Our goal was to describe in more detail the evolutionary history of Gamma and two
derived lineages (P.1.1 and P.1.2), which are part of the arms race that
SARS-CoV-2 wages with its host. A total of 4,977 sequences of the Gamma strain
of SARS-CoV-2 from Brazil were analyzed. We detected 194 sites under positive
selection in 12 genes/ORFs:
Spike, N, M, E, ORF1a, ORF1b, ORF3, ORF6,
ORF7a, ORF7b, ORF8,
and
ORF10
. Some diagnostic
sites for Gamma lacked a signature of positive selection in our study, but these
were not fixed, apparently escaping the action of purifying selection. Our
network analyses revealed branches leading to expanding haplotypes with sites
under selection only detected when P.1.1 and P.1.2 were considered. The P.1.2
exclusive haplotype H_5 originated from a non-synonymous mutational step
(H3509Y) in H_1 of
ORF1a.
The selected allele, 3509Y,
represents an adaptive novelty involving
ORF1a
of P.1. Finally,
we discuss how phenomena such as epistasis and antagonistic pleiotropy could
limit the emergence of new alleles (and combinations thereof) in SARS-COV-2
lineages, maintaining infectivity in humans, while providing rapid response
capabilities to face the arms race triggered by host immuneresponses.