Contributions of juvenile and adult diet to the lifetime reproductive success and lifespan of a spider

Food availability can vary widely for animals in nature and can have large effects on growth, reproduction and survival. While the consequences of food limitation for animals have been extensively studied, significant questions still remain including how ontogenetic variation in food availability contributes to lifetime reproductive success. We tested the effects of juvenile and adult food limitation on the lifetime reproductive success and lifespan of bridge spiders, Larinioides sclopetarius. Food availability was manipulated (low or high) over the entire juvenile and adult stage in a full‐factorial design and reproductive output and lifespan were measured. Juvenile and adult food limitation both reduced lifetime egg and hatchling production with effect sizes that were not significantly different from each other. Unlike some other arthropods, where juvenile food limitation reduces fecundity by reducing adult body size, body size was not affected by juvenile diet in bridge spiders. Clutch size was also significantly reduced by both juvenile and adult food limitation. The effect of adult diet on clutch size was stronger than that of juvenile diet. Juvenile and adult food limitation both extended total lifespan, and adult food limitation extended adult longevity (i.e. time from maturation to death). However, juvenile food limitation decreased adult longevity, in contrast to what would be predicted by dietary or caloric restriction. Compensatory feeding and growth are widely recognized mechanisms through which animals can ameliorate some of the negative effects of periods of food limitation. Yet our results combined with studies of a range of other species suggest that there may be lasting consequences of juvenile food limitation on lifetime reproductive success that cannot be compensated for by adult feeding in some species.     

You Are What You Eat: Food Limitation Affects Reproductive Fitness in a Sexually Cannibalistic Praying Mantid

Resource limitation during the juvenile stages frequently results in developmental delays and reduced size at maturity, and dietary restriction during adulthood can affect longevity and reproductive output. Variation in food intake can also result in alteration to the normal pattern of resource allocation among body parts or life-history stages. My primary aim in this study was to determine how varying juvenile and/or adult feeding regimes affect particular female and male traits in the sexually cannibalistic praying mantid Pseudomantis albofimbriata. Praying mantids are sit-and-wait predators whose resource intake can vary dramatically depending on environmental conditions within and across seasons, making them useful for studying the effects of feeding regime on various facets of reproductive fitness. In this study, there was a significant trend/difference in development and morphology for males and females as a result of juvenile feeding treatment, however, its effect on the fitness components measured for males was much greater than on those measured for females. Food-limited males were less likely to find a female during field enclosure experiments and smaller males were slower at finding a female in field-based experiments, providing some of the first empirical evidence of a large male size advantage for scrambling males. Only adult food limitation affected female fecundity, and the ability of a female to chemically attract males was also most notably affected by adult feeding regime (although juvenile food limitation did play a role). Furthermore, the significant difference/trend in all male traits and the lack of difference in male trait ratios between treatments suggests a proportional distribution of resources and, therefore, no trait conservation by food-limited males. This study provides evidence that males and females are under different selective pressures with respect to resource acquisition and is also one of very few to show an effect of juvenile food quantity on adult reproductive fitness in a hemimetabolous insect.     

Having it all: historical energy intakes do not generate the anticipated trade-offs in fecundity

An axiom of life-history theory, and fundamental to our understanding of ageing, is that animals must trade-off their allocation of resources since energy and nutrients are limited. Therefore, animals cannot "have it all"--combine high rates of fecundity with extended lifespans. The idea of life-history trade-offs was recently challenged by the discovery that ageing may be governed by a small subset of molecular processes independent of fitness. We tested the "trade-off" and "having it all" theories by examining the fecundities of C57BL/6J mice placed onto four different dietary treatments that generated caloric intakes from -21 to +8.6% of controls. We predicted body fat would be deposited in relation to caloric intake. Excessive body fat is known to cause co-morbidities that shorten lifespan, while caloric restriction enhances somatic protection and increases longevity. The trade-off model predicts that increased fat would be tolerated because reproductive gain offsets shortened longevity, while animals on a restricted intake would sacrifice reproduction for lifespan extension. The responses of body fat to treatments followed our expectations, however, there was a negative relationship between reproductive performance (fecundity, litter mass) and historical intake/body fat. Our dietary restricted animals had lower protein oxidative damage and appeared able to combine life-history traits in a manner contrary to traditional expectations by having increased fecundity with the potential to have extended lifespans.     

