Biology
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Item The Impact of Planktivory on the Life Histories of Estuarine Crabs(1986) Morgan, Steven G.; Reaka, Marjorie L.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Estuarine crabs commonly display two larval dispersal patterns in which larvae are either exported from or retained within estuaries. Explanations for the disparate dispersal patterns are that larvae differ in their susceptibility to predation, which is greater within the estuary than offshore, or in their physiological tolerances to the large temperature and salinity fluctuations of the estuary. Crab larvae which are exported from the estuary survived better in stressful temperature and salinity combinations than those which are retained, and thus the physiological stress hypothesis was rejected. However, exported larvae were more vulnerable to predation by fishes and invertebrates than were retained larvae. The long spines, large body sizes and behavioral responses of retained crab larvae were more effective at deterring predation by two fishes and eleven invertebrates in the laboratory, than were the short spines and small body sizes of exported larvae. Spines generally were more effective against planktivorous fishes than against invertebrates. Spines operated by effectively increasing the size of the larvae and their unpalatability to fishes. Behavioral observations revealed that fishes repeatedly attacked zoeae, but would quickly learn to avoid the noxious prey. The armor of crab larvae enabled them to survive attacks, and fishes repeatedly attempting to swallow long-spined crab larvae frequently would die. Spines did not assist in the flotation or stabilization of crab larvae. Electivities of the three predominant fishes sampled from the Newport River estuary, North Carolina, also were greater for exported than retained species of crab larvae. Predation by larval and juvenile fishes was greater upstream compared to downstream, and greater diurnally than nocturnally. By hatching on nocturnal high tides, larvae rapidly disperse downstream where the probability of predation diminishes. Semiterrestrial crabs hatch on nocturnal spring tides to prevent stranding in tidal creeks. Thus, the hatching rhythms and dispersal patterns of crabs appear to have evolved in concert to transport larvae into coastal waters where the risk of predation is reduced, or to retain larvae within estuaries depending upon the vulnerability of the larva to predation.Item Branched Chain Amino Acids: Requirements and Antagonism in the Male Broiler Chick(1987) Farran, Mohamad Talal; Thomas, Owen P.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Experiments were conducted to study the effect of feeding the branched-chain amino acids (BCAA), leucine (Leu), isoleucine (Ile) and valine (Val) to 7-21 day old male broiler chicks. Using the central composite rotatable design, the results of response surface regression analysis showed that optimum body weight gain (BWG) and feed conversion values (FC) would be obtained with dietary levels of 1.16, 0.81 and 0.90% for Leu, Ile and Val respectively. Chicks fed a Val deficient diet ad libitum exhibited a ricket-like condition which was characterized by a low Ca content in the bone. The value was 134 as compared to 156 and 172 mg/g dry bone for chicks fed a diet deficient in the three BCAAs and a Val supplemented diet respectively. similar results were obtained when equal amounts of the three diets were given to the birds by using pair feeding and force feeding techniques. Although birds fed the Val deficient diet and those pair fed the BCAA deficient diet had similar BWG, bone measurements (bone ash, dry bone, and bone Ca) were significantly lower (p < 0.05) for the Val deficient group. Serum ca (mg/dl) was not significantly different. Excretion of urinary ca, however, was enhanced by feeding a Val deficient diet as compared to the Val supplemented treatment suggesting that a proper ratio of the BCAAs may be required to form the bone matrix which serves as a base for mineral deposition. Feeding a Val deficient diet significantly (p < 0.05) lowered the protein content of the feathers. The value was 82.7% as compared to 85.0 and 88.0% for all BCAA deficient and Val supplemented diets respectively. Valine deficiency also changed the pattern of feather amino acids by increasing the levels of aspartic acid, glutamic acid, methionine, tyrosine, histidine and lysine. Cysteine level, however, was decreased. High dietary Leu(≥ 3.0%) depressed BWG and FC of ad libitum fed birds. When Ile and Val were simultaneously added to the diet the growth rate and FC were similar to the controls. The ketogenic property of Leu was tested by measuring β-OH-butyrate level in the plasma (mg/1) and found to be nonsignificant.Item Morphology and neuromuscular properties of chelae of decapod crustacean species from temperate and tropical populations(1986) Blundon, Jay Arthur; Vermeij, Gerrat J.