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.