Volatiles of symbiotic bacterial origin explain ectoparasitism and fledging success of hoopoes

BACKGROUND

Some parasites use olfactory cues to detect their hosts and, since bacterial symbionts are partially responsible for animal odours, they could influence host parasitism. By autoclaving nest materials of hoopoe (Upupa epops) nests before reproduction started, we explored the hypothetical links between host-associated bacteria, volatiles and parasitism. During the nestling stage, we (i) estimated the level of ectoparasitism by chewing lice (Suborder Mallophaga) in adult hoopoe females and by Carnus haemapterus flies in nestlings, and (ii) characterized microbial communities and volatile profiles of nest environments (nest material and nest cavity, respectively) and uropygial secretions.

RESULTS

Experimental nests had less diverse bacterial communities and more diverse volatile profiles than control nests, while occupants experienced lower intensity of parasitism in experimental than in control nests. The experiment also affected beta diversity of the microbial communities of nest material and of the volatiles of the nestling uropygial secretions. Moreover, microbial communities of uropygial secretions and of nest materials covaried with their volatile profiles, while the volatile profile of the bird secretions explained nest volatile profile. Finally, a subset of the volatiles and bacteria detected in the nest material and uropygial secretions were associated with the ectoparasitism intensity of both adult females and nestlings, and with fledging success.

CONCLUSIONS

These results show that a component of animal odours is linked with the microbial communities of the host and its reproductive environment, and emphasize that the associations between bacteria, ectoparasitism and reproductive success are partially mediated by volatiles of bacterial origin. Future work should focus on mechanisms underlying the detected patterns.

Extra Nestlings That Are Condemned to Die Increase Reproductive Success in Hoopoes

AbstractThe adaptive value of routinely laying more eggs than can be successfully fledged has intrigued evolutionary biologists for decades. Extra eggs could, for instance, be adaptive as insurance against hatching failures. Moreover, because recent literature demonstrates that sibling cannibalism is frequent in the Eurasian hoopoe (Upupa epops), producing extra offspring that may be cannibalized by older siblings might also be adaptive in birds. Here, directed to explore this possibility in hoopoes, we performed a food supplementation experiment during the laying period and a clutch size manipulation during the hatching stage. We found that females with the food supplement laid on average one more egg than control females and that the addition of a close-to-hatch egg at the end of the hatching period increased the intensity of sibling cannibalism and enhanced fledging success in hoopoe nests. Because none of the extra nestlings from the experimental extra eggs survived until fledging, these results strongly suggest that hoopoes obtain fitness advantages by using temporarily abundant resources to produce additional nestlings that will be cannibalized. These results therefore suppose the first experimental demonstration of the nutritive adaptive function of laying extra eggs in vertebrates with parental care.

Mixed-species assemblages and disease: the importance of differential vector and parasite attraction in transmission dynamics

Individuals from multiple species often aggregate at resources, group to facilitate defense and foraging, or are brought together by human activity. While it is well-documented that host-seeking disease vectors and parasites show biases in their responses to cues from different hosts, the influence of mixed-species assemblages on disease dynamics has received limited attention. Here, we synthesize relevant research in host-specific vector and parasite bias. To better understand how vector and parasite biases influence infection, we provide a conceptual framework describing cue-oriented vector and parasite host-seeking behaviour as a two-stage process that encompasses attraction of these enemies to the assemblage and their choice of hosts once at the assemblage. We illustrate this framework, developing a case study of mixed-species frog assemblages, where frog-biting midges transmit trypanosomes. Finally, we present a mathematical model that investigates how host species composition and asymmetries in vector attraction modulate transmission dynamics in mixed-species assemblages. We argue that differential attraction of vectors by hosts can have important consequences for disease transmission within mixed-species assemblages, with implications for wildlife conservation and zoonotic disease. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Habitat-dependent Culicoides species composition and abundance in blue tit (Cyanistes caeruleus) nests

