Targets of selection
Although the phenotypes that we measured and observed in association
with candidate SNPs cannot be concluded to be the causal variants that
are the actual targets of selection, we can use the
genotype-by-phenotype associations to guide future research aimed to
identify these targets. Further, we can also narrow down some traits and
life stages that do not appear relevant to any observed adaptive
variation. For example, the adaptive genetic variation had no predictive
ability for the short-term swimming ability of migration-phase adult
lamprey at Bonneville Dam or the growth differences among young-of-year
larvae. These two cases of failure to reject a null hypothesis help
narrow down the search for a mechanism that manifests in large body size
adults that tend to travel further upstream to spawn (a trait highly
associated with genes on chromosome 2). These genes apparently do not
confer adult swimming endurances, at least for the short timeframe that
could be tested in swim trials at Bonneville Dam. Further, these adult
body size differences do not translate to faster growth in young of year
larvae. However, these adult body size differences could be influenced
by differential growth at older life stages; prey selection, length of
time in the ocean, or ocean distribution likely affect growth (Clemens
et al. 2019). It will require further investigation of multiple life
stages in both freshwater and the ocean to understand Pacific lamprey
life history strategies. For the maturity trait, gene ontology could
suggest other traits to examine as potential targets of selection
including circadian rhythm.