Physiological zoology最新文献

Numerous studies have demonstrated how the performance physiology of fish may change when they are acclimated to designated laboratory temperatures, but few researchers have examined naturally occurring seasonal effects on several physiological parameters associated with swimming performance. Using field-acclimatized smallmouth buffalo (Ictiobus bubalus) collected each season, we report significant seasonal effects in the following variables: critical swimming speed (modified), metabolic rate (standard, active, and scope for activity), and swimming efficiency (total and net cost of transport). Underlying seasonal changes in performance was the reproductive cycle of buffalo, particularly the period of fall gonadal recrudescence. Compared with spring, fall buffalo had a significantly lower mean critical swimming speed (72%) and lower active metabolic rate (53%), even when tested at similar temperatures. During spring, buffalo had a high mean critical swimming speed and low net cost of transport in comparison with other seasons. Buffalo are known to participate in a spring migration and spawning that may require the increased performance and efficiency observed during that season. In addition, significant sex effects were detected in winter measurements of standard metabolic rate and net cost of transport, with females the more efficient swimmers.

California grunion, Leuresthes tenuis (Osteichthyes: Atherinidae), leave the ocean to spawn in the sand following extreme high tides in summer. Eggs develop out of water and are able to hatch within 9-13 d, the primary hatching period. Eggs hatch on immersion and agitation by waves at the next extreme high-tide series. However, if the waves do not reach them and hatching is not induced, eggs remain viable in the sand for several weeks. During this period, grunion eggs will delay hatching, but will hatch at any time if immersed and agitated in seawater. Egg metabolism during embryonic development was measured by aerial respirometry. Metabolism increased linearly until the first date at which eggs were able to hatch. At that time, metabolic rate stabilized and remained constant for two additional weeks of embryonic incubation. Larvae induced to hatch after different durations of incubation within this period were not significantly different in length; however, the amount of oil contained in the yolk decreased linearly during the delayed hatching period. We suggest that the increase in grunion egg metabolism during the time to primary hatching capability, and the steady, high metabolic rate throughout the delayed hatching period, permit reproduction in the unique niche of these marine eggs. These semiterrestrial anamniotic eggs develop quickly and remain continuously ready to hatch over an extended period in response to an environmentally dependent and somewhat unpredictable embryonic timetable.

The primary energy source for migration is fat, but nonfat body components can vary in concert with lipid stores in some migrants. The goals of this study were (1) to validate for a small Old World warbler (the blackcap, Sylvia atricapilla) non-destructive methods to measure lean and fat mass, (2) to quantify the relative contribution of lean mass to body-mass change of migrants, and (3) to ascertain what lean tissues might be involved. Using total-body electrical conductivity and dilution space of isotope-labeled water, we measured lean and fat mass with precision of 3%-4% and 10%-15%, respectively. In newly arrived migrants with apparently similar structural size (tarsus length), there was a significant positive correlation between lean mass and fat mass; 37% of each unit change was lean mass and 63% fat. Captive blackcaps, fed ad lib. for 7 d, gained body mass, with 40% being lean mass. When captives were fasted 1.5-3 d, both body mass and lean mass declined; lean mass accounted for 42% of body mass lost. In fasted birds, the masses of liver, stomach, and small intestine declined and accounted for 44% of the total lean mass decline, a disproportionate amount considering that these organs make up only 11% of a blackcap's lean mass. In freshly captured blackcaps, organ masses were positively correlated with lean mass minus the organ masses, suggesting that these organs are a source of lean mass catabolized by migrants. We conclude that migrants' need for protein to rebuild lean mass during stopover could constrain diet selection and require increased foraging time, thus slowing mass gain and lengthening overall migration time. Also, stopover time may be lengthened if time is required to rebuild atrophied organs that are important in food digestion and assimilation.

The ability of West Indian manatees (Trichechus manatus latirostris and Trichechus manatus manatus) to inhabit both freshwater and marine habitats presents an interesting model to study osmoregulation in sirenians. Blood samples were analyzed from manatees held in fresh- and saltwater and from wild animals captured in fresh-, brackish, and saltwater for concentrations of aldosterone, arginine vasopressin, plasma renin activity, Na+, K+, Cl-, and osmolality. Two separate experiments were also conducted on captive animals to evaluate osmoregulatory responses to acute saltwater exposure and freshwater deprivation. Spurious differences were observed in plasma electrolyte and osmolality among the captive and wild groups. Wild brackish water animals exhibited the highest vasopressin concentrations, while wild freshwater manatees had the highest aldosterone levels. A significant correlation between mean vasopressin and osmolality was demonstrated for captive and wild animals. When freshwater animals were acutely exposed to saltwater, osmolality, Na+, and Cl- increased 5.5%, 8.0%, and 14%, respectively, while aldosterone decreased 82.6%. Saltwater animals deprived of freshwater exhibited an almost twofold increase in aldosterone during the deprivation period and a fourfold decrease when freshwater was again provided. Within this group, osmolality increased significantly by 3.4% over the course of the study; however, electrolytes did not change. The lack of consistent differences in electrolyte and osmolality among wild and captive groups suggests that manatees are good osmoregulators regardless of the environment. The high aldosterone levels in wild freshwater animals may indicate a need to conserve Na+, while the high vasopressin levels in wild brackish-water manatees suggest an antidiuretic state to conserve water. Vasopressin levels appear to be osmotically mediated in manatees as in other mammals.

