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  • 1
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    Effects of host diet and thermal state on feeding performance of the flea Xenopsylla ramesis
    The Company of Biologists ; 2012
    In:  Journal of Experimental Biology Vol. 215, No. 9 ( 2012-05-01), p. 1435-1441
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 215, No. 9 ( 2012-05-01), p. 1435-1441
    Abstract: We examined feeding performance of the flea Xenopsylla ramesis on three different hosts: its natural, granivorous, rodent host, Sundevall’s jird (Meriones crassus); the frugivorous Egyptian fruit bat (Rousettus aegyptiacus); and an insectivorous bat, Kuhl’s pipistrelle (Pipistrellus kuhlii). Because these fleas are not known to occur on bats, we hypothesized that the fleas’ feeding performance (i.e. feeding and digestion rates) would be higher when feeding on their natural host than on either of the bats that they do not naturally parasitize. We found that mass-specific blood-meal size of both male and female fleas was significantly lower when feeding on Kuhl’s pipistrelles than on the other two species, but was not different in female fleas feeding on fruit bats or on jirds at all stages of digestion. However, more male fleas achieved higher levels of engorgement if they fed on Sundevall’s jirds than if they fed on Egyptian fruit bats. The fleas digested blood of fruit bats and jirds significantly faster than blood of Kuhl’s pipistrelle. In addition, after a single blood meal, the survival time of fleas fed on normothermic Kuhl’s pipistrelles was significantly shorter than that of fleas fed on Sundevall’s jirds and even lower when male fleas fed on Egyptian fruit bats. Thus, our prediction was partially supported: normothermic Kuhl’s pipistrelles were inferior hosts for fleas compared with Sandevall’s jirds and Egyptian fruit bats. Interestingly, the proportion of engorged fleas that fed on torpid Kuhl’s pipistrelles was significantly higher than the proportion of the fleas that fed on normothermic individuals, indicating that becoming torpid might be a liability, rather than an effective defense against parasites.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.061796
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2012
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  • 2
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    Transient-state mechanisms of wind-induced burrow ventilation
    The Company of Biologists ; 2015
    In:  Journal of Experimental Biology Vol. 218, No. 2 ( 2015-01-15), p. 170-175
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    In: Journal of Experimental Biology, The Company of Biologists, Vol. 218, No. 2 ( 2015-01-15), p. 170-175
    Abstract: Burrows are common animal habitations, yet living in a burrow presents physiological challenges for its inhabitants because the burrow isolates them from sources and sinks for oxygen, carbon dioxide, water vapor and ammonia. Conventionally, the isolation is thought to be overcome by either diffusion gas exchange within the burrow or some means of capturing wind energy to power steady or quasi-steady bulk flows of air through it. Both are examples of what may be called ‘DC’ models, namely steady to quasi-steady flows powered by steady to quasi-steady winds. Natural winds, however, are neither steady nor quasi-steady, but are turbulent, with a considerable portion of the energy contained in so-called ‘AC’ (i.e. unsteady) components, where wind velocity varies chaotically and energy to power gas exchange is stored in some form. Existing DC models of burrow gas exchange do not account for this potentially significant source of energy for ventilation. We present evidence that at least two AC mechanisms operate to ventilate both single-opening burrows (of the Cape skink, Trachylepis capensis) and double-opening model burrows (of Sundevall's jird, Meriones crassus). We propose that consideration of the physiological ecology and evolution of the burrowing habit has been blinkered by the long neglect of AC ventilation.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.110858
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2015
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  • 3
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    Ammonotely in a passerine nectarivore: the influence of renal and post-renal modification on nitrogenous waste product excretion
    The Company of Biologists ; 2002
    In:  Journal of Experimental Biology Vol. 205, No. 12 ( 2002-06-15), p. 1735-1745
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 205, No. 12 ( 2002-06-15), p. 1735-1745
    Abstract: Most aquatic vertebrates are ammonotelic, whereas terrestrial vertebrates are typically uricotelic or ureotelic. However, the principal form of nitrogenous waste product in the urine of an animal may vary, depending on environmental conditions. Anna's hummingbird (Calypte anna) was found to switch from uricotely at high ambient temperature (Ta)to ammonotely at lower Ta, when energy demands and consequent nectar intake rates were high. In extension of this, we hypothesised that nectarivorous birds would switch from uricotely to ammonotely when water intake rates were high or when protein or salt intake rates were low. We examined the influence of water, electrolyte and protein intake and of Ta on the excretion of ammonia, urea and urate (uric acid and its salts) in nectarivorous Palestine sunbirds(Nectarinia osea). The proportion of ammonia in ureteral urine and excreted fluid was not influenced by total water or salt intake or by Ta. Protein intake did not influence nitrogenous waste product concentrations in ureteral urine. However, when protein intake was reduced, the proportion of ammonia in excreted fluid was higher because of the reduced urate concentration. This reduction in urate concentration leads to`apparent' ammonotely. We suggest that ammonotely may not be a unique feature of nectarivorous birds. It could occur in any species in which breakdown of urate in the hindgut allows the uric acid-nitrogen concentration in the excreta to fall below that of the ammonia-nitrogen concentration.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.205.12.1735
