Armelle Vallat

Corticosterone: effects on feather quality and deposition into feathers

Summary 1. The concentration of the glucocorticoid hormone corticosterone (CORT) is increasingly used in ecology and conservation biology as an integrated measure of the historical record of an individual’s hypothalamo–pituitary– adrenal (HPA) activity during feather growth. However, where and how CORT is incorporated in feathers is incompletely known. 2. We therefore examined whether CORT is reliably measured with an enzyme immunoassay, where CORT is incorporated in the feather and where it affects feather quality, and whether CORT incorporation is related to plasma CORT levels, feather growth rate and melanin pigmentation. 3. During the regrowth of plucked tail feathers, we injected pigeons with tritium-labelled CORT, and implanted a CORT-releasing pellet to increase plasma CORT concentration for about 3 days. In feather segments, we measured labelled CORT (DPM3H) and we quantified CORT with an enzyme immunoassay EIA (CORTEIA )a nd double-checked the results with ultra-high performance liquid chromatography–tandem mass spectrometry (LCMS) (CORTMS). 4. Administered CORT affected feather structure and colour at the very base of the feather (epidermal collar, ramogenic zone) and reduced growth rate. In contrast, incorporation of CORT into the feather happened mainly in the blood quill, as shown with all three methods (DPM3H, CORTEIA and CORTMS). 5. Incorporation of CORT into feathers was only roughly proportional to plasma concentration, proportional to feather growth rate and increased with melanin pigmentation. 6. Measuring CORT in feather is a way to reveal past events of increased stress during feather growth in birds.

The Arabidopsis Pep-PEPR system is induced by herbivore feeding and contributes to JA-mediated plant defence against herbivory

Highlight Dysfunction of the Pep-PEPR system and its interplay with JA signalling results in increased plant susceptibility towards herbivore attack indicating that endogenous signalling also contributes to herbivore defence.

Microbiome affects egg carotenoid investment, nestling development and adult oxidative costs of reproduction in Great tits

Summary 1. Parasites influence allocation trade-offs between reproduction and self-maintenance and consequently shape host life-history traits. The host microbiome includes pathogenic and commensal micro-organisms that are remarkable in their diversity and ubiquity. However, experimental studies investigating whether the microbiome shapes host reproduction are still lacking. 2. In this study, we tested whether the microbiome affects three important components of bird reproduction, namely (i) the maternal transfer of anti-microbial compounds to the eggs, (ii) the development of nestlings and (iii) the trade-off between reproduction and self-maintenance, here measured by the oxidative costs of reproduction. 3. We experimentally modified the microbiome of wild breeding Great tits (Parus major )b y spraying nests with liquid solution that either favoured or inhibited bacterial growth compared to a control. These treatments modified the bacterial communities in the nests and on adult feathers. 4. We found that females from the treatment that decreased bacterial densities in the nests laid eggs with less carotenoids than females from the control, while we found no significant effect of increasing bacterial densities and modifying community composition compared to the control. Nestlings exposed to decreased bacterial densities grew faster and had longer tarsus length at fledging. Moreover, our analyses revealed that the relationship between investment in reproduction and oxidative damage was affected by the treatments. Adults raising larger clutches suffered higher oxidative damage in control nests, whereas this oxidative cost of reproduction was not detected when we modified bird microbiome. 5. Our study provides experimental evidence for an effect of the microbiome on egg carotenoid investment, nestling development and oxidative cost of reproduction and thus highlights the major effect that the microbiome may have on the evolution of host life-history strategies.

Intra- and interspecific challenges modulate cortisol but not androgen levels in a year-round territorial damselfish

Interactions between individuals of different species are commonplace in animal communities. Some behaviors displayed during these interspecific social interactions may be very similar to those displayed during intraspecific social interactions. However, whether functional analogies between intra- and interspecific behaviors translate at the proximate level into an overlap in their underlying endocrine mechanisms remains largely unknown. Because steroids both mediate social behaviors and respond to them, we approached this question by comparing the behavioral and steroid response of free-living dusky gregories (Stegastes nigricans) to standardized territorial intrusions (sTI) of either conspecific or heterospecific food competitors. Stegastes nigricans is a year-round territorial fish that ‘cultivates’ the algae on which it feeds and is highly aggressive to both intra- and interspecific intruders. Behavioral differences between intra- and interspecific aggressive responses to sTI were marginal, and sTI tests caused an increase in cortisol levels that was positively related with the levels of aggression. In contrast, androgen levels did not increase in response to sTI, yet they showed a positive relationship with agonistic behavior. These results parallel a pattern that was first described for year-round territorial bird species. Furthermore, they suggest that changes in endocrine-hormone levels during territoriality might be independent of the species that induces the territorial response.

Wood ants produce a potent antimicrobial agent by applying formic acid on tree-collected resin.

