Five generations of selective breeding for ultrasonic vocalization (USV) responses in N:NIH strain rats

This article reports on early results from an ongoing selective breeding study in which rats were selected for different rates of ultrasonic vocalization (USV) in response to isolation. Using the N:NIH strain, all litters were screened at 10 (+/- 1) days of age in a 2-min isolation test, and those males and females with the highest (or lowest) rates in each litter were selected for later breeding with like breeders from unrelated litters. A Random line (unselected control) was also bred. In the first selected generation (S1), the Low line diverged from Random line controls, and has maintained significantly lower rates over all generations since. In the S3 generation, the High line diverged significantly from Random line controls, and has shown significantly higher USV rates in each succeeding generation. No line differences were found in other behaviors measured in isolation. Data from a small sample of S5 pups tested at postnatal Days 3, 10, 14, and 18 days showed that individual pups' rates of USV from Day 10 predicted those at Day 14, consistent with findings from an unselected generation. Ambient temperature, modulated by body weight, controlled USV at Day 3, whereas at Days 10 and 14 line accounted for most of the variance in USV. This is the first instance of laboratory selection occurring on the basis of an infantile trait.