Physiological flexibility in the Andean lizard <Emphasis Type="Italic">Liolaemus bellii</Emphasis>: seasonal changes in energy acquisition,storage and expenditure

According to the “barrel model”, an organism may be represented by a container, with input energy constraints (foraging, digestion, and absorption) symbolized by funnels connected in tandem, and energy outputs (maintenance, growth, and reproduction) symbolized by a series of spouts arranged in parallel. Animals can respond to changes in environmental conditions, through adjustments in the size of the funnels, the fluid stored inside the barrel, or the output flow through the spouts. In the present study, we investigate the interplay among these processes through the analysis of seasonal changes in organ size and metabolic rate in a lizard species (Liolaemus bellii) that inhabits extremely seasonal environments in the Andes range. We found that digestive organ size showed the greatest values during spring and summer, that is, during the foraging seasons. Energy reserves were larger during summer and autumn, and then decreased through winter and spring, which was correlated with overwintering maintenance and reproductive costs. Standard metabolic rate was greater during the high-activity seasons (spring and summer), but this increase was only noticeable at higher environmental temperatures. The ability of many lizard species to reduce their maintenance cost during the cold months of the year, beyond what is expected from temperature decrease, is probably related to their success in coping with highly fluctuating environments. Here, we demonstrate that this ability is correlated with high physiological flexibility, which allows animals to adjust energy acquisition, storing and expenditure processes according to current environmental conditions.     

Optimal body size and energy expenditure during winter: why are voles smaller in declining populations?

Winter is energetically challenging for small herbivores because of greater energy requirements for thermogenesis at a time when little energy is available. We formulated a model predicting optimal wintering body size, accounting for the scaling of both energy expenditure and assimilation to body size, and the trade-off between survival benefits of a large size and avoiding survival costs of foraging. The model predicts that if the energy cost of maintaining a given body mass differs between environments, animals should be smaller in the more demanding environments, and there should be a negative correlation between body mass and daily energy expenditure (DEE) across environments. In contrast, if animals adjust their energy intake according to variation in survival costs of foraging, there should be a positive correlation between body mass and DEE. Decreasing temperature always increases equilibrium DEE, but optimal body mass may either increase or decrease in colder climates depending on the exact effects of temperature on mass-specific survival and energy demands. Measuring DEE with doubly labeled water on wintering Microtus agrestis at four field sites, we found that DEE was highest at the sites where voles were smallest despite a positive correlation between DEE and body mass within sites. This suggests that variation in wintering body mass between sites was due to variation in food quality/availability and not adjustments in foraging activity to varying risks of predation.     

When to store energy in a stochastic environment

The ability to store energy enables organisms to deal with temporarily harsh and uncertain conditions. Empirical studies have demonstrated that organisms adapted to fluctuating energy availability plastically adjust their storage strategies. So far, however, theoretical studies have investigated general storage strategies only in constant or deterministically varying environments. In this study, we analyze how the ability to store energy influences optimal energy allocation to storage, reproduction, and maintenance in environments in which energy availability varies stochastically. We find that allocation to storage is evolutionarily optimal when environmental energy availability is intermediate and energy stores are not yet too full. In environments with low variability and low predictability of energy availability, it is not optimal to store energy. As environments become more variable or more predictable, energy allocation to storage is increasingly favored. By varying environmental variability, environmental predictability, and the cost of survival, we obtain a variety of different optimal life-history strategies, from highly iteroparous to semelparous, which differ significantly in their storage patterns. Our results demonstrate that in a stochastically varying environment simultaneous allocation to reproduction, maintenance, and storage can be optimal, which contrasts with previous findings obtained for deterministic environments.     

Optimal Reproductive Strategy of Plants, with Special Reference to the Modes of Reproductive Resource Allocation

