Diet affects female mating behaviour in a seed‐feeding beetle

In species where males provide nuptial gifts, females can improve their nutritional status and thus increase their fecundity by mating when in need of resources. However, mating can be costly, so females should only mate to acquire resources when the need for resources is large, such as when females are nutritionally‐deprived. Two populations of the seed‐feeding beetle Callosobruchus maculatus, a species that produces relatively large nuptial gifts, are used to test whether female nutritional status affects mating behaviour. Female access to water, sugar and yeast are manipulated and the fitness consequences of these manipulations are examined together with the effects of diet on the propensity of nonvirgin females to mate. Access to water has a small but significant effect on mass loss over time, lifespan and fecundity of females, relative to unfed controls. Access to sugar (dissolved in water) improves female fecundity and lifespan above that of hydrated females but access to yeast has no positive effects on female survival or reproduction. Diet has a large effect on both receptivity of nonvirgin females to a male and how quickly they accept that male. Unfed females are both more likely to mate, and accept a mate more quickly, than females provided access to water, which are more likely to mate and accept a mate more quickly than females provided with sugar. This rank order of behaviours matches the order predicted if females increase their mating rate when nutritionally deprived (i.e. it matches the effect of diet on female fitness). The results obtained also suggest that mate choice may be condition‐dependent: females from one population (Burkina Faso) show a preference for large males when well‐fed but not when unfed, although this result is not found in a second population (South India). It is concluded that nutritionally‐deprived females are more receptive to mates than are well‐fed females, consistent with the hypothesis that females ‘forage’ for nuptial gifts, or at least more willingly accept sperm in exchange for nuptial gifts, when they are nutritionally deprived.     

Manipulation of parental nutritional condition reveals competition among family members

Parental care is thought to be costly, as it consumes time and energy. Such costs might be reduced in animal parents that raise their young on valuable food sources such as dung or carcasses, as parents are able to invest in self‐maintenance by feeding from the same resource. However, this might lower the nutritional value for other family members and, as a consequence, food competition might arise. To promote our understanding of the outcome of such competition, we manipulated the necessity of parents to feed from the resource. Using a full factorial design, we paired food‐deprived or well‐fed males with food‐deprived or well‐fed females of burying beetles, which are known to raise their young on vertebrate cadavers. We found that food‐deprived parents consumed more of the carrion than those that were well‐fed and this had a negative impact on other family members. However, the outcome of the competition depended on the sex of the parents, with females suffering when males fed more and offspring suffering when females fed more. Thus, family life involves selfish elements, as both parents remove resources for the purpose of self‐maintenance. However, females show altruistic aspects, as they appear to restrict their food consumption for the benefit of their offspring when paired with a food‐deprived male. Interestingly, males extend their stay with the brood when having faced food scarcity prior to reproduction, presumably to replenish their energy reserves. Our study therefore reveals that breeding on shared resources can promote family living, but also results in competition.     

Female meadow voles,Microtus pennsylvanicus,do not alter their over-marking in response to female conspecifics that were food deprived

Many terrestrial mammals will deposit scent marks and over-marks, the latter being the overlapping scent marks of two conspecifics. Studies have shown that male rodents that are exposed to the overlapping scent marks of two female conspecifics later spend more time investigating the mark of the top-scent female than that of the bottom-scent female. This suggests that over-marking is a form of competition and that the top-scent female is more likely than the bottom-scent female to be chosen as a potential mate. Thus, females should over-mark the scents of neighboring females at a rate that will maximize their chances of attracting males. However, meadow voles live in areas that may contain patchy food availability and residents may differ in their nutritional status. Females in a better nutritional state may be more likely than those in poorer nutritional states to indicate their presence in an area, signal possession of a territory, and to attract mates. Thus, we tested the prediction that female meadow voles, Microtus pennsylvanicus, that were not food deprived would deposit more over-marks than female voles that were food deprived for 6 h. Food-deprived female voles and female voles that had continuous access to food deposited a similar number of scent marks and used a similar proportion of those marks as over-marks when they encountered the scent marks of female conspecifics. These findings suggest that the nutritional status of female voles does not affect their ability to signal their presence in an area marked by a female conspecific.     

