Plasticity In Life-history Traits Research Articles

Early life food intake modulates effects of diet restriction on lifespan and fecundity in later life in a predatory mite (Acari: Phytoseiidae)

Abstract The nutritional status of an individual can significantly influence its life history traits, including development, growth, reproduction, and survival. In the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae), the plasticity of life history traits, such as developmental time and size at maturity, is influenced by the quality and quantity of food. This study aimed to investigate the effects of dietary restriction at different life stages (i.e., juvenile, early adulthood, and later adulthood) on the lifespan and fecundity of P. persimilis. We found that reduced dietary intake during early adulthood resulted in a shorter lifespan for both male and female P. persimilis. Furthermore, this study demonstrated a sex-specific response to dietary restriction: it extended the lifespan of males but reduced that of females during later adulthood. Diet restriction during the postovipositional period of females showed the most variable life history trait response. Our results showed that the impact of diet restriction at different life stages can have combined influences on the postovipositional duration of P. persimilis, where the individuals receiving diet restriction during immature development and early adulthood had a greater reduction in ovipositional duration as those experiencing diet restriction during late adulthood. In addition, we observed a positive correlation between the lifespan and fecundity of females, with higher prey availability increasing both. The insights obtained from our research contribute to a better understanding of the aging process and dietary requirements of P. persimilis, which can facilitate the development of more effective biological control strategies using this predator for spider mites in agriculture.

Variation and plasticity in life-history traits and fitness of wild Arabidopsis thaliana populations are not related to their genotypic and ecological diversity

BackgroundDespite its implications for population dynamics and evolution, the relationship between genetic and phenotypic variation in wild populations remains unclear. Here, we estimated variation and plasticity in life-history traits and fitness of the annual plant Arabidopsis thaliana in two common garden experiments that differed in environmental conditions. We used up to 306 maternal inbred lines from six Iberian populations characterized by low and high genotypic (based on whole-genome sequences) and ecological (vegetation type) diversity.ResultsLow and high genotypic and ecological diversity was found in edge and core Iberian environments, respectively. Given that selection is expected to be stronger in edge environments and that ecological diversity may enhance both phenotypic variation and plasticity, we expected genotypic diversity to be positively associated with phenotypic variation and plasticity. However, maternal lines, irrespective of the genotypic and ecological diversity of their population of origin, exhibited a substantial amount of phenotypic variation and plasticity for all traits. Furthermore, all populations harbored maternal lines with canalization (robustness) or sensitivity in response to harsher environmental conditions in one of the two experiments.ConclusionsOverall, we conclude that the environmental attributes of each population probably determine their genotypic diversity, but all populations maintain substantial phenotypic variation and plasticity for all traits, which represents an asset to endure in changing environments.

Diet-induced plasticity of life-history traits and gene expression in outbred Drosophila melanogaster population.

Food is fundamental for the survival of organisms, governing growth, maintenance, and reproduction through the provision of essential macronutrients. However, access to food with optimum macronutrient composition, which will maximize the evolutionary fitness of an organism, is not always guaranteed. This leads to dietary mismatches with potential impacts on organismal performance. To understand the consequences of such dietary mismatches, we examined the effects of isocaloric diets varying in macronutrient composition on eight key organismal traits spanning across the lifespan of a large outbred Drosophila melanogaster population (n ~ 2500). Our findings reveal that carbohydrate-reduced isocaloric diets correlates to accelerated pre-adult development and boosts reproductive output without impacting pre-adult viability and body size. Conversely, an elevated dietary carbohydrate content correlated to reduced lifespan in flies, evidenced by accelerated functional senescence including compromised locomotor activity and deteriorating gut integrity. Furthermore, transcriptomic analysis indicated a substantial difference in gene regulatory landscapes between flies subject to high-carbohydrate versus high-protein diet, with elevated protein levels indicating transcriptomes primed for reduced synthesis of fatty acids. Taken together, our study helps advance our understanding of the effect of macronutrient composition on life history traits and their interrelations, offering critical insights into potential adaptive strategies that organisms might adopt against the continual dietary imbalances prevalent in the rapidly evolving environment.

