B. Irene Tieleman

Resource acquisition and allocation are central to life history theory, explaining the diversity of strategies among species as well as the distribution of events over the annual cycle. Moult is a major phase in the annual cycle of birds, but explanations for moult scheduling are heavily biased towards temperate systems with seasonal breeding patterns. Our research on a year‐round breeding tropical bird, the common bulbul Pycnonotus barbatus (bulbul), tests whether moult depends primarily on stored body reserves (capital) or on resources acquired throughout the moult period (income). Making this distinction elucidates trade‐offs between moult, and other annual cycle events, and responses to environmental change. We estimated moult start date and duration in captive bulbuls whose body condition we experimentally manipulated by feeding them fruits or invertebrates 6–3 and 3–0 months before moult, and fruits or a mixed diet during moult. We studied free‐living bulbuls as reference group. We found that moult onset is best predicted by diet‐manipulated condition just before moult, while moult duration is best predicted by diet‐manipulated condition during moult. Specifically, invertebrate‐fed bulbuls started moult 33 days later than fruit‐fed bulbuls. In addition, once invertebrate‐fed bulbuls were switched to a mixed diet, they moulted 52 days quicker than fruit‐fed bulbuls, albeit still 36 days slower than free‐living bulbuls on average. Males started moult 15 days earlier and had a more variable start of 20 days, but did not moult quicker than females on average. Our findings indicate that moult in bulbuls is both income‐ and capital‐dependent, with moult initiation determined by individual body reserves and feather growth still occurring on a fruit‐only‐diet, but is significantly improved by dietary proteins from a mixed diet and in field bulbuls. In this year‐round breeding bird, moult seasonality is maintained in the absence of breeding, but heavily influenced by foraging conditions.

The Bar‐tailed Lark Ammomanes cinctura is a polytypic bird species with a wide distribution. One of its three subspecies, A. c. arenicolor , has previously been found to show deep mitochondrial divergence between its geographically most distant populations, from Morocco and Saudi Arabia, respectively. We applied an integrative approach using genome‐wide single nucleotide polymorphisms (SNPs), mitochondrial DNA (mtDNA), morphological and bioacoustic data to investigate the evolutionary divergence within A. cinctura . We confirmed the existence of two distinct mitochondrial clades: one including samples from Morocco and Cape Verde Islands and the other including samples from Saudi Arabia and Iran. We estimated that these lineages diverged 2.14 million years ago (Mya). In contrast, we recovered shallow divergence in the nuclear SNPs (estimated split time: 0.08 Mya) between the samples from Cape Verde–Morocco versus Saudi Arabia–Iran, and population structure analyses favored a single genetic cluster. Analyses of museum specimens confirmed earlier statements that the eastern subspecies, A. c. zarudnyi , has slightly longer wing and tail than the two others, and that the three subspecies are slightly divergent in plumage. Finally, our analyses of vocalisations suggested that some geographical differences might exist, but the commonest song type is found across the range. The reasons for the considerably deeper divergence in mitochondrial DNA relative to that of nuclear SNPs are unresolved and will require more comprehensive sampling to elucidate.

Preen gland bacteria are thought to be the key producers of preen oil components such as chemosignalling molecules including volatile organic compounds (VOCs) and antimicrobial compounds including peptides and antimicrobial VOCs. However, data on the preen oil bacteriome and chemical composition are limited to a small subset of bird species, and the presence of antimicrobial peptides is largely unexplored. Here, we performed an exploratory study to characterize, for the first time, the preen oil chemical and proteomic profiles and to explore the possible contribution of the bacteriome to the production of preen oil VOCs and antimicrobial peptides (bacteriocins) in eight passerine species, each represented by a single individual. Preen oil bacteriome, chemical and proteomic profiles varied among birds. The bacterial profiles were dominated by the genera Streptococcus , Lactococcus , Corynebacterium and Cutibacterium . The chemical profiles mainly consisted of alcohols, ketones and carboxylic acids. The biological functions primarily associated with the proteomic profiles were proteolysis and response to oxidative stress. Although we were unable to explore a direct association between the bacteriome and chemical profiles, the preen oil contained bacteriocin- and VOC-producing bacterial genera capable of producing detected microbially-derived VOCs (mVOCs), the relative abundance of which varied between birds. Riparian species showed the highest chemical diversity and high abundances of putative preen oil mVOC-producing bacteria, which could suggest habitat-specific adaptations. This exploratory study may significantly contribute to the formulation of hypotheses on the potential role of host ecological factors in the variation of preen oil bacterial, chemical and proteomic profiles in passerines.

