Food restriction, ionizing radiation, and natural selection

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 175:109-119 (1998) - doi:10.3354/meps175109 Moulting and growth of the early stages of two species of Antarctic calanoid copepod in relation to differences in food supply Rachael S. Shreeve*, Peter Ward British Antarctic Survey, Natural Environment Research Council, Madingley Road, Cambridge CB3 OET, United Kingdom *E-mail: rssh@pcmail.nerc-bas.ac.uk ABSTRACT: Instantaneous measurements of moulting and growth of the early copepodite stages of 2 species of Antarctic copepod, Rhincalanus gigas and Calanoides acutus, were made at 4 regions around South Georgia during austral summer 1996/1997. Sea surface temperature was ~3°C across the study area whereas chlorophyll a concentrations were considerably higher towards the western end of the island. Despite this, moulting rate experiments showed that stage durations of both species were invariably short with no significant regional differences. Stage durations of R. gigas CI, CII and CIII averaged 9, 28 and 15 d respectively, and those of CII, CIII and CIV C. acutus were 4, 7, and 16 d respectively. Daily mass-specific growth rates were lower and less variable in R. gigas (mean 0.05 d-1) than in C. acutus (mean 0.14 d-1), and showed no measurable regional differences. Those for C. acutus however, were higher off-shelf at the western end of the island where the copepodites were heavier than elsewhere. In addition to variations in concentration of chlorophyll a, qualitative differences in the microplankton food supply may also have influenced growth rates. Large diatoms were far more abundant off-shelf at the western end of the island compared to elsewhere, where micro-flagellates and small diatoms dominated. It is suggested that the more opportunistic feeding mode of R. gigas gave stability to its growth rate, whereas C. acutus, which is predominantly herbivorous, was affected by the fluctuations in phytoplankton concentrations and species composition. Moulting occurred within a narrow range of carbon and dry mass for both species, although this range varied between stations. KEY WORDS: Rhincalanus gigas · Calanoides acutus · Moulting rates · Growth · Production · Southern Ocean · South Georgia Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 175. Publication date: December 17, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Non-invasive assessment of metabolic responses to food restriction using urinary triiodothyronine and cortisol measurement in macaques

Calorie Restriction— the SIR2 Connection

Food resources play an important role in the regulation of animals' physiology and behavior. We investigated the effect of short-term food restriction on metabolic thermogenesis of Chinese bulbuls (Pycnonotus sinensis) by measuring changes in body mass, body fat, basic metabolic rate (BMR), and organ mass of wild-caught Chinese bulbuls from Wenzhou, China. Short-term food restriction induced a significant decrease in body mass and body fat but body mass returned to normal levels soon after food was no longer restricted. Food restriction caused a significant reduction in BMR after 7 days (P<0.05), which returned to normal levels after food restriction ceased. Log total BMR was positively correlated with log body mass (r(2)=0.126, P<0.05). The dry masses of livers and the digestive tract were higher in birds that had been subject to temporary food restriction than in control birds and those subject to continual food restriction (P<0.001 and P<0.05, respectively). There was also significant differences in the dry mass of the lungs (P<0.05), heart (P<0.01), and spleen (P<0.05) in birds subject to short-term food restriction compared to control birds and those subject to continual food restriction. BMR was positively correlated with body and organ (heart, kidney and stomach) mass. These results suggest that the Chinese bulbul adjusts to restricted food availability by utilizing its energy reserves, lowering its BMR and changing the weight of various internal organs so as to balance total energy requirements. These may all be survival strategies that allow birds to cope with unpredictable variation in food abundance.

Population Regulation, Convergence, and Cannibalism in Notonecta (Hemiptera)

SUMMARYIn spite of a considerable literature on fruit‐eating, the general evolutionary implications of fruit as a source of food for birds have been neglected. A preliminary attempt is made to explore the evolutionary and ecological consequences of fruit‐eating, considered as a mutual interaction between parent plant and dispersal agent.The relationship considered is that obtaining between fleshy fruits and the “legitimate” fruit‐eating birds which digest the fleshy part of the fruit and void the seed intact. Evolutionary aspects of seed‐eating are also briefly discussed.The “strategies” adopted by fruits for dispersal by birds result in the production of abundant food supplies which are easy of access and exploitable by many species of birds. By contrast, the predation of birds on insects leads to a heterogeneous, sparse and cryptic food supply, to exploit which many different hunting techniques are necessary. Two important evolutionary developments in birds are attributed to these differences in food supply: there tend to be more species in families of insectivorous than of frugivorous birds, and lek behaviour in tropical forest has evolved in predominantly frugivorous birds.The seasonal succession of fruits in temperate latitudes is discussed, and contrasted with the situation in the tropics, using examples from Europe and Trinidad. In general, the succession of ripe fruits in Europe seems to be adapted to the seasonal shifts of the bird populations, and the more nutritious fruits tend to have a more southerly distribution and to ripen later than the more succulent fruits. In the tropics the distinction between nutritious and succulent fruits seems to be largely one of habitat.The constant succession of ripe fruits throughout the year in the tropics probably depends on competition for dispersal by frugivorous birds, which thus ensure the maintenance of their own food supply. This may be regarded as a symbiosis at the level of the ecosystem.

