Heritability
Heritability estimates provide information as to the extent to which
phenotypic trait variation has a genetic basis and the potential for
adaptive change in these traits (Visscher et al., 2008). SNPs are
intrinsically linked to narrow-sense heritability given
h2 is proportional to the product of the number of
SNPs and their effect size (Holland et al., 2019).
We found a high level of variation
in survival, bleaching, and growth attributed to narrow-sense
heritability (h2) when pooled at the level of
population cross, which varied in juveniles infected with C.
goreaui across the two temperatures tested here (see Supplementary
Information for further details on S. tridacnidorum and D.
trenchii ).
Interestingly, additive genetic
variance was only important in influencing survival at 31°C when
infected with C. goreaui but not at 27.5°C. Hence, it is likely
that there is significant selection on survival at high temperatures forC. goreaui , consistent with the generally overall poorer
performance of these symbionts at both temperatures (S.
tridacnidorum ) or at higher temperatures in coral juveniles (C.
goreaui ) (see Table 6.1 in Quigley, Baker, Coffroth, Willis, & van
Oppen, 2018). The shapes of the posterior heritability distributions are
informative for generating hypotheses concerning the underlying genomic
architecture associated with selective breeding. Bimodal heritability
estimates can be driven by single large effect eQTLs (as seen generally
for traits with high heritability), whereas multiple loci of small
effect size generally result in unimodal distributions (Rudra et al.,
2017). The influence of cis and trans co-regulation of the
traits may also influence the underlying distribution (Yang et al.,
2014). Bimodal heritability (often with wide credibility intervals)
estimates can also be driven by high underlying within-population
variability even with large sample sizes (mirrored in the high
phenotypic variability between genotypes, Quigley et al., 2020), and
have been recorded across a range of disease-related expression of genes
(Yang et al., 2014). High heritability at ambient temperatures may also
be common (Kronenberg et al., 2019), and potentially indicative of core
traits under continual selective pressures. Finally, it is likely that
not all the SNPs associated with these three phenotypes have been
captured although narrow-sense heritability should incorporate
additively all the common SNPs associated (Holland et al., 2019) and it
will be important to use these methods under a variety of experimental
settings to fully develop models of adaptive selection.