Age-dependent gene expression in the inner ear of big brown bats (Eptesicus fuscus)

Abstract

For echolocating bats, hearing is essential for survival. Specializations for detecting and processing high frequency sounds are apparent throughout their auditory systems. Recent studies on echolocating mammals have reported evidence of parallel evolution in some hearing-related genes in which distantly related groups of echolocating animals (bats and toothed whales), cluster together in gene trees due to apparent amino acid convergence. However, molecular adaptations can occur not only in coding sequences, but also in the regulation of gene expression. The aim of this study was to examine the expression of hearing-related genes in the inner ear of developing big brown bats, Eptesicus fuscus, during the period in which echolocation vocalizations increase dramatically in frequency. We found that seven genes were significantly upregulated in juveniles relative to adults, and that the expression of four genes through development correlated with estimated age. Compared to available data for mice, it appears that expression of some hearing genes is extended in juvenile bats. These results are consistent with a prolonged growth period required to develop larger cochlea relative to body size, a later maturation of high frequency hearing, and a greater dependence on high frequency hearing in echolocating bats.

Bats experience age-related hearing loss (presbycusis)

“…Sensitive hearing, especially at high frequencies, is necessary for echolocating bats ( Mao et al, 2017 ), because they must be able to detect the faint echoes that return immediately after the much louder emitted echolocation signals ( Grinnell, 2018 ). Notably, as bats typically live very long ( Pollard et al, 2019 ), hearing impairment might have a serious effect on their fitness.…”

“…As nocturnal mammals, most bat species echolocate by emitting high-frequency ultrasonic signals and processing these signals’ returned reflections of obstacles and targets in their environment ( Surlykke et al, 2014 ; Fenton et al, 2016 ). Thus, although high-frequency hearing confers a survival benefit for many animals, it is essential for the survival of echolocating bats, which rely on it for orienting in their environment ( Mao et al, 2017 ). This combination of extreme longevity and reliance on high-frequency hearing makes bats very relevant models for studying age-related hearing loss.…”

Comparative cochlear transcriptomics of echolocating bats provides new insights into different nervous activities of CF bat species

“…The divergence of gene expression is an important component of molecular adaptation and an essential way to generate biological diversity 1 – 3 . Comparisons of gene expression levels within and between species have become a powerful method for studying the genetic basis of phenotypic variation 4 , as well as for studying the evolution of gene regulation 5 – 7 .…”