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      Altered expression of pectoral myosin heavy chain isoforms corresponds to migration status in the white-crowned sparrow ( Zonotrichia leucophrys gambelii)

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          Abstract

          Birds undergo numerous changes as they progress through life-history stages, yet relatively few studies have examined how birds adapt to both the dynamic energetic and mechanical demands associated with such transitions. Myosin heavy chain (MyHC) expression, often linked with muscle fibre type, is strongly correlated with a muscle's mechanical power-generating capability, thus we examined several morphological properties, including MyHC expression of the pectoralis, in a long-distance migrant, the white-crowned sparrow ( Zonotrichia leucophrys gambelii) throughout the progression from winter, spring departure and arrival on breeding grounds. White-crowned sparrows demonstrated significant phenotypic flexibility throughout the seasonal transition, including changes in prealternate moult status, lipid fuelling, body condition and flight muscle morphology. Pectoral MyHC expression also varied significantly over the course of the study. Wintering birds expressed a single, newly classified adult fast 2 isoform. At spring departure, pectoral isoform expression included two MyHC isoforms: the adult fast 2 isoform along with a smaller proportion of a newly present adult fast 1 isoform. By spring arrival, both adult fast isoforms present at departure remained, yet expression had shifted to a greater relative proportion of the adult fast 1 isoform. Altering pectoral MyHC isoform expression in preparation for and during spring migration may represent an adaptation to modulate muscle mechanical output to support long-distance flight.

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          Most cited references 34

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          Photoperiodic control of seasonality in birds.

          This review examines how birds use the annual cycle in photoperiod to ensure that seasonal events--breeding, molt, and song production--happen at the appropriate time of year. Differences in breeding strategies between birds and mammals reflect basic differences in biology. Avian breeding seasons tend to be of shorter duration and more asymmetric with respect to changes in photoperiod. Breeding seasons can occur at the same time each year (predictable) or at different times (opportunistic), depending on the food resource. In all cases, there is evidence for involvement of photoperiodic control, nonphotoperiodic control, and endogenous circannual rhythmicity. In predictable breeders (most nontropical species), photoperiod is the predominant proximate factor. Increasing photoperiods of spring stimulate secretion of gonadotropin-releasing hormone (GnRH) and consequent gonadal maturation. However, breeding ends before the return of short photoperiods. This is the consequence of a second effect of long photoperiods--the induction of photorefractoriness. This dual role of long photoperiods is required to impart the asymmetry in breeding seasons. Typically, gonadal regression through photorefractoriness is associated with a massive decrease in hypothalamic GnRH, essentially a reversal to a pre-pubertal condition. Although breeding seasons are primarily determined by photoperiodic control of GnRH neurons, prolactin may be important in determining the exact timing of gonadal regression. In tropical and opportunistic breeders, endogenous circannual rhythmicity may be more important. In such species, the reproductive system remains in a state of "readiness to breed" for a large part of the year, with nonphotic cues acting as proximate cues to time breeding. Circannual rhythmicity may result from a temporal sequence of different physiological states rather than a molecular or cellular mechanism as in circadian rhythmicity. Avian homologues of mammalian clock genes Per2, Per3, Clock, bmal1, and MOP4 have been cloned. At the molecular level, avian circadian clocks appear to function in a similar manner to those of mammals. Photoperiodic time measurement involves interaction between a circadian rhythm of photoinducibility and, unlike mammals, deep brain photoreceptors. The exact location of these remains unclear. Although the eyes and pineal generate a daily cycle in melatonin, this photoperiodic signal is not used to time seasonal breeding. Instead, photoperiodic responses appear to involve direct interaction between photoreceptors and GnRH neurons. Thyroid hormones are required in some way for this system to function. In addition to gonadal function, song production is also affected by photoperiod. Several of the nuclei involved in the song system show seasonal changes in volume, greater in spring than in the fall. The increase in volume is, in part, due to an increase in cell number as a result of neurogenesis. There is no seasonal change in the birth of neurons but rather in their survival. Testosterone and melatonin appear to work antagonistically in regulating volume.
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            Transitions of muscle fiber phenotypic profiles.

             R B Staron,  D Pette (2001)
            Skeletal muscle is a complex, versatile tissue composed of a large variety of functionally diverse fiber types. The overall properties of a muscle largely result from a combination of the individual properties of its different fiber types and their proportions. Skeletal muscle fiber types, which can be delineated according to various parameters, for example, myofibrillar protein isoforms, metabolic enzyme profiles, and structural and contractile properties, are not fixed units but are capable of responding to altered functional demands and a variety of signals by changing their phenotypic profiles. This brief review summarizes our current understanding of the delineation of fiber types, modulations of their phenotypic profiles as induced under various conditions, and potential mechanisms involved in these transitions.
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              Carrying large fuel loads during sustained bird flight is cheaper than expected.

              Birds on migration alternate between consuming fuel stores during flights and accumulating fuel stores during stopovers. The optimal timing and length of flights and stopovers for successful migration depend heavily on the extra metabolic power input (fuel use) required to carry the fuel stores during flight. The effect of large fuel loads on metabolic power input has never been empirically determined. We measured the total metabolic power input of a long-distance migrant, the red knot (Calidris canutus), flying for 6 to 10 h in a wind tunnel, using the doubly labelled water technique. Here we show that total metabolic power input increased with fuel load, but proportionally less than the predicted mechanical power output from the flight muscles. The most likely explanation is that the efficiency with which metabolic power input is converted into mechanical output by the flight muscles increases with fuel load. This will influence current models of bird flight and bird migration. It may also help to explain why some shorebirds, despite the high metabolic power input required to fly, routinely make nonstop flights of 4,000 km longer.
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                Author and article information

                Journal
                R Soc Open Sci
                R Soc Open Sci
                RSOS
                royopensci
                Royal Society Open Science
                The Royal Society Publishing
                2054-5703
                November 2016
                30 November 2016
                30 November 2016
                : 3
                : 11
                Affiliations
                [1 ]Department of Biological Sciences, University of Toronto Scarborough , 1265 Military Trail, Toronto, Ontario, CanadaM1C 1A4
                [2 ]Center for the Neurobiology of Stress, University of Toronto Scarborough , 1265 Military Trail, Toronto, Ontario, CanadaM1C 1A4
                [3 ]Center for the Analysis of Genome Evolution and Function, University of Toronto , 25 Willcocks Street, Toronto, Ontario, CanadaM5S 3B2
                [4 ]Department of Neurobiology Physiology Behavior, University of California , Davis, One Shields Avenue, Davis, CA 95616, USA
                Author notes
                Author for correspondence: Brandy P. Velten e-mail: brandy.velten@ 123456mail.utoronto.ca

                Electronic supplementary material is available online at https://dx.doi.org/10.6084/m9.figshare.c.3576341.

                Article
                rsos160775
                10.1098/rsos.160775
                5180162
                © 2016 The Authors.

                Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

                Product
                Funding
                Funded by: Natural Sciences and Engineering Research Council of Canada http://dx.doi.org/10.13039/501100000038
                Funded by: University of Toronto Scarborough Research Competitiveness Fund
                Funded by: National Science Foundation http://dx.doi.org/10.13039/100000001
                Award ID: ARC-1147289
                Categories
                1001
                202
                Biology (Whole Organism)
                Research Article
                Custom metadata
                November, 2016

                muscle, myosin, migration

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