Abstract A growth model for reproductive energy allocation pattern and schedule is proposed. Assumptions are as follows: (1) the assimilation rate for an individual is given by a logistic curve of vegetative dry weight; (2) size variability is expressed by the parameter W of the logistic curve (asymptotic value of vegetative dry weight); (3) a plant controls allocation of the assimilate to vegetative and reproductive structures so as to maximize the reproductive energy investment at the end of the growth period. The models were analyzed in comparison with field and experimental observations and gave reasonable explanations for the reproductive allocation pattern of individuals which reflects ecological preferences and life history characteristics, such as environmental conditions of habitats (stable or changing), length of life span (annual, biennial or perennial) and growth form (erectophile or planophile). Decreasing RA (reproductive allocation) with individual size and delayed switchover time from vegetative to reproductive growth were found in plants which occur in stable environments and have a more or less fixed growth period; in those which occur in changing environments where growth period depends on individual size, RAs that remain constant or increase with variations in individual size and early switchover time were detected. Most perennials conform to the former case, but annuals and biennials conform to the latter case. Under extremely overcrowded conditions, planophiles, which are much more subject to crowding effect than erectophiles, tend to have increasing RA with increasing size, while erectophiles tend to have almost constant RA irrespective of size. These trends are discussed in the light of the life history characteristics and ecological distribution of plant species studied.     

Morphological trends and environment: a case study on Early Cretaceous Myophorelloidea (Bivalvia,Trigoniida) from Neuquén Basin,Argentina

Trigoniide clams were conspicuous components of bivalve faunas in shallow seas during most of the Mesozoic. Morphological trends in different features of shell shape and ornamentation of three related species of myophorelloids from the Agrio Formation (Early Cretaceous of Neuquén Basin, Argentina) that inhabited environments of different hydrodynamic energy conditions are explored in this study by means of a detailed morphometric analysis. Four hydrodynamic energy categories were established for depositional environments, from most (1), to least (4), energetic. General shell shape was characterized by measurements of height, length and width. New quantitative methods were developed to evaluate the distribution of costae along the marginal carina and the divergence of costae along the flank. Morphometric variables were detrended with respect to size, to avoid ontogenetic variability in further analyses. Relative width of the shell increases as environments become higher in hydrodynamic energy; this unusual trend may be interpreted as an anchoring/stabilizing strategy developed by the lineage in shallow marine environments. Trends in ornamentation correspond to more densely distributed costae in environments of higher hydrodynamic energy, a pattern that improves substrate penetration.     

Population size and identity influence the reaction norm of the rare,endemic plant Cochlearia bavarica across a gradient of environmental stress

Habitat degradation and loss can result in population decline and genetic erosion, limiting the ability of organisms to cope with environmental change, whether this is through evolutionary genetic response (requiring genetic variation) or through phenotypic plasticity (i.e., the ability of a given genotype to express a variable phenotype across environments). Here we address the question whether plants from small populations are less plastic or more susceptible to environmental stress than plants from large populations. We collected seed families from small (<100) versus large natural populations (>1,000 flowering plants) of the rare, endemic plant Cochlearia bavarica (Brassicaceae). We exposed the seedlings to a range of environments, created by manipulating water supply and light intensity in a 2 x 2 factorial design in the greenhouse. We monitored plant growth and survival for 300 days. Significant effects of offspring environment on offspring characters demonstrated that there is phenotypic plasticity in the responses to environmental stress in this species. Significant effects of population size group, but mainly of population identity within the population size groups, and of maternal plant identity within populations indicated variation due to genetic (plus potentially maternal) variation for offspring traits. The environment x maternal plant identity interaction was rarely significant, providing little evidence for genetically- (plus potentially maternally-) based variation in plasticity within populations. However, significant environment x population-size-group and environment x population-identity interactions suggested that populations differed in the amount of plasticity, the mean amount being smaller in small populations than in large populations. Whereas on day 210 the differences between small and large populations were largest in the environment in which plants grew biggest (i.e., under benign conditions), on day 270 the difference was largest in stressful environments. These results show that population size and population identity can affect growth and survival differently across environmental stress gradients. Moreover, these effects can themselves be modified by time-dependent variation in the interaction between plants and their environment.     

Inactivation of Rheb by PRAK-mediated phosphorylation is essential for energy-depletion-induced suppression of mTORC1

Cell growth can be suppressed by stressful environments, but the role of stress pathways in this process is largely unknown. Here we show that a cascade of p38β mitogen-activated protein kinase (MAPK) and p38-regulated/activated kinase (PRAK) plays a role in energy-starvation-induced suppression of mammalian target of rapamycin (mTOR), and that energy starvation activates the p38β-PRAK cascade. Depletion of p38β or PRAK diminishes the suppression of mTOR complex 1 (mTORC1) and reduction of cell size induced by energy starvation. We show that p38β-PRAK operates independently of the known mTORC1 inactivation pathways--phosphorylation of tuberous sclerosis protein 2 (TSC2) and Raptor by AMP-activated protein kinase (AMPK)--and surprisingly, that PRAK directly regulates Ras homologue enriched in brain (Rheb), a key component of the mTORC1 pathway, by phosphorylation. Phosphorylation of Rheb at Ser 130 by PRAK impairs the nucleotide-binding ability of Rheb and inhibits Rheb-mediated mTORC1 activation. The direct regulation of Rheb by PRAK integrates a stress pathway with the mTORC1 pathway in response to energy depletion.     

