4 DISCUSSION
This study compared the gut bacterial community between female and maleP. astrigera . Although all individual spiders using in the present study were collected at early spring season from a highly homogeneous cornfield in very small range, however, dramatic divergences in gut bacterial diversity and composition were found between the two sexes. Despite Hu (2019) observed that bacterial diversity indices and relative abundance of dominant bacteria have no significant difference between female and male spiders, our results proved that sexual variation is a crucial factor in shaping the gut bacterial community in spider.
Contrary to the previous results with high gut bacterial diversity were found in female insects (Han et al., 2017; Mason et al., 2019; Wan et al., 2020; Xu et al., 2016), however, we found male spiders had significantly higher gut bacterial richness than female. Environmental factors have been proved to be an important role in gut microbiota assembly in arthropods (Chandler, Lang, Bhatnagar, Eisen, & Kopp, 2011; Wong, Chaston, & Douglas, 2013), for insects can obtain microbiota from their surrounding environments (Douglas, 2011). For the reason that female P. astrigera takes a “sit and wait” strategy during breeding period, so the male has to wandering around to find female, thus they have chances to face more diverse environment and different preys in the meantime. The big deviation of Sobs and Chao1 indices in male also matched the judgment that environmental microbiota has an important impact on gut microbiota. Consistent with our first hypothesis, this sex-related behavior of male P . astrigera results in a significantly higher bacterial richness than female. This finding corresponds with those of Foster (1995) and Zouache et al. (2011) who suggested that less dispersal and tending to remain close to breeding sites could be a factor constraining bacterial diversity of male mosquitoes. Similarly, Ng et al. (2013) considered that reduced constant exposure to diverse environmental microbiota could result in decrease in gut bacterial diversity in crickets. The results of bacterial β-diversity showed that female and male distributed on the two side of the biplot, with more dispersed male’ points, which confirmed the importance of dispersal capabilities for diversity of spider gut bacteria.
Our results showed dramatic shifts in gut bacterial community composition between female and male P. astrigera , the relative abundance of dominant bacteria between two sexes differed in different taxon level. Furthermore, the divergences of gut bacterial community composition are mainly reflected from the different bacterial groups involved in metabolic activities, which is due to the different nutritional needs caused by sex differences. Female spiders try to avoid the reduction of energy and accumulate substantial nutrients for spawning simultaneously. As a result, very high Actinobacteriota and Rhodococcus (belongs to Actinobacteriota) found in female probably due to Actinobacteriota appears to supplement nutrition and are required for normal growth (Salem, Kreutzer, Sudakaran, & Kaltenpoth, 2013). On the contrary, we found that male have higher Firmicutes and F/B ratio than female, which contribute to the decomposition of complex carbohydrates, fatty acids, polysaccharides (Flint, Bayer, Rincon, Lamed, & White, 2008) and conduce to energy harvest (Ng, Stat, Bunce, & Simmons, 2018; Turnbaugh et al., 2006; Yu, Shen, Li, Yao, & Yin, 2020). Therefore, high Firmicutes and F/B ratio might meet the energy needs of male spiders that have to walk around in the breeding period to find their partners. We also note simultaneously that bacterial genera not related to sex were rather similar between female and male P. astrigera . For example, fenithrotion-resistantBurkholderia has ability to hydrolyze the compound, thus protecting its host (Kikuchi, Hosokawa, & Fukatsu, 2011).
Our results also affirmed that the same conclusion of effects of sex on gut bacteria found in insects, that is P. astrigera spider has significant differences in gut bacteria due to different behavior and physiological needs. Male P. astrigerahas to wandering around to find female, thus has a significantly higher gut bacterial richness than a “sit and wait” female. Moreover, the female has a high relative abundance of Actinobacteriota to meet their need of spawning and reproduction, by contrary, the male has a high relative abundance of Firmicutes and F/B ratio due to their energy demand of looking for partners. For the reason that sexual dimorphism is a very common phenomenon in spiders, the potential importance of sex on gut bacteria should not be ignored in future research in spider.