Effects of larval energetic resources on life history and adult allocation patterns in a caddisfly (Trichoptera: Phryganeidae)

Abstract 1. How populations respond to environmental change depends, in part, on the connection between environmental variance during early life stages and its effect on subsequent life‐history traits. For example, environmental variation during the larval stage can influence the life histories of organisms with complex life cycles by altering the amount of time spent in each stage of the life cycle as well as by altering allocation to life‐history traits during metamorphosis. 2. The effects of larval energetic resources on developmental timing, adult mass, fecundity, mating success, and allocation to adult body structures (thorax, abdomen, wings) were examined in an aquatic caddisfly (Agrypnia deflata Milne, Trichoptera: Phryganeidae). Larval energetic reserves were manipulated by removing larval cases just prior to pupation. In the first experiment, cases of all individuals were removed just prior to pupation; experimental individuals were required to build a new case whereas control individuals were allowed to re‐enter their case without building. In the second experiment, energy differences were maximised between the two treatments by supplementing the larval diet of the control group and removing cases and not supplementing the diet of the experimental group. 3. Male and female development time, adult mass, and female fecundity were not influenced by case removal or diet supplementation. In contrast, allocation to adult body parts indicated a trade‐off between abdominal and thoracic mass among case‐removal females, suggesting that, under larval resource stress, females adjust resource allocation during metamorphosis to alleviate potential negative impacts on clutch size. In addition, latency to copulation increased when cases were removed, indicating larval resource stress could influence male mating success. 4. This study suggests that, under larval energetic stress, the negative impacts on female reproduction might be mitigated by re‐allocating resources during metamorphosis, whereas male allocation strategies might not be as flexible as female strategies.     

Sequential predator effects across three life stages of the African tree frog, <Emphasis Type="Italic">Hyperolius spinigularis</Emphasis>

While theoretical studies of the timing of key switch points in complex life cycles such as hatching and metamorphosis have stressed the importance of considering multiple stages, most empirical work has focused on a single life stage. However, the relationship between the fitness components of different life stages may be complex. Ontogenetic switch points such as hatching and metamorphosis do not represent new beginnings—carryover effects across stages can arise when environmental effects on the density and/or traits of early ontogenetic stages subsequently alter mortality or growth in later stages. In this study, I examine the effects of egg- and larval-stage predators on larval performance, size at metamorphosis, and post-metamorphic predation in the African tree frog Hyperolius spinigularis. I monitored the density and survival of arboreal H. spinigularis clutches in the field to estimate how much egg-stage predation reduced the input of tadpoles into the pond. I then conducted experiments to determine: (1) how reductions in initial larval density due to egg predators affect larval survival and mass and age at metamorphosis in the presence and absence of aquatic larval predators, dragonfly larvae, and (2) how differences in mass or age at metamorphosis arising from predation in the embryonic and larval environments affect encounters with post-metamorphic predators, fishing spiders. Reduction in larval densities due to egg predation tended to increase per capita larval survival, decrease larval duration and increase mass at metamorphosis. Larval predators decreased larval survival and had density-dependent effects on larval duration and mass at metamorphosis. The combined effects of embryonic and larval-stage predators increased mass at metamorphosis of survivors by 91%. Larger mass at metamorphosis may have immediate fitness benefits, as larger metamorphs had higher survival in encounters with fishing spiders. Thus, the effects of predators early in ontogeny can alter predation risk even two life stages later.     

Carry-over effects of the larval environment on post-metamorphic performance in two hylid frogs

Life history theory and empirical studies suggest that large size or earlier metamorphosis are suitable proxies for increased lifetime fitness. Thus, across a gradient of larval habitat quality, individuals with similar phenotypes for these traits should exhibit similar post-metamorphic performance. Here we examine this paradigm by testing for differences in post-metamorphic growth and survival independent of metamorphic size in a temperate (spring peeper, Pseudacris crucifer) and tropical (red-eyed treefrog, Agalychnis callidryas) anuran reared under differing larval conditions. For spring peepers, increased food in the larval environment increased post-metamorphic growth efficiency more than predicted by metamorphic phenotype and led to increased mass. Similarly, red-eyed treefrogs reared at low larval density ended the experiment at a higher mass than predicted by metamorphic phenotype. These results show that larval environments can have delayed effects not captured by examining only metamorphic phenotype. These delayed effects for the larval environment link larval and juvenile life history stages and could be important in the population dynamics of organisms with complex life cycles.     