Wild birds are hosts of Culicoides from as early on as the nesting stage when constrained to their nests. However, the environmental factors which determine the abundance and composition of Culicoides species within each bird nest are still understudied. We sampled Culicoides from Eurasian blue tit (Cyanistes caeruleus) nests found in 2 types of forests located in southern Spain. Firstly, we monitored the abundance of Culicoides species in bird nests from a dry Pyrenean oak deciduous forest and a humid mixed forest comprising Pyrenean and Holm oaks throughout 2 consecutive years. During the 3rd year, we performed a cross-fostering experiment between synchronous nests to differentiate the role of rearing environment conditions from that of the genetically determined or maternally transmitted cues released by nestlings from each forest. We found 147 female Culicoides from 5 different species in the birds' nests. The abundance of Culicoides was higher in the dry forest than in the humid forest. Culicoides abundance, species richness and prevalence were greater when the nestlings were hatched later in the season. The same pattern was observed in the cross-fostering experiment, but we did not find evidence that nestling's features determined by the forest of origin had any effect on the Culicoides collected. These results support the notion that habitat type has a strong influence on the Culicoides affecting birds in their nests, while some life history traits of birds, such as the timing of reproduction, also influence Culicoides abundance and species composition.

Stimuli Followed by Avian Malaria Vectors in Host-Seeking Behaviour

Vector-borne infectious diseases (e.g., malaria, dengue fever, and yellow fever) result from a parasite transmitted to humans and other animals by blood-feeding arthropods. They are major contributors to the global disease burden, as they account for nearly a fifth of all infectious diseases worldwide. The interaction between vectors and their hosts plays a key role driving vector-borne disease transmission. Therefore, identifying factors governing host selection by blood-feeding insects is essential to understand the transmission dynamics of vector-borne diseases. Here, we review published information on the physical and chemical stimuli (acoustic, visual, olfactory, moisture and thermal cues) used by mosquitoes and other haemosporidian vectors to detect their vertebrate hosts. We mainly focus on studies on avian malaria and related haemosporidian parasites since this animal model has historically provided important advances in our understanding on ecological and evolutionary process ruling vector-borne disease dynamics and transmission. We also present relevant studies analysing the capacity of feather and skin symbiotic bacteria in the production of volatile compounds with vector attractant properties. Furthermore, we review the role of uropygial secretions and symbiotic bacteria in bird-insect vector interactions. In addition, we present investigations examining the alterations induced by haemosporidian parasites on their arthropod vector and vertebrate host to enhance parasite transmission. Finally, we propose future lines of research for designing successful vector control strategies and for infectious disease management.

Microbially Mediated Chemical Ecology of Animals: A Review of Its Role in Conspecific Communication, Parasitism and Predation

Microbial symbionts are nowadays considered of pivotal importance for animal life. Among the many processes where microorganisms are involved, an emerging research avenue focuses on their major role in driving the evolution of chemical communication in their hosts. Volatiles of bacterial origin may underlie chemical communication and the transfer of social information through signals, as well as inadvertent social information. We reviewed the role of microorganisms in animal communication between conspecifics, and, because the microbiome may cause beneficial as well as deleterious effects on their animal hosts, we also reviewed its role in determining the outcome of the interactions with parasites and predators. Finally, we paid special attention to the hypothetical role of predation and parasitism in driving the evolution of the animal microbiome. We highlighted the novelty of the theoretical framework derived from considering the microbiota of animals in scenarios of communication, parasitism, and predation. We aimed to encourage research in these areas, suggesting key predictions that need to be tested to better understand what is one of the main roles of bacteria in animal biology.

Understanding host utilization by mosquitoes: determinants, challenges and future directions

Mosquito host utilization is a key factor in the transmission of vector-borne pathogens given that it greatly influences host-vector contact rates. Blood-feeding patterns of mosquitoes are not random, as some mosquitoes feed on particular species and/or individuals more than expected by chance. Mosquitoes use a number of cues including visual, olfactory, acoustic, and thermal stimuli emitted by vertebrate hosts to locate and identify their blood meal sources. Thus, differences in the quality/intensity of the released cues may drive host selection by mosquitoes at both inter- and intra-specific levels. Such patterns of host selection by mosquitoes in space and time can be structured by factors related to mosquitoes (e.g. innate host preference, behavioural plasticity), to hosts (e.g. emission of host-seeking cues, host availability) or to both (e.g. pathogen infection). In this study, we review current evidence, from phenomena to mechanisms, of how these factors influence host utilization by mosquitoes. We also review the methodologies commonly used in this research field and identify the major challenges for future studies. To bridge the knowledge gaps, we propose improvements to strengthen traditional approaches and the use of a functional trait-based approach to infer mosquito host utilization in natural communities.