Data derived from molecular microbiological investigations of the human vagina have led to the discovery of resident bacterial communities that exhibit marked differences in terms of species composition. All undergo dynamic changes that are likely due to intrinsic host and behavioral factors. Similar types of bacteria have been found in both amniotic fluid and the vagina, suggesting a potential route of colonization. Given that not all of the species involved in intrauterine infections are readily cultivated, it is important that culture-independent methods of analysis must be used to understand the etiology of these infections. Further research is needed to establish whether an ascending pathway from the vagina to the amniotic cavity enables the development of intrauterine infections.

Inflammatory bowel disease (IBD) is an immunologically mediated disease and may be caused by abnormal immunological response to gut microbes. Although several studies on the ecological changes associated with IBD, such as community diversities, were reported, no previous studies have investigated the changes in the spatial heterogeneity and the mechanism of community assembly of the gut microbiota associated with IBD. In the present study, we first applied the Taylor’s power law extensions to compare the community spatial heterogeneity between the gut microbial communities of the IBD patients and those of the healthy individuals. We found that the community spatial heterogeneity of gut microbiota in IBD patients is slightly lower than in the healthy individuals. This finding suggests that IBD may lower the spatial heterogeneity of gut microbiota, possibly via lowering the abundance of dominant species. We further applied the neutral theory of biodiversity to comparatively investigate the community assembly and diversity maintenance of the gut microbiota with and without IBD, and our application suggested that deterministic factors such as host immunity should be dominant forces shaping gut microbiota assembly, and diseases such as IBD may not be strong enough to change the trend set by the deterministic host factors.

15Maintaining sexual reproduction in a highly competitive world is still one of the major mysteries 16 of biology given the apparently high efficiency of asexual reproduction. Co-evolutionary theories 17 such as the Red Queen hypothesis would suggest that the microbiomes in human reproductive 18 systems, specifically the microbiomes contained in semen and vaginal fluids, should reach some 19 level of homogeneity thanks to arguably the most conspicuous microbiome transmission between 20 two sexes. The long-term sexual coevolution should favor the dynamic homogeneity or stability, 21 which should also be beneficial for sexual reproduction such as sperm survival or fertilization on 22 physiological/ecological time scale. We present a piece of quantitative evidence in the form of 23 microbial community spatial heterogeneity to support the stability notion by analyzing three big 24 datasets of the human vaginal, semen and gut microbiome. Methodologically, we applied a 25 recent community-level extension to the classic Taylor's power law (Taylor 1961(Taylor , 1988: Nature), 26 which reached the rare status of ecological law and has found applications beyond biology. The 27 power law analysis revealed that human vaginal and semen microbiomes exhibited the same 28 scaling parameter size in their community spatial (inter-individual) heterogeneities, while both 29 exhibited significantly different heterogeneity scaling parameter with the human gut 30 microbiome. Both ecological and evolutionary theories, such as hologenome/holobiont and Red 31 Queen, even first principle, would predict that microbiome transmissions between two sexes 32 should have homogenizing effects on the composition and stability of the microbiomes in human 33 reproductive systems. 34 35 Running Head: Human reproductive system microbiomes 36 Keywords: Human gut microbiome; Human vaginal microbiome; Semen microbiome; 37 Heterogeneity; Power law extensions (PLEs); Red Queen theory; Hologenome 38 2 39 Importance 40 41Maintaining sexual reproduction in a highly competitive world is still one of the major mysteries 42 of biology given the apparently high efficiency of asexual reproduction. Co-evolutionary theories 43 such as the Red-Queen hypothesis would suggest that the microbiomes in human reproductive 44 systems, specifically the microbiomes contained in semen and vaginal fluids, should reach some 45 level of homogeneity thanks to arguably the most conspicuous microbiome transmission between 46 two sexes. The long-term sexual co-evolution should favor the dynamic homogeneity or stability, 47 which should also be beneficial for sexual reproduction such as sperm survival or fertilization on 48 physiological/ecological time scale. We present a piece of quantitative evidence in the form of 49 microbial community spatial heterogeneity to support the stability notion by analyzing three big 50 datasets of the human vaginal, semen and gut microbiome. Both ecological and evolutionary 51 theories would predict that microbiome transmissions between two sexes shou...

Understanding ecological linkages between above- and below-ground biota is critical for deepening our knowledge on the maintenance and stability of ecosystem processes. Nevertheless, direct comparisons of plant-microbe diversity at the community level remain scarce due to the knowledge gap between microbial ecology and plant ecology. We compared the α- and β- diversities of plant and soil bacterial communities in two temperate forests that represented early and late successional stages. We documented different patterns of aboveground-belowground diversity relationships in these forests. We observed no linkage between plant and bacterial α-diversity in the early successional forest, and even a negative correlation in the late successional forest, indicating that high bacterial α-diversity is not always linked to high plant α-diversity. Beta-diversity coupling was only found at the late successional stage, while in the early successional forest, the bacterial β-diversity was closely correlated with soil property distances. Additionally, we showed that the dominant competitive tree species in the late successional forest may play key roles in driving forest succession by shaping the soil bacterial community in the early successional stage. This study sheds new light on the potential aboveground-belowground linkage in natural ecosystems, which may help us understand the mechanisms that drive ecosystem succession.