Host plant chemical composition critically shapes the performance of insect herbivores feeding on them. Some insects have become specialized on plant secondary metabolites, and even use them to their own advantage such as defense against predators. However, infection by plant pathogens can seriously alter the interaction between herbivores and their host plants. We tested whether the effects of the plant secondary metabolites, iridoid glycosides (IGs), on the performance and immune response of an insect herbivore are modulated by a plant pathogen. We used the IG-specialized Glanville fritillary butterfly Melitaea cinxia, its host plant Plantago lanceolata, and the naturally occurring plant pathogen, powdery mildew Podosphaera plantaginis, as model system. Pre-diapause larvae were fed on P. lanceolata host plants selected to contain either high or low IGs, in the presence or absence of powdery mildew. Larval performance was measured by growth rate, survival until diapause, and by investment in immunity. We assessed immunity after a bacterial challenge in terms of phenoloxidase (PO) activity and the expression of seven pre-selected insect immune genes (qPCR). We found that the beneficial effects of constitutive leaf IGs, that improved larval growth, were significantly reduced by mildew infection. Moreover, mildew presence downregulated one component of larval immune response (PO activity), suggesting a physiological cost of investment in immunity under suboptimal conditions. Yet, feeding on mildew-infected leaves caused an upregulation of two immune genes, lysozyme and prophenoloxidase. Our findings indicate that a plant pathogen can significantly modulate the effects of secondary metabolites on the growth of an insect herbivore. Furthermore, we show that a plant pathogen can induce contrasting effects on insect immune function. We suspect that the activation of the immune system toward a plant pathogen infection may be maladaptive, but the actual infectivity on the larvae should be tested.

Antibiotics have long been used in the raising of animals for agricultural, industrial or laboratory use. The use of subtherapeutic doses in diets of terrestrial and aquatic animals to promote growth is common and highly debated. Despite their vast application in animal husbandry, knowledge about the mechanisms behind growth promotion is minimal, particularly at the molecular level. Evidence from evolutionary research shows that immunocompetence is resource-limited, and hence expected to trade off with other resource-demanding processes, such as growth. Here, we ask if accelerated growth caused by antibiotics can be explained by genome-wide trade-offs between growth and costly immunocompetence. We explored this idea by injecting broad-spectrum antibiotics into wood tiger moth (Arctia plantaginis) larvae during development. We follow several life-history traits and analyse gene expression (RNA-seq) and bacterial (r16S) profiles. Moths treated with antibiotics show a substantial depletion of bacterial taxa, faster growth rate, a significant downregulation of genes involved in immunity and significant upregulation of growth-related genes. These results suggest that the presence of antibiotics may aid in up-keeping the immune system. Hence, by reducing the resource load of this costly process, bodily resources may be reallocated to other key processes such as growth.

A major goal in biology is to understand how evolution shapes variation in individual life histories. Genome-wide association studies have been successful in uncovering genome regions linked with traits underlying life history variation in a range of species. However, lack of functional studies of the discovered genotype-phenotype associations severely restrains our understanding how alternative life history traits evolved and are mediated at the molecular level. Here, we report acis-regulatory mechanism whereby expression of alternative isoforms of the transcription co-factorvestigial-like 3(vgll3) associate with variation in a key life history trait, age at maturity, in Atlantic salmon (Salmo salar). Using a common-garden experiment, we first show thatvgll3genotype associates with puberty timing in one-year-old salmon males. By way of temporal sampling ofvgll3expression in ten tissues across the first year of salmon development, we identify a pubertal transition invgll3expression where maturation coincided with a 66% reduction in testicularvgll3expression. Thelatematuration allele was not only associated with a tendency to delay puberty, but also with expression of a rare transcript isoform ofvgll3pre-puberty. By comparing absolutevgll3mRNA copies in heterozygotes we show that the expression difference between theearlyandlatematurity alleles is largelycis-regulatory. We propose a model whereby expression of a rare isoform from thelateallele shifts the liability of its carriers towards delaying puberty. These results exemplify the potential importance of regulatory differences as a mechanism for the evolution of life history traits. Author summary Alternative life history strategies are an important source of diversity within populations and promote the maintenance of adaptive capacity and population resilience. However, in many cases the molecular basis of different life history strategies remains elusive. Age at maturity is a key adaptive life history trait in Atlantic salmon and has a relatively simple genetic basis. Using salmon age at maturity as a model, we report a mechanism whereby different transcript isoforms of the key age at maturity gene,vestigial-like 3(vgll3), associate with variation in the timing of male puberty. Our results show how gene regulatory differences in conjunction with variation in gene transcript structure can encode for complex alternative life histories.

