Early Succession of Community Structures and Biotic Interactions of Gut Microbes in Eriocheir sinensis Megalopa after Desalination

Abstract

As an enduring Chinese freshwater aquaculture product, the Eriocheir sinensis has a high economic value and is characterized by a catadromous life style that undergoes seawater-freshwater migration. However, little is known about their gut microbial status as they move from saltwater to freshwater acclimatization. Here, we sampled and cultivated Eriocheir sinensis megalopa from three aquaculture desalination ponds and investigated their gut microbiota diversity, community structures and biotic interactions from megalopa stage to the first juvenile stage after desalination for 9 days. Our results revealed that during the transition from megalopa to the first juvenile in Eriocheir sinensis, a significant change in gut microbial composition was observed (for instance, changes in relative abundance of dominant phyla), which was, however, not influenced by different sampling sites. The species diversity (such as the richness) of the gut microbiota showed a hump-shaped pattern along the succession. However, the compositional differences of the gut microbes showed constantly increasing patterns during the succession after freshwater adaption for all three sampling sites. Further co-occurrence analysis also showed that the complexity of the ecological networks in gut microbes was significantly enhanced during the development, such as increasing numbers of network links, connectivity and modularity, and was confirmed by decreasing average path length and proportions of negative links. Taken together, the differences in community structures and biological interactions of gut microorganisms were more pronounced in Eriocheir sinensis megalopa during desalination than in diversity and species compositions. This implies that the gut microbes of Eriocheir sinensis megalopa would become more robust and adaptive during the developmental process.

Keywords: Eriocheir sinensis megalpopa; bacterial community; gut co-occurrence network; gut microbiota; larval development.

Figure 1

Sampling sites in this study.

Figure 2

Relative abundance of intestinal microbes in Eriocheir sinensis megalopa at the Phylum level (A) and Genus level (B).

Figure 3

Differences in alpha diversity measures (Richness, Shannon index, Simpson index, Pielou’s evenness, invsimpson index, Chao1 index, ACE index and Good’s coverage) of the bacterial species in the intestines of megalopa at different developmental time.

Figure 4

Differentiation and succession of gut microbiota in Eriocheir sinensis megalopa over development time. Principal coordinate analysis (PCoA) visualizing compositional variations of Eriocheir sinensis megalopa gut bacterial communities in different spawning sites based on Bray–Curtis dissimilarity (A) and different developmental times (B). Based on Wilcox’s t-test was conducted to compare and obtain the differences between the community and the initial community on the Day 5 and Day 9, respectively, visualizing and standardizing the differences between different sample communities using the Unifrac index (C) and the Sorensen index (D). The “ns” stands for no significant difference, * p < 0.05, ** p < 0.01 represent significant differences.

Figure 5

Total co-occurrence network of the gut microbial community. (A) The co-occurrence network of the gut microbiome of Eriocheir sinensis in DT, RD, and SY group at the OTU level. Each of the nodes represents unique OTUs in the data sets. The size of each node is proportional to the number of connections (that is, degree). OTUs are colored by different sites. The red side is positive correlation and the blue side is negative correlation. (B) The relationship between network topology characteristics and time of gut microbiome communities. Different lowercase letters indicate significant differences (p < 0.05) at different times in the same group. Bars represent the mean ± SD (N = 18).