Factors affecting microbial community assembly during succession on the egg surface of the Lake Sturgeon and the effect of microbial succession processes on host life history traits

Background/Question/Methods

Succession involves the colonization of open space and subsequent sequential changes in species and community composition. Microbes serve as ideal targets for studying succession because the microbial succession can be effectively controlled and observed in an experimental setting, thus allowing for novel information to be learned about factors affecting the succession process. We investigated the process of microbial succession on the egg surfaces of the Lake Sturgeon (Acipenser fulvescens), a threatened fish species inhabiting the Great Lakes. Our previous studies revealed that microbial community assemblages on the egg surfaces changed over time during the incubation periods. To elucidate the factors influencing such changes, we designed a two factor experiment to analyze the effect of water type (stream water and UV/filter-treated stream water) and temperature (warm and cold) on microbial community assemblages throughout the incubation period. Genomic DNA was extracted from the egg surface and microbial communities were examined using 16S rDNA based Terminal Restriction Fragment Length Polymorphism (TRFLP). TRFLP-derived microbial community data were subsequently analyzed for similarities/clustering using principal components analysis (PCA). Microbial quantity was determined by quantitative PCR (QPCR). We monitored egg mortality and measured larval size at hatch.  Significant effects were tested using general linear models.

Results/Conclusions

PCA revealed that water type was the dominant factor over the effect of temperature in explaining the microbial community assemblage during the succession process. PC1 and PC2 separated egg surface microbial communities reared in stream water from those reared in UV/filter-treated water, and PC3 accounted for variation due to temperature. QPCR showed that significantly more microbes were attached to egg surfaces reared in stream water than in UV/filter-treated water (F_1,102=43.37, p<0.001). We also found significantly higher egg mortality and smaller yolk sac to body area ratio of larvae at hatch for eggs reared in stream water compared to UV/filter-treated water (F_1,17=13.42, p=0.002 and F_1,410=17.07, p<0.001, respectively). The latter may be because embryos used yolk sac resources for defenses against microbes that colonized the egg surfaces. The results have broader implications for understanding microbial succession on hosts because they provide evidence of egg surface microbial communities varying as a function of environmental factors and influencing life history traits of the host. This study also has significant implications for managing threatened host populations such as the Lake Sturgeon inhabiting human-altered rivers, since it demonstrates the potential effect of dams (which alter water microbial community and temperature) on downstream ecosystems.