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2002
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  • 4
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    Absorption of sugars in the Egyptian fruit bat ( Rousettus aegyptiacus ): a paradox explained
    The Company of Biologists ; 2007
    In:  Journal of Experimental Biology Vol. 210, No. 10 ( 2007-05-15), p. 1726-1734
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 210, No. 10 ( 2007-05-15), p. 1726-1734
    Abstract: Two decades ago D. J. Keegan reported results on Egyptian fruit bats(Rousettus aegyptiacus, Megachiroptera) that were strangely at odds with the prevailing understanding of how glucose is absorbed in the mammalian intestine. Keegan's in vitro tests for glucose transport against a concentration gradient and with phloridzin inhibition in fruit bat intestine were all negative, although he used several different tissue preparations and had positive control results with laboratory rats. Because glucose absorption by fruit bats is nonetheless efficient, Keegan postulated that the rapid glucose absorption from the fruit bat intestine is not through the enterocytes, but must occur via spaces between the cells. Thus, we hypothesized that absorption of water-soluble compounds that are not actively transported would be extensive in these bats, and would decline with increasing molecular mass in accord with sieve-like paracellular absorption. We did not presume from Keegan's studies that there is no Na+-coupled, mediated sugar transport in these bats, and our study was not designed to rule it out, but rather to quantify the level of possible non-mediated absorption. Using a standard pharmacokinetic technique, we fed,or injected intraperitonealy, the metabolically inert carbohydrates l-rhamnose (molecular mass=164 Da) and cellobiose (molecular mass=342 Da), which are absorbed by paracellular uptake, and 3-O-methyl-d-glucose (3OMd-glucose), a d-glucose analog that is absorbed via both mediated(active) and paracellular uptake. As predicted, the bioavailability of paracellular probes declined with increasing molecular mass (rhamnose,62±4%; cellobiose, 22±4%) and was significantly higher in bats than has been reported for rats and other mammals. In addition, fractional absorption of 3OMd-glucose was high (91±2%). We estimated that Egyptian fruit bats rely on passive, paracellular absorption for the majority of their glucose absorption (at least 55% of 3OMd-glucose absorption), much more than in non-flying mammals.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.02766
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2007
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  • 5
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    Allocation of endogenous and dietary protein in the reconstitution of the gastrointestinal tract in migratory blackcaps at stopover sites
    The Company of Biologists ; 2012
    In:  Journal of Experimental Biology Vol. 215, No. 7 ( 2012-04-01), p. 1069-1075
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 215, No. 7 ( 2012-04-01), p. 1069-1075
    Abstract: During migratory flight, the mass of the gastrointestinal tract (GIT) and its associated organs in small birds decreases in size by as much as 40%, compared with the preflight condition because of the catabolism of protein. At stopover sites, birds need 2–3 days to rebuild their GIT so that they can restore body mass and fat reserves to continue migration. The source of protein used to rebuild the GIT may be exogenous (from food ingested) or endogenous (reallocated from other organs) or both. Because the relative contribution of these sources to rebuild the GIT of migratory birds is not yet known, we mimicked in-flight fasting and then re-feeding in two groups of blackcaps (Sylvia atricapilla), a Palearctic migratory passerine. The birds were fed a diet containing either 3% or 20% protein to simulate different refueling scenarios. During re-feeding, birds received known doses of 15N-l-leucine before we measured the isotope concentrations in GIT and associated digestive organs and in locomotory muscles. We then quantified the extent to which blackcaps rebuilt their GIT with endogenous and/or dietary protein while refeeding after a fast. Our results indicate that blackcaps fed the low-protein diet incorporated less exogenous nitrogen into their tissues than birds fed the 20% protein diet. They also allocated relatively more exogenous protein to the GIT than to pectoral muscle than those birds re-fed with the high-protein diet. However, this compensation was not sufficient for birds eating the low-protein diet to rebuild their intestine at the same rate as the birds re-fed the high-protein diet. We concluded that blackcaps must choose stopover sites at which they can maximize protein intake to minimize the time it takes to rebuild their GIT and, thus, resume migration as soon as possible.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.062547
