| Abstrak/Abstract |
Odorant coreceptor (Orco) represents one of the essential genes in the insect olfactory system, which facilitates
signal transduction and heterodimerization with different odorant receptors (Ors) in the insect antennal dendritic
membrane. Evolutionary analysis by detecting positive selection is important to examine the functional flexibility
of Orco that potentially supports insect survival. The maximum likelihood codon substitution model was applied
using CODEML program as implemented in PAML ver 4.9e package across 59 Orco codon sequences available
from GenBank. These sequences represented five major insect orders and two reproductive systems (holometabola
and nonholometabola). In the site model that identified common ? values for Orco, it was clearly shown that Orco
was under strong purifying selection, indicated by the ? value that was far from 1 (?: 0.03). However, in to the
branch model, positive selection was detected to be acting on Dipteran lineages, whereas in the branch-site model,
several sites were under significant positive selection occurring in the following four clades: Coleoptera, Diptera,
Lepidoptera, and Psocodea. The typical evolutionary mode acting on Orco was consistent with the entropy value
[H(x)], confirming that 48.9% of the Orco site was under conservation (H(x) < 0.5), whereas 26.9% of the Orco sites
was under high variation (H(x) > 1). These findings confirmed that Orco genes are generally highly conserved and
can possibly be used for the manipulation of insect pest control programs. However, positive selection that acts on
certain lineages suggested future adaptive evolutionary ability of Orco to anticipate flexible functions for successful
olfactory processes.
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