The gut bacterial community affects immunity but not metabolism in a specialist herbivorous butterfly

1. Plant tissues often lack essential nutritive elements and may contain a range of secondary toxic compounds. As nutritional imbalance in food intake may affect the performances of herbivores, the latter have evolved a variety of physiological mechanisms to cope with the challenges of digesting their plant‐based diet. Some of these strategies involve living in association with symbiotic microbes that promote the digestion and detoxification of plant compounds or supply their host with essential nutrients missing from the plant diet. In Lepidoptera, a growing body of evidence has, however, recently challenged the idea that herbivores are nutritionally dependent on their gut microbial community. It is suggested that many of the herbivorous Lepidopteran species may not host a resident microbial community, but rather a transient one, acquired from their environment and diet. Studies directly testing these hypotheses are however scarce and come from an even more limited number of species.
2. By coupling comparative metabarcoding, immune gene expression, and metabolomics analyses with experimental manipulation of the gut microbial community of prediapause larvae of the Glanville fritillary butterfly (Melitaea cinxia, L.), we tested whether the gut microbial community supports early larval growth and survival, or modulates metabolism or immunity during early stages of development.
3. We successfully altered this microbiota through antibiotic treatments and consecutively restored it through fecal transplants from conspecifics. Our study suggests that although the microbiota is involved in the up‐regulation of an antimicrobial peptide, it did not affect the life history traits or the metabolism of early instars larvae.
4. This study confirms the poor impact of the microbiota on diverse life history traits of yet another Lepidoptera species. However, it also suggests that potential eco‐evolutionary host‐symbiont strategies that take place in the gut of herbivorous butterfly hosts might have been disregarded, particularly how the microbiota may affect the host immune system homeostasis.

     

Effects of prey quality and availability on the life history of a trap-building predator

Although generalist predators catch a great diversity of prey species, foraging theory has mostly been concerned with quantitative aspects and neglected questions about the nutrient quality of prey. Here, we test the hypothesis that the life history of a trap-building predator is affected by both prey availability and by the nutrient quality of prey. Under controlled laboratory conditions, orb-weaving spiders ( Zygiella x-notata ) were raised from hatchlings to maturity on prey of different nutrient quality and in different amounts. Both prey nutrient quality and availability had significant but different effects on many important life history traits, such as instar duration, number of instars used in the development, body weight at maturation and development time. Prey availability was especially important for growth rates whereas prey nutrient quality had the most severe effects on juvenile survivorship and female fecundity. Furthermore, while prey of low quality tended to reduce the number of instars used in the development, prey availability induced sex-specific responses in instar numbers. Thus, both prey nutrient quality and availability may be important factors shaping the evolution of life history traits in generalist predators.     

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

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

A high‐throughput method to quantify feeding rates in aquatic organisms: A case study with Daphnia

1. Food ingestion is one of the most basic features of all organisms. However, obtaining precise—and high‐throughput—estimates of feeding rates remains challenging, particularly for small, aquatic herbivores such as zooplankton, snails, and tadpoles. These animals typically consume low volumes of food that are time‐consuming to accurately measure.
2. We extend a standard high‐throughput fluorometry technique, which uses a microplate reader and 96‐well plates, as a practical tool for studies in ecology, evolution, and disease biology. We outline technical and methodological details to optimize quantification of individual feeding rates, improve accuracy, and minimize sampling error.
3. This high‐throughput assay offers several advantages over previous methods, including i) substantially reduced time allotments per sample to facilitate larger, more efficient experiments; ii) technical replicates; and iii) conversion of in vivo measurements to units (mL^‐1 hr^‐1 ind^‐1) which enables broad‐scale comparisons across an array of taxa and studies.
4. To evaluate the accuracy and feasibility of our approach, we use the zooplankton, Daphnia dentifera, as a case study. Our results indicate that this procedure accurately quantifies feeding rates and highlights differences among seven genotypes.
5. The method detailed here has broad applicability to a diverse array of aquatic taxa, their resources, environmental contaminants (e.g., plastics), and infectious agents. We discuss simple extensions to quantify epidemiologically relevant traits, such as pathogen exposure and transmission rates, for infectious agents with oral or trophic transmission.