Variation in the prenatal and postnatal environments can have long-term effects on adult phenotype. In humans and other animals, exposure to stressors can lead to long-term changes in physiology. These changes may predispose individuals to disease, especially disorders involving energy metabolism. In addition, by permanently altering metabolic rates and energy requirements, such effects could have important fitness consequences. We determined the effects of early-life food restriction and corticosterone (CORT) treatment on growth and adult body size, body composition (assessed via quantitative magnetic resonance) and metabolic rates in the song sparrow, Melospiza melodia. Nestlings were hand-raised in captivity from 3 days of age. Treatments (ad libitum food, food restriction or CORT treatment) lasted from day 7 to day 60. Both experimental treatments had sex-specific effects on growth. In the nestling period, CORT-treated males weighed more than controls, whereas CORT-treated females weighed less than controls. Food-restricted males weighed the same as controls, whereas food-restricted females weighed less than controls. Both experimental treatments also had sex-specific effects on standard metabolic rate (SMR). Females exposed to food restriction or CORT treatment during development had higher SMRs in adulthood than control females, but neither stressor affected SMR in males. There were no effects of either treatment on adult body size, body composition (lean or fat mass) or peak metabolic rate. Therefore, early-life stress may have sex-specific programming effects on metabolic rates and energy expenditure in song sparrows. In addition, both treatments affected nestling growth in a manner that exaggerated the typical sex difference in nestling mass, which could provide male nestlings with a competitive advantage over their sisters when developing in a poor-quality environment.

When fed ad libitum (AL), ectothermic animals usually grow faster and have higher metabolic rate at higher ambient temperature. However, if food supply is limited, there is an energy tradeoff between growth and metabolism. Here we hypothesize that for ectothermic animals under food restriction (FR), high temperature will lead to a high metabolic rate, but growth will slow down to compensate for the high metabolism. We measure the rates of growth and metabolism of 4 cohorts of 5th instar hornworms (Manduca sexta larvae) reared at 2 levels of food supply (AL and FR) and 2 temperatures (20 and 30 °C). Our results show that, compared to the cohorts reared at 20 °C, the ones reared at 30 °C have high metabolic rates under both AL and FR conditions, but a high growth rate under AL and a low growth rate under FR, supporting this hypothesis.

Metabolic rate (MR) is widely regarded as an important component of aging processes. Decreased MR has been suggested as a possible mechanism of the life-prolonging action of food restriction in rodents and recent reports show lowered plasma levels of tri-iodothyronine (T3), a regulator of MR, in food restricted rodents. In order to study the relationship between MR, food restriction, thyroid status and aging we measured the Minimal Oxygen Consumption (MOC) of barrier-raised Fischer 344 male rats fed ad libitum (Group A) or fed a diet restricted to 60% of ad libitum intake (Group R). Oxygen consumption (VO2) was also measured over 24 hr to establish the relationship between MOC and VO2 under usual living conditions. Results show: (i) MOC declines with age in both groups of rats; (ii) there is no difference in MOC of Groups A and R rats; (iii) MOC of Group R rats is significantly more sensitive to doses of injected T3 than MOC of Groups A rats at all ages; and (iv) MOC of both groups of rats is significantly lower than the lowest VO2 recorded under usual living conditions. The results indicate that a decrease in MR is not the mechanism by which food restriction retards aging processes in rodents. The results also suggest no change in thyroid status due to restriction of food although there is increased sensitivity to T3 in food restricted rats.

Metabolic turnover rate: A physiological meaning of the metabolic rate per unit body weight

1 Contrasting results of relations between standard metabolic rate, behaviour and performance suggest that the evolutionary trade-offs in energy allocation between metabolisms and other parts of the energy budget depend on environmental conditions. Here, we show how habitat complexity changes the relationship between standard metabolic rate, behaviour and performance (winter energy loss-rates) in juvenile Atlantic salmon (Salmo salar L.). 2 Juvenile Salmon, individually screened for standard metabolic rate, were stocked in replicated semi-natural stream channels with and without sheltering possibilities under ledge cover. We recorded the use of ledged areas, energy-loss rates and feeding activity during a 61-day period. 3 In the channels with ledge cover, individuals with relatively higher standard metabolic rates used areas outside of the cover more frequently and had higher feeding frequency than individuals with lower standard metabolic rates. No relationship was apparent between areas used, feeding and standard metabolic rate for the individuals within the no-cover treatments. In channels without cover, there was a negative relationship between standard metabolic rate and performance (energy balance), whereas standard metabolic rate did not affect performance in channels with ledge cover. 4 The effect of standard metabolic rate on performance depended on habitat complexity expressed through differences in behaviour. In channels with ledge cover, individuals with higher standard metabolic rates were apparently able to compensate for higher metabolic costs by utilizing a riskier habitat outside the cover and attaining a higher feeding success. 5 The present study demonstrates that the relationship between standard metabolic rate and performance may be dependent on habitat complexity and vary on small spatial scales, contributing to the persistence of large variation in standard metabolic rate within populations.

