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.