Plasticity of Life-History Traits and Adult Fitness of Fall Webworm in Relation to Climate Change.

Temperature is an important environmental factor influencing the life-history traits of ectotherms. This study investigated the effects of larval-rearing temperature (21, 23, 25, and 27 °C) on the life-history traits and adult fitness of the fall webworm, Hyphantria cunea, an economically important invasive pest of China. With the increase in temperature during the larval stage, the larval developmental duration was significantly shortened, and the body mass was significantly increased, as was that of the body mass and size of pupae. The carbohydrate and lipid content of pupae significantly decreased with increasing larval-rearing temperature, whereas the protein content significantly increased. Adult body size and egg production increased significantly with increasing larval-rearing temperature, whereas there was no significant difference in egg diameter. These results indicate that H. cunea demonstrates life-history traits plasticity. In addition, the increase in fecundity would maintain a stable population size of H. cunea under higher temperatures. Such characteristics could enable H. cunea to spread to the more southern, warmer areas of China, posing an increased risk to the forestry industry in these regions.

Variation and trade-offs in life history traits of the protist parasite Monocystis perplexa (Apicomplexa) in its earthworm host Amynthas agrestis.

The life history of a parasite describes its partitioning of assimilated resources into growth, reproduction, and transmission effort, and its precise timing of developmental events. The life cycle, in contrast, charts the sequence of morphological stages from feeding to the transmission forms. Phenotypic plasticity in life history traits can reveal how parasites confront variable environments within hosts. Within the protist phylum Apicomplexa major clades include the malaria parasites, coccidians, and most diverse, the gregarines (with likely millions of species). Studies on life history variation of gregarines are rare. Therefore, life history traits were examined for the gregarine Monocystis perplexa in its host, the invasive earthworm Amynthas agrestis at three sites in northern Vermont, United States of America. An important value of this system is the short life-span of the hosts, with only seven months from hatching to mass mortality; we were thus able to examine life history variation during the entire life cycle of both host and parasite. Earthworms were collected (N=968 over 33 sample periods during one host season), then parasites of all life stages were counted, and sexual and transmission stages measured, for each earthworm. All traits varied substantially among individual earthworm hosts and across the sites. Across sites, timing of first appearance of infected earthworms, date when transmission stage (oocysts packed within gametocysts) appeared, date when number of both feeding (trophic) cells and gametocysts were at maximum, and date when 100% of earthworms were infected differed from 2-8 weeks, surprising variation for a short season available for parasite development. The maximal size of mating cells varied among hosts and across sites and this is reflected in the number of oocysts produced by the gametocyst. A negative trade-off was observed for the number of oocysts and their size. Several patterns were striking: (1) Prevalence reached 100% at all sites by mid season, only one to three weeks after parasites first appeared in the earthworms. (2) The number of parasites per host was large, reaching 300 × 103 cells in some hosts, and such high numbers were present even when parasites first appeared in the host. (3) At one site, few infected earthworms produced any oocysts. (4) The transmission rate to reach such high density of parasites in hosts needed to be very high for a microbe, from >0.33% to >34.3% across the three sites. Monocystis was one of the first protist parasites to have its life cycle described (early 19th century), but these results suggest the long-accepted life cycle of Monocystis could be incomplete, such that the parasites may be transmitted vertically (within the earthworm's eggs) as well as horizontally (leading to 100% prevalence) and merogony (asexual replication) could be present, not recognized for Monocystis, leading to high parasitemia even very early in the host's season.