The developmental period is a critical phase in birds, influencing even lifetime reproductive success. The gut microbiome (GM) is important herein, affecting digestive capacity and immune function. Diet impacts the GM, but wild nestlings may experience resource limitations, which may also affect the GM. We investigated the effects of a week of food restriction early in life on the GM in captive rock pigeon nestlings (Columba livia). We sampled the GM at 0, 2, 4, 7, 8, 12, 20, 27, and 38 days and in foster parents. Alpha diversity varied only with age. However, differences in alpha diversity between nestlings and adults were larger during food restriction. Beta diversity varied with age, food treatment, and their interaction term. Four of the eleven major genera varied with age, while four others did not vary with age or food treatment. Major genera that contained potential pathogens (Escherichia-Shigella and Clostridium sensu stricto 1) were more abundant under food restriction. Food restriction thus affected GM development. The increase in alpha diversity and potential pathogens suggest that suppressed immune function may mediate the impact of food restriction on the GM. The effect diminished when food restriction was ended, suggesting that in wild nestlings, the impact of food restriction on the GM may be short-term.

Context.Stellar populations and their distribution differ widely across the Galaxy, which is likely to affect planet demographics. Our local neighbourhood is dominated by young, metal-rich stars in the galactic thin disc, while the stellar halo and galactic bulge host a large fraction of older, metal-poor stars.Aims.We study the impact of these variations on planet populations in different regions of the Galaxy by combining a high-resolution galaxy formation simulation with state-of-the-art planet population synthesis models.Methods.We constructed a population model to estimate occurrence rates of different planet types, based on the New Generation Planet Population Synthesis (NGPPS). We applied this model to a simulated Milky Way (MW) analogue in the HESTIA galaxy formation simulation. We studied the planet occurrence rate in the metal-rich regions of the inner Galaxy, namely, in the galactic bulge and thin disc. We compared these result with the frequencies in the more distant, metal-poor region such as the thick disc and stellar halo.Results.We find that the planet demographics in the central, metal-rich regions of the MW analogue differ strongly from the planet populations in the more distant, metal-poor regions. The occurrence rate of giant planets (>300M_⊕) is 10–20 times larger in the thin disc compared to the thick disc, driven by the low amounts of solid material available for planet formation around metal-poor stars. Similarly, low-mass Earth-like planets around Sun-like stars are most abundant in the thick disc, being 1.5 times more frequent than in the thin disc. Moreover, low-mass planets are expected to be abundant throughout the galaxy, from the central regions to the outer halo, due to their formation processes being less dependent on stellar metallicity. The planet populations differ more strongly around Sun-like stars compared to dwarfs with masses 0.3–0.5M_⊙, caused by a weaker correlation between [Fe/H] metallicity and planet mass. However, it is important to note that the occurrence rates of low-mass planets are still uncertain, making our findings strongly model-dependent. Massive planets are more comprehensively understood and our findings are more robust. Nonetheless, other systematic effects have the potential to alter the giant planet population that we have not addressed in this study. We discuss some of these limitations and offer further directions for future research.

The species complex comprising the rufous-naped lark Corypha africana, Sharpe’s lark Corypha sharpii, the red-winged lark Corypha hypermetra, the Somali long-billed lark Corypha somalica and Ash’s lark Corypha ashi encompasses 31 recognised taxa across sub-Saharan Africa, many of which are extremely poorly known and some not observed for decades. Only 17 taxa have been studied molecularly and none comprehensively for morphology, vocalisations or other behaviours. Here, we undertake comprehensive integrative taxonomic analyses based on plumage and morphometrics (for 97% of the taxa), mitochondrial and nuclear loci (77%), ≤ 1.3 million genome-wide single nucleotide polymorphisms (68%), song (many described for the first time; 52%) and additional behavioural data (45%). All polytypic species as presently circumscribed are paraphyletic, with eight primary clades separated by ≤ 6.3–6.8 Myr, broadly supported by plumage, morphometrics, song and other behaviours. The most recent divergences concern sympatric taxon pairs usually treated as separate species, whereas the divergence of all clades including C. africana subspecies is as old as sister species pairs in other lark genera. We propose the recognition of nine instead of five species, while C. ashi is synonymised with C. somalica rochei as C. s. ashi. The geographical distributions are incompletely known, and although the nine species are generally para-/allopatric, some might be sympatric.