Food hoarding is increased by food deprivation and decreased by leptin treatment in Syrian hamsters

Compensatory increases in food intake are commonly observed after a period of food deprivation in many species, including laboratory rats and mice. Thus it is interesting that Syrian hamsters fail to increase food intake after a period of food deprivation, despite a fall in plasma leptin concentrations similar to those seen in food-deprived rats and mice. In previous laboratory studies, food-deprived Syrian hamsters increased the amount of food hoarded. We hypothesized that leptin treatment during food deprivation would attenuate food-deprivation-induced increases in hoarding. Baseline levels of hoarding were bimodally distributed, with no hamsters showing intermediate levels of hoarding. Both high (HH) and low hoarding (LH) hamsters were included in each experimental group. Fifty-six male hamsters were either food deprived or given ad libitum access to food for 48 h. One-half of each group received intraperitoneal injections of leptin (4 mg/kg) or vehicle every 12 h during the food-deprivation period. Within the HH group, the hoarding score increased significantly in food-deprived but not fed hamsters (P < 0.05). Leptin treatment significantly decreased hoarding in the food-deprived HH hamsters (P < 0.05). The LH hamsters did not increase hoarding regardless of whether they were food deprived or had ad libitum access to food. These results are consistent with the idea that HH hamsters respond to energetic challenges at least in part by changing their hoarding behavior and that leptin might be one factor that mediates this response.     

Effects of food availability on proceptivity: A test of the reproduction at all costs and metabolic fuels hypotheses

Proceptive behaviours are used by animals to indicate interest in opposite-sex conspecifics. These behaviours can be affected by an individual's nutritional status. Two mutually exclusive hypotheses have been proposed to account for the effects of food availability on reproduction. These are the metabolic fuels hypothesis and the reproduction at all costs hypothesis. It is not known if food availability affects proceptive behaviours such as scent marking, over-marking, and self-grooming. In this study, we tested the hypothesis that food-deprived and nonfood-deprived meadow voles, Microtus pennsylvanicus, differ in the number of scent marks they deposit, the proportion of over-marks they deposit, and the amount of time they spend self-grooming when they encounter the scent marks of opposite-sex conspecifics. We tested this hypothesis by exposing meadow voles that either had continuous access to food or were food-deprived for either 6hours or 24hours to the scent marks of an opposite-sex conspecific. Due to differences in the natural history of male and female meadow voles, we predicted that female voles' behaviour will best be explained by the metabolic fuels hypothesis whereas males' behaviour will best be explained by the reproduction at all costs hypothesis. We found that both male and female voles deprived of food for either 6hours or 24hours spent less time self-grooming compared to nonfood-deprived voles. However, food availability did not affect the scent marking and over-marking behaviour of male and female voles. Differences in the effects of food availability on these proceptive behaviours are discussed within the context of the natural history of meadow voles.     

Features of begging calls reveal general condition and need of food of barn swallow (Hirundo rustica) nestlings

Altricial offspring of birds solicit food provisioning by complexbegging displays, implying acoustic and visual signals. Differentcomponents of begging behavior may function as reliable signalsof offspring state and thus reproductive value, on which parentsbase optimal parental decisions about allocation of criticalresources (e.g., food). We experimentally manipulated componentsof general condition of nestling barn swallows (Hirundo rustica)by (1) altering brood size by cross-fostering an unbalanced number of nestlings between pairs of synchronous broods andthus manipulating the level of within-brood competition forfood, (2) injecting some nestlings with a harmless immunogen,simulating an infection, and (3) preventing part of the nestlingsfrom receiving food for a short period while establishing controlgroups. We recorded rate of begging response by individual nestlings as parents visited the nest and recorded begging calls usinga DAT recorder to analyze six sonagraphic features of vocalizations.Our factorial experiment revealed that nestlings deprived offood begged more frequently when parents visited the nest comparedto their non—food-deprived nest mates. Food deprivationincreased duration of syllables forming begging calls, whereas brood size enlargement resulted in increased latency of responseto parental calls. Heavy nestlings in good body condition vocalizedat a relatively low peak frequency. To our knowledge, thisis the first study in which begging rate and sonagraphic structureof begging calls are shown to reliably reveal a diverse setof components of offspring general state, on which parental decisions may be based.     

Do maternal food deprivation and offspring predator cues interactively affect maternal effort in fish?

