It is becoming increasingly understood that the gut microbiota can influence body development, physiology, and ecological inter- or intraspecific interactions [36–39]. The microbial community, however, is also plastic. Several factors can alter the composition of the gut microbial community [22, 23] and thus have the potential to shape the community function [40, 22]. According to prior studies, the influence of many factors on the microbiota is context dependent and might only be observed above a certain threshold; for instance, the composition of the predominant termite gut microbiota remained largely constant despite variations in diet [41]. In contrast, dietary differences markedly altered the gut bacterial community in gypsy moths [42]. However, studies on whether and/or which factors shape the gut microbiota of widespread predators—such as spiders—that play a key role in ecosystem stability have rarely been reported. We fed spiders with three groups of ants, which all had different nutritional contents and microbiota. We then profiled the gut bacterial communities of the spiders under different dietary conditions and identified how variations in nutrients or diet-associated bacteria affected spiders’ gut microbiota. Considering the relatively slow digestion and the strikingly endurance of starvation of the spider, the spiders were dissected 48 hours after feeding with ants. Furthermore, a pilot experiment showed that the starvation for at least 7 days had no obvious effect on total abundance of the spider’s gut microbiota. Our results demonstrated that the gut bacterial communities were similar across diets, despite differences in nutritional content or ingested microbes. Discrepancies between the two studies indicate that further research is needed to better understand the relationship between spider food and the stability of their gut microbiota.
Variations in both nutritional level and the microbial community associated with their prey can both influence predator’s gut microbiota [43], we collected two species of ants from different geographic sites to research food induced gut bacterial community changes. Previous studies suggested that feeding fish with certain species improve muscle function [37]. The protein content in diets varies considerably even in the same species [44]. To achieve a more comprehensive measurement of dietary differences, we evaluated compositional variations in protein, GT, trehalose, and glucose levels, three of which varied significantly between the L. niger and T. caespitum ant diets. In a previous study of ants, the authors found similarities in the bacterial communities between species of the same trophic level [45]. Conversely, some studies have provided evidence that the bacteria community is significantly varied across species rather than biogeography [46, 37]. To determine whether the microorganisms in spiders’ food impact their gut microbiota, we analyzed the microbial diversity of feed ants, examining both different species and the same species from different locations. We found that the microbiota composition of the feed ants varied significantly, despite all belonging to Formicidae. In our results, both geographic location and species impacted gut microbiota to varying degrees. Accordingly, spiders were divided into three groups and fed on one diverse ant subset, to assess if variations in feed created variations in spider gut microbiota.
We used Illumina MiSeq sequencing of 16S rRNA genes to test whether spiders that ate different ants would also exhibit a difference in microbial composition. Our results demonstrated that the gut microbiota in all spiders maintained a consistent composition, with Pseudomonas as the dominant genus, which is known for its metabolic diversity and its ability to colonize many niches, including the gut [47]. To ensure the abundance of Pseudomonas did not result from contamination, we performed negative extraction and PCR control, which was visualized using a 2% agarose gel. Our results found no band for the negative extraction and PCR control and an obvious band for the positive control. The presence of this OTU makes it likely to be unintentionally sequenced, however, this OTU accounted for more than 90% of total sequences in our experimental samples. Our results indicate that the high percentage of Pseudomonas in our study was not due to contamination. Compared with common spiders living in cotton fields (where 237 genera were detected at the genus level [27]), C. campanulata could maintain a relatively simple gut environment. This could be due to its limited diet. Intriguingly, Badumna Longinqua, whose diet includes crickets and fruit flies, showed the opposite result [48]. And its gut microbiome experiences pronounced temporal fluctuations and slowly approaches its initial state after more than 658 h. The difference between the results obtained by our study and that of previous research could be due to several factors, including the different spider species used and their rearing conditions. Their prey typically contains a rich microbiome, and the spiders sometimes ingest and maintain certain microbes from prey in their gut. This mimics a pattern of stability in the spider’s gut microbiota. Additionally, spider habitat and taxonomy could influence their gut microbiota [49], however, without knowing the natural state of the spider microbiomes obtained from the field, we can only conclude that the gut bacterial communities in groups fed different diets were similar, despite differences in their nutrients or ingested microbes.
Comparing the composition of the microbial community between predators and prey at the intraspecific level, we found that C. campanulata could maintain a relatively high level of Pseudomonas, which has been reported to produce tannase to detoxify or tolerate tannis in food [50, 51]. Interestingly, we detected no Acinetobacter in the spiders, despite its prevalence in the feed ants. This implies that not all microorganisms obtained from food can successfully colonize a spider gut, suggesting the host can prevent the colonization of new bacteria, possibly as a way to defend against pathogens [52]. In most cases, the intestinal bacterial community is short-lived and opportunistic, with widely diverse bacteria stemming from a constantly changing environment [53–55]. This stabilization of gut microbial diversity could be due to microbial competition or interference following the introduction of exogenous bacteria [56], however, further investigation is required to confirm either of these hypotheses.
The life history of spiders has rarely been studied due to a lack of reliable rearing methods and the difficulty of providing an artificial diet. Since spiders are primarily carnivorous, they require specific kinds of prey. Divina M. Analin et al. found that the survival rate of sac spiders was influenced by different artificial diets [57]. Several studies have demonstrated that the animal gut microbiome is important for nutritional absorption [58], while the diet-altered gut microbiota of spiders can influence its development and survival rate under artificial rearing conditions. Future work assessing whether or how gut microbiomes affect spider survival should be the focus of future studies.
In conclusion, when we analyzed the microbial composition in three spider groups with different diets, we observed no dynamic changes in gut microbiota. This indicates that diet has minimal effect on gut microbiota of C. campanulata, despite variations in feed microbial community and nutrients, ensuring normal physiological function and development. It is worth noting that identifying a mechanism by which this action takes place was beyond the scope of this study. Future studies should include additional types of prey and spiders to analyze these results on a larger scale and outline a potential mechanism for host regulation in gut microbial homeostasis. The analysis of spiders’ intestinal microbiota in conjunction with soil layer microorganisms analysis is also worthwhile endeavor, to determine if the dominant microorganisms in the spiders’ gut microbiota are a result of their environment. This work provides a blueprint for future investigation into the gut microorganisms of spiders and highlights the potential existence of a unique gut modulatory mechanism.