Michelle Shero - Academia.edu (original) (raw)

Papers by Michelle Shero

Deep Sea Research Part II: Topical Studies in Oceanography, 2016

The Anatomical Record, 2015

The utility of transrectal ultrasonography was tested in a field setting to characterize the repr... more The utility of transrectal ultrasonography was tested in a field setting to characterize the reproductive tract and detect early pregnancy (embryonic vesicles < 3 mm in diameter) in 17 multiparous female Weddell seals (Leptonychotes weddellii). Female Weddell seals give birth in October/November each year, followed by the breeding season (December) and embryonic diapause. Transrectal ultrasonography was attempted in January/February 2014 to examine the entire reproductive tract (uterine horns and body, ovaries with follicles and corpora lutea) using a 5-10 MHz linear-array probe with a 70 cm-long extension. A single pregnancy was detected in 14 of 17 seals (82.4%) as a circular or guitar-pick shaped non-echogenic (black) vesicle with a clearly visible echogenic border within the lumen of uterus. The stage of embryonic development (ostensibly the gestational age) varied markedly among individuals, ranging from a vesicle with no embryo proper to a large fetus with an ocular orbit, nose/mouth, limb buds, spinal column, umbilical cord, and prominent vasculature. Two of the pregnant seals were re-examined 3-6 days after the initial examination, to obtain longitudinal growth rates. Images of one or both ovaries were obtained in nine and seven of the 19 examinations, respectively. Numerous ovarian follicles (3 to 12 mm diameter) were detected and animals typically had a single well-perfused corpus luteum (determined by Doppler color-flow) ipsilateral to the uterine horn containing the pregnancy. We conclude that real-time transrectal ultrasonography is an effective tool for characterizing reproductive events in phocids including ovarian dynamics, and for elucidating the nature of embryonic diapause. This article is protected by copyright. All rights reserved.

Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, Jan 12, 2015

Adult Weddell seals (Leptonychotes weddellii) haul-out on the ice in October/November (austral sp... more Adult Weddell seals (Leptonychotes weddellii) haul-out on the ice in October/November (austral spring) for the breeding season and reduce foraging activities for ~4 months until their molt in the austral fall (January/February). After these periods, animals are at their leanest and resume actively foraging for the austral winter. In mammals, decreased exercise and hypoxia exposure typically lead to decreased production of O2-carrying proteins and muscle wasting, while endurance training increases aerobic potential. To test whether similar effects were present in marine mammals, this study compared the physiology of 53 post-molt female Weddell seals in the austral fall to 47 pre-breeding females during the spring in McMurdo Sound, Antarctica. Once body mass and condition (lipid) were controlled for, there were no seasonal changes in total body oxygen (TBO2) stores. Within each season, hematocrit and hemoglobin values were negatively correlated with animal size, and larger animals had...

Functional Ecology, 2015

1. Reproductive success can be influenced by maternal physiological condition at the time of embr... more 1. Reproductive success can be influenced by maternal physiological condition at the time of embryo implantation and by foraging success during gestation. Polar marine mammals experience drastic fluctuations in body composition (lipid stores) as a result of life-history events and large-scale changes in seasonal productivity and environmental conditions. These species provide the opportunity to explore physiological parameters important to reproductive success. 2. There are conflicting physiological demands on Weddell seal (Leptonychotes weddellii) females during the moult period, when animals are at their leanest but still must generate an energetically costly new pelage and begin active gestation. 3. To investigate the impact of post-moult condition and hormonal mediators on the reproductive success of the southernmost breeding mammal, body composition was determined for post-moult (fall; 53 non-reproductive) and pre-breeding (spring; 31 non-reproductive, 17 reproductive) adult female Weddell seals. Animals were significantly larger and had greater lipid stores in spring, after the winter foraging period. There were no differences in the proportion of mass or condition gained overwinter between females that gave birth (n = 12) and those that did not (n = 8) the following year. 4. Changes in body condition were correlated with endocrine factors that influence energy allocation, such as cortisol, growth hormone (GH), insulin-like growth factor (IGF)-1 and thyroid hormones (T 3 and T 4 ). Of these, GH and T 4 were significantly higher during the post-moult period, likely to promote protein sparing and hair regeneration. In addition, females that had higher T 4 concentrations in fall were significantly more likely to have a pup the following year, possibly due to the role of thyroid hormones in embryo attachment. This suggests that hormones influencing fuel use during the moult may also impact subsequent reproductive success. 5. Unlike some other large pinnipeds, Weddell seals are not capital breeders. This work indicates that gestating Weddell seals do not gain as much mass or energy overwinter in preparation for lactation the following year as lower-latitude phocid species, which might explain why female Weddell seals rely on foraging to meet energetic demands during lactation.