The state of the environment parents are exposed to during reproduction can either facilitate or impair their ability to take care of their young. Thus, the environmental conditions experienced by parents can have a transgenerational impact on offspring phenotype and survival. Parental energetic needs and the variance in offspring predation risk have both been recognized as important factors influencing the quality and amount of parental care, but surprisingly, they are rarely manipulated simultaneously to investigate how parents adjust care to these potentially conflicting demands. In the maternally mouthbrooding cichlid Simochromis pleurospilus, we manipulated female body condition before spawning and exposure to offspring predator cues during brood care in a two‐by‐two factorial experiment. Subsequently, we measured the duration of brood care and the number and size of the released young. Furthermore, we stimulated females to take up their young by staged predator attacks and recorded the time before the young were released again. We found that food‐deprived females produced smaller young and engaged less in brood care behaviour than well‐nourished females. Final brood size and, related to this, female protective behaviour were interactively determined by nutritional state and predator exposure: well‐nourished females without a predator encounter had smaller broods than all other females and at the same time were least likely to take up their young after a simulated predator attack. We discuss several mechanisms by which predator exposure and maternal nutrition might have influenced brood and offspring size. Our results highlight the importance to investigate the selective forces on parents and offspring in combination, if we aim to understand reproductive strategies.     

Turbidity Hampers Mate Choice in a Pipefish

European coastal waters have in recent years become more turbid as algal growth has increased, probably due to eutrophication, global warming and changes in fish communities. Turbidity reduces visibility, and such changes may in turn affect animal behaviour as well as evolutionary processes that are dependent on visual stimuli. In this study we experimentally manipulated water visibility and olfactory cues to investigate mate choice using the sex role‐reversed broad‐nosed pipefish Syngnathus typhle as our study organism. We show that males spent significantly longer time assessing females when they had access to full visual cues, compared to when visibility was reduced. Presence or absence of olfactory cues from females did not affect mate choice, suggesting that the possible use of smell could not make up for a reduction in visibility. This implies that mate choice is environmentally dependent and that an increased turbidity may affect processes of sexual selection through an impaired possibility for visually based mate choice.     

Public information for solitary foragers: timber rattlesnakes use conspecific chemical cues to select ambush sites

Many animals use public information (PI) gathered from conspecificsto assess the quality of potential foraging locations. To date,research on this phenomenon has focused almost exclusively onsocial foragers that live in groups and monitor nearby individuals.PI is potentially available to solitary foragers as well, inthe form of cues (such as chemical cues) that persist in theenvironment after conspecifics are no longer present. In thisstudy, I examined the response of a solitary sit-and-wait predator,the timber rattlesnake (Crotalus horridus), to chemical cuesfrom conspecifics that had recently fed as opposed to thosethat had been deprived of food. Experiments with a T-maze indicatedthat timber rattlesnakes always follow conspecific chemicaltrails out of the maze, regardless of whether or not the individualleaving the trail had recently fed. However, an enclosure choicetest found that individuals are more likely to select ambushsites in areas with chemical cues from conspecifics that hadrecently fed. These results indicate that snakes may use conspecificchemical cues not only to find mates, shelter sites, and hibernaculabut also profitable food patches. Additionally, this study highlightsthe possibility that other solitary foragers may use PI to guidetheir foraging behavior.     

Food deprivation affects reproduction in adult female mice (Mus musculus) and the age of puberty for their female progeny

Three experiments were designed to test the effects of food deprivation during various phases of the reproductive cycle on fertility and fecundity of the dams and on the age of sexual maturation and body growth of their female progeny. Food deprivation consisted of removal of all food every other day. Animals were deprived of food either during the period prior to pairing, during the period between pairing and conception or during gestation. Both fertility and fecundity were affected by food deprivation in some, but not all manipulations. The female progeny of food-deprived females reached puberty significantly later than the progeny of non-deprived dams when the food deprivation occurred during the week prior to pairing and up until successful insemination after pairing with a fertile male, but not when food deprivation occurred at other times during the reproductive cycle. Body growth did not differ in the daughters of food-deprived dams across the treatments for any of the experiments.     