Phenotypic plasticity in reproductive and somatic efforts of female Columbian ground squirrels

Phenotypic plasticity of life-history traits is well known among vertebrate species. We estimated reproductive and somatic efforts of female Columbian ground squirrels ( Urocitellus columbianus (Ord, 1815)) to test for plasticity of these important resource allocations. We examined a 27-year dataset of life-history traits on these long-living (8–10 years), hibernating, montane-living mammals. Environmental variation was estimated from two important traits of mothers, their relative timing of breeding and spring maternal body mass (initial “capital” for use in subsequent reproduction). Results from 183 known-aged mothers and 508 litters revealed considerable variation in the relative timing of breeding, initial maternal mass, and reproductive and somatic efforts, as well as significant variation among ages and years. Results from 125 mothers that reproduced more than once (and 450 litters) revealed significant plasticity of reproductive and somatic efforts with respect to relative timing of breeding and spring maternal mass. A within-subject centering statistical approach showed that phenotypically plastic reproductive and somatic efforts were due to variation within individuals, but were not always reflected by the pattern of responses among individuals in the population. The plastic responses of different mothers appeared to be similar in strength.

Life history variation of the Hairy-tailed Akodont (Necromys lasiurus, Rodentia, Sigmodontinae) in the Caatinga biome of northeastern Brazil

Abstract Rodents are notable for their unique life history traits that render a fast-breeding capacity. Their short generation times allow local adaptations to appear, and several studies have tried to understand if—and how—geographical variables influence local adaptation in life history traits. We compared demographic and life history traits of the Neotropical cricetid Necromys lasiurus based on 7,400 museum specimens collected daily and simultaneously over 5 years at several sites in the Caatinga biogeographic domain subject to heterogeneous geographic and climatological variables. This sample, assembled by the National Plague Service between 1951 and 1955, includes skulls, skins, and individual specimen data currently deposited in the Museu Nacional (Rio de Janeiro, Brazil). Based on this material, we analyzed population fluctuation, breeding season, sexual size dimorphism, sexual maturity, and litter size. We also hypothesized that geographic variables (elevation, rainfall, temperature, longitude, and latitude) influence key life history traits, such as size at birth and litter size. Overall, N. lasiurus showed plastic reproductive patterns, with few traits shared among populations. Notably, there is strong seasonal variation in population fluctuation patterns, breeding events clumped in early dry season and old individuals distributed throughout all the year, as has been seen for populations in other biomes. Geography had no influence on size at birth but litter size was explained by the interaction between maternal weight and geographical variables. Plastic life history traits so intimately responsive to climatological variables likely contribute to N. lasiurus having one of the largest geographic ranges among Neotropical cricetids, as well as to its status as the most important plague reservoir in the Caatinga domain.

Life-History traits of Hollandichthys multifasciatus (Eigenmann & Norris, 1900) (Characiformes: Characidae) in coastal Atlantic Forest blackwater streams from Southeastern Brazil

Ecological and life history traits have been used to understand the basic ecology of fishes. This study aimed to examine the existence of plasticity in life history traits of populations of Hollandichthys multifasciatus in ten blackwater streams. This is an inseminating Characidae, endemic to the Atlantic coastal drainages of Brazil. Different aspects of the life-history of the species, such as mean length, sex ratio, absolute and relative fecundity, gonadosomatic index, condition factor, length-weight relationship and the growth parameter (b) of 185 specimens were studied during the period of low precipitation (June-September). Fish samples were obtained along a 100 m stretch of each stream, and some habitat variables recorded. ANOVA and Kruskal-Wallis tests indicated a similarity in most of the analyzed traits, with exception of the mean length of immatures, Gonadosomatic Index of mature males and condition factor of immatures and mature adults. Also, slope tests of the length-weight relationship were significantly different for immatures. The observed differences were attributed to heterogeneity in food availability and/or other site-specific factors, which may influence growth and/or breeding aspects among the studied localities. The approach used herein may improve understanding of trait plasticity under natural conditions, helping to understand fish-community responses to anthropogenic changes.