Journal of Comparative Physiology B, 2012

Northern fur seal (Callorhinus ursinus; NFS) populations have been declining, perhaps due to limi... more Northern fur seal (Callorhinus ursinus; NFS) populations have been declining, perhaps due to limited foraging ability of pups. Because a marine mammal's proficiency at exploiting underwater prey resources is based on the ability to store large amounts of oxygen (O 2 ) and to utilize these reserves efficiently, this study was designed to determine if NFS pups had lower blood, muscle, and total body O 2 stores than adults. Pups (\1month old) had a calculated aerobic dive limit only *40% of adult females due to lower blood and, to a much greater extent, muscle O 2 stores. Development of the Pectoralis (Pec) and Longissimus dorsi (LD) skeletal muscles was further examined by determining their myosin heavy chain (MHC) composition and enzyme activities. In all animals, the slow MHC I and fast-twitch IIA proteins typical of oxidative fiber types were dominant, but adult muscles contained more (Pec *50%; LD *250% higher) fasttwitch MHC IID/X protein characteristic of glycolytic muscle fibers, than pup muscles. This suggests that adults have greater ability to generate muscle power rapidly and/ or under anaerobic conditions. Pup muscles also had lower aerobic and anaerobic ATP production potential, as indicated by lower metabolically scaled citrate synthase, b-hydroxyacyl CoA dehydrogenase, and lactate dehydrogenase activities (all P values B0.001). In combination, these findings indicate that pups are biochemically and physiologically limited in their diving capabilities relative to adults. This may contribute to lower NFS first year survival.

Circulation Research, 2009

Rationale-Glutamate is a major signaling molecule that binds to glutamate receptors including the... more Rationale-Glutamate is a major signaling molecule that binds to glutamate receptors including the ionotropic glutamate receptors; kainate (KA) receptor (KAR), the N-methyl-D-aspartate (NMDA) receptor (NMDAR), and the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR). Each is well characterized in the central nervous system (CNS), but glutamate has important signaling roles in peripheral tissues as well, including a role in regulating platelet function.

PLoS ONE, 2014

Mass and body composition are indices of overall animal health and energetic balance and are ofte... more Mass and body composition are indices of overall animal health and energetic balance and are often used as indicators of resource availability in the environment. This study used morphometric models and isotopic dilution techniques, two commonly used methods in the marine mammal field, to assess body composition of Weddell seals (Leptonychotes weddellii, N = 111). Findings indicated that traditional morphometric models that use a series of circular, truncated cones to calculate marine mammal blubber volume and mass overestimated the animal's measured body mass by 26.961.5% SE. However, we developed a new morphometric model that uses elliptical truncated cones, and estimates mass with only 22.861.7% error (N = 10). Because this elliptical truncated cone model can estimate body mass without the need for additional correction factors, it has the potential to be a broadly applicable method in marine mammal species. While using elliptical truncated cones yielded significantly smaller blubber mass estimates than circular cones (10.260.8% difference; or 3.560.3% total body mass), both truncated cone models significantly underestimated total body lipid content as compared to isotopic dilution results, suggesting that animals have substantial internal lipid stores (N = 76). Multiple linear regressions were used to determine the minimum number of morphometric measurements needed to reliably estimate animal mass and body composition so that future animal handling times could be reduced. Reduced models estimated body mass and lipid mass with reasonable accuracy using fewer than five morphometric measurements (root-mean-square-error: 4.91% for body mass, 10.90% for lipid mass, and 10.43% for % lipid). This indicates that when test datasets are available to create calibration coefficients, regression models also offer a way to improve body mass and condition estimates in situations where animal handling times must be short and efficient.