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)...Both species of decapods showed no seasonal differences in chela muscle performance. Their ability to function over wide ranges of temperatures is undoubtly essential in their successful latitudinal distribution. The difference in the capacity of these two species to rapidly acclimate to cold temperatures is reflected in their natural habitats. C. sapidus lives in estuaries where large short term temperature fluctuations are common. M. mercenaria, a marine coastal subtidal dweller, lives where temperature fluctuations are smaller.Item Functional and Adaptive Significance of Mobbing and Alarm Calls of the Common Crow (Corvus brachyrhynchos)(1983) Brown, Eleanor D.; Schleidt, Wolfgang M.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)This study is an analysis of the functional and adaptive significance of "caw" calls used by common crows (Corvus brachyrhynchos) in contexts involving danger. Seven tame birds, including three siblings and several birds familiar to the siblings (i.e., within their sight and hearing), were the subjects of playback experiments. Four types of caws associated with danger were played back as test calls: screams, mixed caws, inflected alarm caws, and alert caws. These four test caws were recorded from each of six different individuals (senders) and played back to the experimental subjects (receivers). The vocalizations of the three sibling receivers were tape recorded during playback trials, and three types of response caws were scored: mixed caws, alert caws, and long caws. By counting caws in each 10 s interval during the 1 min before, 20 s during, and 20 s after playback, the following functional interrelationships among cawtypes were found. Mixed caw responses were elicited immediately by, and only by, screams and mixed caws. These caws are used in harassing a predator, and seem to function in part to assemble and coordinate a mobbing group. Alert caw responses were suppressed over the 20 s during which caws were played back for all types of presentations except those of alert caws, but reached a peak just after playback. Alert caws seem to be multifunctional, probably indicating either mildly threatening objects or cessation of danger. Long caw responses were suppressed during the 20 s presentations of all cawtypes, but reached a peak after scream and mixed caw playbacks. Long caws seem to indicate either cessation of danger or continuation of normal activities. By further subdividing numbers of responses on the basis of social familiarity between senders and receivers, the effect of social relationship on responses was examined. The senders were either siblings of, familiar to (heard and seen only from a distance), or unknown to the receivers. The receivers did not respond more to the voices of senders from any particular social category (G goodness-of-fit tests) although the data were not conclusive. The results are discussed in terms of the information encoded in mobbing and alarm calls, the functions of those calls, and the sources of natural selection which may have shaped the evolution of mobbing and alarm vocalizations.Item Probing the Nature of the Voltage-Sensing Mechanism of the Mitochondrial Outer Membrane Channel, VDAC: Initial Kinetic Analysis and Aluminum Chloride-Induced Alterations(1987) Dill, Eleanor Therese; Colombini, Marco; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)VDAC channels are the major permeability pathways through the mitochondrial outer membrane. They exist in a high conducting, "open," state at low potentials and a low conducting, "closed," state at high potentials (>+/- 20mV). The mechanism underlying voltage-dependent behavior is poorly understood. VDAC isolated from Neurospora crassa were studied in planar phospholipid membranes. Aluminum chloride interaction with the protein and analysis of the rates of channel opening and closing were used to probe the mechanism of voltage-dependence. Micromolar amounts of aluminum chloride (>1 uM) decreased the steepness of the voltage-dependence and increased the voltage needed to close half the channels. Open and closed channel conductance levels were essentially unchanged. Neither channel conformation nor ion selectivity were altered. The effective aluminum species is either, or both, aluminate or aluminum hydroxide. The rate constants of channel opening and closing were determined from multi-channel membrane studies. Closure rate constants increased exponentially with increased negative applied voltages, from 0.01/sec at -30 mV to 1.77/sec at -80 mV. Short periods (< 4-6 min) in the open state before closure decreased closure rates, indicating the presence of at least two open states. Opening rates were at least an order of magniture faster than closure rates and had no marked voltage-dependence between -15 mV and -5 mV or +5 mV and +10 mV. Channel closure accounts for 80%, or more, of the voltage-dependence observed in the steady state. Implications of these findings for modeling the action of the channel are discussed. As a result of these studies future models of the VDAC channel and research must consider these new complexities: distinct groups of charges are responsible for voltage-gating and selectivity; the sensor is likely outside the channel proper; channel opening may involve a large dipole; and opening and closing may occur via different molecular pathways.