Physiological responses to variable environments: storage and respiration in starving rotifers

1. Zooplankton exist in environments where food availability varies greatly over time, and success depends in part on the ability to store resources when food is abundant and to conserve them when food is scarce. This paper reports on interspecific differences in the size of stored reserves, and in respiration rate during food deprivation, of four species of planktonic rotifers.
2. The size of reserves varied from 42 to 71% of initial (well-fed) body mass. Interspecific differences in reserve size explained some of the previously observed differences in starvation time.
3. The initial response of respiration rate to food deprivation was quite variable between species. Brachionus calyciflorus was the only species to conserve energy by decreasing respiration rate in response to food deprivation. In contrast, the respiration rate of starved Asplanchna priodonta increased, while that of A. silvestrii and Synchaeta pectinata did not change, during food deprivation.
4. Theory predicts that temporal variation in resource level may facilitate the coexistence of competing species. This theory depends upon trade-offs between traits that confer competitive success in different environments. Although rotifers show a trade-off between competitive ability and maximum population growth rate, we found no evidence for trade-offs between either of those two traits and the size of reserves.     

Acoustic indicators for targeted detection of stored product and urban insect pests by inexpensive infrared, acoustic, and vibrational detection of movement

Crawling and scraping activity of three stored-product pests, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), and Stegobium paniceum (L.) (Coleoptera: Anobiidae), and two urban pests, Blattella germanica (L.) (Blattodea: Blattellidae) and Cimex lectularius L. (Hemiptera: Cimicidae), were monitored individually by infrared sensors, microphones, and a piezoelectric sensor in a small arena to evaluate effects of insect locomotory behavior and size on the ability of an inexpensively constructed instrument to detect insects and distinguish among different species. Adults of all species could be detected when crawling or scraping. The smallest insects in the study, first-fourth-instar C. lectularius nymphs, could not be detected easily when crawling, but could be detected when scraping. Sound and vibration sensors detected brief, 3-10-ms impulses from all tested species, often grouped in distinctive trains (bursts), typical of impulses in previous acoustic detection experiments. To consider the potential for targeting or focusing detection on particular species of interest, indicators were developed to assess the likelihood of detection of C. lectularius. Statistically significant differences were found between C. lectularius and other species in distributions of three measured variables: infrared signal durations, sound impulse-burst durations, and sound pressure levels (energy) of impulses that best matched an averaged spectrum (profile) of scraping behavior. Thus, there is potential that signals collected by an inexpensive, polymodal-sensor instrument could be used in automated trapping systems to detect a targeted species, 0.1 mg or larger, in environments where servicing of traps is difficult or when timeliness of trapping information is important.     

Post-Viking Microbiology: New Approaches,New Data,New Insights

In the 20 years since the Viking experiments, major advances have been made in the areas of microbial systematics, microbial metabolism, microbial survival capacity, and the definition of environments on earth, suggesting that life is more versatile and tenacious than was previously appreciated. Almost all niches on earth which have available energy, and which are compatible with the chemistry of carbon-carbon bonds, are known to be inhabited by bacteria. The oldest known bacteria on earth apparently evolved soon after the formation of the planet, and are heat loving, hydrogen and/or sulfur metabolizing forms. Among the two microbial domains (kingdoms) is a great deal of metabolic diversity, with members of these forms being able to grow on almost any known energy source, organic or inorganic, and to utilize an impressive array of electron acceptors for anaerobic respiration. Both hydrothermal environments and the deep subsurface environments have been shown to support large populations of bacteria, growing on energy supplied by geothermal energy, thus isolating these ecosystems from the rest of the global biogeochemical cycles. This knowledge, coupled with new insights into the history of the solar system, allow one to speculate on possible evolution and survival of life forms on Mars.     

