Ontogeny shapes individual dietary specialization in female European brown bears (Ursus arctos)

Individual dietary specialization, where individuals occupy a subset of a population's wider dietary niche, is a key factor determining a species resilience against environmental change. However, the ontogeny of individual specialization, as well as associated underlying social learning, genetic, and environmental drivers, remain poorly understood. Using a multigenerational dataset of female European brown bears (Ursus arctos) followed since birth, we discerned the relative contributions of environmental similarity, genetic heritability, maternal effects, and offspring social learning from the mother to individual specialization. Individual specialization accounted for 43% of phenotypic variation and spanned half a trophic position, with individual diets ranging from omnivorous to carnivorous. The main determinants of dietary specialization were social learning during rearing (13%), environmental similarity (5%), maternal effects (11%), and permanent between-individual effects (9%), whereas the contribution of genetic heritability (3%) was negligible. The trophic position of offspring closely resembled the trophic position of their mothers during the first 3-4 years of independence, but waned with increasing time since separation. Our study shows that social learning and maternal effects were more important for individual dietary specialization than environmental composition. We propose a tighter integration of social effects into studies of range expansion and habitat selection under global change.

Learning to Hunt on the Go: Dietary Changes During Development of Rhinolophid Bats

Mammals may experience physical changes from birth, and their diet varies at different stages of life. This study investigates the impact of development on the diet composition of three horseshoe bats: Rhinolophus euryale, R. hipposideros, and R. ferrumequinum in the Basque Country, north of the Iberian Peninsula. The diets of juvenile and adult individuals of each species were obtained by analysing their droppings using metabarcoding and then compared at (1) the taxonomic and (2) prey trait levels (size, flying speed, hardness). The diets of juvenile and adult individuals of R. euryale and R. hipposideros showed significant differences at the taxonomic level and regarding prey traits. In contrast, in the case of R. ferrumequinum, we could only observe discernible diet patterns through the trait analysis. Additionally, we discovered a shared pattern: younger individuals tend to feed on easier-to-hunt and/or handle smaller and smoother prey. The varying degrees of dissimilarity between juvenile and adult diets observed in this study suggest that the relative importance of psychomotor development, foraging strategies, prey discrimination, and/or spatial learning may differ among species. These findings contribute to conservation efforts, especially by recognising the dietary needs of juveniles for their survival and successful development.

Eco-Evolutionary Consequences of Dispersal Syndromes during Colonization in a Passerine Bird

AbstractIn most animal species, dispersing individuals possess phenotypic attributes that mitigate the costs of colonization and/or increase settlement success in new areas (dispersal syndromes). This phenotypic integration likely affects population dynamics and the direction of selection, but data are lacking for natural populations. Using an approach that combines population dynamics, quantitative genetics, and phenotypic selection analyses, we reveal the existence of dispersal syndromes in a pied flycatcher (Ficedula hypoleuca) population in the Netherlands: immigrants were larger, tended to have darker plumage, bred earlier, and produced larger clutches than local recruits, and some of these traits were genetically correlated. Over time, the phenotypic profile of the population gradually changed: each generation advanced arrival and breeding and exhibited longer wings as a result of direct and indirect selection on these correlated traits. Although phenotypic attributes of immigrants were favored by selection during the early phase of colonization, observed phenotypic changes were similar for immigrants and local recruits. We propose that immigrants facilitated initial population establishment but that temporal changes likely resulted from climate change-induced large-scale selection. This study highlights that newly established populations are of nonrandom composition and that phenotypic architecture affects evolutionary population trajectories.

The effect of aquatic and terrestrial prey availability on metal accumulation in pied flycatcher (Ficedula hypoleuca) nestlings

Ingestion of contaminated prey is a major route for metal exposure in terrestrial insectivores. In terrestrial ecosystems adjacent to lakes and streams, emerging aquatic insects can transport metals, accumulated during their larval stage, from aquatic to terrestrial ecosystems. However, contaminant exposure via aquatic insects has often been ignored in terrestrial environments, despite such insects representing a substantial part of the diet for terrestrial insectivores living close to lakes and streams. In this study, we investigated how dietary lead (Pb) and calcium (Ca) exposure from different aquatic and terrestrial prey types affects Pb accumulation in pied flycatcher (Ficedula hypoleuca) nestlings living close to a former Pb/zinc (Zn) mine in northern Sweden, which closed in 2001. Stable isotope analysis (δ ¹³C and δ¹⁵N) of nestling blood and different prey types was used to estimate nestlings' diet. Ants, Lepidoptera larvae and Trichoptera were the most common prey types in the nestlings' diet, in which aquatic prey types (Trichoptera included) accounted for 2.0-96.4%. Ingestion of specific prey groups, such as aquatic insects and ants, were important for Pb accumulation in nestlings, and when access to aquatic prey was low, ants were the predominant source of Pb. The influence of dietary Ca on Pb accumulation was less consistent, but Ca availability was relatively high and often co-occurred with high Pb concentrations in invertebrates. The study shows that both the proportion of different prey and their individual metal concentrations need to be considered when estimating exposure risks for insectivores. Further, it highlights the need to account for metal exposure from emerging aquatic insects for terrestrial insectivores living close to lakes and streams.

