Audible calls and their ontogenetic relationship with ultrasonic vocalization in a rodent with a wide vocal range, the fat-tailed gerbil (Pachyuromys duprasi).

Ontogeny of audible and ultrasonic calls is poorly studied in Gerbillinae rodents. In this study, analysis of calls, emitted by pup and adult fat-tailed gerbils Pachyuromys duprasi during 420-s isolation-and-handling procedures, allowed testing two hypotheses. Hypothesis1 predicted that audible squeaks and clicks follow the same ontogenetic pathway (towards higher-frequency and shorter calls) that has been previously documented for the ultrasonic calls of fat-tailed gerbil. Hypothesis2 predicted that the audible call types would alternate with the ultrasonic call types along ontogeny in this species. Hypothesis1 was tested with comparison of acoustic variables of audible calls (squeaks and clicks), emitted by 1-10-day old pups and by adults. Clicks of 8.3-8.7 kHz and high-frequency squeaks of 1.92-3.57 kHz were present in pups and adults, whereas mid-frequency squeaks of 0.31-0.67 kHz and low-frequency squeaks of 0.04-0.11 kHz were only present in pups. In agreement with Hypothesis1, pup high-frequency squeaks were longer, lower in fundamental frequency and higher in peak frequency. Against predictions, clicks did not differ acoustically between pups and adults. Hypothesis2 was tested with comparison of percentages of test trials containing the audible and/or ultrasonic call types of pups, repeatedly tested in 15 age classes along ontogeny from 1 to 40 days of age and in adults. The audible calls occurred in all age classes, whereas the ultrasonic calls emerged from day five of pup life and then prevailed over the audible squeaks in all age classes. We discuss that, in fat-tailed gerbil, ontogenetic pathways of acoustic variables of audible and ultrasonic calls (towards higher-frequency and shorter calls) are unusual for rodents although are typical for social and echolocation calls of bats. The is another parallelism of acoustic communication between bats and rodents aside from the recently discovered similarity between bat ultrasonic echolocation and echo-based navigation with bouts of ultrasonic calls in blind leaping rodents.