Deep Sea Research Part II: Topical Studies in Oceanography, 2016

The Anatomical Record, 2015

The utility of transrectal ultrasonography was tested in a field setting to characterize the repr... more The utility of transrectal ultrasonography was tested in a field setting to characterize the reproductive tract and detect early pregnancy (embryonic vesicles < 3 mm in diameter) in 17 multiparous female Weddell seals (Leptonychotes weddellii). Female Weddell seals give birth in October/November each year, followed by the breeding season (December) and embryonic diapause. Transrectal ultrasonography was attempted in January/February 2014 to examine the entire reproductive tract (uterine horns and body, ovaries with follicles and corpora lutea) using a 5-10 MHz linear-array probe with a 70 cm-long extension. A single pregnancy was detected in 14 of 17 seals (82.4%) as a circular or guitar-pick shaped non-echogenic (black) vesicle with a clearly visible echogenic border within the lumen of uterus. The stage of embryonic development (ostensibly the gestational age) varied markedly among individuals, ranging from a vesicle with no embryo proper to a large fetus with an ocular orbit, nose/mouth, limb buds, spinal column, umbilical cord, and prominent vasculature. Two of the pregnant seals were re-examined 3-6 days after the initial examination, to obtain longitudinal growth rates. Images of one or both ovaries were obtained in nine and seven of the 19 examinations, respectively. Numerous ovarian follicles (3 to 12 mm diameter) were detected and animals typically had a single well-perfused corpus luteum (determined by Doppler color-flow) ipsilateral to the uterine horn containing the pregnancy. We conclude that real-time transrectal ultrasonography is an effective tool for characterizing reproductive events in phocids including ovarian dynamics, and for elucidating the nature of embryonic diapause. This article is protected by copyright. All rights reserved.

Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, Jan 12, 2015

Adult Weddell seals (Leptonychotes weddellii) haul-out on the ice in October/November (austral sp... more Adult Weddell seals (Leptonychotes weddellii) haul-out on the ice in October/November (austral spring) for the breeding season and reduce foraging activities for ~4 months until their molt in the austral fall (January/February). After these periods, animals are at their leanest and resume actively foraging for the austral winter. In mammals, decreased exercise and hypoxia exposure typically lead to decreased production of O2-carrying proteins and muscle wasting, while endurance training increases aerobic potential. To test whether similar effects were present in marine mammals, this study compared the physiology of 53 post-molt female Weddell seals in the austral fall to 47 pre-breeding females during the spring in McMurdo Sound, Antarctica. Once body mass and condition (lipid) were controlled for, there were no seasonal changes in total body oxygen (TBO2) stores. Within each season, hematocrit and hemoglobin values were negatively correlated with animal size, and larger animals had...

Functional Ecology, 2015

1. Reproductive success can be influenced by maternal physiological condition at the time of embr... more 1. Reproductive success can be influenced by maternal physiological condition at the time of embryo implantation and by foraging success during gestation. Polar marine mammals experience drastic fluctuations in body composition (lipid stores) as a result of life-history events and large-scale changes in seasonal productivity and environmental conditions. These species provide the opportunity to explore physiological parameters important to reproductive success. 2. There are conflicting physiological demands on Weddell seal (Leptonychotes weddellii) females during the moult period, when animals are at their leanest but still must generate an energetically costly new pelage and begin active gestation. 3. To investigate the impact of post-moult condition and hormonal mediators on the reproductive success of the southernmost breeding mammal, body composition was determined for post-moult (fall; 53 non-reproductive) and pre-breeding (spring; 31 non-reproductive, 17 reproductive) adult female Weddell seals. Animals were significantly larger and had greater lipid stores in spring, after the winter foraging period. There were no differences in the proportion of mass or condition gained overwinter between females that gave birth (n = 12) and those that did not (n = 8) the following year. 4. Changes in body condition were correlated with endocrine factors that influence energy allocation, such as cortisol, growth hormone (GH), insulin-like growth factor (IGF)-1 and thyroid hormones (T 3 and T 4 ). Of these, GH and T 4 were significantly higher during the post-moult period, likely to promote protein sparing and hair regeneration. In addition, females that had higher T 4 concentrations in fall were significantly more likely to have a pup the following year, possibly due to the role of thyroid hormones in embryo attachment. This suggests that hormones influencing fuel use during the moult may also impact subsequent reproductive success. 5. Unlike some other large pinnipeds, Weddell seals are not capital breeders. This work indicates that gestating Weddell seals do not gain as much mass or energy overwinter in preparation for lactation the following year as lower-latitude phocid species, which might explain why female Weddell seals rely on foraging to meet energetic demands during lactation.