Histone acetylation regulates the expression of genes involved in worker reproduction in the ant Temnothorax rugatulus

BackgroundIn insect societies, queens monopolize reproduction while workers perform tasks such as brood care or foraging. Queen loss leads to ovary development and lifespan extension in workers of many ant species. However, the underlying molecular mechanisms of this phenotypic plasticity remain unclear. Recent studies highlight the importance of epigenetics in regulating plastic traits in social insects. Thus, we investigated the role of histone acetylation in regulating worker reproduction in the ant Temnothorax rugatulus. We removed queens from their colonies to induce worker fecundity, and either fed workers with chemical inhibitors of histone acetylation (C646), deacetylation (TSA), or the solvent (DMSO) as control. We monitored worker number for six weeks after which we assessed ovary development and sequenced fat body mRNA.ResultsWorkers survived better in queenless colonies. They also developed their ovaries after queen removal in control colonies as expected, but not in colonies treated with the chemical inhibitors. Both inhibitors affected gene expression, although the inhibition of histone acetylation using C646 altered the expression of more genes with immunity, fecundity, and longevity functionalities. Interestingly, these C646-treated workers shared many upregulated genes with infertile workers from queenright colonies. We also identified one gene with antioxidant properties commonly downregulated in infertile workers from queenright colonies and both C646 and TSA-treated workers from queenless colonies.ConclusionOur results suggest that histone acetylation is involved in the molecular regulation of worker reproduction, and thus point to an important role of histone modifications in modulating phenotypic plasticity of life history traits in social insects.

Invasion of pumpkinseed Lepomis gibbosus is facilitated by phenotypic plasticity across its invasion gradient

As a non-native species invades a new region, individuals at the range front are often characterised by differences in their traits and behaviours versus individuals in the established ‘core’ area. Here, differences in life history traits of invading pumpkinseed Lepomis gibbosus were assessed across a fine spatial scale in the Saricay Stream, Turkey, with seven locations sampled between their core area and the invasion front. Following genetic analyses that suggested the pumpkinseed all originated from the same founding population, life history trait analyses revealed pronounced differences between the sites at the core and front that were independent of environmental factors. Pumpkinseed in sites towards the invasion front were of relatively low abundance and displayed relatively high reproductive investment, with heavier gonads, higher fecundity and smaller eggs. They also had faster growth rates than pumpkinseed in sites towards the core of the invasion. The traits displayed by pumpkinseed at sites in the mid-range were intermediate between the extremes displayed by fish at core and frontal sites. These results suggested high plasticity in life history traits of these pumpkinseed across this fine-scale invasion gradient and was considered to be most likely due to responses to low intra-specific competition at the invasion front that had shifted selective pressures towards higher investment in somatic growth and reproduction.

Shallow seamounts represent speciation islands for circumglobal yellowtail Seriola lalandi

Phenotypic plasticity in life-history traits in response to heterogeneous environments has been observed in a number of fishes. Conversely, genetic structure has recently been detected in even the most wide ranging pelagic teleost fish and shark species with massive dispersal potential, putting into question previous expectations of panmixia. Shallow oceanic seamounts are known aggregation sites for pelagic species, but their role in genetic structuring of widely distributed species remains poorly understood. The yellowtail kingfish (Seriola lalandi), a commercially valuable, circumglobal, epipelagic fish species occurs in two genetically distinct Southern Hemisphere populations (South Pacific and southern Africa) with low levels of gene-flow between the regions. Two shallow oceanic seamounts exist in the ocean basins around southern Africa; Vema and Walters Shoal in the Atlantic and Indian oceans, respectively. We analysed rare samples from these remote locations and from the South African continental shelf to assess genetic structure and population connectivity in S. lalandi and investigated life-history traits by comparing diet, age, growth and maturation among the three sites. The results suggest that yellowtail from South Africa and the two seamounts are genetically and phenotypically distinct. Rather than mere feeding oases, we postulate that these seamounts represent islands of breeding populations with site-specific adaptations.

Breeding structure and invasiveness in social insects.

