Selection on ultrasonic call rate in neonatal rats affects low frequency, but not ultrasonic, vocalizations in adults

Abstract

Pleiotropy is a pervasive phenomenon in evolution. Its relevance and existence were recognized early in medical syndromes, but the term "pleiotropy" was first coined by Ludwig Plate in 1910 (Stearns, 2010). Pleiotropy is an important concept with many different facets and definitions, but generally describes "the phenomenon of a single gene affecting multiple traits" (Paaby & Rockman, 2013). Here, we investigated the emergence of unselected by-products coupled to an originally selected for trait, including across developmental stages, as a possible example of pleiotropy, but we make no claims about genetics (Paaby & Rockman, 2013). Coherent development throughout developmental stages is essential for functionality in morphological structures (Cheverud, 1996), and pleiotropic traits can thus be representative of adaptive developmental processes that form and shape structures in organisms (Klingenberg, 2008). A potential example of a pleiotropic effect can be found in dogs and other domesticated mammals. Human selection for tameness in these animals has been suggested to lead to downregulation of neural crest cell development and migration (Wilkins, Wrangham,

Selection on vocal output affects laryngeal morphology in rats

“…This confirms our hypothesis that selective breeding can lead to changes in laryngeal morphology. Our anatomical findings are consistent with previous evaluations of acoustic measures in the same rat lines (Lesch et al, 2020).…”

“…The differences in vocal fold length found in the current study thus explain the line difference we observed in the fundamental frequency of low-frequency calls in our previous study (i.e. high line males producing higher frequencies than low line males; Lesch et al, 2020).…”

“…Therefore it is important to document and understand possible changes to the vocal production mechanisms that may arise as a result of selective breeding (and, by extension, natural selection). In Lesch et al (2020), analyses of vocal outputs from rat lines selectively‐bred for USVs as pups showed that line breeding affected the fundamental frequency of low‐frequency calls but not USVs in adults. The likely mechanism by which these low‐frequency calls are produced is standard vocal fold vibration in the larynx, as detailed in the myo‐elastic aerodynamic theory (Elemans et al, 2015; Titze, 2006), implicating potential differences in vocal fold length as the main cause of these differing fundamental frequencies (Herbst et al, 2012; Riede et al, 2011; Roberts, 1975a).…”

“…Within five generations the high line pups produced up to 300 USVs within two minutes whereas the low line pups produced less than 50 calls. In the 58th generation high line individuals produced on average over 300 calls with some individuals reaching over 400 USVs; low line individuals produced less than 50 USVs with the exception of one individual that produced 86 USVs (Lesch et al, 2020). The breeding was conducted at Williams College Animal Facility and all procedures were approved by the Williams College Animal Care and Use Committee.…”

“…This sustained artificial selection upon USV call rate in pups yielded two distinct rat lines with both different vocal behavior and distinctive stress responses (Brunelli & Hofer, 2007; Zimmerberg, Brunelli & Hofer, 1994). An earlier study of rats from these two selected lines revealed clear effects of selection on vocal acoustics (Lesch et al, 2020), but the morphological basis of the line‐specific acoustic differences documented there remain unknown.…”