Home ranges in adult Scandinavian brown bears (Ursus arctos): effect of mass, sex, reproductive category, population density and habitat type

Annual home-range size indices for 36 male and 52 female adult brown bears Ursus arctos in two study areas in central and northern Scandinavia were estimated to evaluate factors believed to influence home-range size. Male home ranges were larger than home ranges of lone females after controlling for the sexual size dimorphism acting on metabolic needs. Further, home ranges of females with cubs were smaller than home ranges of lone females and females with yearlings. Thus, differences in metabolic need were not able to explain the variation in range size among females of different reproductive categories or between males and females, suggesting roaming behaviour of males in this promiscuous species. Home-range size in both males and females was inversely related to population density along a density gradient that was not linked to food availability. This contradicts the hypothesis that females use the minimum areas that sustain their energy requirements. However, on a large geographical scale a negative relationship between range size and food availability was evident. The annual home ranges in inland boreal environments in Scandinavia are the largest reported for brown bears in Eurasia, and similar to those in inland boreal and montane environments in North America.     

Sphingomonas alaskensis strain AFO1, an abundant oligotrophic ultramicrobacterium from the North Pacific.

Numerous studies have established the importance of picoplankton (microorganisms of < or =2 microm in length) in energy flow and nutrient cycling in marine oligotrophic environments, and significant effort has been directed at identifying and isolating heterotrophic picoplankton from the world's oceans. Using a method of diluting natural seawater to extinction followed by monthly subculturing for 12 months, a bacterium was isolated that was able to form colonies on solid medium. The strain was isolated from a 10(5) dilution of seawater where the standing bacterial count was 3.1 x 10(5) cells ml(-1). This indicated that the isolate was representative of the most abundant bacteria at the sampling site, 1.5 km from Cape Muroto, Japan. The bacterium was characterized and found to be ultramicrosized (less than 0.1 microm(3)), and the size varied to only a small degree when the cells were starved or grown in rich media. A detailed molecular (16S rRNA sequence, DNA-DNA hybridization, G+C mol%, genome size), chemotaxonomic (lipid analysis, morphology), and physiological (resistance to hydrogen peroxide, heat, and ethanol) characterization of the bacterium revealed that it was a strain of Sphingomonas alaskensis. The type strain, RB2256, was previously isolated from Resurrection Bay, Alaska, and similar isolates have been obtained from the North Sea. The isolation of this species over an extended period, its high abundance at the time of sampling, and its geographical distribution indicate that it has the capacity to proliferate in ocean waters and is therefore likely to be an important contributor in terms of biomass and nutrient cycling in marine environments.     

Xantusiid lizards have low energy, water, and food requirements

Lizards in the family Xantusiidae (the night lizards) are known to have resting metabolic rates that are only half those of other lizards of comparable size. We evaluated whether xantusiids also have low field metabolic rates (FMR) and food requirements by measuring FMR and water flux rates with doubly labeled water in three xantusiid species in their natural habitats. Free-living Xantusia vigilis, Xantusia henshawi, and Xantusia riversiana processed energy and water very slowly, about one-third as fast as do other reptiles of similar size. Xantusiid lizards have a distinctive life history that is characterized by very slow growth and low reproductive rates, and they are intensely reclusive. This general lifestyle is also found in some species that live in environments with scarce food resources, such as in caves and in arid habitats, and these species may also have relatively low energy requirements.     

A theoretical investigation of the effect of latitude on avian life histories

Tropical birds lay smaller clutches than birds breeding in temperate regions and care for their young for longer. We develop a model in which birds choose when and how often to breed and their clutch size, depending on their foraging ability and the food availability. The food supply is density dependent. Seasonal environments necessarily have a high food peak in summer; in winter, food levels drop below those characteristic of constant environments. A bird that cannot balance its energy needs during a week dies of starvation. If adult predation is negligible, birds in low seasonal environments are constrained by low food during breeding seasons, whereas birds in high seasonal environments die during the winter. Low food seasonality selects for small clutch sizes, long parental care times, greater age at first breeding, and high juvenile survival. The inclusion of adult predation has no major effect on any life-history variables. However, increased nest predation reduces clutch size. The same trends with seasonality are also found in a version of the model that includes a condition variable. Our results show that seasonal changes in food supply are sufficient to explain the observed trends in clutch size, care times, and age at first breeding.     

