Postpartum Dynamics of Reproductive Hormones in Gray and Hooded Seals

Mellish, Jo‐Ann E.; Iverson, Sara J.

doi:10.1111/j.1748-7692.2005.tb01217.x

Cited by 9 publications

(8 citation statements)

References 21 publications

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“…This spike in total estrogens might be interpreted as the preovulatory surge that accompanies estrus, yet it is derived from the CL rather than ovarian follicles. In this case, both the pregnant and unbred females exhibited elevated estrogen concentrations within their CL (Fig 2) providing further support that the unbred females were exhibiting a physiological pseudopregnancy, as elevated estrogen levels support fetal growth [46,47]. The circulation of this hormone from the ovaries to the fetus would explain the lower concentrations found in the pregnant animals than the unbred females.…”

Section: Total Estrogenssupporting

confidence: 55%

Endocrine profiling of reproductive status and evidence of pseudopregnancy in the Pacific walrus (Odobenus rosmarus divergens)

Tempel

Atkinson

2020

PLoS ONE

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Endocrine profiling is an increasingly utilized tool for detecting pregnancies in wild populations of mammals. Given the difficulty in calculating reproductive rates of Pacific walruses (Odobenus rosmarus divergens) the use of endocrine techniques for determining pregnancy rates could be particularly useful for management of the population. The goals of this study were to 1) determine if progesterone and total estrogen concentrations in ovarian tissues of female walruses could be used to determine reproductive state and 2) determine if walruses undergo a functional postpartum estrus, as is seen in other pinnipeds. Ovaries were collected from female walruses (n = 13) hunted in subsistence hunts by Alaska Native communities. Females were categorized as postpartum, full-term pregnant, pregnant diapause or unbred. Total estrogen concentrations were greatest in unbred (n = 2) and pregnant (n = 2) females. Progesterone concentrations were also nominally larger in unbred (n = 2) than pregnant (n = 2) and postpartum (n = 9) animals. Small samples sizes precluded the use of statistical comparisons among groups. Corpora lutea tissue samples in this study did not reflect the presence of a postpartum estrus in the month of May as postpartum females yielded lower total estrogen concentrations than unbred or pregnant animals. Both unbred animals were in a state of pseudopregnancy, which has not been physiologically described for this species before. The progesterone profiles in late (59 ng/g) and early (140 ng/g) pregnancy were lower than expected and fell within the range of the postpartum females (36-210 ng/g), suggesting low production of the hormone by the corpus luteum during these phases of pregnancy. Profiling reproductive hormones in free-ranging walruses demonstrates that an endocrine approach may be a valuable tool for determining reproductive status of females, however increased sample sizes and time of year must be considered to accurately separate pregnant versus pseudopregnant individuals.

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Section: Total Estrogenssupporting

confidence: 55%

Endocrine profiling of reproductive status and evidence of pseudopregnancy in the Pacific walrus (Odobenus rosmarus divergens)

Tempel

Atkinson

2020

PLoS ONE

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“…More specifically, in vitro studies with grey seals liver microsomes showed that 2β (CYP3A), 6β (CYP3A, CYP1A), and 16β (CYP2B) hydroxylation of T4 in this species (Li et al 2003). P4 and E2 levels in female ringed and grey seals were in the same range as those reported for harbour, grey seals, and spotted seals at the same reproductive stage (Boyd 1983;Reijnders 1990;Gardiner et al 1996;Mellish and Iverson 2005;Lydersen and Kovacs 2004;Zhang et al 2014). For both species studied, T4 concentrations were higher than those reported in the only other report of T4 in female pinnipeds in otariid seals (Browne et al 2006).…”

Section: Hormone Concentrationssupporting

confidence: 67%

Polychlorinated Biphenyls (PCBs) and Sex Hormone Concentrations in Ringed and Grey Seals: A Possible Link to Endocrine Disruption?

