Microbes vs. host patterns
Suberites diversicolor is categorized as a Low Microbial
Abundance (LMA) sponge (Weisz, Lindquist and Martens, 2008; Clearyet al. , 2013). A recent study into prokaryotic communities ofS. diversicolor (5 lakes overlap with the current study) showed a
pattern of distinct broad geographic groups (>1,400km) but
no distinction between host genetic lineages and only some clustering
per lake (Ferreira et al. , 2020). When comparing the microbial
patterns observed by Ferreira et al (2020) to genetic structure
of S. diversicolor from the current study, interestingly we find
no relationship apart from the broad geographic distinction
(>1,400km). This is consistent with a study by Noyer and
Becerro, (2012) that did not find correlations between host genetic and
microbial diversity for the sponge Spongia lamella in the
Mediterranean (<500km). Perhaps microbial communities are
evolving separately from their host for some sponges, such as S.
diversicolor . Or perhaps the microbial community was not measured
extensively enough since there are known differences between the
relatively stable core microbiome and the environmentally variable
microbiome (Pita et al. , 2018).
Changing oceans may shift symbioses of sponge holobiont (Fan et
al. , 2013). It is already known that sponge-associated microbiomes can
respond to temperature (Webster, Cobb and Negri, 2008), although
dependent on the extent of the heat stress (Simister et al. ,
2012), and pH (Cleary et al. , 2013; Morrow, Fiore and Lesser,
2016; Coelho et al. , 2018). Responses of microbes may have
effects on host persistence and viability. It is expected that the
microbiome can respond more quickly than the host to changing
environments due to shorter generation times (Reshef et al. ,
2006; Pita et al. , 2018). However, here, the opposite seems to be
the case, where the sponge host is adjusting to specific marine lake
environments (or genetic drift) while microbes appear to remain stable
along the marine lake gradient. Moving on from 16S-amplicon sequencing
to whole bacterial genome or gene expression analyses (Liu et
al. , 2012) will allow for a better understanding of microbial community
structure and function, and could provide the necessary depth to move
forward in exploring how sponges function as holobionts.