Plasticity in life history traits is commonly used to explain the invasion success of social insects. While intraspecific plasticity is often recognized, interspecific variability is easily overlooked, whereby different species exhibit different strategies. The presence of many queens per colony and the collapse of colony boundaries have favored invasiveness for many ant species. However, these strategies are absent from other successful social invaders. Here, we report that various life-history traits may differentially enhance the invasion success in social insects. We suggest that other aspects of their breeding system, like asexual reproduction, intranidal mating and pre-adaptation to inbreeding may enhance their invasion success. Thorough comparative studies between native and introduced populations or studies of closely related species will help identify additional traits favoring the invasion success of social insects, and ultimately provide a more comprehensive picture of the evolutionary factors enhancing invasiveness across this phylogenetically and ecologically diverse group.

Reproductive traits of the dwarf gobies Pandaka trimaculata and Pandaka lidwilli in the western Pacific Ocean: histological evidence from one of the smallest fishes in the world.

Gobies are generally small fishes which play important roles in estuarine ecosystems, yet little attention has been paid to their life-history traits in the western Pacific region. In the present study, the reproductive traits of the dwarf gobies Pandaka trimaculata and Pandaka lidwilli were explored by examining their populations in a subtropical estuary on Okinawa-jima Island, Japan, over 15 months. The Okinawan populations of both species shared similar reproductive traits. Pandaka trimaculata and P. lidwilli exhibited early female maturation at minimum sizes of 8.8 and 9.4 mm standard length (SL), respectively, which indicate that populations of the Pandaka species in the subtropical region represent some of the smallest fishes in the world. Nonetheless, they also had high relative body sizes at maturity relative to the attained asymptotic SLs, ranging from 75.8% to 80.4%, which suggests that their populations are vulnerable to negative impacts. Both the species also had prolonged spawning periods, extending from February to November (P. trimaculata) and from January to October (P. lidwilli), indicating that these local populations have a high potential for maintenance and resilience. Their spawning periods, sizes at maturity and fecundities varied among seasons and latitudes, possibly because of low water temperatures affecting the relative allocation of energy to growth and reproduction. Such plasticity of life-history traits in these small fishes indicates that they would be suitable models for understanding the evolution of life-history strategies and monitoring the responses of organisms to climate change.

Germination time influences post-germination life-history traits and progeny seed germination patterns in the desert annual Erodium laciniatum (Geraniaceae)

Annual plants in arid regions germinate at different times within a growing season, from early in the season to late, and this may affect post-germination traits. For this study, I tested the effect of germination timing on post-germination life-history traits, including progeny seed germination in the desert annual Erodium laciniatum var. pulverulentum (Cav.) Boiss. Traits of November- and February-germinated individuals were studied in a field survey carried out in northwestern Saudi Arabia, and the germination of freshly matured and after-ripened seeds from both early- and late-germinated plants was assessed. Overall, E. laciniatum showed significant phenotypic plasticity in life-history traits arising from different germination times. Density, survivorship and reproductive success of early-germinated plants were all significantly greater than for those that germinated later. Late-germinated plants flowered earlier, bolted at smaller size and allocated more biomass to reproduction than did early-germinated individuals. Delayed germination shortened both flowering period and life span. Seeds produced by late-germinated plants had greater germination percentage than did seeds from early-germinated plants.

Stagewise resolution of temperature-dependent embryonic and postembryonic development in the cowpea seed beetle Callosobruchus maculatus (F.)

BackgroundThe thermal plasticity of life-history traits receives wide attention in the recent biological literature. Of all the temperature-dependent traits studied, developmental rates of ectotherms are especially often addressed, and yet surprisingly little is known about embryonic responses to temperature, including changes in the thermal thresholds and thermal sensitivity during early development. Even postembryonic development of many cryptically living species is understood superficially at best.ResultsThis study is the first to estimate the exact durations of developmental stages in the cowpea seed beetle C. maculatus from oviposition to adult emergence at five permissive constant temperatures from 20 to 32 °C. Early embryonic development was tracked and documented by means of destructive sampling and subsequent confocal imaging of fluorescently stained specimens. Late embryonic and early larval development was studied with the use of destructive sampling and light microscopy. Well-resolved temporal series based on thousands of embryos allowed precise timing of the following developmental events: formation of the blastoderm; formation, elongation, and retraction of the germ band; dorsal closure; the onset and completion of sclerotization of the cuticle; hatching, and penetration of the first-instar larva into the cowpea seed. Pupation and adult eclosion were observed directly through an incision in the seed coat. The thermal phenotype of C. maculatus was found to vary in the course of ontogeny and different stages scaled disproportionately with temperature, but pitfalls and caveats associated with analyses of relative durations of individual stages are also briefly discussed.ConclusionDisproportionate changes in developmental durations with temperature may have important implications when study design requires a high degree of synchronization among experimental embryos or when the occurrence of particular stages in the field is of interest, as well as in any other cases when development times need to be estimated with precision. This work provides one of the first examples of integration of embryological techniques with ecophysiological concepts and will hopefully motivate similar projects in the future. While experiments with Drosophila continue to be the main source of information on animal development, knowledge on other model species is instrumental to building a broader picture of developmental phenomena.