     

Factors affecting the reproductive success of the crab spider Misumenoides formosipes: the covariance between juvenile and adult traits

Summary To examine the importance of covariance between stages in traits related to foraging, we quantified the relationships between reproductive success and sizerelated variability in weight gain in juvenile and adult instars of the crab spider Misumenoides formosipes (Araneae: Thomisidae). Prereproductive weight and fecundity are both highly correlated with carapace width, a linear measure of size which does not change within an instar. In field populations, adult females with larger carapaces gain more weight and are more likely to reproduce than females with smaller carapaces. The growth rate of spiders fed ad libitum in the laboratory is unrelated to size, suggesting that size-related differences in the field are due to variation in prey-capture success. Adult females with a carapace width less than 3.4 mm comprised 22% of the population, but were never found to reproduce. Of the individuals that did reproduce, a 17% increase in carapace width resulted in a 100% increase in fecundity. Juvenile stages must be examined to understand adult foraging and reproductive success, because the net weight gained by juvenile instars determines adult size. The final weight gained by spiders in the antepenultimate and penultimate instars explained nearly all the variation in carapace width in the penultimate and adult instars, respectively. We found that constraints on foraging in late juvenile stages are different from the adult stage. Penultimate foraging behavior differs from that of adults, because of constraints on foraging in the period preceding ecdysis. Additionally, in both late juvenile instars, carapace width had little or no effect on the final weight gained within the instar suggesting that factors that affect foraging are different between the juvenile and adult stages. These analyses stress the fact that to fully understand the effects of foraging on reproductive success, we must examine stage-specific constraints throughout an organism's life history.     

Life‐history differences across latitude in common side‐blotched lizards (Uta stansburiana)

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Applying life-history strategies for freshwater macroinvertebrates to lentic waters

• 1 Effective environmental management requires a sound understanding of the causal mechanisms underlying the relationship of species with their environment. Mechanistic explanations linking species and environment are ultimately based on species traits. Many tools for ecological assessment and biomonitoring lack such explanations. Elsewhere, we have defined life‐history strategies, based on the interrelations between species traits and their functional implications.
• 2 This study tests the hypothesis that life‐history strategies represent different solutions to particular ecological problems, thus connecting species and their environment through species traits. Data on aquatic macroinvertebrates in a variety of waterbodies were analysed in terms of life‐history strategies. These waterbodies differed in environmental conditions and macroinvertebrate assemblages. Solutions to the ecological problems present in each type of water body were expected to be reflected in the abundance of (species exhibiting) different life‐history strategies.
• 3 Results show clear differences in strategy composition between the different water types, which could be related to the prevailing environmental conditions through mechanistic explanations. For example, species with a long period of juvenile development and a synchronized emergence of short‐lived adults were most dominant in large mesotrophic waterbodies with stable and predictable environmental conditions. In contrast, species that have a rapid development and spread successive reproduction attempts over a longer time period were most abundant in waterbodies with fluctuating and less predictable environmental conditions.
• 4 Differences in strategy composition provide insight into the prevailing environmental conditions related to temporal predictability, and habitat favourability, from the perspective of the species themselves. By reducing diverse species assemblages to a small number of strategies, representing easily interpretable relationships, this approach may be useful in environmental quality assessment programmes, including those required by the European Water Framework Directive. Based on mechanistic explanations, life‐history strategies may generate testable predictions and guide future research. Further research may focus on expanding life‐history strategies to include other species groups and ecosystems.