Energy allocation for maternal maintenance and milk production was examined in lactating hispid cotton rats (Sigmodon hispidus) supporting three to seven offspring at 10 degrees or 24 degrees C. Lactating mothers obtained most of their energy from dietary intake (ca. 90%), and the remainder was withdrawn from maternal stores. There was no indication that a central limit to maternal energy assimilation constrained lactational performance. Maternal energy assimilation increased with a larger litter size (a higher production cost) and a decline in ambient temperature (a higher thermoregulatory cost) during lactation, without reaching an apparent limit. Further, there was no evidence of competitive energy allocation, which might occur if maternal energy assimilation were limited. Hence, increases in maternal thermoregulatory expenditure during lactation did not decrease the energy allocation for milk production. Lactating mothers had a capacity to increase milk production. Nonetheless, the milk flow did not fully satisfy the energy requirements of dependent offspring in larger litters or at the lower ambient temperature (growth rates of offspring declined in both cases). Local physiological constraints and behavioral effects appear to limit maternal allocation during lactation. Constraints to allocation may be favored by selection because they reduce maternal risk or reproductive cost.

Since a decline in temperature decreases aerobic capacity and slows the kinetics of exercise-to-rest transitions in ectotherms, we manipulated body temperature to better understand the performance limits of intermittent locomotion. Distance capacity (i.e., the total distance traveled before fatigue) of the ghost crab, Ocypode quadrata, was determined during acute exposure to 15 degrees C inside a treadmill-respirometer. Instead of exacerbating the near-paralyzing effects of low body temperature resulting from the frequent transitions, intermittent locomotion allowed animals to exceed the performance limits measured during steady-state locomotion. At low temperature, distance capacity for continuous locomotion at 0.04 m s(-1) (83% maximum aerobic speed) was 60 m. When 30 s of exercise at 0.08 m s(-1) (166% maximum aerobic speed) was alternated with 30 s of rest, distance capacity increased to 271 m, 4.5-fold greater than continuous locomotion at the same average speed (83% maximum aerobic speed). A 30-s pause following a 30-s exercise period was sufficient for maintaining low lactate concentrations in muscle and for partial resynthesis of arginine phosphate. A greater dependency on nonoxidative metabolism due to slowed oxygen uptake kinetics at low temperature resulted in a decreased duration of the critical exercise period, which increased performance relative to that measured at higher temperatures (30 s at 15 degrees C vs. 120 s at 24 degrees C). Despite the ghost crab's limited aerobic capacity at 15 degrees C, distance capacity during intermittent locomotion at low temperature can be comparable to that of a crab moving continuously at a body temperature 10 degrees C warmer. While endurance capacity is generally correlated with maximum aerobic speed, we have demonstrated that both locomotor behavior and body temperature must be considered when characterizing performance limits.

This study examined daily and seasonal activity and thermoregulatory behaviour of the sleepy lizard, Tiliqua rugosa, a large, diurnally active temperate-dwelling Australian lizard, in the field and laboratory. Activity temperatures in the field were compared with those selected by lizards in laboratory thermal gradients in order to assess the extent to which endogenous versus exogenous factors contribute to seasonal variations in thermoregulatory behaviour. In the field, lizards are most active in late winter-spring (August-November), during which their activity varies from mostly unimodal on days of mild temperature to bimodal on hot days. In late spring-summer (November-January), activity is largely restricted to early morning, and at all other seasons sleepy lizards are rarely active. The winter-spring activity of sleepy lizards is constrained by low environmental temperatures, as lizards at these seasons have low body temperatures in the field but higher temperatures in laboratory thermal gradients. The lower temperatures selected in the laboratory in the summer-autumn months suggest the avoidance of high ambient temperatures and general inactivity in the field at these times. Thermal selection in the laboratory at the eight times of year tested showed that the phase of the minimum and maximum temperature selected and the amplitude of the rhythm of temperature selected varied continuously with the time of year. These daily and seasonal shifts in thermoregulatory behaviour may be regulated by endogenous physiological mechanisms coupled with seasonal ecological constraints such as food availability.

We manipulated diet quality, food availability, and ambient temperature to investigate the role of these variables in fat deposition by growing prairie voles (Microtus ochrogaster) and fat use by adult voles. Exposure to either 5 degrees C or a high-fiber diet reduced fat deposition by growing voles and also reduced growth as measured by body length. Adult voles on the high-fiber diet reduced fat content, but exposure to 5 degrees C had no effect on body composition. Both the high-fiber diet and exposure to 5 degrees C caused increased food intake and reduced diet digestibility for adult voles. Restricting access to food resulted in reduced lipid mass of all adult voles and reduced fat-free mass of those held at 5 degrees C. When faced with poor food quality or cold ambient temperature, voles will increase food intake rather than catabolize lipid tissue. When food availability is limited, however, voles will use fat stores to meet the balance of their energy requirements.

In order to evaluate the normal (fed conditions) substrate utilization rates of rainbow trout (Oncorhynchus mykiss) brain, CO2 production from glucose, lactate, and beta-hydroxybutyrate was tested in pooled brains. Oxidation rates, as well as the capacity for metabolism of carbohydrate and ketone bodies, were also evaluated in brain of rainbow trout that were food-deprived for 14 d. Under normal (fed) conditions, rainbow trout brain oxidized glucose and lactate at rates higher than those described for mammals; oxidation rates of beta-hydroxybutyrate were lower in rainbow trout brain than those observed for lactate and glucose, and also lower than those described for mammals. Under food-deprivation conditions, glucose and lactate oxidation rates decreased in brains, suggesting the existence of brain metabolic depression, and beta-hydroxybutyrate oxidation rates sharply increased, suggesting increased utilization of ketone bodies.