Phenotypic plasticity in adult life-history strategies compensates for a poor start in life in Trinidadian guppies (Poecilia reticulata)

Low food availability during early growth and development can have long-term negative consequences for reproductive success. Phenotypic plasticity in adult life-history decisions may help to mitigate these potential costs, yet adult life-history responses to juvenile food conditions remain largely unexplored. I used a food-manipulation experiment with female Trinidadian guppies (Poecilia reticulata) to examine age-related changes in adult life-history responses to early food conditions, whether these responses varied across different adult food conditions, and how these responses affected overall reproductive success. Guppy females reared on low food as juveniles matured at a later age, at a smaller size, and with less energy reserves than females reared on high food as juveniles. In response to this setback, they changed their investment in growth, reproduction, and fat storage throughout the adult stage such that they were able to catch up in body size, increase their reproductive output, and restore their energy reserves to levels comparable to those of females reared on high food as juveniles. The net effect was that adult female guppies did not merely mitigate but surprisingly were able to fully compensate for the potential long-term negative effects of poor juvenile food conditions on reproductive success.     

Effects of Increased Flight on the Energetics and Life History of the Butterfly Speyeria mormonia

Movement uses resources that may otherwise be allocated to somatic maintenance or reproduction. How does increased energy expenditure affect resource allocation? Using the butterfly Speyeria mormonia, we tested whether experimentally increased flight affects fecundity, lifespan or flight capacity. We measured body mass (storage), resting metabolic rate and lifespan (repair and maintenance), flight metabolic rate (flight capacity), egg number and composition (reproduction), and food intake across the adult lifespan. The flight treatment did not affect body mass or lifespan. Food intake increased sufficiently to offset the increased energy expenditure. Total egg number did not change, but flown females had higher early-life fecundity and higher egg dry mass than control females. Egg dry mass decreased with age in both treatments. Egg protein, triglyceride or glycogen content did not change with flight or age, but some components tracked egg dry mass. Flight elevated resting metabolic rate, indicating increased maintenance costs. Flight metabolism decreased with age, with a steeper slope for flown females. This may reflect accelerated metabolic senescence from detrimental effects of flight. These effects of a drawdown of nutrients via flight contrast with studies restricting adult nutrient input. There, fecundity was reduced, but flight capacity and lifespan were unchanged. The current study showed that when food resources were abundant, wing-monomorphic butterflies living in a continuous meadow landscape resisted flight-induced stress, exhibiting no evidence of a flight-fecundity or flight-longevity trade-off. Instead, flight changed the dynamics of energy use and reproduction as butterflies adopted a faster lifestyle in early life. High investment in early reproduction may have positive fitness effects in the wild, as long as food is available. Our results help to predict the effect of stressful conditions on the life history of insects living in a changing world.     

Effects of food restriction across stages of juvenile and early adult development on body weight,survival and adult life history

Organisms have to allocate limited resources among multiple life‐history traits, which can result in physiological trade‐offs, and variation in environmental conditions experienced during ontogeny can influence reproduction later in life. Food restriction may lead to an adaptive reallocation of the limited resources among traits as a phenotypically plastic adjustment, or it can act as an overall constraint with detrimental effects throughout reproductive life. In this study, we investigated experimentally the effects of food restriction during different stages of the juvenile and early adult development on body weight, survival and reproductive success in females and males of the European earwig Forficula auricularia. Individuals either received limited or unlimited access to food across three different stages of development (fully crossed) allowing us to identify sensitive periods during development and to test both additive and interactive effects of food limitation across stages on development and reproduction. Food restriction during the early and late juvenile stage had additive negative effects on juvenile survival and adult body weight. With regard to reproductive success of females which produce up to two clutches in their lifetime, restriction specifically in the late juvenile stage led to smaller first and second clutch size, lower probability of second clutch production and reduced hatching success in the second clutch. Reproductive success of females was not significantly affected when their male mates experienced food restriction during their development. Our findings in general support the ‘silver‐spoon’ hypothesis in that food restriction during juvenile development poses constraints on development and reproduction throughout life.     