Energy-efficient indoor search by swarms of simulated flying robots without global information

Swarms of flying robots are a promising alternative to ground-based robots for search in indoor environments with advantages such as increased speed and the ability to fly above obstacles. However, there are numerous problems that must be surmounted including limitations in available sensory and on-board processing capabilities, and low flight endurance. This paper introduces a novel strategy to coordinate a swarm of flying robots for indoor exploration that significantly increases energy efficiency. The presented algorithm is fully distributed and scalable. It relies solely on local sensing and low-bandwidth communication, and does not require absolute positioning, localisation, or explicit world-models. It assumes that flying robots can temporarily attach to the ceiling, or land on the ground for efficient surveillance over extended periods of time. To further reduce energy consumption, the swarm is incrementally deployed by launching one robot at a time. Extensive simulation experiments demonstrate that increasing the time between consecutive robot launches significantly lowers energy consumption by reducing total swarm flight time, while also decreasing collision probability. As a trade-off, however, the search time increases with increased inter-launch periods. These effects are stronger in more complex environments. The proposed localisation-free strategy provides an energy efficient search behaviour adaptable to different environments or timing constraints.     

The effects of food shortage during larval development on adult body size, body mass, physiology and developmental time in a tropical damselfly

Few studies have looked jointly at the effects of larval stressors on life history and physiology across metamorphosis, especially in tropical insects. Here we investigated how the variation of food availability during the larval stage of the tropical and territorial American rubyspot damselfly (Hetaerina americana) affects adult body size and body mass, and two physiological indicators of condition--phenoloxidase activity (an indicator of immune ability) and protein concentration. We also investigated whether larval developmental time is prolonged when food is scarce, an expected situation for tropical species whose larval time is less constrained, compared to temperate species. Second instar larvae were collected from their natural environments and reared in one of two diet regimes: (i) "rich" provided with five Artemia salina prey every day, and (ii) "poor" provided with two A. salina prey every day. In order to compare how distinct our treatments were from natural conditions, a second set of last-instar larvae were also collected and allowed to emerge. Only body size and phenoloxidase increased in the rich regime, possibly to prioritize investment on sexually selected traits (which increase mating opportunities), and immune ability, given pathogen pressure. The sexes did not differ in body size in relation to food regimes but they did differ in body mass and protein concentration; this can be explained on the basis of the energetically demanding territorial activities by males (for the case of body mass), and female allocation to egg production (for the case of protein). Finally, animals delayed larval development when food was scarce, which is coherent for tropical environments. These findings provide key insights in the role of food availability in a tropical species.     

Relationships among Egg Size, Composition, and Energy: A Comparative Study of Geminate Sea Urchins

Egg size is one of the fundamental parameters in the life histories of marine organisms. However, few studies have examined the relationships among egg size, composition, and energetic content in a phylogenetically controlled context. We investigated the associations among egg size, composition, and energy using a comparative system, geminate species formed by the closure of the Central American Seaway. We examined western Atlantic (WA) and eastern Pacific (EP) species in three echinoid genera, Echinometra, Eucidaris, and Diadema. In the genus with the largest difference in egg size between geminates (Echinometra), the eggs of WA species were larger, lipid rich and protein poor compared to the smaller eggs of their EP geminate. In addition, the larger WA eggs had significantly greater total egg energy and summed biochemical constituents yet significantly lower egg energy density (energy-per-unit-volume). However, the genera with smaller (Eucidaris) or no (Diadema) differences in egg size were not significantly different in summed biochemical constituents, total egg energy, or energy density. Theoretical models generally assume a strong tradeoff between egg size and fecundity that limits energetic investment and constrains life history evolution. We show that even among closely-related taxa, large eggs cannot be assumed to be scaled-up small eggs either in terms of energy or composition. Although our data comes exclusively from echinoid echinoderms, this pattern may be generalizable to other marine invertebrate taxa. Because egg composition and egg size do not necessarily evolve in lockstep, selective factors such as sperm limitation could act on egg volume without necessarily affecting maternal or larval energetics.     

Physiology of intermittent feeding: integrating responses of vertebrates to nutritional deficit and excess