Uncovering unique plasticity in life history of an endangered centenarian fish

The ability to adapt to changing environments is fundamental for species persistence. Both plasticity and genetic selection are potential drivers that allow for traits to be advantageous, thus leading to increases in survival or fitness. Identifying phenotypic plasticity in life history traits of long-lived organisms can be difficult owing to high survival, long generation times, and few studies at sufficient spatial and temporal scales to elicit a plastic response within a population. To begin to understand phenotypic plasticity of a long-lived freshwater fish in response to environmental conditions, we used a long-term data set consisting of over 1,200 mark-recapture events to inform our understanding of dynamic rate functions and life history attributes. Furthermore, we used a common garden experimental approach to confirm whether changes in life history traits are in response to plasticity in the reaction norm or are genetically derived. Using these approaches, we demonstrated differences in life history traits among Pallid Sturgeon (Scaphirhynchus albus) occupying river segments of varying physical and hydrological stress. The common garden experiment corroborated plastic phenotypic expression in reaction norms for age at first maturity, longevity, fecundity, and maximum size. These growth-mediated attributes resulted in differences in overall fitness traits, where Pallid Sturgeon fecundity was greater than a tenfold difference and 3–6 times the number of life-time spawning events. Anthropogenic modifications to river form and function are likely responsible for the variation in life history attributes resulting from an increased metabolic demand for maintaining station, foraging, and migration. Collectively, our approach provided surprising insight into the capabilities of a centenarian fish to dramatically respond to a changing environment.

The desert locust, Schistocerca gregaria, plastically manipulates egg size by regulating both egg numbers and production rate according to population density

Egg-size adjustment is one of the important plastic life-history traits for animals living in heterogeneous environments. The adaptive investment hypothesis predicts that mothers should increase progeny size according to certain cues predicting adverse future conditions of their offspring. However, reproductive resources are limited, and females have to simultaneously reduce egg number to allocate more resources to increase size. It remains unclear how single individuals alter egg size and number according to temporally heterogeneous environments. In the present study, we examined how desert locusts, Schistocerca gregaria, plastically alter egg size and number according to population density. We also investigated the trans-generational maternal effects on progeny characteristics as well as their own maternal physiological response (oviposition interval). Females kept in crowded conditions laid significantly larger and heavier eggs by reducing clutch size (number of eggs per egg pod) compared to isolated females, suggesting the existence of a reproductive trade-off between the two traits. The crowding-forced isolated females induced concerted changes not only in egg size but also in egg number tending towards those characteristics of gregarious control, implying that single individuals showed trade-off when egg size was increased. Double-blind testing confirmed the rapid crowding effects on egg size. Females also responded to crowding by extending the oviposition interval. As the oviposition interval extended, egg size increased, but clutch size decreased. Eggs from crowding-forced isolated females began to produce gregarious-phase type hatchlings (large and black) instead of solitarious-phase type ones (small and green). These results suggested that S. gregaria plastically manipulate egg size by regulating egg numbers and egg production rate, and indicated the presence of trans-generational maternal effects on progeny phase.