SELECTION ON HERBIVORE LIFE-HISTORY TRAITS BY THE FIRST AND THIRD TROPHIC LEVELS: THE DEVIL AND THE DEEP BLUE SEA REVISITED

Abstract The timing of life‐history events in insects can have important consequences for both survival and reproduction. For insect herbivores with complex life histories, selection is predicted to favor those combinations of traits that increase the size at metamorphosis while minimizing the risk of mortality from natural enemies. Studies quantifying selection on life‐history traits in natural insect herbivore populations, however, have been rare. The purpose of this study was to measure phenotypic selection imposed by elements of the first and third trophic levels on variation in two life‐history traits, the timing of egg hatch and pupal mass, in a population of oak‐feeding caterpillars, Psilocorsis quercicella (Lepidoptera: Oecophoridae). Larvae were collected from the field throughout each of two generations per year for three years and reared to determine the effects of the date of egg hatch on both the risk of attack from parasitoids and the pupal mass of the survivors. The direction and strength of phenotypic selection attributed to aspects of the first and third trophic levels, as well as their combined effects, on the date of egg hatch was measured for each of the six generations. Heritabilities of and genetic correlations between pupal mass and the date of adult emergence from diapause (the life‐history trait expected to have the largest influence on the timing of egg hatch, and thus larval development) were estimated from laboratory matings. In four of the six generations examined, significant directional selection attributed to the first trophic level was detected, always favoring early‐hatching cohorts predicted to experience higher leaf quality than late‐hatching cohorts. Directional phenotypic selection by the third trophic level was detected in only one of three years, and in that year the direction of selection was in opposite directions during the two successive generations. The combined effect of selection by both trophic levels indicated that the third trophic level acted to either reduce or enhance the more predictable pattern of selection attributed to the first trophic level. In addition, I found evidence of truncation selection acting to increase the mean and decrease the variance of pupal mass during the pupa‐adult transition in the laboratory. Pupal mass and diapause duration were found to vary significantly among full‐sibling families; upper bounds for heritability estimates were 0.57 and 0.30, respectively. Furthermore, these two traits were found to be positively genetically correlated (families with larger pupae had longer diapause durations), resulting in a fitness trade‐off, because larger pupae enjoy higher survival through metamorphosis and female fecundity but emerge later, when average leaf quality for offspring is generally poorer.     

Thyroid hormone responsive QTL and the evolution of paedomorphic salamanders

The transformation of ancestral phenotypes into novel traits is poorly understood for many examples of evolutionary novelty. Ancestrally, salamanders have a biphasic life cycle with an aquatic larval stage, a brief and pronounced metamorphosis, followed by a terrestrial adult stage. Repeatedly during evolution, metamorphic timing has been delayed to exploit growth-permissive environments, resulting in paedomorphic salamanders that retain larval traits as adults. We used thyroid hormone (TH) to rescue metamorphic phenotypes in paedomorphic salamanders and then identified quantitative trait loci (QTL) for life history traits that are associated with amphibian life cycle evolution: metamorphic timing and adult body size. We demonstrate that paedomorphic tiger salamanders (Ambystoma tigrinum complex) carry alleles at three moderate effect QTL (met1–3) that vary in responsiveness to TH and additively affect metamorphic timing. Salamanders that delay metamorphosis attain significantly larger body sizes as adults and met2 explains a significant portion of this variation. Thus, substitution of alleles at TH-responsive loci suggests an adaptive pleiotropic basis for two key life-history traits in amphibians: body size and metamorphic timing. Our study demonstrates a likely pathway for the evolution of novel paedomorphic species from metamorphic ancestors via selection of TH-response alleles that delay metamorphic timing and increase adult body size.     

Energy beyond the pupal stage: larval nutrition and its long-time consequences for male mating performance in a scorpionfly

The basic requirement for selection to take effect is variation in fitness relevant traits among individuals of a population. This study is concerned with the question whether environmental conditions met during an early phase of life history that is dominated by the natural component of selection will affect traits and behaviour in a sexual selection context after metamorphosis in a holometabolous insect species. We examined the effects of nutrition as a proximate factor responsible for intrasexual phenotypic variation in the mating performance of male Panorpa vulgaris (Mecoptera: Panorpidae). For this purpose, we manipulated food availability during larval development as well as during adulthood. To obtain matings and to increase their reproductive success males must secrete salivary masses which are then consumed by the females during copulation. The results of the present study are consistent with those of previous studies demonstrating a strong effect of nutrition during adulthood on various fitness relevant traits (salivary gland development, saliva investment in copulations, etc.). But moreover, we could show that food availability during larval development affected male body weight and that there was an interaction between larval and adult diet affecting salivary gland weight relative to body weight. Therefore, food availability during the larval stage can become an important and limiting factor for salivary gland development (and mating success) depending on food availability during adulthood. Several other variables (number of salivary masses, copulation duration, salivary mass weight and saliva investment) seemed not to be associated with larval nutrition.     