The influence of juvenile and adult environments on life-history trajectories

There is increasing evidence that the environment experienced early in life can strongly influence adult life histories. It is largely unknown, however, how past and present conditions influence suites of life-history traits regarding major life-history trade-offs. Especially in animals with indeterminate growth, we may expect that environmental conditions of juveniles and adults independently or interactively influence the life-history trade-off between growth and reproduction after maturation. Juvenile growth conditions may initiate a feedback loop determining adult allocation patterns, triggered by size-dependent mortality risk. I tested this possibility in a long-term growth experiment with mouthbrooding cichlids. Females were raised either on a high-food or low-food diet. After maturation half of them were switched to the opposite treatment, while the other half remained unchanged. Adult growth was determined by current resource availability, but key reproductive traits like reproductive rate and offspring size were only influenced by juvenile growth conditions, irrespective of the ration received as adults. Moreover, the allocation of resources to growth versus reproduction and to offspring number versus size were shaped by juvenile rather than adult ecology. These results indicate that early individual history must be considered when analysing causes of life-history variation in natural populations.     

Effect of food restriction on survival and reproduction of a termite

Food availability affects the trade-off between maintenance and reproduction in a wide range of organisms, but its effects on social insects remain poorly understood. In social insects, the maintenance-reproduction trade-off seems to be absent in individuals but may appear at the colony level, although this is rarely investigated. In this study, we restricted food availability in a termite species to test how it affects survival and reproduction, both at the individual and colony level. Using Bayesian multivariate response models, we found very minor effects of food restriction on the survival of queens, individual workers or on the colonies. In contrast, queen fecundity was significantly reduced, whereas colony-level fecundity (i.e., the number of dispersing alates, future reproductives) increased under food restriction as workers gave up cooperation within the colony and became alates that dispersed. Our study shows that life-history trade-offs can be mitigated by individuals' social behaviours in social organisms.     

Effect of periodical starvation on the life history of Brachionus plicatilis O.F. Müller (Rotifera): a possible strategy for population stability

To estimate the changes in the life history of the rotifer Brachionus plicatilis O.F. Müller under starvation, we carried out an individual culture and determined the effects of periodical food deprivation on its asexual reproductive characteristics such as lifespan, reproductive period, age at first egg and offspring production, and lifetime fecundity (total number of offspring produced in her lifetime). Rotifers were fed for 1-3 h daily, and were then starved until the next day. Control animals were fed throughout their lifespan. Starved rotifers matured and produced their first offspring at an older age than the control animals. The periodical starvation resulted in a decrease in the lifetime fecundity to less than half that of the non-starved control. The reproductive period and lifespan were 2-3 times longer in the starved animals than in the control animals. The negative relationship between lifespan and lifetime fecundity is interpreted as a trade-off in an alternative life-history strategy of rotifers under starved conditions. The great decrease in fecundity and extension of lifespan enables rotifers to compensate to keep the population in equilibrium.     

A minimalist approach to the effects of density-dependent competition on insect life-history traits

Abstract  1. Due to its effects on the phenotypic and genotypic expression of life-history traits, density-dependent competition is an important factor regulating the growth of populations. Specifically for insects, density-dependent competition among juveniles is often associated with increased juvenile mortality, delayed maturity, and reduced adult size.
2. The aim of the work reported here was to test whether the established phenotypic effects of density-dependent competition on life-history traits could be reproduced in an experimental design requiring a minimal number of individuals. Larvae of the mosquito Aedes aegypti were reared at densities of one, two, or three individuals per standard Drosophila vial and in six different conditions of larval food availability. This design required relatively few individuals per independent replicate and included a control treatment where individuals reared at a density of one larva per vial experienced no density-dependent interactions with other larvae.
3. Increased larval densities or reduced food availability led to increased larval mortality, delayed pupation, and the emergence of smaller adults that starved to death in a shorter time (indicating emergence with fewer nutritional reserves).
4. Female mosquitoes were relatively larger than males (as measured by wing length) but males tended to survive for longer. These differences increased as larval food availability increased, indicating the relative importance of these two traits for the fitness of each sex. The role of nutritional reserves for the reproductive success of males was highlighted in particular.
5. This minimalist approach may provide a useful model for investigating the effects of density-dependent competition on insect life-history traits.     

