Abstract
Investigating inter-subject heterogeneity (or spatial distribution) of human semen microbiome diversity is of important significance. Theoretically, the spatial distribution of biodiversity constitutes the core of microbiome biogeography. Practically, the inter-subject heterogeneity is crucial for understanding the normal (healthy) flora of semen microbiotas as well as their possible changes associated with abnormal fertility. In this article, we analyze the scaling (changes) of semen microbiome diversity across individuals with DAR (diversity-area relationship) analysis, a recent extension to classic SAR (species-area relationship) law in biogeography and ecology. Specifically, the unit of “area” is individual subject, and the microbial diversity in seminal fluid of an individual (area) is assessed via metagenomic DNA sequencing technique and measured in the Hill numbers. The DAR models were then fitted to the accrued diversity across different number of individuals (area size). We further tested the difference in DAR parameters among the healthy, subnormal, and abnormal microbiome samples in terms of their fertility status based on a cross-sectional study of a Chinese cohort. Given that no statistically significant differences in the DAR parameters were detected among the three groups, we built unified DAR models for semen microbiome by combining the healthy, subnormal, and abnormal groups. The model parameters were used to (i) estimate the microbiome diversity scaling in a population (cohort), and construct the so-termed DAR profile; (ii) predict/construct the maximal accrual diversity (MAD) profile in a population; (iii) estimate the pair-wise diversity overlap (PDO) between two individuals and construct the PDO profile; (iv) assess the ratio of individual diversity to population (RIP) accrual diversity. The last item (RIP) is a new concept we propose in this study, which is essentially a ratio of local diversity to regional or global diversity (LRD/LGD), applicable to general biodiversity investigation beyond human microbiome.
Highlights
The parameters of the alpha-Diversity-Area Relationship (DAR) models and beta-DAR models for the three different groups were listed in Tables S1, S2 of the online supplementary information (OSI), respectively
The results of DAR analysis presented above revealed that fertility status did not have a significant influence on biogeography of semen microbiome, on the inter-subject heterogeneity in terms of either alpha-diversity or beta-diversity
Previous studies have suggested changes in semen microbiome diversity associated with fertility health (Hou et al, 2013; Weng et al, 2014), no rigorous statistical tests were performed with the published studies
Summary
Similar to other human microbiome habitats such as gut, vaginal, or breast milk, human seminal fluid hosts a microbiome including several hundreds of bacterial species per individual with various levels of abundances (Kiessling et al, 2008; Moretti et al, 2009; De Francesco et al, 2011; Hou et al, 2013; Weng et al, 2014). It has been widely recognized that seminal microbiome is implicated, at least in some of the male infertilities (Kiessling et al, 2008; Moretti et al, 2009; De Francesco et al, 2011; Domes et al, 2012; Hou et al, 2013; Weng et al, 2014). Investigating the biogeography or spatial distribution of seminal microbiome diversity is necessary for deep understanding the seminal microbiome as well as their implications for male infertility
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