Epibiota dispersed more with increased temperature (ii)
As host performance declined with increased temperature,
within-population beta diversity increased as well. This observation is
in line with the Anna Karenina principle which predicts that conditions
stressful to the host promote a decline in stability in the associated
microbial community. It also supports our second hypothesis that thermal
stress increases beta diversity in epibiota among individuals from the
same population. Along with this increase in beta diversity, alpha
diversity (both richness and evenness) increased as well. This could
reflect higher metabolic rates at elevated temperature (Clarke &
Fraser, 2004; Gillooly, Brown, West, Savage, & Charnov, 2001) promoting
proliferation, dispersal and succession rates. However, the increase in
alpha-diversity could at the same time be another indicator of a
relaxation of influence from the host (and thus a relative increase in
stochasticity) at elevated temperature. The production of defense
related metabolites (Saha et al., 2016; Wang, Wang, et al., 2017) could,
for instance, be reduced under stress, resulting in a higher probability
for random microbes to temporarily settle in the community. On the other
hand, increased alpha-diversity may benefit the host under stressful
conditions by promoting functional redundancy (Girvan, Campbell,
Killham, Prosser, & Glover, 2005) and support the holobiont to retain
essential bacterial functions.