Fitness consequences of larval traits persist across the metamorphic boundary

Metamorphosis is thought to provide an adaptive decoupling between traits specialized for each life-history stage in species with complex life cycles. However, an increasing number of studies are finding that larval traits can carry-over to influence postmetamorphic performance, suggesting that these life-history stages may not be free to evolve independently of each other. We used a phenotypic selection framework to compare the relative and interactive effects of larval size, time to hatching, and time to settlement on postmetamorphic survival and growth in a marine invertebrate, Styela plicata. Time to hatching was the only larval trait found to be under directional selection, individuals that took more time to hatch into larvae survived better after metamorphosis but grew more slowly. Nonlinear selection was found to act on multivariate trait combinations, once again acting in opposite directions for selection acting via survival and growth. Individuals with above average values of larval traits were most likely to survive, but surviving individuals with intermediate larval traits grew to the largest size. These results demonstrate that larval traits can have multiple, complex fitness consequences that persist across the metamorphic boundary; and thus postmetamorphic selection pressures may constrain the evolution of larval traits.     

Effects of size at metamorphosis on stonefly fecundity, longevity, and reproductive success

Many organisms with complex life cycles show considerable variation in size and timing at metamorphosis. Adult males of Megarcyssignata (Plecoptera: Perlodidae) are significantly smaller than females and emerge before females (protandry) from two western Colorado streams. During summer 1992 stoneflies from a trout stream emerged earlier in the season and at larger sizes than those from a colder fishless stream, and size at metamorphosis did not change over the emergence period in either stream. We performed two experiments to determine whether variation in size at metamorphosis affected the fecundity, reproductive success and longevity of individuals of this stonefly species and if total lifetime fecundity was affected by the number of matings. In the first experiment, total lifetime fecundity (eggs oviposited) was determined for adult females held in small plastic cages in the field. Males were removed after one copulation, or pairs were left together for life and allowed to multiply mate. Most copulations occurred in the first few days of the experiment. Females in treatments allowing multiple matings had significantly lower total lifetime fecundity and shorter adult longevity than females that only mated once. Multiple matings also reduced longevity of males. Fecundity increased significantly with female body mass at emergence, but only for females that mated once. While multiple matings eliminated the fecundity advantage of large female body size, number of matings did not affect the significant positive relationship between body mass at metamorphosis and longevity of males or females. In a second experiment designed to determine if body mass at emergence affected male mating success, we placed one large and one small male Megarcys in an observation arena containing one female and recorded which male obtained the first mating. The large and the small male had equal probabilities of copulating with the female. Copulations usually lasted all night, and the unmated male made frequent, but unsuccessful attempts to take over the copulating female. Our data suggest that selection pressures determining body size at metamorphosis may operate independently on males and females, resulting in evolution of sexual size dimorphism, protandry, and mating early in the adult stage. We emphasize the importance of interpreting the fitness consequences of larval growth and development on the timing of and size at metamorphosis in the context of the complete life cycle. Received: 1 July 1997 / Accepted: 12 November 1997     

Heritability of and strong single gene (Pgi) effects on life‐history traits in the Glanville fritillary butterfly

We estimated broad‐sense heritabilities (H²) of 13 female and seven male life‐history traits of the Glanville fritillary butterfly (Melitaea cinxia) under semi‐natural conditions in a large outdoor population cage. The analysis was based on full‐sib families collected as young larvae in the field and reared under common garden conditions. We found significant genetic variance in female lifespan, fecundity, number of matings and host‐plant preference as well as in male body mass and mobility. Apart from host‐plant preference, female traits that were more strongly correlated with lifetime reproductive success (LRS; measured as total number of eggs laid) had higher H². LRS itself exhibited significant heritability. Host‐plant preference had very high H², consistent with a previously reported genetically determined geographical cline in host‐plant preference in the study area. Lifespan and egg hatching rate were significantly associated with a SNP in the coding region of the Pgi gene, for which there is previous evidence for balancing selection. Selection on Pgi, which furthermore shows spatial and temporal variation, may maintain genetic variance in fitness‐related life‐history traits. In contrast, we found no strong evidence for life‐history trade‐offs.     