Abstract Wood ants fight pathogens by incorporating tree resin with antimicrobial properties into their nests. They also produce large quantities of formic acid in their venom gland, which they readily spray to defend or disinfect their nest. Mixing chemicals to produce powerful antibiotics is common practice in human medicine, yet evidence for the use of such “defensive cocktails” by animals remains scant. Here, we test the hypothesis that wood ants enhance the antifungal activity of tree resin by treating it with formic acid. In a series of experiments, we document that (i) tree resin had much higher inhibitory activity against the common entomopathogenic fungus Metarhizium brunneum after having been in contact with ants, while no such effect was detected for other nest materials; (ii) wood ants applied significant amounts of endogenous formic and succinic acid on resin and other nest materials; and (iii) the application of synthetic formic acid greatly increased the antifungal activity of resin, but had no such effect when applied to inert glass material. Together, these results demonstrate that wood ants obtain an effective protection against a detrimental microorganism by mixing endogenous and plant‐acquired chemical defenses. In conclusion, the ability to synergistically combine antimicrobial substances of diverse origins is not restricted to humans and may play an important role in insect societies.

Badge Size Reflects Sperm Oxidative Status within Social Groups in the House Sparrow Passer domesticus

The phenotype-linked fertility hypothesis proposes that male ornaments reflect male fertility. Male ornaments could honestly signal sperm quality due to the high susceptibility of sperm to free radicals on the one hand and the negative impact of oxidative stress on ornament elaboration on the other hand. Thus, only males with superior antioxidant defences could bear the cost of more elaborated sexual ornaments without suffering adverse fitness costs. Yet, in species where males experience differential access to fertile females, a trade-off emerges between investing into traits favouring mating opportunities (e.g. secondary sexual ornaments, social dominance, mate-guarding behaviours, etc.) or into traits favouring sperm competitive ability (e.g. sperm numbers and quality). When male sexual ornaments promote greater access to fertile females, a negative relationship can then be predicted between ornamentation and sperm quality. We tested the latter hypothesis and the phenotype-linked fertility hypothesis in wild House Sparrows Passer domesticus by exploring the relationships between sperm quality, melanin-based ornamentation, and redox status in blood and sperm. We found no correlation between badge size and sperm swimming performance. However, we found that within a social group, large-badged males better protect their ejaculates from oxidative stress, and thus produce less oxidized ejaculates. Additionally, we found that badge size did not reflect social dominance, and thus the protection of the ejaculate is independent of males’ ability to monopolize resources. Our results suggest that badge size might reflect male investment into the antioxidant protection of their sperm relative to a given social environment, and thus females may accrue both direct and indirect benefits by mating with large-badged males producing less oxidized ejaculates.

Environmental stress linked to consumption of maternally derived carotenoids in brown trout embryos (Salmo trutta)

Abstract The yellow, orange, or red colors of salmonid eggs are due to maternally derived carotenoids whose functions are not sufficiently understood yet. Here, we studied the significance of naturally acquired carotenoids as maternal environmental effects during embryo development in brown trout (Salmo trutta). We collected eggs from wild females, quantified their egg carotenoid content, fertilized them in vitro in full‐factorial breeding blocks to separate maternal from paternal effects, and raised 3,278 embryos singly at various stress conditions until hatching. We found significant sire effects that revealed additive genetic variance for embryo survival and hatching time. Dam effects were 5.4 times larger than these sire effects, indicating that maternal environmental effects play an important role in determining embryo stress tolerance. Of the eight pigment molecules that we targeted, only astaxanthin, zeaxanthin (that both affected egg redness), and lutein were detected above our confidence thresholds. No strong link could be observed between carotenoid content in unfertilized eggs and embryo mortality or hatching timing. However, the consumption of carotenoids during our stress treatment was negatively correlated to embryo survival among sib groups and explained about 14% of the maternal environmental variance. We conclude that maternally derived carotenoids play a role in the ability of embryos to cope with environmental stress, but that the initial susceptibility to the organic pollution was mainly determined by other factors.

Antioxidant allocation modulates sperm quality across changing social environments

