Chemical regulation of body feather microbiota in a wild bird.

The microbiota has a broad range of impacts on host physiology and behaviour, pointing out the need to improve our comprehension of the drivers of host-microbiota composition. Of particular interest is whether the microbiota is acquired passively, or whether and to what extent hosts themselves shape the acquisition and maintenance of their microbiota. In birds, the uropygial gland produces oily secretions used to coat feathers that have been suggested to act as an antimicrobial defence mechanism regulating body feather microbiota. However, our comprehension of this process is still limited. In this study, we for the first time coupled high-throughput sequencing of the microbiota of both body feathers and the direct environment (i.e., the nest) in great tits with chemical analyses of the composition of uropygial gland secretions to examine whether host chemicals have either specific effects on some bacteria or nonspecific broad-spectrum effects on the body feather microbiota. Using a network approach investigating the patterns of co-occurrence or co-exclusions between chemicals and bacteria within the body feather microbiota, we found no evidence for specific promicrobial or antimicrobial effects of uropygial gland chemicals. However, we found that one group of chemicals was negatively correlated to bacterial richness on body feathers, and a higher production of these chemicals was associated with a poorer body feather bacterial richness compared to the nest microbiota. Our study provides evidence that chemicals produced by the host might function as a nonspecific broad-spectrum antimicrobial defence mechanism limiting colonization and/or maintenance of bacteria on body feathers, providing new insight about the drivers of the host's microbiota composition in wild organisms.

Chemical Composition and Behavioral Effects of Five Plant Essential Oils on the Green Pea Aphid Acyrthosiphon pisum (Harris) (Homoptera: Aphididae).

Essential oils (EOs) from Schinus molle, Helichrysum gymnocephalum, Cedrelopsis grevei and Melaleuca viridiflora, four aromatic and medicinal plants, are commonly used in folk medicine. EOs were characterized by gas chromatography/mass spectrometry (GC/MS) and quantified by gas chromatography-flame ionization detection (GC-FID); then evaluated for their behavioral effects on adults of the green pea aphid Acyrthosiphon pisum (Harris) using a Perspex four-armed olfactometer in order to test the compatibility of their use as phytoinsecticides to control this insect pest. Our results showed that the EOs from the leaves of S. molle, M. viridiflora and C. grevei did not change aphids' behavior. However, S. molle fruits EO seemed to be attractive while H. gymnocephalum leaves EO exhibited repellency towards aphids at a dose of 10 µl. The major compounds in S. molle fruits EO were 6-epi-shyobunol (16.22%) and d-limonene (15.35%). While, in H. gymnocephalum leaves EO, 1,8-cineole was the main compound (47.4%). The difference in aphids' responses to these two EOs could be attributed to the differences in their compositions. Our findings suggest that these two EOs have potential applications for the integrated pest management of A. pisum (Harris).

Uropygial gland size and composition varies according to experimentally modified microbiome in Great tits.

BACKGROUND: Parasites exert important selective pressures on host life history traits. In birds, feathers are inhabited by numerous microorganisms, some of them being able to degrade feathers or lead to infections. Preening feathers with secretions of the uropygial gland has been found to act as an antimicrobial defence mechanism, expected to regulate feather microbial communities and thus limit feather abrasion and infections. Here, we used an experimental approach to test whether Great tits (Parus major) modify their investment in the uropygial gland in response to differences in environmental microorganisms. RESULTS: We found that males, but not females, modified the size of their gland when exposed to higher bacterial densities on feathers. We also identified 16 wax esters in the uropygial gland secretions. The relative abundance of some of these esters changed in males and females, while the relative abundance of others changed only in females when exposed to greater bacterial loads on feathers. CONCLUSION: Birds live in a bacterial world composed of commensal and pathogenic microorganisms. This study provides the first experimental evidence for modifications of investment in the defensive trait that is the uropygial gland in response to environmental microorganisms in a wild bird.

The evolution of chemical defenses along invasion routes: Harmonia axyridis Pallas (Coccinellidae: Coleoptera) as a case study.

The evolution of increased competitive ability (EICA) hypothesis (Blossey & Nötzold, 1995) postulates that escaping from coevolved enemies increases invaders fitness by energy reallocation from defenses and immunity to growth and reproduction. In this context, we evaluated the evidence of evolutionary change in invasive populations of Harmonia axyridis Pallas (Coccinellidae: Coleoptera). We measured egg defenses-cocktail of hydrocarbons on the egg's surface flagging egg toxicity and the concentration of the main alkaloid harmonine-in individuals from three populations along the invasion route (Japan: native, United States: introduced more than 30 years ago, South Africa: introduced in the early 2000s) in a common garden experiment. Our results support the EICA hypothesis: We found changes along the invasion route in the profiles of the hydrocarbons coating the eggs' surface and a decrease in the concentration of harmonine in eggs from the most recent invasive South African population compared to the long established in the United States and the native Japanese ones.

Preen secretions encode information on MHC similarity in certain sex-dyads in a monogamous seabird.

Animals are known to select mates to maximize the genetic diversity of their offspring in order to achieve immunity against a broader range of pathogens. Although several bird species preferentially mate with partners that are dissimilar at the major histocompatibility complex (MHC), it remains unknown whether they can use olfactory cues to assess MHC similarity with potential partners. Here we combined gas chromatography data with genetic similarity indices based on MHC to test whether similarity in preen secretion chemicals correlated with MHC relatedness in the black-legged kittiwake (Rissa tridactyla), a species that preferentially mates with genetically dissimilar partners. We found that similarity in preen secretion chemicals was positively correlated with MHC relatedness in male-male and male-female dyads. This study provides the first evidence that preen secretion chemicals can encode information on MHC relatedness and suggests that odor-based mechanisms of MHC-related mate choice may occur in birds.