Pleiotropic effects of juvenile hormone in ant queens and the escape from the reproduction–immunocompetence trade-off

The ubiquitous trade-off between survival and costly reproduction is one of the most fundamental constraints governing life-history evolution. In numerous animals, gonadotropic hormones antagonistically suppressing immunocompetence cause this trade-off. The queens of many social insects defy the reproduction–survival trade-off, achieving both an extraordinarily long life and high reproductive output, but how they achieve this is unknown. Here we show experimentally, by integrating quantification of gene expression, physiology and behaviour, that the long-lived queens of the ant Lasius niger have escaped the reproduction–immunocompetence trade-off by decoupling the effects of a key endocrine regulator of fertility and immunocompetence in solitary insects, juvenile hormone (JH). This modification of the regulatory architecture enables queens to sustain a high reproductive output without elevated JH titres and suppressed immunocompetence, providing an escape from the reproduction–immunocompetence trade-off that may contribute to the extraordinary lifespan of many social insect queens.     

Life-history phenotypes in populations of Brachyrhaphis episcopi (Poeciliidae) with different predator communities

Variation among populations in extrinsic mortality schedules selects for different patterns of investment in key life-history traits. We compared life-history phenotypes among 12 populations of the live-bearing fish Brachyrhaphis episcopi. Five populations co-occurred with predatory fish large enough to prey upon adults, while the other seven populations lacked these predators. At sites with large predatory fish, both sexes reached maturity at a smaller size. Females of small to average length that co-occurred with predators had higher fecundity and greater reproductive allotment than those from populations that lacked predators, but the fecundity and reproductive allotment of females one standard deviation larger than mean body length did not differ among sites. In populations with large predatory fish, offspring mass was significantly reduced. In each population, fecundity, offspring size and reproductive allotment increased with female body size. When controlling for maternal size, offspring mass and number were significantly negatively correlated, indicating a phenotypic trade-off. This trade-off was non-linear, however, because reproductive allotment still increased with brood size after controlling for maternal size. Similar differences in life-history phenotypes among populations with and without large aquatic predators have been reported for Brachyrhaphis rhabdophora in Costa Rica and Poecilia reticulata (a guppy) in Trinidad. This may represent a convergent adaptation in life-history strategies attributable to predator-mediated effects or environmental correlates of predator presence.     

Experimental increase in fecundity causes upregulation of fecundity and body maintenance genes in the fat body of ant queens

In most organisms, fecundity and longevity are negatively associated and the molecular regulation of these two life-history traits is highly interconnected. In addition, nutrient intake often has opposing effects on lifespan and reproduction. In contrast to solitary insects, the main reproductive individual of social hymenopterans, the queen, is also the most long-lived. During development, queen larvae are well-nourished, but we are only beginning to understand the impact of nutrition on the queens'' adult life and the molecular regulation and connectivity of fecundity and longevity. Here, we used two experimental manipulations to alter queen fecundity in the ant Temnothorax rugatulus and investigated associated changes in fat body gene expression. Egg removal triggered a fecundity increase, leading to expression changes in genes with functions in fecundity such as oogenesis and body maintenance. Dietary restriction lowered the egg production of queens and altered the expression of genes linked to autophagy, Toll signalling, cellular homeostasis and immunity. Our study reveals that an experimental increase in fecundity causes the co-activation of reproduction and body maintenance mechanisms, shedding light on the molecular regulation of the link between longevity and fecundity in social insects.     

Are there interactive effects of mate availability and predation risk on life history and defence in a simultaneous hermaphrodite?

