Abstract: The development of litter and individual differences in the rate of ultrasonic signaling of neonatal rats was studied. Systematic variations among litters and individuals emerged, without differential treatment. These differences were not correlated with variations in general development as indexed by body weight. Two experiments using a cross-fostering design showed that litter differences developed independently of variations in postnatal environment. These results indicate that the variations among litters in ultrasound rate have a prenatal, possibly genetic, etiology and may represent reliable indicants of response to environmental stress.

Abstract: The authors sacrificed fifty-five horses originated from the “Pantanal”, lowlands in the State of Mato Grosso in two different periods, droughty period and flooded and they described for the first time the Dictyocaulus arnfieldi in Mato Grosso. Relationship between droughty and flooded periods proved not to occur.