Troisi

Barton

Liori

et al. 2020

Arch Environ Contam Toxicol

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Polychlorinated biphenyls (PCBs) are recognised reproductive and immune system toxicants in marine mammals mediated by endocrine-disrupting mechanisms. As with other predators, seals are exposed to elevated bioaccumulated concentrations of PCBs and other persistent organic pollutants (POPs). Cryopreserved plasma samples from adult ringed (Phoca hispida; n = 39) and grey (Halichoerus grypus; n = 38) seals, sampled between 1998 and 2002 from Baltic Sea, Svalbard, and Sable Island (Canada) were used to investigate relationships between PCB exposure and sex hormone concentrations (progesterone; P4, 17α-hydroxy progesterone; 17α-OH-P4, testosterone; T4, 17β-estradiol; E2, estrone; E3). Immunoassay methods were used for quantification of analytes due to the limited sample volumes available. PCB concentrations were found to be significantly higher in Baltic seals than other sampling locations and were classed as "Exposed" seals while Svalbard and Sable Is seal were classed "Reference" seals (sexes and species separate). Mean hormone concentrations in Exposed seal were lower than Reference seals, and this was statistically significantly for 17α-OH-P4 (both sexes and both species), E2 (ringed and grey seal females), and E3 (grey seal females). Regression analyses (PCB v hormone concentrations) for each sex and species revealed significant correlations for P4 (Sable Is. female grey seals and female ringed seals), 17α-OH-P4 (Sable Is. male grey seals and Svalbard male ringed seals), T4 (Svalbard male ringed seals), E2 (female ringed seals), and E3 (female ringed seals and Baltic female grey seals). Although significant correlations are not evidence of cause and effect, the potential impact of hormone changes on endocrine homeostasis and reproductive health for seal populations warrants further investigation given that PCB concentrations found here are in the same range as those currently reported in seals from these populations.

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“…In large-bodied phocid seals the mobilization of body fat accounts for ;90% of maternal energy loss over the course of lactation (Mellish et al 1999, Crocker et al 2001. Therefore, changes in the levels of body energy stores, particularly fat, have the potential to act as a metabolic signal for triggering oestrus and weaning (see Mellish and Iverson 2005). If, as our data suggest, the proportion of body energy stores used serves as a consistent cue for weaning, this would place a limit on the duration of lactation within females and, as a result, their ability to transfer available energy to their pups.…”

Section: Lactation Lengthmentioning

confidence: 99%

Repeatability in lactation performance and the consequences for maternal reproductive success in gray seals

Lang

Iverson

Bowen

2009

Ecology

Self Cite

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In mammals, the most significant maternal effect on offspring growth during lactation is the ability of females to efficiently transfer milk energy to their neonates. However, despite the importance of the transfer of milk energy to both maternal and offspring fitness, nothing is known about the extent to which variation among females may be attributed to differences in individual quality or environmental variation in natural populations. We measured repeatability over multiple lactation periods in components of lactation performance in free-ranging, multiparous gray seal (Halichoerus grypus) females to examine to what extent variation among females in pup weaning mass may be attributed to inherent differences in their physiological capacity to deliver milk energy. Levels of repeatability were high for milk composition (r = 0.38-0.50), daily milk output (r = 0.46), and the duration of lactation (r = 0.57), demonstrating that there are consistent differences among females in these characters across lactations and that the overall capacity of gray seal females to deliver milk energy to their pups is characteristic of individuals. The repeatability in pup weaning mass (r = 0.48) was consistent with the values for the components of total milk energy output and suggests that, over a large proportion of their reproductive life, individual gray seal females will consistently wean pups with greater or lesser probabilities of survival. Our results suggest that inherent differences among females in their physiological capacity to deliver milk energy may be an important component of variation in individual quality and, thus, lifetime reproductive success in mammals. High levels of repeatability also suggest that components of milk energy transfer may have a significant heritable genetic basis.

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Postpartum Dynamics of Reproductive Hormones in Gray and Hooded Seals

Cited by 9 publications

References 21 publications

Endocrine profiling of reproductive status and evidence of pseudopregnancy in the Pacific walrus (Odobenus rosmarus divergens)

Endocrine profiling of reproductive status and evidence of pseudopregnancy in the Pacific walrus (Odobenus rosmarus divergens)

Polychlorinated Biphenyls (PCBs) and Sex Hormone Concentrations in Ringed and Grey Seals: A Possible Link to Endocrine Disruption?

Repeatability in lactation performance and the consequences for maternal reproductive success in gray seals

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