Phenotypic plasticity and local adaptation in freeze tolerance: Implications for parasite dynamics in a changing world

Marshallagia marshalli is a multi-host gastrointestinal nematode that infects a variety of artiodactyl species from temperate to Arctic latitudes. Eggs of Marshallagia are passed in host faeces and develop through three larval stages (L1, L2, and L3) in the environment. Although eggs normally hatch as L1s, they can also hatch as L3s. We hypothesised that this phenotypic plasticity in hatching behaviour may improve fitness in subzero and highly variable environments, and this may constitute an evolutionary advantage under current climate change scenarios. To test this, we first determined if the freeze tolerance of different free-living stages varied at different temperatures (−9 °C, −20 °C and −35 °C). We then investigated if there were differences in freeze tolerance of M. marshalli eggs sourced from three discrete, semi-isolated, populations of wild bighorn and thinhorn sheep living in western North America (latitudes: 40°N, 50°N, 64°N). The survival rates of eggs and L3s were significantly higher than L1s at −9 °C and −20 °C, and survival of all three stages decreased significantly with increasing freeze duration and decreasing temperature. The survival of unhatched L1s was significantly higher than the survival of hatched L1s. There was no evidence of local thermal adaptation in freeze tolerance among eggs from different locations. We conclude that developing to the L3 in the egg may result in a fitness advantage for M. marshalli, with the egg protecting the more vulnerable L1 under freezing conditions. This phenotypic plasticity in life-history traits of M. marshalli might be an important capacity, a potential exaptation capable of enhancing parasite fitness under temperature extremes.

Plasticity in life history traits of a cyprinid fish in an intermittent river

The extreme seasonal environmental variation of intermittent rivers has a profound effect on freshwater fish communities. Yet, few studies have examined the consequences of the seasonal cycles of flooding and drying to fish condition and reproduction in these ecosystems. In this study, we compared the body condition, reproduction and diet of two chub populations from two adjacent sites (a perennial and an intermittent site) on the main stem of a Mediterranean river (Evrotas River, S. Greece). The study was conducted in spring 2017, three months after flow resumption and before the onset of chub reproductive period. Condition (net weight adjusted for length) of fish did not differ significantly between the two sites, despite lower aquatic macroinvertebrate availability at the intermittent site. Fish at the intermittent site compensated for the lower aquatic prey availability by increasing their feeding intensity and by shifting to higher terrestrial prey consumption. In addition, chub liver weight (adjusted for length) and gonadal weight (adjusted for length) were significantly higher at the intermittent site, indicating higher somatic and reproductive investment. These results highlight the resilience of fish populations inhabiting streams with extreme variation in flow, due to natural and/or anthropogenic drought.

The early-life environment and individual plasticity in life-history traits.

We tested whether the early‐life environment can influence the extent of individual plasticity in a life‐history trait. We asked: can the early‐life environment explain why, in response to the same adult environmental cue, some individuals invest more than others in current reproduction? Moreover, can it additionally explain why investment in current reproduction trades off against survival in some individuals, but is positively correlated with survival in others? We addressed these questions using the burying beetle, which breeds on small carcasses and sometimes carries phoretic mites. These mites breed alongside the beetle, on the same resource, and are a key component of the beetle's early‐life environment. We exposed female beetles to mites twice during their lives: during their development as larvae and again as adults during their first reproductive event. We measured investment in current reproduction by quantifying average larval mass and recorded the female's life span after breeding to quantify survival. We found no effect of either developing or breeding alongside mites on female reproductive investment, nor on her life span, nor did developing alongside mites influence her size. In post hoc analyses, where we considered the effect of mite number (rather than their mere presence/absence) during the female's adult breeding event, we found that females invested more in current reproduction when exposed to greater mite densities during reproduction, but only if they had been exposed to mites during development as well. Otherwise, they invested less in larvae at greater mite densities. Furthermore, females that had developed with mites exhibited a trade‐off between investment in current reproduction and future survival, whereas these traits were positively correlated in females that had developed without mites. The early‐life environment thus generates individual variation in life‐history plasticity. We discuss whether this is because mites influence the resources available to developing young or serve as important environmental cues.