Unravelling the causes and consequences of dispersal syndromes in a wild passerine

Evidence accumulates that dispersal is correlated with individual behavioural phenotype (dispersal syndrome). The evolutionary causes and consequences of such covariation depend on the degree of plasticity versus inheritance of the traits, which requires challenging experiments to implement in mobile organisms. Here, we combine a forced dispersal experiment, natural colonization and longitudinal data to establish if dispersal and aggression levels are integrated and to test their adaptive nature in pied flycatchers (Ficedula hypoleuca). We found that (forced) dispersers behaved more aggressively in their first breeding year after dispersal and decreased their aggression in following years. Strength of dispersal syndrome and direction of fecundity selection on aggression in newly colonized areas varied between years. We propose that the net benefits of aggression for dispersers increase under harsh conditions (e.g. low food abundance). This hypothesis now warrants further testing. Overall, this study provides unprecedented experimental evidence that dispersal syndromes can be remodelled via adaptive plasticity depending on the individuals' local breeding experience and/or year-specific ecological conditions. It highlights the importance of individual behavioural variation in population dynamics.

DNA metabarcoding quantifies the relative biomass of arthropod taxa in songbird diets: Validation with camera‐recorded diets

Ecological research is often hampered by the inability to quantify animal diets. Diet composition can be tracked through DNA metabarcoding of fecal samples, but whether (complex) diets can be quantitatively determined with metabarcoding is still debated and needs validation using free‐living animals. This study validates that DNA metabarcoding of feces can retrieve actual ingested taxa, and most importantly, that read numbers retrieved from sequencing can also be used to quantify the relative biomass of dietary taxa. Validation was done with the hole‐nesting insectivorous Pied Flycatcher whose diet was quantified using camera footage. Size‐adjusted counts of food items delivered to nestlings were used as a proxy for provided biomass of prey orders and families, and subsequently, nestling feces were assessed through DNA metabarcoding. To explore potential effects of digestion, gizzard and lower intestine samples of freshly collected birds were subjected to DNA metabarcoding. For metabarcoding with Cytochrome Oxidase subunit I (COI), we modified published invertebrate COI primers LCO1490 and HCO1777, which reduced host reads to 0.03%, and amplified Arachnida DNA without significant changing the recovery of other arthropod taxa. DNA metabarcoding retrieved all commonly camera‐recorded taxa. Overall, and in each replicate year (N = 3), the relative scaled biomass of prey taxa and COI read numbers correlated at R = .85 (95CI:0.68–0.94) at order level and at R = .75 (CI:0.67–0.82) at family level. Similarity in arthropod community composition between gizzard and intestines suggested limited digestive bias. This DNA metabarcoding validation demonstrates that quantitative analyses of arthropod diet is possible. We discuss the ecological applications for insectivorous birds.

Effects of manipulated levels of predation threat on parental provisioning and nestling begging

Parental provisioning behavior is a major determinant of offspring growth and survival, but high provisioning rates might come at the cost of increased predation threat. Parents should thus adjust provisioning activity according to current predation threat levels. Moreover, life-history theory predicts that response to predation threat should be correlated with investment in current reproduction. We experimentally manipulated perceived predation threat in free-living great tits (Parus major) by presenting parents with a nest predator model while monitoring different aspects of provisioning behavior and nestling begging. Experiments were conducted in 2 years differing greatly in ecological conditions, including food availability. We further quantified male territorial aggressiveness and male and female exploratory tendency. Parents adjusted provisioning according to current levels of threat in an apparently adaptive way. They delayed nest visits during periods of elevated perceived predation threat and subsequently compensated for lost feeding opportunities by increasing provisioning once the immediate threat had diminished. Nestling begging increased after elevated levels of predation threat, but returned to baseline levels by the end of the experiment, suggesting that parents had fully compensated for lost feeding opportunities. There was no evidence for a link between male exploration behavior or aggressiveness and provisioning behavior. In contrast, fast-exploring females provisioned at higher rates, but only in the year with poor environmental conditions, which might indicate a greater willingness to invest in current reproduction in general. Future work should assess whether these personality-related differences in delivery rates under harsher conditions came at a cost of reduced residual reproductive value.