Consequences of induced hatching plasticity depend on predator community

Many prey species face trade-offs in the timing of life history switch points like hatching and metamorphosis. Costs associated with transitioning early depend on the biotic and abiotic conditions found in the subsequent life stage. The red-eyed treefrog, Agalychnis callidryas, faces risks from predators in multiple, successive life stages, and can hatch early in response to mortality threats at the egg stage. Here we tested how the consequences of life history plasticity, specifically early hatching in response to terrestrial egg predators, depend on the assemblage of aquatic larval predators. We predicted that diverse predator assemblages would impose lower total predation pressure than the most effective single predator species and might thereby reduce the costs of hatching early. We then conducted a mesocosm experiment where we crossed hatchling phenotype (early vs. normal hatching) with five larval-predator environments (no predators, either waterbugs, dragonflies, or mosquitofish singly, or all three predator species together). The consequences of hatching early varied across predator treatments, and tended to disappear through time in some predation treatments, notably the waterbug and diverse predator assemblages. We demonstrate that the fitness costs of life history plasticity in an early life stage depend critically on the predator community composition in the next stage.     

Sublethal larval exposure to imidacloprid impacts adult behaviour in Drosophila melanogaster

Pesticides are now chronically found in numerous ecosystems incurring widespread toxic effects on multiple organisms. For insects, the larvae are very exposed to pesticide pollution and the acute effect of insecticides on larvae has been characterized in a range of species. However, the carry‐on effects in adults of sublethal exposure occurring in larvae are not well characterized. Here, we use a collection of strains of Drosophila melanogaster differing in their larval resistance to a commonly used insecticide, imidacloprid, and we test the effect of larval exposure on behavioural traits at the adult stage. Focusing on locomotor activity and on courtship and mating behaviour, we observed a significant carry‐on effect of imidacloprid exposure. The heritability of activity traits measured in flies exposed to imidacloprid was higher than measured in controls and in these, courtship traits were genetically less correlated from mating success. Altogether, we did not observe a significant effect of the larval insecticide resistance status on adult behavioural traits, suggesting that selection for resistance in larvae does not involve repeatable behavioural changes in adults. This lack of correlation between larval resistance and adult behaviour also suggests that resistance at the larval stage does not necessarily result in increased behavioural resilience at a later life stage. These findings imply that selection for resistance in larvae as well as for behavioural resilience to sublethal exposure in adult will combine and impose a greater evolutionary constraint. Our conclusions further substantiate the need to encompass multiple trait measures and life stages in toxicological assays to properly assess the environmental impact of pesticides.     

Effects of Egg and Circulating Testosterone on Ring‐Necked Pheasant (Phasianus colchicus) Male Traits and Combat Outcome

Studies of avian species have shown that maternal effects mediated by the transfer of egg hormones can profoundly affect offspring phenotype and fitness. We previously demonstrated that the injection of a physiological amount of testosterone (T) in the eggs of ring‐necked pheasants (Phasianus colchicus) disrupted the covariation among male morphological traits at sexual maturity and positively affected male mating success. Here, we investigate whether egg T exposure affected adult male circulating T levels at the onset of the breeding season (reflecting gonadal maturation), and the relationship between circulating T and male traits. Egg T exposure did not affect pre‐mating plasma T. T levels were not associated with the expression of secondary sexual and non‐sexual traits or socio‐sexual behaviour (social rank, overall fighting ability and mating success). However, wattle brightness decreased with increasing circulating T in males hatched from T‐eggs (T‐males) but not among control males. In dyadic encounters during the peak mating period, control males with higher pre‐mating T levels had higher chances of being dominant over other control males. However, higher pre‐mating T levels did not predict success in male‐male competition in encounters involving T‐males. We suggest that the long‐term effects of egg T on male phenotype do not originate from differential gonadal maturation according to egg T treatment. Rather, prenatal androgens may have priming effects on functioning of target tissues, translating into differential phenotypic effects according to androgen exposure during embryonic development.     