Food intakes of wild animals may not match their requirements for nutrients and energy but may vary between periods of nutritional excess (hyperphagia) and nutritional deficit (hypophagia) at timescales that vary from days to months. We present a simple model of feeding patterns and requirements of vertebrates. Frequent fasts and high intakes are typical of endothermic predators and migratory birds, whereas slow cycles and long deficits typify feeding patterns of ectothermic predators and ungulates in seasonal environments. We propose that hyperphagia is constrained by the ability to increase processes of digestion, absorption, intermediary metabolism, net deposition in tissue, and excretion to match loads of digesta and metabolites. Hyperphagia on high-quality diets is limited by the clearance of metabolites, whereas digestive tract capacity and flow limit consumption of low-quality diets. Of all digestive strategies, small omnivores with simple digestive systems may be the most tolerant of frequent hyperphagia. Tolerance of hypophagia favors large endogenous stores or low mass-specific rates of metabolism and reproductive output. Large animals may be most able to sustain reproduction during prolonged deficits in seasonal environments. Responses to excessive and deficient intakes of food are constrained by the length of the feeding cycle. Animals adapted to short feeding cycles may be best suited to unpredictable food supplies but at the energetic cost of maintaining spare capacity for digestion and absorption. Predictions of the response to food disruption are best evaluated in the context of body size, nutritional physiology, and life history of the species and the time for internal response.     

Feeding, growth, and fecundity of Abarenicola pacifica in relation to sediment organic concentration

For marine deposit-feeding invertebrates, the distribution of species with different life history strategies has long been known to be correlated with sediment organic concentration. Large populations of opportunistic species are found in sediments with enriched organic concentration, while equilibrium species populate low organic concentration sediments. Differences in both behavioral (e.g. feeding rate) and physiological (e.g. growth rate, reproductive output) adaptations determine the ability of species to establish populations in different environments. By systematically documenting differences in the way these factors vary as sediment organic concentration varies for both opportunistic and equilibrium species, we can better understand the mechanisms underlying this correlation between sediment organic concentration and species distributions. Here, we present the results of experiments examining the interactions among food concentration, feeding rate, growth rate, and reproductive output (measured as egg number and size) for the equilibrium species Abarenicola pacifica. A. pacifica is a large, long-lived, iteroparous, sub-surface deposit-feeding polychaete. Individual worms were reared throughout most of one generation in sediments differing only in the concentration of organic matter. Juveniles (<20 mg AFDW) had higher feeding rates and growth rates in sediments of higher organic concentration throughout the range tested. These results are consistent with the predictions from optimal foraging theory. As worms grew, however, these patterns changed. Once worms reached a mean body size of approximately 50 mg AFDW, feeding rate was greater on sediments of lower organic concentration (although it took worms in the sediments with lower organic concentration longer to reach this size). Differences in growth rates among treatments decreased as worms grew. For worms >100 mg AFDW, growth rates were uniformly low ( approximately 1%/day) on all sediments, but the early advantage obtained by worms in the high organic treatments resulted in much greater body sizes after 200 days. Worms had higher tissue triacylglyceride concentrations and produced more eggs (independent of worm size) as sediment organic concentration increased. We conclude that A. pacifica alters its feeding rate in response to variations in food resources in such a way as to maximize its energy intake and thereby maximize fitness. Future studies should investigate whether opportunistic species (as well as other equilibrium species) also have this ability.     

BODY FAT, PUBERTY AND FERTILITY

1. The high percentage of fat, about 26–28% in the mature human female, may influence reproductive ability directly through two mechanisms: ( a ) fat converts androgens to oestrogens; ( b ) relative fatness influences the direction of metabolism of oestrogen to the most potent or least potent forms. The relative degree of fatness thus is directly related to both the quantity of circulating oestrogen and the biological effectiveness of the oestrogen. This is a neat mechanism for relating rates of growth, nutrition and energy outputs to the energy requirements for reproduction. Fat is the most labile body tissue; it therefore reflects environmental changes more rapidly than other tissues of the body.
2. The slow maturation of the hypothalamus and pituitary up to menarche, or first oestrus, is accompanied by a slow maturation of the body, which changes not only in size but in the relative proportion of bone, muscle, and fat. Evidence is presented that a particular threshold ratio of fat to lean mass is normally necessary for puberty and the maintenance of female reproductive ability in the human and in the rat. The synchronizing mechanisms may be metabolic, relating food intake to core temperature and/or fat storage.
3. Undernutrition and weight loss in the range of 10–15 % of normal weight for height delays menarche and causes amenorrhoea. Ballet dancers and athletes also have delayed menarche and amenorrhoea. The cessation of reproduction in both groups can be considered adaptive. Refeeding and/or cessation of intense activity results in the initiation or resumption of menstrual cycles after varying periods of time. A necessary threshold weight for height can be predicted from a fatness index.
4. Differences in the natural fertility of historical and contemporary populations may be explained by a direct effect of food intake and energy outputs on fecundity.
5. The late maturing fat - 'sex fat' - may have a special role in reproduction.