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2012
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  • 6
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    Age at weaning, immunocompetence and ectoparasite performance in a precocial desert rodent
    The Company of Biologists ; 2014
    In:  Journal of Experimental Biology
    Details
    In: Journal of Experimental Biology, The Company of Biologists
    Abstract: We studied the effects of early weaning on immunocompetence and parasite resistance in a precocial rodent Acomys cahirinus. We hypothesized that if parasite resistance is energetically expensive and nutritional and immunological support from mothers are necessary for the long-term health of offspring, then early weaned animals would be immunologically weaker and less able to defend themselves against parasites than later weaned animals. We weaned pups at 14, 21, or 28 d after birth and assessed their immunocompetence and resistance against fleas Parapulex chephrenis when they attained adulthood. Immunocompetence was assessed using leukocyte concentrations (LC) and a phytohaemagglutinin injection assay (PHA test). To estimate resistance against fleas, we measured performance of fleas via the number of produced eggs and duration of development and resistance to starvation of the flea offspring. We found a significant positive effect of weaning age on the PHA response but not on LC. The effect of age at weaning on flea egg production was manifested in male but not female hosts, with egg production being higher if a host was weaned at 14 than at 28 d. Weaning age of the host did not affect either duration of development or resistance to starvation of fleas produced by mothers fed on these hosts. We concluded that even in relatively precocial mammals, weaning age is an important indicator of future immunological responses and the ability of an animal to resist parasite infestations. Hosts weaned at an earlier age make easier, less-resistant targets for parasite infestations than hosts weaned later in life.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.106005
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2014
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  • 7
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    Heterothermy in small, migrating passerine birds during stopover: use of hypothermia at rest accelerates fuel accumulation
    The Company of Biologists ; 2009
    In:  Journal of Experimental Biology Vol. 212, No. 19 ( 2009-10-01), p. 3068-3075
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 212, No. 19 ( 2009-10-01), p. 3068-3075
    Abstract: For small endothermic animals, heterothermy serves as an energy-saving mechanism for survival in challenging environments, but it may also accelerate fat accumulation in individuals preparing for fuel-demanding activities. This is the first study to demonstrate adaptive hypothermic responses in migrating passerines. While monitoring body temperature (Tb) of eight blackcaps (Sylvia atricapilla) by radiotelemetry, we found that during daytime Tb=42.5±0.4°C (mean ±s.d.); at night Tb decreased to a minimum between 33 and 40°C. We determined the lower limit for normothermy at 37.4°C and found that on 12 out of 34 bird-nights of observations under semi-natural conditions blackcaps reduced their Tb below normothermic resting levels with minimum values of 33 and 34.5°C compared with rest-phase normothermic Tb of 38.8±0.8°C. In birds of body mass (mb) & lt;16.3 g, minimum Tb at night correlated with the individual's mb (r=0.67, P & lt;0.01, N=17),but this was not the case in birds with mb & gt;16.3 g. Minimum nocturnal Tb did not correlate with night-time air temperature (Ta). Measurements of metabolic rate in birds subjected to a Ta of 15°C showed that hypothermia of this magnitude can lead to a reduction of some 30% in energy expenditure compared with birds remaining normothermic. Our data suggest that by reducing the Tb–Ta gradient, blackcaps accelerate their rate of fuel accumulation at a stopover. When body energy reserves are low blackcaps may achieve this reduction by entering hypothermia. Since hypothermia, as seen in blackcaps, may lead to significant energy savings and facilitate body mass gain, we predict that it is common among small migrating passerines.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.033001
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2009
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  • 8
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    Respiratory water loss in free-flying pigeons
    The Company of Biologists ; 2001
    In:  Journal of Experimental Biology Vol. 204, No. 21 ( 2001-11-01), p. 3803-3814
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 204, No. 21 ( 2001-11-01), p. 3803-3814
