Physiological zoology最新文献

The role of steroids in locomotor performance and growth was examined in free-living lizards. Male northern fence lizards (Sceloporus undulatus hyacinthinus) with experimentally elevated plasma testosterone concentrations had greater sprint speed (+24%) and burst stamina (+17%) than sham-implanted males after 14-23 d in the field. This enhanced performance was associated with significant energetic costs, as the testosterone-implanted lizards had reduced growth rates, and, in a companion experiment, field-active testosterone-implanted lizards had smaller fat-body masses than controls after just 3-4 wk. These results suggest that, in addition to influencing a variety of behavioral and morphological traits, testosterone may play an important role in the regulation of locomotor performance. Also, natural levels of locomotor performance may be constrained, in part, by associated costs of elevated plasma testosterone concentrations.

We studied the effects of substrate moisture and flooding on the arboreal eggs of Chirixalus eiffingeri and determined the possible causes of egg mortality. Eggs appear highly permeable to water vapor, losing 16.24% and 38.38% of initial egg mass in 2 h at 90% and 45% relative humidity, respectively. Eggs that experienced positive water uptake developed faster, hatched earlier with larger hatchlings, and had greater hatching success than eggs that experienced negligible or negative water uptake. The hatching success of eggs that were submerged in water in bamboo stumps was significantly lower than that of eggs that were incubated on the water surface and was significantly correlated with the water PO2. In some bamboo stumps, we observed chironomid and tipulid larvae preying on submerged eggs. A dilution of water collected from bamboo stumps did not increase the hatching success of eggs. The water PO2 of bamboo stumps in the field was 67.4+/-18.8 mmHg, and the degree of hypoxia of water in each bamboo stump was correlated with the turbidity. Our findings demonstrated that the vertical distribution of C. eiffingeri eggs on walls of bamboo stumps significantly influenced the growth, development, and survival of embryos. Eggs deposited too far from the water may become desiccated, while eggs deposited too close to the water may become submerged and die of hypoxia or predation by insect larvae.

Adult penguins and their chicks differ considerably in their apparent body insulation. The chicks are covered in down, whereas the adults have the short, hard body feathers characteristic of the family, so mechanisms of heat loss may vary considerably between the two groups. We examined radiative heat loss by measuring body surface temperatures of gentoo penguins (Pygoscelis papua) in Antarctica. At the time the birds were considered to be in their thermoneutral zone, and there was little or no wind. Measurements of infrared emission were made on breeding adults and in large downy, and thermally independent, chicks in relation to environmental temperature. All 28 external body surface sites measured were positively correlated with ambient temperature, although there was considerable intersite variability in the relationship between site temperature and ambient temperature. Foot temperature increased most rapidly per degree ambient temperature increase, followed by the flippers, followed by the trunk. This pattern was particularly pronounced in the chicks, indicating that the exceptional heat-loss capacities of the feet may counteract for the reduced capacity of the flippers. Net heat transfer by radiation was examined using Stefan-Boltzmann's law and preliminary data on the surface area of a gentoo penguin body. This showed that between ground temperatures of 5 degrees and 15 degrees C overall heat transfer remains essentially constant, although radiative heat loss from the trunk decreases, this being counteracted by increasing heat transfer from the flippers and feet. Over the same temperature range the specific radiation heat transfer of the feet increased approximately 100 times faster per degree ambient temperature increase than did that of the flippers. This and the bimodality in foot temperature found in the study birds even under constant ambient temperatures indicate that within the thermoneutral zone heat loss by radiation in gentoo penguins is primarily executed using the feet, through which the blood circulates in pulses.

Numerous studies have examined sexual dimorphism in the morphology and behavior of vertebrates; very few, however, have explicitly investigated the possibility of gender differences in physiological performance, despite the observations of such differences in humans. In this study, I investigated physiological sexual dimorphism in the lizard genus Cnemidophorus by measuring five whole-animal traits, all of which are likely to influence fitness in these species: burst speed, endurance, maximal exertion capacity, standard metabolic rate, and evaporative water loss rate. Because at least some of these traits are known to be strongly influenced by body size, I tested for dimorphism using both absolute and size-corrected trait values. An examination of six Cnemidophorus species and subspecies revealed a strong trend toward higher absolute trait values in males for all variables except endurance. Most of the dimorphism in standard metabolic rate and evaporative water loss rate could be explained by differences in body mass between males and females; for the locomotor traits, however, body size explained only a small fraction of the overall sexual dimorphism. The portion of trait differences not explained by body size was likely due to gender differences in physiology, such as differences in relative muscularity and fat content.

