Biology

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1993 - 19993

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Start date: 1990End date: 1999

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    STUDIES ON THE GNRH/GTH SYSTEM OF FEMALE STRIPED BASS (Marone saxatilis): EFFECTS OF GNRH AGONJST THERAPY AND COMPARISON OF REPRODUCTIVE ENDOCRINE PARAMETERS BETWEEN WILD AND CAPTIVE FISH
    (1999) Steven, Colin R.; Zohar, Yonathan; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    In the striped bass (Marone saxatilis), and many other commercially important fish species, captivity results in an inability to complete final oocyte maturation (FOM), ovu lation , and spawning. We hypothesize that this effect is mediated by a disruption of the hypothalamo-pituitary-gonadal (HPG) axis at the level of the gonadotropin -releasing hormones (GnRHs). To confirm this hypothesis research was conducted focused on three objectives: First, to complement the battery of assays previously developed for analysis of the GnRH/GtH system in striped bass, an RNAse protection assay was developed to measure specific expression of the three forms of GnRH in striped bass (salmon GnRH, chicken GnRH-If and seabream GnRH). Secondly, effects of GnRH agonist-induced ovulation on the HPG axis of captive striped bass was examined by comparison of several reproductive endocrine parameters between females sampled at four stages of oocyte development. Finally, differences were examined between the reproductive endocrine status of wild and captive female striped bass. We conclude that sbGnRH is the most important form for the preovulatory release of pituitary GtH-II in striped bass. We suggest that captive females synthesize levels of GnRH mRNA that are comparable to their wild counterparts, however fail to release adequate quantities of bioactive GnRH within the pituitary to stimulate completion of FOM. This data may indicate that regulation of sbGnRH in striped bass occurs via post-transcriptional/ translational mechanisms. Furthermore, the presence of salmon GnRH in the pituitaries of captive fema les may be indicative of a possible role for salmon GnRH in the regulation of FOM.
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    Production and energetics of Atlantic menhaden in Chesapeake Bay
    (1993) Rippetoe, Thomas Hunt; Brandt, Stephen B.; Marine-Estuarine-Environmental Sciences Program; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
    Laboratory experiments were conducted to examine the effects of temperature and prey type on maximum consumption, absorption efficiency and gastric evacuation rates of age 0 Atlantic menhaden Brevoortia tyrannus. Maximum consumption reached a peak or asymptote between 25 and 29°C. Temperature had no effect on absorption efficiency, but gastric evacuations rates increased with increasing temperatures. Artemia sp. nauplii were absorbed more efficiently than the diatom Ditylum brightwelli. Prey type had no effect on gastric evacuation rates at temperatures below 25°C but D. brightwelli was evacuated faster than Artemia sp. nauplii at 28°C. Field estimates of daily ration based on stomach content analyses for age 0 menhaden were 5.5% of dry body weight (3.6% wet weight) in June and 3.6% of dry body weight (3.0% wet weight) in August. Most prey in menhaden stomachs were dinoflagellates, diatoms and a mixture of amorphic phytoplankton and detritus. Less than 1% of total biomass in menhaden stomachs was copepods. A diurnal feeding periodicity was apparent with peaks in stomach contents occurring around dusk. A bioenergetics model was developed for age 0 menhaden in mid-Chesapeake Bay. The model incorporated temperature and weight-specific parameters for consumption and respiration and site-specific parameters for growth, diet, energy density of predator and prey and water temperatures. Model estimates of population consumption and production were sensitive to assumptions about annual mortality rates. Daily population consumption peaked in September which coincided with the second annual peak in primary productivity typical of mid-Chesapeake Bay. Daily production peaked from mid-August through September. Model results showed that in 1990 menhaden population consumption would have removed <5% of primary production in mid-Chesapeake Bay from June through October.
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    BEHAVIORAL ECOLOGY OF JUVENILE PALILA (Loxioides bailleui): FORAGING DEVELOPMENT, SOCIAL DYNAMICS, AND HELPING BEHAVIOR
    (1998) Miller, Linda Joyce; Gill, Douglas E.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
    The purpose of this study was to systematically document helping development of foraging in juvenile Palila, an endangered Hawaiian honeycreeper found only on Mauna Kea on the island of Hawaii. Though incidental observations of helpers-at-the-nest have been made, intensive nest monitoring revealed that 30 to 50% of nests had one extra after-second-year male provisioning food to the nestling(s). Helping at the fledgling stage was also confirmed. Radiotracking revealed information regarding foraging development and movement patterns of juveniles. Adult males provided one-on-one food supplementation and foraging instruction to young for three to four months after fledging. Particular benchmarks in the development of foraging skills in juveniles were identified. Juvenile survival may be a factor limiting the Palila population. This investigation constitutes the first detailed study of a juvenile Hawaiian forest bird, and thus, may serve as model for understanding the ecology of other species.