    Abstract: We assessed respiratory and cutaneous water loss in trained tippler pigeons (Columba livia) both at rest and in free flight. In resting pigeons, exhaled air temperature Tex increased with ambient air temperature Ta (Tex=16.3+0.705Ta) between 15°C and 30°C, while tidal volume VT (VT=4.7±1.0 ml, mean ± s.d. at standard temperature and pressure dry) and breathing frequency fR (fR=0.46±0.06 breaths s–1) were independent of Ta. Respiratory water loss, RWL, was constant over the range of Ta (RWL=1.2±0.4 mg g–1 h–1) used. In flying pigeons, Tex increased with Ta (Tex=25.8+0.34Ta), while fR was independent of Ta (fR=5.6±1.4 breaths s–1) between 8.8°C and 27°C. Breathing frequency varied intermittently between 2 and 8 breaths s–1 during flight and was not always synchronized with wing-beat frequency. RWL was independent of air temperature (RWL=9.2±2.9 mg g–1 h–1), but decreased with increasing inspired air water vapor density (ρin) (RWL=12.5–0.362ρin), whereas cutaneous water loss, CWL, increased with air temperature (CWL=10.122+0.898Ta), but was independent of ρin. RWL was 25.7–32.2 %, while CWL was 67.8–74.3 % of the total evaporative water loss. The data indicate that pigeons have more efficient countercurrent heat exchange in their anterior respiratory passages when at rest than in flight, allowing them to recover more water at rest at lower air temperatures. When evaporative water loss increases in flight, especially at high Ta, the major component is cutaneous rather than respiratory, possibly brought about by reducing the skin water vapor diffusion resistance. Because of the tight restrictions imposed by gas exchange in flight, the amount of water potentially lost through respiration is limited.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.204.21.3803
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2001
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  • 9
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    Renal function in Palestine sunbirds: elimination of excess water does not constrain energy intake
    The Company of Biologists ; 2004
    In:  Journal of Experimental Biology Vol. 207, No. 19 ( 2004-09-01), p. 3391-3398
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 207, No. 19 ( 2004-09-01), p. 3391-3398
    Abstract: Although the renal responses of birds to dehydration have received significant attention, the consequences of ingesting and processing large quantities of water have been less studied. Nectar-feeding birds must often deal with exceptionally high water intake rates in order to meet their high mass-specific energy demands. Birds that ingest large volumes of water may either eliminate excess water in the kidney or regulate the volume of water absorbed in the gastrointestinal tract. Because water absorption in the gastrointestinal tract of Palestine sunbirds (Nectarinia osea)decreases with increasing water ingestion rate, we predicted that glomerular filtration rate (GFR) in these birds would not be unusually high in spite of large ingested water loads. When feeding on dilute sucrose solutions, sunbirds ingested between 4 and 6 times their body mass in nectar per day, yet they were able to compensate for varying nectar energy density and increased thermoregulatory energy demands with no apparent difficulty. GFR was lower than predicted (1976.22±91.95 μl h-1), and was not exceptionally sensitive to water loading. Plasma glucose concentrations were high, and varied 1.8-fold between fasted (16.08± 0.75 mmol l-1) and fed (28.18±0.68 mmol l-1) sunbirds, but because GFR was low, glucose filtered load also remained relatively low. Essentially the entire glucose filtered load (98%) was recovered by the kidney. Renal fractional water reabsorption (FWR) decreased from 0.98 to 0.64 with increasing water intake. The ability of Palestine sunbirds to reduce the absorption of ingested water in the gastrointestinal tract may resolve the potential conflict between filtering a large excess of absorbed water in the kidney and simultaneously retaining filtered metabolites.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.01169
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2004
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  • 10
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    Waking to drink: rates of evaporative water loss determine arousal frequency in hibernating bats
    The Company of Biologists ; 2013
    In:  Journal of Experimental Biology Vol. 216, No. 4 ( 2013-02-15), p. 573-577
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 216, No. 4 ( 2013-02-15), p. 573-577
    Abstract: Bats hibernate to cope with low ambient temperatures (Ta) and low food availability during winter. However, hibernation is frequently interrupted by arousals, when bats increase body temperature (Tb) and metabolic rate (MR) to normothermic levels. Arousals account for more than 85% of a bat’s winter energy expenditure. This has been associated with variation in Tb, Ta or both, leading to a single testable prediction, i.e. that torpor bout length (TBL) is negatively correlated with Ta and Tb. Ta and Tb were both found to be correlated with TBL, but correlations alone cannot establish a causal link between arousal and Tb or Ta. Because hydration state has also been implicated in arousals from hibernation, we hypothesized that water loss during hibernation creates the need in bats to arouse to drink. We measured TBL of bats (Pipistrellus kuhlii) at the same Ta but under different conditions of humidity, and found an inverse relationship between TBL and total evaporative water loss, independent of metabolic rate, which directly supports the hypothesis that hydration state is a cue to arousal in bats.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.078790
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2013
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