Encountering mates and avoiding predators are ubiquitous challenges faced by many organisms and they can affect the expression of many traits including growth, timing of maturity and resource allocation to reproduction. However, these two factors are commonly considered in isolation rather than simultaneously. We examined whether predation risk and mate availability interact to affect morphology and life-history traits (including lifetime fecundity) of a hermaphroditic snail (Physa acuta). We found that mate availability reduced juvenile growth rate and final size. Predator cues from crayfish induced delayed reproduction, but there were no reduced fecundity costs associated with predator induction. Although there were interactive effects on longevity, lifetime fecundity was determined by the number of reproductive days. Therefore, our results indicate a resource-allocation trade-off among growth, longevity and reproduction. Future consideration of this interaction will be important for understanding how resource-allocation plasticity affects the integration of defensive, life-history and mating-system traits.     

Linking reproductive and feeding strategies in the parasitoid Ibalia leucospoides: does feeding always imply profit?

Resource acquisition and allocation to different biological functions over the course of life have strong implications for animal reproductive success. Animals can experience different environmental conditions during their lifetime, and this may play an important role in shaping their life-history and resource allocation strategies. In this study we investigate larval and adult resource allocation to reproductive and survival functions in the parasitoid wasp Ibalia leucospoides (family Ibaliidae). The pattern of larval resource allocation was inferred from the relationship between adult body size and ovigeny index (OI; a relative measure of investment in early reproduction determined as the ratio between the initial egg load and the potential lifetime fecundity); and adult resource allocation was explored through the influence of adult feeding on reproduction, maintenance and metabolism, in laboratory experiments. Food acquisition by this parasitoid in the wild was also examined. The relationship between size and OI was constant, suggesting no differential resource allocation to initial egg load and potential lifetime fecundity with size. This finding is in line with that predicted by adaptive models for the proovigenic egg maturation strategy (OI = 1). Despite of this, I. leucospoides showed a high OI of 0.77, which places this species among the weakly synovigenic ones (OI < 1). Adult feeding had no effect on post-emergence egg maturation. However, wasps extended their lifespan through feeding albeit only when food was provided ad libitum. Although the information we obtained on the feeding behaviour of free-foraging wasps is limited, our results suggest that food intake in the wild, while possible, may not be frequent in this parasitoid. We discuss the results relative to the environmental factors, such as reproductive opportunities and food availability, which may have driven the evolution of larval and adult pattern of resource allocation in parasitoids.     

Effects of experimental manipulations on the life history pattern of Lymnaea stagnalis appressa say (pulmonata: lymnaeidae)

Field sampling of an Iowa population of Lymnaea stagnalis appressa Say indicated an annual generation pattern, with survivorship to maturity of i percent or less. Estimates of adult fecundity ranged from about 300 to 800 eggs.Density and food manipulations were performed to determine whether density dependent limitation of growth rates, maturation, or fecundity occurs in this fresh water pulmonate snail. Addition of a high quality food resource, spinach, accelerated growth rates, but did not drastically accelerate maturity, nor increase fecundity. Density increments lowered growth rates, delayed maturity, and lowered fecundity, and the addition of spinach did not counteract high densities. Adult densities are fairly low in the field population, and adults are randomly dispersed, indicating little density dependent regulation of fecundity in this population. However, the low survivorship to maturity, response in growth rates with food addition, and increasing survivorship with age and size indicate that juvenile mortality may play an important role in structuring life history patterns in this population.     

蜡皮蜥的两性异形和繁殖输出

为研究蜡皮蜥(Leiolepis reevesii)两性异形和繁殖输出,于2002、2003年4月下旬从海南乐东一种群捕获423头蜡皮蜥。经检测得到繁殖雌体的最小体长为89．0mm,据此判定≥89．0mm的个体为性成熟。研究结果表明：①蜡皮蜥具有两性异形,雄性大于雌性且具有较大的头部。成体雄性头长和头宽随体长的增长速率大于雌性,幼体头长和头宽随体长的增长速率无显著的两性差异。以性别和年龄(成、幼体)为因子的双因子ANOVA比较两性头长和头宽与体长的回归剩余值发现,雄性头部大于雌性,幼体头部相对大于成体。②饲养于实验室的母体中有42头于2002、2003年5月22日～7月16日产出正常卵,这些繁殖雌体具有年产多窝卵的潜力。窝卵数和卵重的变异系数分别为0．18和0．13,前者变异度大于后者。窝卵数、窝卵重和卵重均与母体体长无关。卵重与相对生育力之间无显著的负相关性,表明蜡皮蜥缺乏卵数量与卵大小之间的权衡。相对窝卵重与母体体长呈显著的负相关,表明较小的母体具有相对较大的繁殖输出。因雌体繁殖会滞缓其生长,小母体具有相对较大的繁殖输出,至少部分地解释了雌性蜡皮蜥的成体为什么个体较小。     