The innate immune system is essential for survival, yet many immune traits are highly variable between and within individuals. In recent years, attention has shifted to the role of environmental factors in modulating this variation. A key environmental factor is food availability, which plays a major role in shaping life histories, and may affect resource allocation to immune function through its effect on nutritional state. We developed a technique to permanently increase foraging costs in seed‐eating birds, and leveraged this technique to study the effects of food availability on the innate immune system over a 3‐year period in 230 zebra finches housed in outdoor aviaries. The immune components we studied were haptoglobin, ovotransferrin, nitric oxide, natural antibodies through agglutination, complement‐mediated lysis, and killing capacity of Escherichia coli and Candida albicans, covering a broad spectrum of the innate immune system. We explored the effects of food availability in conjunction with other potentially important variables: season, age, sex and manipulated natal brood size. Increased foraging costs affected multiple components of the immune system, albeit in a variable way. Nitric oxide and agglutination levels were lower under harsh foraging conditions, while Escherichia coli killing capacity was increased. Agglutination levels also varied seasonally, but only at low foraging costs. C. albicans killing capacity was lower in winter, and even more so for animals in harsh foraging conditions that were raised in large broods. Effects of food availability on ovotransferrin were also seasonal, and only apparent in males. Haptoglobin levels were independent of foraging costs and season. Males had higher levels of immune function than females for three of the measured immune traits. Innate immune function was independent of age and manipulated natal brood size. Our finding that food availability affects innate immune function suggests that fitness effects of food availability may at least partially be mediated by effects on the immune system. However, food availability effects on innate immunity varied in direction between traits, illustrating the complexity of the immune system and precluding conclusions on the level of disease resistance.

Background: In a diverse microbial world immune function of animals is essential. Diverse microbial environments may contribute to extensive variation in immunological phenotypes of vertebrates, among and within species and individuals. As maternal effects benefit offspring development and survival, whether females use cues about their microbial environment to prime offspring immune function is unclear. To provide microbial environmental context to maternal effects, we asked if the bacterial diversity of the living environment of female zebra finchesTaeniopygia guttatashapes maternal effects on egg immune function. We manipulated environmental bacterial diversity of birds and tested if females increased immunological investment in eggs in an environment with high bacterial diversity (untreated soil) versus low (gamma-sterilized soil). We quantified lysozyme and ovotransferrin in egg albumen and IgY in egg yolk and in female blood, and we used 16S rRNA gene sequencing to profile maternal cloacal and eggshell microbiotas.Results: We found a maternal effect on egg IgY concentration that reflected environmental microbial diversity: females who experienced high diversity deposited more IgY in their eggs, but only if maternal plasma IgY levels were relatively high. We found no effects on lysozyme and ovotransferrin concentrations in albumen. Moreover, we uncovered that variation in egg immune traits could be significantly attributed to differences among females: for IgY concentration in yolk repeatabilityR = 0.80; for lysozyme concentration in albumenR = 0.27. Furthermore, a partial least squares path model (PLS-PM) linking immune parameters of females and eggs, which included maternal and eggshell microbiota structures and female body condition, recapitulated the treatment-dependent yolk IgY response. The PLS-PM additionally suggested that the microbiota and physical condition of females contributed to shaping maternal effects on egg immune function, and that (non-specific) innate egg immunity was prioritized in the environment with low bacterial diversity.Conclusions: The microbial environment of birds can shape maternal effects on egg immune function. Since immunological priming of eggs benefits offspring, we highlight that non-genetic maternal effects on yolk IgY levels based on cues from the parental microbial environment may prove important for offspring to thrive in the microbial environment that they are expected to face.

Background: Gut microbiotas play a pivotal role in host physiology and behaviour, and may affect host life-history traits such as seasonal variation in host phenotypic state. Generally, seasonal gut microbiota variation is attributed to seasonal diet variation. However, seasonal temperature and day length variation may also drive gut microbiota variation. We investigated summer-winter differences in gut microbiota in 14 homing pigeons living outdoors under a constant diet by collecting cloacal swabs in both seasons during two years. Because temperature effects may be mediated by host metabolism, we determined basal metabolic rate (BMR) and body mass. Immune competence is influenced by day length and has a close relationship with gut microbiota, and it may thus be a link between day length and gut microbiota. Therefore, we measured seven innate immune indices. We expected gut microbiota to show summer-winter differences and gut microbiota to correlate with metabolism and immune indices. Results: BMR, body mass, and two immune indices varied seasonally, other host factors did not. Gut microbiota showed differences between seasons and sexes, and correlated with metabolism and immune indices. The most abundant genus ( Lachnoclostridium 12 , 12%) and associated higher taxa, were more abundant in winter, though not significantly at the phylum level, Firmicutes. Bacteroidetes were more abundant in summer. The Firmicutes : Bacteroidetes ratio tended to be higher in winter. The KEGG ortholog functions for fatty acid biosynthesis and linoleic acid metabolism (PICRUSt2) had increased abundances in winter. Conclusions: The gut microbiota of homing pigeons varied seasonally, even under a constant diet. The correlations between immune indices and gut microbiota did not involve consistently specific immune indices and included only one of the two immune indices that showed seasonal differences, suggesting that immune competence may be an unlikely link between day length and gut microbiota. The correlations between gut microbiota and metabolism indices, the higher Firmicutes : Bacteroidetes ratio in winter, and the resemblance of the summer-winter differences in gut microbiota with the general temperature effects on gut microbiota in the literature, suggest that temperature partly drove the summer-winter differences in gut microbiota in homing pigeons.