Journal of Comparative Physiology B, 2012

Northern fur seal (Callorhinus ursinus; NFS) populations have been declining, perhaps due to limi... more Northern fur seal (Callorhinus ursinus; NFS) populations have been declining, perhaps due to limited foraging ability of pups. Because a marine mammal's proficiency at exploiting underwater prey resources is based on the ability to store large amounts of oxygen (O 2 ) and to utilize these reserves efficiently, this study was designed to determine if NFS pups had lower blood, muscle, and total body O 2 stores than adults. Pups (\1month old) had a calculated aerobic dive limit only *40% of adult females due to lower blood and, to a much greater extent, muscle O 2 stores. Development of the Pectoralis (Pec) and Longissimus dorsi (LD) skeletal muscles was further examined by determining their myosin heavy chain (MHC) composition and enzyme activities. In all animals, the slow MHC I and fast-twitch IIA proteins typical of oxidative fiber types were dominant, but adult muscles contained more (Pec *50%; LD *250% higher) fasttwitch MHC IID/X protein characteristic of glycolytic muscle fibers, than pup muscles. This suggests that adults have greater ability to generate muscle power rapidly and/ or under anaerobic conditions. Pup muscles also had lower aerobic and anaerobic ATP production potential, as indicated by lower metabolically scaled citrate synthase, b-hydroxyacyl CoA dehydrogenase, and lactate dehydrogenase activities (all P values B0.001). In combination, these findings indicate that pups are biochemically and physiologically limited in their diving capabilities relative to adults. This may contribute to lower NFS first year survival.

Circulation Research, 2009

Rationale-Glutamate is a major signaling molecule that binds to glutamate receptors including the... more Rationale-Glutamate is a major signaling molecule that binds to glutamate receptors including the ionotropic glutamate receptors; kainate (KA) receptor (KAR), the N-methyl-D-aspartate (NMDA) receptor (NMDAR), and the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR). Each is well characterized in the central nervous system (CNS), but glutamate has important signaling roles in peripheral tissues as well, including a role in regulating platelet function.

PLoS ONE, 2014

Mass and body composition are indices of overall animal health and energetic balance and are ofte... more Mass and body composition are indices of overall animal health and energetic balance and are often used as indicators of resource availability in the environment. This study used morphometric models and isotopic dilution techniques, two commonly used methods in the marine mammal field, to assess body composition of Weddell seals (Leptonychotes weddellii, N = 111). Findings indicated that traditional morphometric models that use a series of circular, truncated cones to calculate marine mammal blubber volume and mass overestimated the animal's measured body mass by 26.961.5% SE. However, we developed a new morphometric model that uses elliptical truncated cones, and estimates mass with only 22.861.7% error (N = 10). Because this elliptical truncated cone model can estimate body mass without the need for additional correction factors, it has the potential to be a broadly applicable method in marine mammal species. While using elliptical truncated cones yielded significantly smaller blubber mass estimates than circular cones (10.260.8% difference; or 3.560.3% total body mass), both truncated cone models significantly underestimated total body lipid content as compared to isotopic dilution results, suggesting that animals have substantial internal lipid stores (N = 76). Multiple linear regressions were used to determine the minimum number of morphometric measurements needed to reliably estimate animal mass and body composition so that future animal handling times could be reduced. Reduced models estimated body mass and lipid mass with reasonable accuracy using fewer than five morphometric measurements (root-mean-square-error: 4.91% for body mass, 10.90% for lipid mass, and 10.43% for % lipid). This indicates that when test datasets are available to create calibration coefficients, regression models also offer a way to improve body mass and condition estimates in situations where animal handling times must be short and efficient.