Abundance and growth ofEchinocardium cordatum at 28 stations on the Dogger Bank were analysed in May 1996–1998 and compared to data from 1985–1988 in order (i) to investigate the large-scale spatial variability of abundance and size ofE. cordatum in the late 80s and 90s, (ii) to relate abundance and growth ofE. cordatum to the quantity and quality of its food and (iii) to compare differences in results from the 80s and the 90s in relation to food supply and environmental changes due to hydroclimate change. In addition, phytopigment contents in the guts of sea urchins were analysed in May 1999 and compared to those in the surrounding sediments along a transect from the German Bight towards the Dogger Bank to detect differences in food supply. Differences in growth and size of the sea urchins were found to be positively correlated with total organic carbon (TOC) contents in the sediment fine fraction (<63 µm), but negatively correlated with the sediment fine fraction as well as with TOC content and C/N ratio of the total sediments. Abundances of adultE. cordatum were positively correlated with the fine fraction and sediment bulk parameters. Phytopigment analyses showed no significant differences of chlorophylla contents in the guts between the different sites, but differences in quality of the ingested material were detected. That indicates that abundance ofE. cordatum was related to food quantity, whereas growth was dependent on food quality. With regard to the long-term comparison, the decrease in abundance ofE. cordatum in the eastern shallow part of the Dogger Bank corresponded to the increased hydrodynamics which resulted in reduced food supply for surface deposit feeders such asE. cordatum.

Viability of hatching birds may be affected by the composition of the eggs from which they come. Egg composition may be influenced by the diet of the female. I examined whether wild Black-billed Magpies (Pica pica) varied the composition of their eggs in response to differences in food supply. Supplemental food was provided on some territories, and the composition of eggs from control and food-supplemented territories was compared. Supplemental feeding had few effects on egg composition. Egg size – water content relationships differed between eggs from food-supplemented and control territories and there was a greater variability in yolk and shell mass within clutches from food-supplemented territories. These results show that food supply to the female can affect the composition of an egg relative both to other eggs in the same clutch and to eggs in other clutches. However, it is not clear whether the observed variation in egg composition would have an effect on the viability of the eggs.

Partitioning the contributions of mega-, macro- and meiofauna to benthic metabolism on the upper continental slope of New Zealand: Potential links with environmental factors and trawling intensity

David Lack (1947, 1969) argued that interspecific competition for food has played a significant role in the adaptive radiation of Darwin's Finches. He regularly invoked competition to explain morphological and distributional patterns in the finches. An important example is the altitudinal distribution of Geospiza difficilis in relation to G. fuliginosa (Fig. 1). Low elevation, dry islands in the Galapagos are occupied by one of the two species, but never both. Islands possessing a highland vegetation zone may have both species but here they are altitudinally segregated, with G. fuliginosa occupying the lowlands and G. difficilis the highlands. Lack noted the morphological similarity of these finch species and suggested that G. difficilis had been excluded on low islands or altitudinally restricted on high islands through competition for food by G. fuliginosa wherever the species had come into contact. Bowman (1961), however, suggested instead that the unique food requirements of the two species and differences in food supply among islands, once known, would suffice to explain the pattern. The ecology of these two species was recently investigated over a calendar year on Isla Pinta where they coexist (Schluter, 1982a, 1982b). Surveys conducted on this island and on Islas San Salvador and Fernandina (unpubl. observ.) revealed that G. difficilis and G. fuliginosa are not allopatric as Lack believed. Their altitudinal ranges overlap extensively year-round although they are not coextensive (Fig. 2). Detailed observations of behavior and abundance strongly suggested that interspecific competition between them is presently weak. Food supply was probably limiting over part of the year, but interspecific aggression (e.g., territoriality) was not observed, and their diets and feeding positions were very different. The distributions and abundance of both species along the elevational gradient on Isla Pinta could easily be interpreted as being determined by the availability of their different foods. The question of whether past competition has influenced the distribution of G. difficilis in relation to G. fuliginosa remains. Significantly, G. difficilis varies in size and shape from island to island. For example on Isla Genovesa the species resembles the missing G. fuliginosa (Lack, 1947; see also Grant, in press). Possibly G. difficilis has adapted to exploit lowland environments on islands without a highland zone, and it is this lowland form which cannot coexist with G. fuliginosa. Observed differences in sympatry might also be the result of past competition. Lack's competition hypothesis is therefore still consistent with the observed insular distributions of these two species. Here we report the results of a field study which tested the argument that competition has influenced the distributions on low islands, against two alternative hypotheses based on Bowman's (1961) suggestions. We use information gained on diets, density and food supply of G. difficilis and G. fuliginosa on Pinta (Schluter, 1982b) to predict attributes of the two species in allopatry. The three hypotheses make different predictions, and these are tested with field data. The allopatric populations we used were G. difficilis on Genovesa and G. fuliginosa on Marchena (Fig. 2).