Larval food limitation in butterflies: effects on adult resource allocation and fitness

Allocation of larval food resources affects adult morphology and fitness in holometabolous insects. Here we explore the effects on adult morphology and female fitness of larval semi-starvation in the butterfly Speyeria mormonia. Using a split-brood design, food intake was reduced by approximately half during the last half of the last larval instar. Body mass and forewing length of resulting adults were smaller than those of control animals. Feeding treatment significantly altered the allometric relationship between mass and wing length for females but not males, such that body mass increased more steeply with wing length in stressed insects as compared to control insects. This may result in changes in female flight performance and cost. With regard to adult life history traits, male feeding treatment or mating number had no effect on female fecundity or survival, in agreement with expectations for this species. Potential fecundity decreased with decreasing body mass and relative fat content, but there was no independent effect of larval feeding treatment. Realized fecundity decreased with decreasing adult survival, and was not affected by body mass or larval feeding treatment. Adult survival was lower in insects subjected to larval semi-starvation, with no effect of body mass. In contrast, previous laboratory studies on adult nectar restriction showed that adult survival was not affected by such stress, whereas fecundity was reduced in direct 11 proportion to the reduction of adult food. We thus see a direct impact of larval dietary restriction on survival, whereas fecundity is affected by adult dietary restriction, a pattern reminiscent of a survival/reproduction trade-off, but across a developmental boundary. The data, in combination with previous work, thus provide a picture of the intra-specific response of a suite of traits to ecological stress.     

Life stage dependent responses to desiccation risk in the annual killifish Nothobranchius wattersi

To assess whether the annual killifish Nothobranchius wattersi responds plastically to a desiccation risk and whether this response is life stage dependent, life‐history traits such as maturation time, fecundity and life span were experimentally measured in N. wattersi that were subjected to a drop in water level either as juveniles, as adults or both as juveniles and adults. Fish that were exposed to simulated pool drying as juveniles did not show changes in reproductive output or life span. Adults reacted by doubling short term egg deposition at the cost of a shorter lifespan. Overall, these results suggest that annual fish species can use phenotypic plasticity to maximize their reproductive output when faced with early pond drying, but this response appears to be life‐stage specific. In addition to frogs and aquatic insects, phenotypic plasticity induced by forthcoming drought is now also confirmed in annual fishes and could well be a common feature of the limited number of fish taxa that manage to survive in this extreme environment.     

Direct and socially-mediated effects of food availability late in life on life-history variation in a short-lived lizard

Food availability is a major environmental factor that can influence life history within and across generations through direct effects on individual quality and indirect effects on the intensity of intra- and intercohort competition. Here, we investigated in yearling and adult common lizards (Zootoca vivipara) the immediate and delayed life-history effects of a prolonged food deprivation in the laboratory. We generated groups of fully fed or food-deprived yearlings and adults at the end of one breeding season. These lizards were released in 16 outdoor enclosures together with yearlings and adults from the same food treatment and with food-deprived or fully fed juveniles, creating four types of experimental populations. Experimental populations were then monitored during 2 years, which revealed complex effects of food on life-history trajectories. Food availability had immediate direct effects on morphology and delayed direct effects on immunocompetence and female body condition at winter emergence. Also, male annual survival rate and female growth rate and body size were affected by an interaction between direct effects of food availability and indirect effects on asymmetric competition with juveniles. Reproductive outputs were insensitive to past food availability, suggesting that female common lizards do not solely rely on stored energy to fuel reproduction. Finally, food conditions had socially-mediated intergenerational effects on early growth and survival of offspring through their effects on the intensity of competition. This study highlights the importance of social interactions among cohorts for life-history trajectories and population dynamics in stage-structured populations.