In promiscuous species, male reproductive success depends on their ability to mate with fertile females and on the fertilizing ability of their sperm. In such species, theory predicts that, owing to a trade-off between pre- and post-copulatory reproductive traits, males with lesser access to females should increase resource investment into those sperm traits that enhance fertilization success–usually referred to as ejaculate quality. This prediction has been validated in several taxa, yet studies on the physiological mechanisms modulating ejaculate quality are lacking. Sperm cells are highly vulnerable to oxidative stress, which impairs male fertility. Therefore, males that better protect their sperm from oxidative stress are expected to achieve higher ejaculate quality. Based on theoretical expectations, and since social dominance is a major determinant of mating opportunity, we predicted that subordinate males should invest more into the antioxidant protection of their sperm in order to achieve higher ejaculate quality. We maintained 60 male and 60 female wild-caught house sparrows Passer domesticus in outdoor aviaries, where we experimentally manipulated male social status to test our predictions. We measured cellular oxidative stress and enzymatic antioxidant activity in blood and sperm both before and after manipulating social ranks. Before manipulating the social status, we found that ejaculate viability correlated with oxidative stress level in sperm, with dominant males producing more oxidized and less viable ejaculates. Further, males at the lower end of the hierarchy produced ejaculates of similar quality to those of dominant males, suggesting that restricted access to resources might limit male reproductive strategies. After experimentally manipulating the social status, males matched their ejaculate quality to their new rank, while increases in antioxidant investment into ejaculates paralleled increases in ejaculate viability. Oxidative stress has been proposed as a general constraint to the evolution of life histories. Our results highlight oxidative stress and strategic antioxidant allocation as important proximate physiological mechanisms underlying male reproductive strategies.

Comparative genomics of bacillus amyloliquefaciens strains reveals a core genome with traits for habitat adaptation and a secondary metabolites rich accessory genome

The Gram positive, non-pathogenic endospore-forming soil inhabiting prokaryote Bacillus amyloliquefaciens is a plant growth-promoting rhizobacterium. Bacillus amyloliquefaciens processes wide biocontrol abilities and numerous strains have been reported to suppress diverse bacterial, fungal and fungal-like pathogens. Knowledge about strain level biocontrol abilities is warranted to translate this knowledge into developing more efficient biocontrol agents and bio-fertilizers. Ever-expanding genome studies of B. amyloliquefaciens are showing tremendous increase in strain-specific new secondary metabolite clusters which play key roles in the suppression of pathogens and plant growth promotion. In this report, we have used genome mining of all sequenced B. amyloliquefaciens genomes to highlight species boundaries, the diverse strategies used by different strains to promote plant growth and the diversity of their secondary metabolites. Genome composition of the targeted strains suggest regions of genomic plasticity that shape the structure and function of these genomes and govern strain adaptation to different niches. Our results indicated that B. amyloliquefaciens: (i) suffer taxonomic imprecision that blurs the debate over inter-strain genome diversity and dynamics, (ii) have diverse strategies to promote plant growth and development, (iii) have an unlocked, yet to be delimited impressive arsenal of secondary metabolites and products, (iv) have large number of so-called orphan gene clusters, i.e., biosynthetic clusters for which the corresponding metabolites are yet unknown, and (v) have a dynamic pan genome with a secondary metabolite rich accessory genome.

Alternative reproductive tactics, sperm mobility and oxidative stress in Carollia perspicillata (Seba’s short-tailed bat)

In social systems with alternative reproductive tactics, sneakers face a higher level of sperm competition than harem males and hence are predicted to allocate more resources to ejaculates. Antioxidants can protect sperm against oxidative stress, and thus, their allocation to the ejaculate may depend on mating tactic. In this study on the frugivorous bat Carollia perspicillata, we assessed, for harem and sneaker males, four sperm mobility traits, blood and ejaculate markers of the redox balance and the ejaculate to blood ratios of the redox markers. Under higher sperm competition, sneaker males should allocate proportionally more antioxidant resources to the protection of sperm than harem males. In contrast, harem males should favour pre-copulatory functions, which comprise the protection of blood. We found significantly higher sperm velocity and sperm survival in sneakers. There was no correlation between sperm mobility and sperm enzymatic antioxidant activity or ejaculate levels of lipid peroxidation (oxidative damage). Ejaculate levels of lipid peroxidation and sperm survival showed a significantly positive correlation, which could be attributed to the role of reactive oxygen species for sperm capacitation. Harem and sneaker males showed similar levels of redox balance markers in ejaculate and blood. However, harem males showed a higher ratio of oxidized over reduced glutathione in blood, which may indicate higher cellular stress due to higher metabolism. Overall, our findings suggest that sneakers of C. perspicillata compensate for a higher level of sperm competition by higher sperm mobility.Significance statementIn social systems with alternative reproductive tactics, sneakers face higher level of sperm competition than harem males and hence are predicted to allocate more resources to ejaculates. Antioxidants can protect sperm against oxidative stress, and thus, their allocation to the ejaculate may depend on mating tactic. In this study on the frugivorous bat Carollia perspicillata, we found sperm swimming significantly faster and longer in sneaker males compared to harem males. However, traits other than the investigated antioxidant may favour higher sperm mobility. Measured redox pattern in blood of harem males may indicate higher cellular stress due to higher metabolism. Our results provide support to the current sperm competition models at the intraspecific level, which is still debated for internal fertilizers. This study contributes to better understanding the trade-offs and adaptations resulting from alternative reproductive tactics in mammals.