Agouti locus may influence reproduction under food deprivation in the water vole (Arvicola terrestris)

The effect of 16-hr food deprivation on day 3 and again on day 5 of pregnancy on the fecundity of female water voles homozygous (ae/ae) or heterozygous (A/ae) for, an allele at the Agouti (A) locus, non agouti extreme (ae) was studied. 63 A/ae females (mated to ae/ae males) produced 115 food-deprived and 115 control pregnancies, and 52 ae/ae females (mated to A/ae males) produced 55 food-deprived and 57 control pregnancies. Regardless of the experimental group, pregnant ae/ae females weighed less than A/ae females. The effect of food deprivation on fecundity depended on the Agouti-locus genotype of the female. In food-deprived A/ae females, fecundity was diminished due to fewer successful pregnancies (P < 0.001) and lower survival of the young (P < 0.05). In food-deprived ae/ae females, reproductive performance was not changed; a somewhat reduced rate of successful pregnancies was compensated for by significantly increased (P < 0.002) postnatal survival of the young. In progeny weaned from food-deprived mothers, the frequency of A/ae females was diminished. Resistance of ae/ae females to the negative effect of nutritional stress, and predominance of ae/ae young in progeny produced by food-deprived mothers, may favour the maintenance of polymorphism for the Agouti-locus in natural populations of the water vole.     

Sex-specific genotype-by-environment interactions for cuticular hydrocarbon expression in decorated crickets, Gryllodes sigillatus: implications for the evolution of signal reliability

Phenotypic traits that convey information about individual identity or quality are important in animal social interactions, and the degree to which such traits are influenced by environmental variation can have profound effects on the reliability of these cues. Using inbred genetic lines of the decorated cricket, Gryllodes sigillatus, we manipulated diet quality to test how the cuticular hydrocarbon (CHC) profiles of males and females respond across two different nutritional rearing environments. There were significant differences between lines in the CHC profiles of females, but the effect of diet was not quite statistically significant. There was no significant genotype-by-environment interaction (GEI), suggesting that environmental effects on phenotypic variation in female CHCs are independent of genotype. There was, however, a significant effect of GEI for males, with changes in both signal quantity and content, suggesting that environmental effects on phenotypic expression of male CHCs are dependent on genotype. The differential response of male and female CHC expression to variation in the nutritional environment suggests that these chemical cues may be under sex-specific selection for signal reliability. Female CHCs show the characteristics of reliable cues of identity: high genetic variability, low condition dependence and a high degree of genetic determination. This supports earlier work showing that female CHCs are used in self-recognition to identify previous mates and facilitate polyandry. In contrast, male CHCs show the characteristics of reliable cues of quality: condition dependence and a relatively higher degree of environmental determination. This suggests that male CHCs are likely to function as cues of underlying quality during mate choice and/or male dominance interactions.     

Direct and trans-generational responses to food deprivation during development in the Glanville fritillary butterfly

Life history characteristics and resulting fitness consequences manifest not only in an individual experiencing environmental conditions but also in its offspring via trans-generational effects. We conducted a set of experiments to assess the direct and trans-generational effects of food deprivation in the Glanville fritillary butterfly Melitaea cinxia. Food availability was manipulated during the final stages of larval development and performance was assessed during two generations. Direct responses to food deprivation were relatively minor. Food-deprived individuals compensated, via increased development time, to reach a similar mass as adults from the control group. Delayed costs of compensatory growth were observed, as food-deprived individuals had either reduced fecundity or lifespan depending on the type of feeding treatment they had experienced (intermittent vs. continuous). Female food deprivation did not directly affect her offspring’s developmental trajectory, but the way the offspring coped with food deprivation. Offspring of mothers from control or intermittent starvation treatments reached the size of those in the control group via increased development time when being starved. In contrast, offspring of mothers that had experienced 2 days of continuous food deprivation grew even larger than control animals, when deprived of food themselves. Offspring of food-deprived Glanville fritillary initially showed poor immune response to parasitism, but not later on in development.     