     

Relating life‐history traits,environmental constraints and local extinctions in river fish

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Contrasting diel activity and feeding patterns of four instars of Rhyacophila dorsalis (Trichoptera)

1. Ontogenetic shifts in prey choice and predator behaviour can affect food‐web structure. Therefore, it is important to establish if the diet and feeding activity differ between life‐stages of the same species. This hypothesis was tested for second, third, fourth and fifth larval instars of Rhyacophila dorsalis by comparing their diel activity and feeding patterns. Second to fifth instars collected from two streams were used either for gut analyses or for observations of their activity and feeding patterns in three stream tanks. Food was provided in excess; being organisms living in bryophytes on top of a large stone in each tank, augmented by different‐sized larvae of Ephemeroptera, Simuliidae and Chironomidae. As few first instars for gut analyses were found in the field, the diet of first instars reared in the laboratory was also studied. 2. Larvae for gut analyses were taken 1 h before dusk or dawn (n = 50 larvae per instar for each day or night sample). First and second instars fed on the smaller food items with no significant day‐night differences in diet. Gut contents indicated a progressive trend from feeding chiefly at night in third instars to almost exclusively at night in fifth instars. Fourth and fifth instars fed on the larger food items, whilst the diet of the third instar larvae overlapped with that of both the earlier and later instars. 3. Diel activity patterns of single larvae differed between instars but not within each instar (n = 20 larvae per instar). Second instars were active throughout the 24 h, with peaks at dusk, around midnight, dawn and around midday. A similar pattern was shown by third instars but the peak of activity at midday was less than the other three peaks. Prey were captured only during these peaks for both instars. Fourth and fifth instars were most active, and fed only, at night. They used an ambush strategy to capture more active prey at dusk and dawn (e.g. Baetis, Gammarus), and a searching strategy to capture more sedentary prey during the night (e.g. chironomids, simuliids). These experiments provided support for the hypothesis under test. If competition and/or interference occur between instars, then it could be reduced between earlier and later instars because of differences in their diet and diel pattern of feeding activity.     

Environmental,spatial and phylogenetic determinants of fish life‐history traits and functional composition of Australian rivers

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Carryover effects of larval environment on individual variation in a facultatively diadromous fish

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Can biological traits of stream invertebrates help disentangle the effects of multiple stressors in an agricultural catchment?

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Detrital nutrient content determines growth rate and elemental composition of bromeliad‐dwelling insects

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Life‐history trade‐offs vary with resource availability across the geographic range of a widespread plant

• Trade‐offs between reproduction, growth and survival arise from limited resource availability in plants. Environmental stress is expected to exacerbate these negative correlations, but no studies have evaluated variation in life‐history trade‐offs throughout species geographic ranges. Here we analyse the costs of growth and reproduction across the latitudinal range of the widespread herb Plantago coronopus in Europe.
• We monitored the performance of thousands of individuals in 11 populations of P. coronopus, and tested whether the effects of growth and reproduction on a set of vital rates (growth, probability of survival, probability of reproduction and fecundity) varied with local precipitation and soil fertility. To account for variation in internal resources among individuals, we analysed trade‐offs correcting for differences in size.
• Growth was negatively affected by previous growth and reproduction. We also found costs of growth and reproduction on survival, reproduction probability and fecundity, but only in populations with low soil fertility. Costs also increased with precipitation, possibly due to flooding‐related stress. In contrast, growth was positively correlated with subsequent survival, and there was a positive covariation in reproduction between consecutive years under certain environments, a potential strategy to exploit temporary benign conditions.
• Overall, we found both negative and positive correlations among vital rates across P. coronopus geographic range. Trade‐offs predominated under stressful conditions, and positive correlations arose particularly between related traits like reproduction investment across years. By analysing multiple and diverse fitness components along stress gradients, we can better understand life‐history evolution across species’ ranges, and their responses to environmental change.

