Antibacterial defense in bull and boar semen: A putative link to the microbiome and reproductive strategy?

Several domestic and wildlife species have been shown to possess antibacterial defenses in their ejaculate most probably in order to increase the fertilization success and protect against sexually transmitted pathogens. However, very little is known about the consequences and factors influencing the differences within and between species as far as ejaculate-associated immunity. In the present study, we have analyzed bacterial killing activity (BKA) against Escherichia (E.) coli and Staphylococcus (S.) aureus as well as lysozyme concentrations (LC) in seminal plasma from 60 Fleckvieh bulls. Further, sperm quality and its association with BKA and LC were determined. Twenty percent of the individuals displayed BKA against both bacteria, 78.3% against S. aureus only and 1.7% of the bulls did not indicate any BKA in seminal plasma. No bulls with seminal plasma BKA only against E. coli were identified; implying that 80.0% of the tested bulls had no ejaculate associated defense mechanisms against this gram-negative bacterial species in place. This is in striking contrast to results of Pietrain boars within our previous study, in which 42.8% of the 119 boars expressed an antibacterial activity against E. coli in seminal plasma, 10.9% amongst them with BKA against E. coli only. LC was higher in the bull group with BKA against both bacteria (1.2 ± 0.6 µg/mL) compared to the group with BKA against S. aureus only (0.7 ± 0.3 µg/mL), but - if calculated over all individuals - LC in bulls (0.8 ± 0.4 µg/mL) was lower compared to boars (2.4 ± 1.2 µg/mL). LC showed positive correlations to the age of the bulls and sperm quality as well as a negative relation to bacterial load in raw semen although the highest bacterial contamination was found in animals with seminal plasma BKA against both strains. We discuss the obtained results with regards to possible differences within the microbiome of female and male genital tracts and the reproductive strategies (vaginal vs. uterine depositors) in these two livestock species. Besides identifying the responsible molecules, future phylogenetically controlled comparative studies are needed for a better understanding of the evolution of species differences in ejaculate-associated antibacterial defenses.

Anti-NMDA Receptor Encephalitis in the Polar Bear (Ursus maritimus) Knut.

Knut the polar bear of the Berlin Zoological Garden drowned in 2011 following seizures and was diagnosed as having suffered encephalitis of unknown etiology after exhaustive pathogen screening. Using the diagnostic criteria applied to human patients, we demonstrate that Knut's encephalitis is almost identical to anti-NMDA receptor encephalitis which is a severe autoimmune disease representing the most common non-infectious encephalitis in humans. High concentrations of antibodies specific against the NR1 subunit of the NMDA receptor were detected in Knut's cerebrospinal fluid. Histological examination demonstrated very similar patterns of plasma cell infiltration and minimal neuronal loss in affected brain areas. We conclude that Knut suffered anti-NMDA receptor encephalitis making his the first reported non-human case of this treatable disease. The results suggest that anti-NMDA receptor encephalitis may be a disease of broad relevance to mammals that until now has remained undiagnosed.

Polar bear encephalitis: establishment of a comprehensive next-generation pathogen analysis pipeline for captive and free-living wildlife.

This report describes three possibly related incidences of encephalitis, two of them lethal, in captive polar bears (Ursus maritimus). Standard diagnostic methods failed to identify pathogens in any of these cases. A comprehensive, three-stage diagnostic 'pipeline' employing both standard serological methods and new DNA microarray and next generation sequencing-based diagnostics was developed, in part as a consequence of this initial failure. This pipeline approach illustrates the strengths, weaknesses and limitations of these tools in determining pathogen caused deaths in non-model organisms such as wildlife species and why the use of a limited number of diagnostic tools may fail to uncover important wildlife pathogens.

Effect of preen oil on plumage bacteria: an experimental test with the mallard.

Feathers are essential for avian thermoregulation, communication or flight and a reduction of plumage condition may alter these functions and reduce individual fitness. Recently, descriptive studies provided evidence that birds carry feather-degrading bacteria on their plumage that have the ability to degrade feathers rapidly under laboratory conditions. If such bacteria reduce avian fitness, natural selection should favour the evolution of anti-bacterial defences to limit the effects of these detrimental microorganisms. Preening behaviour and associated preen gland secretions have been proposed as the main factor used by birds to limit feather-degrading bacterial growth and some recent in vitro studies provided evidence that uropygial oil inhibited the growth of some keratinolytic strains in passerines. However, preen oil antimicrobial properties remained to be experimentally tested in vivo. We conducted an experiment with mallards (Anas platyrhynchos) onto which we fixed a removable mechanism that blocked access to the uropygial gland in a first group of mallards, whilst birds in a second group had the same removable mechanism but access to their gland and a third group of birds had normal access to their gland. We found no significant effect of our treatment on total and feather-degrading bacterial loads. Three hypotheses may explain the discrepancy between our results and previous in vitro studies. First, in vitro studies may have over-estimated the bactericidal properties of the preen oil. Second, preen gland deprivation may have affected only a small portion of the feather-degrading bacterial community. Third, ducks and passerine oils might have different bactericidal properties.

Maternal investment of female mallards is influenced by male carotenoid-based coloration.

The differential allocation hypothesis predicts that females modify their investment in a breeding attempt according to its reproductive value. One prediction of this hypothesis is that females will increase reproductive investment when mated to high-quality males. In birds, it was shown that females can modulate pre-hatch reproductive investment by manipulating egg and clutch sizes and/or the concentrations of egg internal compounds according to paternal attractiveness. However, the differential allocation of immune factors has seldom been considered, particularly with an experimental approach. The carotenoid-based ornaments can function as reliable signals of quality, indicating better immunity or ability to resist parasites. Thus, numerous studies show that females use the expression of carotenoid-based colour when choosing mates; but the influence of this paternal coloration on maternal investment decisions has seldom been considered and has only been experimentally studied with artificial manipulation of male coloration. Here, we used dietary carotenoid provisioning to manipulate male mallard (Anas platyrhynchos) bill coloration, a sexually selected trait, and followed female investment. We show that an increase of male bill coloration positively influenced egg mass and albumen lysozyme concentration. By contrast, yolk carotenoid concentration was not affected by paternal ornamentation. Maternal decisions highlighted in this study may influence chick survival and compel males to maintain carotenoid-based coloration from the mate-choice period until egg-laying has been finished.