The influence of nutritional state on shoal choice in zebrafish, Danio rerio

We investigated the mechanisms and functions of shoal choice in relation to nutritional state in the zebrafish. Single fish that had been well fed or food deprived for 2 days were presented with a choice between two stimulus shoals. Food-deprived test fish showed a significant preference for well-fed stimulus fish over food-deprived ones whereas well-fed test fish did not exhibit any significant preference. Subsequent experiments showed that food-deprived test fish had a significantly higher foraging success in shoals consisting of well-fed individuals than in ones that comprised food-deprived fish. No difference in the locomotory behaviour of food-deprived and well-fed stimulus fish was found with respect to the proportion of time spent swimming (as opposed to being motionless), the proportion of time spent in the upper part of the test tank and the number of sharp turns. However, body weight, stomach width (measured directly behind the pectoral girdle) and ventro-dorsal height significantly decreased over a 48-h food-deprivation period. The potential use of the latter factors for the recognition of food-deprived individuals is discussed. Copyright 1999 The Association for the Study of Animal Behaviour.     

Food resources, chemical signaling, and nest mate recognition in the ant Formica aquilonia

Animals such as social insects that live in colonies can recognizeintruders from other colonies of the same or different speciesusing colony-specific odors. Such colony odors usually haveboth a genetic and an environmental origin. When within-colonyrelatedness is high (i.e., one or very few reproductive queens),colonies comprise genetically distinct entities, and recognitionbased on genetic cues is reliable. However, when nests containmultiple queens and colonies comprise multiple nests (polydomy),the use of purely genetically determined recognition labelsmay become impractical. This is due to high within-colony geneticheterogeneity and low between-colony genetic heterogeneity.This may favor the use of environmentally determined recognitionlabels. However, because nests within polydomous colonies maydiffer in their microenvironment, the use of environmental labelsmay also be impractical unless they are actively mixed amongthe nests. Using a laboratory experiment, we found that bothisolation per se and diet composition influenced the cuticularchemical profiles in workers of Formica aquilonia. In addition,the level of aggression increased when both the proportionsof dietary ingredients and the availability of food were altered.This suggests that increased aggression was mediated by changesin the chemical profile and that environmental cues can mediaterecognition between colonies. These results also suggest thatthe underlying recognition cues are mutable in response to extrinsicfactors such as the amount and the composition of food.     

The Effect of Female Condition on Maternal Care in the European Earwig

Parental care typically enhances offspring fitness at costs for tending parents. Asymmetries in genetic relatedness entail potential conflicts between parents and offspring over the duration and the amount of care. To understand how these conflicts are resolved evolutionarily, it is important to understand how individual condition affects offspring and parental behaviour and whether parents or offspring make active choices in their interactions. Condition effects on offspring have been broadly studied, but the effect of parental condition on parent–offspring interactions is less well understood, in particular in species where care is facultative and offspring have the option to beg for food from the parents or to self‐forage. In this study, we carried out two experiments in the European earwig Forficula auricularia, a system where females provide facultative care, in which we manipulated female condition (through a high‐food and low‐food treatment) and the degree by which mothers and offspring could make active choices. In a first experiment, where female mobility was limited, female condition had no significant effect on the rate of offspring self‐foraging, which increased with nymph age. In a second experiment, nymph access to food was limited and females in poor nutritional condition provided food to significantly fewer nymphs than high condition females. In both experiments, offspring attendance remained at a constantly high level and was independent of female condition even after experimental separation of females and offspring. Our results show that earwig nymphs do not use cues of female condition to adjust rates of self‐foraging, that females control food provisioning depending on their own condition, and that females and nymphs share control over offspring attendance, a form of care not influenced by female condition.     

A chemical signal of offspring quality affects maternal care in a social insect

Begging signals of offspring are condition-dependent cues that are usually predicted to display information about the short-term need (i.e. hunger) to which parents respond by allocating more food. However, recent models and experiments have revealed that parents, depending on the species and context, may respond to signals of quality (i.e. offspring reproductive value) rather than need. Despite the critical importance of this distinction for life history and conflict resolution theory, there is still limited knowledge of alternative functions of offspring signals. In this study, we investigated the communication between offspring and caring females of the common earwig, Forficula auricularia, hypothesizing that offspring chemical cues display information about nutritional condition to which females respond in terms of maternal food provisioning. Consistent with the prediction for a signal of quality we found that mothers exposed to chemical cues from well-fed nymphs foraged significantly more and allocated food to more nymphs compared with females exposed to solvent (control) or chemical cues from poorly fed nymphs. Chemical analysis revealed significant differences in the relative quantities of specific cuticular hydrocarbon compounds between treatments. To our knowledge, this study demonstrates for the first time that an offspring chemical signal reflects nutritional quality and influences maternal care.     