     

Life-history strategies in freshwater macroinvertebrates

• 1 Explaining spatial and temporal differences in species assemblages is a central aim of ecology. It requires a sound understanding of the causal mechanisms underlying the relationship of species with their environment. A species trait is widely acknowledged to be the key that links pattern and process, although the enormous variety of traits hampers generalization about which combination of traits are adaptive in a particular environment.
• 2 In three steps, we used species traits to match species and environment, and chose lentic freshwater ecosystems to illustrate our approach. We first identified key environmental factors and selected the species traits that enable the organism to deal with them. Secondly, we investigated how investments in these traits are related (e.g. through trade‐offs). Thirdly, we outlined 13 life‐history strategies, based on biological species traits, their interrelations known from life‐history theory and their functional implications.
• 3 Species traits and environmental conditions are connected through life‐history strategies, with different strategies representing different solutions to particular ecological problems. In addition, strategies may present an integrated response to the environment as they are based on many different traits and their interrelationships. The presence and abundance of (species exhibiting) different life‐history strategies in a location may therefore give direct information about how a particular environment is experienced by the species present.
• 4 Life‐history strategies can be used to (i) explain differences in species assemblages either between locations or in different periods; (ii) compare waterbodies separated by large geographical distances, which may comprise different regional species pools or span species distribution areas and (iii) reduce often very complex, biodiverse assemblages into a few meaningful, easily interpretable relationships.

     

Complex offspring size effects: variations across life stages and between species

Classical optimality models of offspring size and number assume a monotonically increasing relationship between offspring size and performance. In aquatic organisms with complex life cycles, the size–performance function is particularly hard to grasp because measures of performance are varied and their relationships with size may not be consistent throughout early ontogeny. Here, we examine size effects in premetamorphic (larval) and postmetamorphic (juvenile) stages of brooding marine animals and show that they vary contextually in strength and direction during ontogeny and among species. Larger offspring of the sea anemone Urticina felina generally outperformed small siblings at the larval stage (i.e., greater settlement and survival rates under suboptimal conditions). However, results differed when analyses were conducted at the intrabrood versus across‐brood levels, suggesting that the relationship between larval size and performance is mediated by parentage. At the juvenile stage (15 months), small offspring were less susceptible than large ones to predation by subadult nudibranchs and both sizes performed similarly when facing adult nudibranchs. In a sympatric species with a different life history (Aulactinia stella), all juveniles suffered similar predation rates by subadult nudibranchs, but smaller juveniles performed better (lower mortalities) when facing adult nudibranchs. Size differences in premetamorphic performance of U. felina were linked to total lipid contents of larvae, whereas size‐specific predation of juvenile stages followed the general predictions of the optimal foraging strategy. These findings emphasize the challenge in gathering empirical support for a positive monotonic size–performance function in taxa that exhibit complex life cycles, which are dominant in the sea.     

Competition during early ontogeny: Effects of native and invasive planktivores on the growth,survival, and habitat use of bluegill

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Spatial and temporal patterns in Arctic mosquito abundance

1. Organisms that undergo a shift in ontogeny and habitat type often change their spatial distribution throughout their life cycle, but how this affects population dynamics remains poorly understood.
2. We examined spatial and temporal patterns in Aedes nigripes abundance, a widespread univoltine Arctic mosquito species (Diptera: Culicidae), hypothesizing that the spatial distribution of adults would be closely tied to aquatic habitat.
3. We tracked adult densities of A. nigripes near Kangerlussuaq, Greenland using emergence traps, CO₂-baited traps, and sweep-nets.
4. In back-to-back years of sampling (2017 and 2018) we found two-fold variation in overall abundance.
5. Adults were spatially patchy when first emerging from aquatic habitats but within a week, mean capture rates for host-seeking adult females were similar across locations, even in places far from larval habitat.
6. Daily variation in mosquito captures was primarily explained by weather, with virtually no mosquito activity when temperatures averaged less than 8°C or wind speeds exceeded 6 m/s. Gravid females (3% of resting adults) were spatially patchy on the landscape, but not always in the same places where most adults emerged.
7. The spatial distribution of adults is quickly uncoupled from the spatial distribution of larvae because A. nigripes females may disperse far from their natal habitats in search of a blood-meal and high-quality oviposition habitat.

8. This research highlights the value of studying ecological processes that act at disparate life stages for understanding the population biology of organisms with complex life cycles.     

The role of fish life histories in allometrically scaled food‐web dynamics

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