Positively selected genes
Species often face various several environmental pressures, which may
explain the presence of several rapidly evolving, positively selected
genes. Some specific gene loci may also undergo nucleotide
substitutions. We determined positively selected genes in B. l.
tsinlingensis and in the salmonid linage with E. lucius as the
only outgroup species. B. l. tsinlingensis has the highest Ka/Ks
value among these species, indicating that B. l. tsinlingensispossessed much more rapidly evolving genes (Figure 4E ). This
result is consistent with the findings above indicating that B. l.
tsinlingensis has the fastest evolutionary rate among salmonids. There
were 36 positively selected genes inB.
l. tsinlingensis and 14 positively selected genes in
salmonids.
Four positively selected genes in B. l. tsinlingensis were
related to the
immune
response, includingc1qb ,cebpb ,tnfa , and psme1 (Table S21 ). c1qb is
associated with the brain immune system and social behavior
(Ma et al. 2015), cebpb is
a key immune-related gene that may be involved in sepsis
(Xu et al. 2020),tnfaplays a vital role in the immune response by regulating several pathways
that produce an immediate inflammatory reaction
(Holbrook et al. 2019), andpsme1may play an important role in the progression of Fanconi anemia to acute
myeloid leukemia (Hou et al.2020). For the salmonid line, two positively selected genes were
related to cell division and muscle development. btg3 may play an
important role in tumor suppression and is a key effector kinase in the
cell cycle checkpoint response (Chenget al.2013).rapsn has been shown to be associated with congenital myasthenic
syndromes.cld10can form paracellular channels with ion selectivity; its variant causes
anhidrosis and kidney damage (Joakimet al. 2017) (Table S22 ). Both muscle function and
kidney function are important for the migration of
salmonids,
as salmonids need to be able to inhabit freshwater and seawater, which
requires adaptation to both types of environments. The long-distance
migration of
salmonids
also requires strong muscles. Both of these genes were positively
selected in the salmonid line, which may be associated with the
migratory habits of these species.