Hidden paths to endless forms most wonderful: Parasite-blind diversification of host quality

Evolutionary diversification can occur in allopatry or sympatry, can be
driven by selection or unselected, and can be phenotypically manifested
immediately or remain latent until realised in a newly encountered
environment. Diversification of host-parasite interactions is frequently
studied in the context of intrinsically selective coevolution, but the
potential for host-parasite interaction phenotypes to diversify latently
during parasite-blind host evolution is rarely considered. Here we use a
social bacterium experimentally adapted to several environments in the
absence of phage to analyse allopatric diversification of host quality -
the degree to which a host population supports a viral epidemic.
Phage-blind evolution reduced host quality overall, with some bacteria
becoming completely resistant to growth suppression by phage.
Selective-environment differences generated only mild divergence in
host-quality. However, selective environments nonetheless played a major
role in shaping evolution by determining the degree of stochastic
diversification among replicate populations within treatments. Ancestral
motility genotype was also found to strongly shape patterns of latent
host-quality evolution and diversification. These outcomes show
that i) adaptive landscapes can differ in how they constrain
stochastic diversification of a latent phenotype and ii) major effects of
selection on biological diversification can be missed by focusing on trait
means. Collectively, our findings suggest that latent-phenotype evolution
(LPE) should inform host-parasite evolution theory and that
diversification should be conceived broadly to include latent phenotypes.