Thermal reaction norms in two Coenagrion damselfly species: contrasting embryonic and larval life-history traits

1. We studied the temperature‐dependence of important life‐history traits both at the embryonic (egg hatching success, embryonic development time and hatchling size) and the larval stage (larval growth rate, larval survival and larval size after 100 days) using full‐sib families of two congeneric damselflies, Coenagrion hastulatum and Coenagrion puella, that differ in latitudinal distribution. Larvae were reared in the laboratory from the egg stage at four temperatures (12, 17, 22 and 27 °C). 2. The observed patterns of thermal plasticity in embryonic traits showed that the northern species was more successful than the southern species at lower temperatures, in line with the pattern of temperature adaptation in thermal reaction norms. 3. At the larval stage, we found no consistent pattern of latitudinal compensation. The thermal family reaction norms indicate, however, the potential for latitudinal compensation to evolve. We observed an ontogenetic shift in thermal optima for larval growth rate, with a higher optimal temperature for growth rate during the first 2 weeks of the larval stage. 4. This is the first indication of the existence of latitudinal compensation at the interspecific level in an invertebrate; it is stage‐specific, being present only in the embryonic stage. We argue that compensation in the embryonic stage may be much more likely than in the larvae and stress the importance of including more then one life‐history stage when drawing conclusions about the adaptiveness of patterns in thermal reaction norms.     

Lifetime egg production and egg mortality in the damselflyPyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae)

Artificial oviposition sites were used to estimate egg deposition rates in the field. Females laid an average of 10.76 eggs/minute with a mean duration of 22.81 minutes, giving an average clutch size of 245 eggs. Since one mating corresponded to one clutch of eggs, lifetime mating success was used as a measure of the number of clutches produced. Mean lifetime clutch production was 5.91 clutches per female, equating to 1447 eggs per female per lifetime. Eggs were hatched in the laboratory at temperatures comparable with those in the field. Hatching was highly synchronised and the overall hatching success was 75.1%. Causes of egg mortality in the laboratory were limited to infertility and unhatchability. Since no other sources of egg mortality could be found at the study site, this value was a good reflection of hatching success in the field. Lifetime egg production and hatching success were used to estimate the number of viable offspring produced per female, giving a higher order estimate of reproductive success than has previously been published for a zygopteran.     

Differences in nutritional quality of parts of Vitis vinifera berries affect fitness of the European grapevine moth

The European grapevine moth, Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae), is a major grapevine pest in Europe. The larva is polyphagous and able to develop on more than 25 plant species, several of them being more suitable than Vitaceae for the fitness of L. botrana. Larvae normally eat the pulp of the berry, but may also consume the seeds according to the development stage of the berry and the larval density per bunch. Understanding the effect on individual fitness of such feeding behaviour is important to assess how suitable the different berry tissues are for this insect. We offered to the larvae either entire berries, seeds, or pulp with skin of the variety Vitis vinifera cv. ‘Cabernet Sauvignon’ as larval food in order to assess several life history traits from egg hatching to adult death. Two control groups were raised on semisynthetic diets, offering a low (no plant material) or a higher (with corn flour) nutritive value medium. The larvae performed differently when fed on diets containing different parts of berries. The larvae fed on a diet containing grape berry seeds had a prolonged development time and showed higher mortality. The females emerging from these larvae had a lower fecundity and mating success than the females emerging from larvae fed on diets containing other parts of the berries. However, their longevity was greater in comparison to the other groups. We conclude that seeds of Cabernet Sauvignon are not toxic to larvae but affect the reproductive life history traits in L. botrana.     

Feedback between size balance and consumption strongly affects the consequences of hatching phenology in size‐dependent predator–prey interactions

In many size‐dependent predator–prey systems, hatching phenology strongly affects predator–prey interaction outcomes. Early‐hatched predators can easily consume prey when they first interact because they encounter smaller prey. However, this process by itself may be insufficient to explain all predator–prey interaction outcomes over the whole interaction period because the predator–prey size balance changes dynamically throughout their ontogeny. We hypothesized that hatching phenology influences predator–prey interactions via a feedback mechanism between the predator–prey size balance and prey consumption by predators. We experimentally tested this hypothesis in an amphibian predator–prey model system. Frog tadpoles Rana pirica were exposed to a predatory salamander larva Hynobius retardatus that had hatched 5, 12, 19 or 26 days after the frog tadpoles hatched. We investigated how the salamander hatch timing affected the dynamics of prey mortality, size changes of both predator and prey, and their subsequent life history (larval period and size at metamorphosis). The predator–prey size balance favoured earlier hatched salamanders, which just after hatching could successfully consume more frog tadpoles than later hatched salamanders. The early‐hatched salamanders grew rapidly and their accelerated growth enabled them to maintain the predator‐superior size balance; thus, they continued to exert strong predation pressure on the frog tadpoles in the subsequent period. Furthermore, frog tadpoles exposed to the early‐hatched salamanders were larger at metamorphosis and had a longer larval period than other frog tadpoles. These results suggest that feedback between the predator‐superior size balance and prey consumption is a critical mechanism that strongly affects the impacts of early hatching of predators in the short‐term population dynamics and life history of the prey. Because consumption of large nutrient‐rich prey items supports the growth of predators, a similar feedback mechanism may be common and have strong impacts on phenological shifts in size‐dependent trophic relationships.     

