Research Note: Morphological and hormonal characterization of wild-derived Japanese quail (Coturnix japonica) strains.

Two wild-derived strains of the Japanese quail were recently established by crossing wild males captured in Tokachi, Hokkaido, Japan, with females of a domestic strain. These new strains (W50 and W75) have approximately 50 % and 75 % wild genetic backgrounds, respectively. This study characterized morphological and hormonal traits of sexually mature male Japanese quail from a domestic strain and both wild-derived strains. Six morphological traits (tarsus length, exposed culmen length, bill width, bill depth, body mass, and cloacal gland volume) and plasma testosterone and thyroxine levels were analyzed. W75 males were significantly lighter than both W50 and domestic males and had shorter tarsi and smaller cloacal glands than W50 males. Hormone assays showed that W75 quail had lower circulating testosterone and thyroxine levels than W50 quail. Within-strain analyses revealed distinct correlation patterns: in domestic quail, tarsus length was positively associated with body mass, whereas in W75 quail, bill height correlated with bill width, and tarsus length with cloacal gland volume. These results indicate that genetic contributions from wild populations shape both morphological and hormonal profiles in Japanese quail. Wild-derived strains such as W50 and W75 provide valuable models for understanding the evolutionary and physiological consequences of avian domestication.