Previous studies on crustacea have demonstrated significant diurnal rhythms in blood glucose. However, glucose concentration in the blood of food-deprived Penaeus monodon, held in indoor or outdoor tanks, did not exhibit a diurnal rhythm under photoperiods of 8 h light and 16 h darkness (8L: 16D) or under a 13.5L: 9.5D photoperiod, with simulated or natural full moon conditions. Prawns held on photoperiods of constant light, 20L : 4D, 16L : 8D, 12L : 12D, 8L : 16D, 4L : 20D, or continuous darkness did not have significantly different mean blood glucose levels. Mean blood glucose levels varied between 0.77 and 1.39 mmol/L, depending on conditions. Pronounced and significant increases in blood glucose levels occurred within 20 min of feeding, with peak levels after 100 min. The rise in blood glucose level observed after feeding was independent of the eyestalks, and hence putative crustacean hyperglycaemic hormone, and was not from endogenous carbohydrate stores. Under appropriately controlled conditions, blood glucose concentrations can be used as an index of nutritional status in penaeid prawns.

Trimethylamine oxide (TMAO) and urea levels in the blood of rainbow smelt, Osmerus mordax, were previously shown to increase dramatically in winter, but the means by which these osmolytes are acquired has remained unclear. In this study, I show that the smelt can synthesize TMAO via liver trimethylamine oxidase activity and thus are not completely dependent on a dietary source of TMAO. Cold-acclimatized Pacific herring, Clupea harengus, were also found to have high levels of TMAO in the blood, while individuals from a temperate-water population of herring did not. Herring also had liver TMA oxidase activity, which appeared to be due to a flavin-containing monooxygenase. In both species, TMA oxidase activity did not appear to be strongly affected by temperature. TMAO data were obtained for three other northern species (Macrozoarces americanus, Eleginus gracilis, and Platichthys stellatus), and these results, together with previously reported data, suggest that TMA oxidase activity is a necessary condition for high levels of TMAO in the blood. In the smelt, urea appears to be synthesized via uricolysis and also through the action of arginase on dietary arginine, while the ornithine urea cycle appears to be nonfunctional. There was no relation among several species of northern fishes between levels of urea in the blood and levels of uricase or arginase activity. Together, these results provide further evidence of the importance of TMAO and urea in some cold water fishes, demonstrate that the synthetic machinery for these osmolytes is present in the liver, and suggest that the elevated levels in response to cold may be due to conservation rather than to increased production.

Northern elephant seals, Mirounga angustirostris, fast completely from food and water during lactation. Previous investigations of maternal investment suggested physiological constraints on the level of energy expenditure during lactation. In this study, two components of phocid fasting physiology, protein sparing and reduced glomerular filtration rate, were examined for effects of changing body composition and lactation duration. Protein catabolism was estimated from 14C-urea turnover in five mid- and five late-lactation females. Body composition was determined by using an ultrasound scanner to measure blubber depth coupled with morphometrics. Glomerular filtration rate was measured in five females at mid- and late-lactation using plasma clearance of 3H-inulin. Protein catabolism increased significantly between measurements. The contribution of protein to metabolism varied with body composition and lactation duration. Mass-proportional glomerular filtration rate increased significantly between measurements. These data suggest that conflicting metabolic demands of lactation and fasting might constrain the duration and magnitude of maternal investment in northern elephant seals.

We used nestling house sparrows (Passer domesticus) under laboratory conditions to test for modulation of digestive efficiencies during periods of low and high food intake and tested the hypothesis that nestlings would exhibit compensatory changes in digestive efficiency following a period of food restriction. During the low intake period, nestlings were held at constant body mass for 48 h beginning on either day 3 or day 6 of life by feeding them at 50% of control rations. After 48 h of food restriction, nestlings were fed as much as they could consume, allowing the nestlings restricted at day 6 (early restriction not assessed) to consume 14% more food than control nestlings. For nestlings restricted at day 6 apparent dry mass assimilation of the entire diet was found to be 5% and 8% lower during food restriction and realimentation, respectively, compared with control nestlings that were not under- or overfed. There were no significant differences in radiolabeled starch assimilation efficiencies between control and restricted nestlings. Starch assimilation efficiencies remained constant from 3 d of age onward in control nestlings. Total starch extracted was lower during food restriction but reached a rate similar to that of control nestlings during the realimentation period. Passage times (time of first defecation, mean retention time, and mode passage time) measured with an indigestible marker were longer during food restriction and shorter during realimentation, relative to control nestlings. During realimentation there was no difference in intestinal rates of hydrolysis or mediated uptake of L-leucine compared with control nestlings. The main effect of changing food intake was apparently to alter flow rate, and hence retention time, causing slight changes in digestive efficiency. Thus, nestlings did not exhibit compensatory changes in digestion rates as implied by the hypothesis. Our finding of a lower dry mass assimilation efficiency and similar total starch assimilation during realimentation (relative to controls) helps explain why nestling house sparrows do not display compensatory growth, despite higher food intake. Our results indicate that the gut has little spare capacity to deal with increased food intake during growth following food restriction.