Begging, food provisioning, and nestling competition in great tit broods infested with ectoparasites

Ectoparasites are a ubiquitous environmental component of breedingbirds, and it has repeatedly been shown that hematoph-agousectoparasites such as fleas and mites reduce the quality andnumber of offspring of bird hosts, thereby lowering the valueof a current brood. Selection acting on the hosts will favorphysiological and behavioral responses that will reduce theparasites' impact. However, the results of the few bird studiesthat addressed the question of whether parasitism leads to ahigher rate of food provisioning are equivocal, and the beggingresponse to infestation has rarely been quantified. A changein begging activity and parental rate of food provisioning couldbe predicted in either direction: parents could reduce theirinvestment in the brood in order to invest more in future broods,or they could increase their investment in order to compensatefor the parasites' effect on the current brood. Since the nestlingsare weakened by the ectoparasites they may beg less, but onthe other hand they may beg more in order to obtain more food.In this study we show experimentally that (1) hen fleas (Ceratophyllusgallinae) reduce the body mass and size of great tit (Parusmajor) nestlings, (2) nestlings of parasitized broods more thandouble their begging rate, (3) the male parents increase thefrequency of feeding trips by over 50%, (4) the females do notadjust feeding rate to the lowered nutritional state of nestlings,and (5) food competition among siblings of parasitized broodsis increased. Ultimately the difference in the parental feedingresponse may be understood as the result of a sex-related differencein the trade-off of i0vesting in current versus future broods.     

Antipredator defense as a limited resource: unequal predation risk in broods of an insect with maternal care

The allocation of parental investment is a potential sourceof conflict within broods whenever offspring are able obtaindifferential access to the parental resource. Unlike the provisioningof food, parental antipredator behavior is usually considereda resource that benefits all offspring simultaneously. In thethornbug treehopper (Umbonia crassicornis), offspring formaggregations in exposed positions on host-plant stems. Theyare subject to intense predation, and maternal defense is theirprimary means of protection. I examined the distribution ofrisk within these offspring groups, using natural variationin the outcome of more than 500 predation attempts (324 recordedon videotape) by vespid wasps (Pseudopolybia compressa) on18 U. crassicornis aggregations. I found three influences onan individual offspring's risk of predation. The first wasthe presence of a defending female: as expected, offspringwere much more likely to survive contact with a wasp if thefemale was present than if the female had disappeared. Thesecond influence was position relative to other offspring: when wasps were successful in removing an individual, they almostalways removed it from the edge of the group. The third influencewas distance from the female: the closer an offspring was tothe female at the time it was contacted by a wasp, the higherits likelihood of survival. The distribution of risk is determinedlargely by the behavior of defending females and the prey-searchingbehavior of wasps. The nature of risk within these aggregations sets the stage for two forms of sibling rivalry: selfish herdbehavior and competition for access to maternal defense. Italso raises the question of how a parent should allocate defenseamong offspring when it is unable to defend them all simultaneously.     

New derivatives of argininosuccinic acid in the urine of a patient with argininosuccinicaciduria

1. The relationships between nutritional state, lipoprotein lipase activity in epididymal fat-pads, and the concentrations of glucose, insulin and unesterified fatty acids in the plasma were studied in rats that had been adapted for 3 weeks to one of two controlled feeding schedules. In one of these, rats had access to food for 14h during each 24h period, and in the other, they had access to food for 14h during each 48h period. Groups of animals were killed at different times during the 14h when they had access to food and during the following period when they were deprived of food. 2. Low lipoprotein lipase activity, low concentrations of plasma glucose and insulin and high concentrations of plasma unesterified fatty acids were found in rats deprived of food for 34h. Feeding resulted in increases in lipoprotein lipase activity and in the concentrations of glucose and insulin in the plasma. Enzyme activity continued to increase during the first 6-9h of the feeding period. 3. After adapted rats had been deprived of food for 12-16h there was a marked and unexpected increase in lipoprotein lipase activity; this occurred even when the rats were kept in an isolated environment. 4. The findings suggest that factors other than the absolute concentrations of insulin and glucose in the blood can exert a considerable influence on lipoprotein lipase activity in the epididymal fat-pad of a rat.