Abstract
Seaweeds are colonized by a microbial community which can be directly
linked to their performance. This community is shaped by an interplay of
stochastic and deterministic processes, including mechanisms which the
holobiont host deploys to manipulate its associated microbiota. The Anna
Karenina Principle predicts that when a holobiont is exposed to
suboptimal or stressful conditions, these host mechanisms may be
compromised. This leads to a relative increase of stochastic processes
that may potentially result in the succession of a microbial community
harmful to the host. Based on this principle, we used the variability in
microbial communities (i.e., beta diversity) as a proxy for stability
within the invasive holobiont Gracilaria vermiculophylla during a
simulated invasion in a common garden experiment. At elevated
temperature (22 °C), host performance declined and disease incidence and
beta diversity increased. At optimal temperature (15 °C), beta diversity
did not differ between native and non-native populations. However, under
thermally stressful conditions beta diversity increased more in epibiota
from native populations. This suggests that epibiota associated with
holobionts from non-native populations are under thermal stress more
stable than holobionts from native populations.
This pattern reflects an increase of deterministic processes acting on
epibiota associated with non-native hosts, which in the setting of a
common garden can be assumed to originate from the host itself.
Therefore, these experimental data suggest that the invasion process may
have selected for hosts better able to maintain stable microbiota during
stress. Future studies are needed to identify the underlying host
mechanisms.
Keywords: holobiont, invasive species, common garden
experiment, Anna Karenina Principle, beta diversity, macro-algae,
microbiota, stability