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.