Letter to the editor: Chronicle for an orphan trait: Comment on Hofer, Shair, Masmela, & Brunelli, "Developmental effects of selective breeding for an infantile trait: The rat pup ultrasonic isolation call"

Hofer Brunelli, Shair and Masmela (2001) examined several behavioral and ph ysiological measures in low; high, and unselected lines obtained from a div ergent selection for ultrasound production (USP) in young rats. Although th e response to selection was clear-cut, few correlated responses appeared. T his surprising result could be explained by two reasons. USP has polygenic correlates in this population, and most of the chromosomal regions that are linked with these measures only, contribute to a small part of the genetic variance. Therefore, correlated responses to selection might exist, but th e common genetic variance between the trait under selection and the indirec tly, selected trait is too small to be detected by a selective breeding str ategy. (C) 2001 John Wiley & Sons, Inc.