4.2 Adaptive mechanism of visual related genes
We tested four visual-related PSGs in four specieslow.ARRDC3 , LZTFL1 , and TRNT1 reveal important roles in
the retina (Sharma et al., 2017;
Ying H et al., 2017;
Ying et al., 2017). RAB8A plays a
vital part in regulating outer segment protein composition and
photoreceptor function (Murga-Zamalloa et
al., 2010). And IGFBPL1 associated with the growth of retinal
ganglion cell (RGC) axons (Guo et al.,
2018).
A previous study has suggested that the enlargement of one area of the
brain might be associated with the reduction in the size of other brain
areas (Harvey and Krebs, 1990). The
auditory cortex and the inferior colliculus are enlarged in volume in
laryngeal echolocating bats, especially in rhinolophoid bats, whereas
visual brain areas are relatively enlarged in Old World fruit bats
(Dechmann and Safi, 2009). Because of the
extreme energetic demands imposed by neural processing, the trade-off
has been proposed in investment in brain tissues. Dong et al. (2013)
showed more visual perception genes have become
pseudogenes in rhinolophoid bats, and
speculate that some visual perception genes may have undergone relaxed
natural selection in echolocating bats. They also found some
hearing-related genes undergone positive selection, and such concordance
suggests that some genes are impacted by natural selection, which raised
the possibility that changes in the sensory genes will have direct
consequences for those genes controlling for other sensory modalities,
perhaps via trade-offs. We found no visual-related genes affected by
positive selection in R. osgoodi emit echolocation with normal
frequency. This finding supports the longstanding but weakly supported
assumption that bats are experiencing a trade-off between vision and
audition (Dong et al., 2013).
Positive selection of both acoustic and visual genes was detected in
specieslow, indicating that there was no obvious
inhibition of the evolution of acoustic related genes and visual related
genes in these species, which were affected by natural selection and
different with other species. These comparative analyses provide
important evidence for the adaptation of specieslow to
their special hearing mechanisms. Although laryngeal echolocation bats
do not rely primarily on vision, the evolution of one sensory related
gene may have influenced the evolution of other senses. So we cannot
rule out the role of these genes in the evolution of bat hearing until
further functional analysis is performed, especially for species in themacrotis group, which has a low dominant frequency of
echolocation.