Abstract
The taxonomic composition of egg-associated microbial communities can play a crucial role in the development of fish embryos. In response, hosts increasingly influence the composition of their associated microbial communities during embryogenesis, as concluded from recent field studies and laboratory experiments. However, little is known about the taxonomic composition and the diversity of egg-associated microbial communities within ecosystems; e.g., river networks. We sampled late embryonic stages of naturally spawned brown trout at nine locations within two different river networks and applied 16S rRNA pyrosequencing to describe their bacterial communities. We found no evidence for a significant isolation-by-distance effect on the composition of bacterial communities, and no association between neutral genetic divergence of fish host (based on 11 microsatellites) and phylogenetic distances of the composition of their associated bacterial communities. We characterized core bacterial communities on brown trout eggs and compared them to corresponding water samples with regard to bacterial composition and its presumptive function. Bacterial diversity was positively correlated with water temperature at the spawning locations. We discuss this finding in the context of the increased water temperatures that have been recorded during the last 25 years in the study area.
Highlights
Community structure of egg-associated bacteria and to identify factors that correlate with the composition of such communities
We found no evidence for a correlation of bacterial phylogenetic distances among spawning places to either geographic distances or genetic differentiation of the brown trout populations
Naturally spawned eggs at one brown trout spawning location in the river Inn harbored the same main bacterial groups as eggs in the Aare the two rivers belong to different basins (Danube and Rhine), and the spawning places differ with regard to altitude
Summary
Community structure of egg-associated bacteria and to identify factors that correlate with the composition of such communities. We concentrated on brown trout (Salmo trutta) and sampled eggs from various natural spawning places Most of these spawning places are located within the sub-alpine Aare river system that is characterized by different habitats and by significant genetic and morphological differentiation among brown trout populations[12]. Among the factors that could potentially influence egg-associated bacteria and contribute to variation in symbiont bacterial communities on a regional scale are geographic distance between sampling locations (isolation by distance17,18), population-specific differences in maternal environmental effects (i.e., egg characteristics19), variation in host genetics[7,11,15] or water temperature. We looked for correlations of the phylogenetic relationship of bacterial communities and geographic distances among different spawning locations, genetic differentiation of the brown trout host, and water temperature as measured during incubation of the eggs
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