Within-population beta diversity as a proxy for stability
Changes in beta diversity within a common garden may be informative in
different ways. Whereas beta diversity among individuals from different
populations (between-population beta diversity) relates to changes
within the holobiont with respect to the environment and other
populations (microbiome flexibility; Voolstra & Ziegler, 2020 or host
promiscuity; Bonthond et al., 2021), the within-population beta
diversity reflects the ratio between deterministic drivers (e.g.,
abiotic variables, mechanisms from the host) and stochastic drivers
(e.g., historical contingency, mass effects, microbe-microbe
interactions) that act on the holobiont. Metabolites involved in
attracting or repelling microbes (Saha & Weinberger, 2019), chemicals
related to defense against fouling (Saha et al., 2016), e.g.,
interfering with quorum sensing (Harder et al., 2012), traits
related to morphology affecting the associated epibiota (Lemay et al.,
2021), or promiscuity of the host towards potential symbionts (Bonthond
et al., 2021; Klock et al., 2015) could represent important
deterministic drivers that stabilize microbial communities. The Anna
Karenina Principle posits that as such host mechanisms are compromised
or affected in response to stress, the associated microbial community is
less shaped by these deterministic drivers and becomes more unstable
(Zaneveld et al., 2017). Instead, stochastic processes acting on the
microbial community become relatively more important, and consequently,
beta diversity among replicated holobionts will increase.
Unlike in their natural habitat where each population is exposed to a
unique environment, in a common garden different populations are exposed
to the same environment, and therefore to the same environmental
deterministic and stochastic processes. Turning the Anna Karenina
Principle around in the common garden, differences in within-group beta
diversity among groups of study, could thus be used as a relative
measure for the contribution of host mechanisms acting on the associated
microbiota. Based on this idea, we used within population beta diversity
as a surrogate for stability. The present study provides an example of
how different groups (here native and non-native populations) can be
compared.