographic variation in population effects observed within the UK during each epizootic appears to have been mainly due to differences in case mortality, with R0 being remarkably similar in all the populations investigated.

Relationships between vitamin A and PCBs in grey seal mothers and pups during lactation.

A previous study has shown a simultaneous increase of vitamin A and PCBs in grey seal (Halichoerus grypus) milk at late lactation (Debier et al., 2004). Here we sought to understand this unexpected relationship by comparing the dynamics of vitamin A and PCBs in the different tissue compartments of transfer. Lactating grey seals and their pups were sampled longitudinally in Scotland during the 2006 breeding season. As blubber reserves decreased, concentrations of vitamin A and PCBs increased during lactation in the inner layer of maternal blubber. A concomitant rise was observed in milk and consequently in the serum of suckling pups. The similar dynamics of vitamin A and PCBs in milk and inner blubber suggest a common mechanism of mobilisation from maternal body stores and transfer into the milk. A panel data analysis highlighted a negative impact of PCBs in milk and pup serum on vitamin A status in pup serum.

Effects of mass and body composition on fasting fuel utilisation in grey seal pups (Halichoerus grypus Fabricius): an experimental study using supplementary feeding.

This study used supplementary feeding to test the hypothesis that fuel partitioning during the postweaning fast in grey seal pups is affected by size and composition of energy reserves at weaning, and by extra provisioning. Mass and body composition changes were measured during suckling and fasting to investigate the effect of natural differences in energy reserves at weaning on subsequent allocation of fat and protein to energy use. We fed seven pups for 5 days after weaning, to investigate the effect of increased fuel availability, and particularly protein, on fuel utilisation. After correcting for protein used during the moult, the proportional contribution of fat was 86-99% of total energy use. Pups with greater energy reserves, i.e. those that were heavier and fatter at weaning, had higher rates of fat and energy use. There was no significant relationship between adiposity at weaning and proportional contribution of fat to energy use, perhaps due to a limited sample size or range of body masses and adiposity. Supplemented individuals used energy, specifically fat, much faster and utilised proportionally less of their endogenous protein by departure than non-supplemented individuals. Fat metabolism contributed a similar percentage to daily energy use in both groups. These findings show that pups spare protein, even when energy use is dramatically increased. Pups that receive greater maternal provisioning and lay down more protein may have increased survival chances at sea. This study highlights the importance of protein reserves in first year survival of grey seal pups.

Finding fathers: spatio-temporal analysis of paternity assignment in grey seals (Halichoerus grypus).

Molecular studies of pinniped breeding systems exhibit a broad range of agreement and disagreement with observational indices of male breeding success. Grey seal studies have reported considerable discrepancies between genetic and behavioural paternity measures that have been interpreted as evidence of previously unidentified male strategies and/or tactics. Therefore, these studies have the power to fundamentally alter our perceptions of mating systems. However, other pinniped studies exhibit no such disagreements, and one possible explanation for disparities may be sampling biases in space and time. Therefore, it is essential that potential sampling biases are examined to evaluate the likelihood of previously unidentified male strategies. We examined paternities assigned at the North Rona grey seal colony between 1999 and 2002 in relation to concurrent detailed behavioural and locational data for males and females. We found that (i) for females observed in sexual interaction(s) during their oestrus period, it was highly probable that one of the interacting males fathered their next pup; (ii) over 80% of assigned paternities agreed with observations of the in-colony behaviour and spatio-temporal proximity of the males and females involved; and (iii) a minority of females exhibit mate choice and seek sires outside their local male's home range, although evidence suggests that these females mate on the colony rather than at sea. In conclusion, nearly all paternities assigned agreed with expectation based upon detailed knowledge of the spatio-temporal patterns of individuals during the breeding season. We found little evidence of unidentified male strategies at North Rona, Scotland, whereas further examination of mechanisms of female choice may be productive.

Incorporating movement into models of grey seal population dynamics.

1. One of the most difficult problems in developing spatially explicit models of population dynamics is the validation and parameterization of the movement process. We show how movement models derived from capture-recapture analysis can be improved by incorporating them into a spatially explicit metapopulation model that is fitted to a time series of abundance data. 2. We applied multisite capture-recapture analysis techniques to photo-identification data collected from female grey seals at the four main breeding colonies in the North Sea between 1999 and 2001. The best-fitting movement models were then incorporated into state-space metapopulation models that explicitly accounted for demographic and observational stochasticity. 3. These metapopulation models were fitted to a 20-year time series of pup production data for each colony using a Bayesian approach. The best-fitting model, based on the Akaike Information Criterion (AIC), had only a single movement parameter, whose confidence interval was 82% less than that obtained from the capture-recapture study, but there was some support for a model that included an effect of distance between colonies. 4. The state-space modelling provided improved estimates of other demographic parameters. 5. The incorporation of movement, and the way in which it was modelled, affected both local and regional dynamics. These differences were most evident as colonies approached their carrying capacities, suggesting that our ability to discriminate between models should improve as the length of the grey seal time series increases.