Unusual brain composition in Crested Ducks (Anas platyrhynchos f.d.)--including its effect on behavior and genetic transmission.

Abstract

Crested Ducks (CR) occasionally show intracranial fat bodies. Additionally, behavioral abnormalities such as motor incoordination can be observed. Here, it is shown that a behavioral test helps to identify CR that have a problematical fat body. The ducks were put on their backs, and the time required for them to stand up was measured. Ten CR exhibited suboptimal motor coordination. The appropriateness of this test has been proved in a special breeding program. To investigate the influence of fat bodies on brain composition, an allometrical comparison of 26 CR brains with those of three uncrested duck breeds was done. The fat bodies of CR varied from 0.3% to 41% of total brain volume, but two CR did not show a fat body. CR with motor incoordination show significantly larger fat bodies and require significantly more time in the test than "normal" CR. Total brain volume was significantly larger in CR, but brain volume minus fat body was significantly smaller compared to reference breeds. Cerebellum, apical hyperpallium, tegmentum and olfactory bulb are significantly reduced in CR. Obviously the behavioral deficits cannot be explained by the existence of a fat body, but they could be explained by functionally suboptimal cerebella and tegmenta. Fat body size seems to be a decisive factor. The relationship between fat body and reduced structures is discussed. By breeding with test-selected ducks the hatching rate increased and the number of ducklings with malformations or motor incoordination decreased.