Effects of domestication on production and perception of mallard maternal alarm calls: developmental lag in behavioral arousal.

The process of domestication involves intense inbreeding. Field and laboratory studies were conducted to assess the effects of such intense genetic selection on the production and perception of the maternal alarm calls of domestic (Peking) and wild mallard ducks (Anas platyrhynchos). With respect to production, the calls of wild and domestic ducks were comparable in four acoustic features and differed only slightly on two features. With respect to perception, the calls of wild and domestic hens were equally effective in promoting behavioral inhibition in wild and domestic ducklings. Although these data revealed little or no effect of domestication on the structure and function of the maternal alarm call, an unexpected effect was found regarding the domestic ducklings' behavior. Specifically, Pekings showed a greater level of behavioral inhibition than did mallards at 24 hr of age. Further experiments indicated that the differential level of inhibition in the wild and domestic birds reflects a developmental lag in arousal consequent to domestication: 72-hr-old Peking ducklings are behaviorally more aroused than 24-hr-old Peking ducklings and are similar to 24-hr-old mallard ducklings in that respect. This appears to be the first demonstration of behavioral heterochrony, which is believed to be an important mechanism of behavioral evolution.