Effects of multiple mating on the fecundity of an invasive pest (Octodonta nipae): the existence of an intermediate optimal female mating rate

Multiple mating is found in many insect taxa where both of the sexes can mate more than once. For males, this leads to the advantage of increasing their paternity by fertilizing more females. However, there is a trade‐off of resource allocation between reproduction and other life‐history characters. In the present study, the impact of increased mating rate on reproductive fitness of the invasive nipa palm hispid beetle Octodonta nipae Maulik (Coleoptera: Chrysomelidae) is investigated. A series of mating frequencies (i.e. 1, 5, 10, 15, 20 times) is selected from video frame playback, ranking from the minimum to maximum mating rate observed under laboratory conditions over a given time period. Fecundity parameters such as lifetime egg production, egg‐hatching rate, effective oviposition period and longevity are investigated for the evaluation of reproductive efficiency. For female O. nipae, increased fecundity is correlated with the mating frequency. Females mating 15 times lay the largest number of eggs (138.82 ± 6.87) and have a hatching rate of 47.43 ± 4.08%. After mating 20 times, females suffer significant declines in oviposition (90.31 ± 8.38 eggs) and egg‐hatching rate (34.16 ± 4.93%). Moreover, the population growth rate reaches a maximum in the females that mate 15 times. The results show that multiple matings in O. nipae have an intermediate optimal range within which female reproductive success is enhanced, providing empirical evidence for the existence of a trade‐off between costs and benefits during copulation based on resource allocation.     

Increased lifetime reproductive success of first‐hatched siblings in Common Kestrels Falco tinnunculus

Order of birth has profound consequences on offspring across taxa during development and can have effects on individuals later in life. In birds, differential maternal allocation and investment in their progeny lead to variance in the environmental conditions that offspring experience during growth within the brood. In particular, laying and hatching order have been proposed to influence individual quality during the growing period, but little is known about the fitness consequences that these two factors have for offspring from a lifetime perspective. We explored the effect of laying and hatching order on post‐fledgling survival (measured as recruitment probability) and lifetime reproductive success (LRS) in Common Kestrels Falco tinnunculus, using a long‐term and individual‐based dataset. First‐hatched chicks showed higher survival probability and LRS than their siblings. This effect was not due to body condition of the individuals at adulthood, the quality of their mates or the reproductive outcome compared with later‐hatched individuals. Instead, first‐hatched chicks had a higher recruitment probability. This could be explained by the higher body condition attained by first‐hatched chicks at the end of the nesting period, perhaps due to an enhanced competitive advantage for food over their siblings at the time of hatching. Laying order, in contrast to hatching order, appeared to have little or no effect on LRS. Our results suggest that hatching order within siblings predicts fitness, and that better early‐life conditions during growth experienced by first‐hatched chicks improve first survival and then recruitment, resulting in an enhanced LRS.     

Short‐term larval food stress and associated compensatory growth reduce adult immune function in a damselfly

Abstract 1. In animals with a complex life cycle, larval stressors may carry over to the adult stage. Carry‐over effects not mediated through age and size at metamorphosis have rarely been studied. The present study focuses on the poorly documented immune costs of short‐term food stress both in the larval stage and after metamorphosis in the adult stage. 2. The present study quantified immune function [number of haemocytes, activity of prophenoloxidase (proPO) and phenoloxidase (PO)] in an experiment where larvae of the damselfly Lestes viridis were exposed to a transient starvation period. 3. Directly after starvation, immune variables were reduced in starved larvae. Levels of proPO and PO remained low after starvation, even after metamorphosis. In contrast, haemocyte numbers were fully compensated by the end of the larval stage, yet were lower in previously starved animals after metamorphosis. This can be explained as a cost of the observed compensatory growth after starvation. Focusing only on potential costs of larval stressors within the larval stage may therefore be misleading. 4. The here‐identified immunological cost in the adult stage of larval short‐term food stress and associated compensatory growth strongly indicates that physiological costs may explain hidden carry‐over effects bridging metamorphosis. This adds to the increasing awareness that the larval and adult stages in animals with a complex life cycle should be jointly studied, as trade‐offs may span metamorphosis.