Central theories explaining the maintenance of individual differences in behavior build on the assumption that behavior mediates life-history trade-offs between current and future reproduction. However, current empirical evidence does not robustly support this assumption. This mismatch might be because current theory is not clear about the role of behavior in individual allocation versus acquisition of resources, hindering empirical testing. The relative importance of allocation compared to acquisition is a key feature of classic life-history theory, but appears to have been lost in translation in recent developments of life-history theory involving behavior. We argue that determining the relative balance between variation in resource allocation and acquisition, and the role of behavior in this process, will help to build more robust and precise predictions.

Hatchery-reared fish show high mortalities after release to the wild environment. Explanations for this include potentially predetermined genetics, behavioral, and physiological acclimation to fish farm environments, and increased vulnerability to predation and parasitism in the wild. We studied vulnerability to Diplostomum spp. parasites (load of eye flukes in the lenses), immune defense (relative spleen size) and antipredator behaviors (approaches toward predator odor, freezing, and swimming activity) in hatchery-reared juvenile Arctic charr (Salvelinus alpinus) using a nested mating design. Fish were exposed to eye-fluke larvae via the incoming water at the hatchery. Fish size was positively associated with parasite load, but we did not find any relationship between relative spleen size and parasitism. The offspring of different females showed significant variation in their parasite load within sires, implying a dam effect in the vulnerability to parasites. However, the family background did not have any effect on spleen size. In the mean sire level over dams, the fish from the bolder (actively swimming) families in the predator trials suffered higher loads of eye flukes than those from more cautiously behaving families. Thus, the results indicate potentially maternally inherited differences in vulnerability to eye-fluke parasites, and that the vulnerability to parasites and behavioral activity are positively associated with each other at the sire level. This could lead to artificial and unintentional selection for increased vulnerability to both parasitism and predation if these traits are favored in fish farm environments.

Reducing Emissions from Deforestation and forest Degradation (REDD+) is envisioned as a performance-based incentive to influence forest use behavior and governance towards the preservation and management of forests. In relatively forest-rich Lao PDR, the policy space that REDD+ planners are attempting to navigate is populated by enduring political and economic interests that affect the country's forest estate. A further layer to the problem of REDD+ planning is the tension between often expert-driven, externally proposed solutions; national ownership over interventions; and the extent of political will to take action to reform currently unsustainable patterns of forest and forest land exploitation. This paper draws from a series of semi-structured interviews conducted in 2013-2014, to develop a political and institutional analysis of the limitations to the effectiveness of REDD+ in steering towards a lower forest-derived emissions trajectory in Lao PDR. While internationally-driven projects follow long-standing national objectives to varying degrees, it remains unclear how REDD+ can target main drivers of deforestation in the absence of a more politically engaged and nationally-owned planning process, that also challenges the prevailing logic of avoiding these drivers. Despite the importance of improving domestic ownership over REDD+, this would arguably be of limited impact unless oriented towards transformational change that would seek to overcome political and economic barriers to avoided deforestation. Stronger ownership could be developed via more mutually driven REDD+ planning, while tackling main drivers of deforestation necessitates as a starting point the engagement of powerful actors that have so far been absent from REDD+ debate.

Atlantic salmon (Salmo salar) is a species with diverse life-history strategies, to which the timing of maturation contributes considerably. Recently, the genome region including the gene vgll3 has gained attention as a locus with a large effect on Atlantic salmon maturation timing, and recent studies on the vgll3 locus in salmon have indicated that its effect might be mediated through body condition and accumulation of adipose tissue. However, the cellular and physiological pathways leading from vgll3 genotype to phenotype are still unknown. Standard metabolic rate is a potentially important trait for resource acquisition and assimilation and we hypothesized that this trait, being a proxy for the maintenance energy expenditure of an individual, could be an important link in the pathway from vgll3 genotype to maturation timing phenotype. As a first step to studying links between vgll3 and the metabolic phenotype of Atlantic salmon, we measured the standard metabolic rate of 150 first-year Atlantic salmon juveniles of both sexes, originating from 14 different families with either late-maturing or early-maturing vgll3 genotypes. No significant difference in mass-adjusted standard metabolic rate was detected between individuals with different vgll3 genotypes, indicating that juvenile salmon of different vgll3 genotypes have similar maintenance energy requirements in the experimental conditions used and that the effects of vgll3 on body condition and maturation are not strongly related to maintenance energy expenditure in either sex at this life stage.