Comparative Postnatal Determination of Absolute Brain Weight and Size using Body Morphometric Parameters in the African Giant Rat (Cricetomys gambianus)

One neuroanatomical measure found to allometrically scale the body is brain's size. Species with larger brains relative to body are better complex information processors. We compared absolute brain weight (ABW), generated regression formulae and determined intelligence level in each age group of African giant rat (AGR) using encephalization quotient (EQ). Twelve rats in each age group, neonates (1-70 g), juveniles (70-450 g) and adults (?700 g) were used. Positive linear relationships existed between live body weight (LBW) and ABW in neonates (r2 = 0.58; p<0.05) and juveniles (r2 = 0.46; p<0.05) with regression formulae y = 0.479 + 0.048x and y = 3.729 + 0.006x deduced for neonates and juveniles, respectively. Positive linear relationship existed between nose-rump length (NRL) and ABW in neonates (r2 = 0.68; p<0.05); with regression formula y = 1.168 + 0.158x. Positive linear relationships existed between tail length (TL) and ABW in neonates (r2 = 0.57; p<0.05); juveniles (r2 = 0.69; p<0.05) and adults (r2 = 0.41; p<0.05) with regression formulae y = 2.303 + 0.081x; y = 2.549 + 0.097x and y = 2.656 + 0.085x deduced for neonates, juveniles and adults, respectively, with correlation being statistically significant (p<0.05) in all age groups. The mean values of EQ were 2.58±0.08a , 1.03±0.03b and 0.59±0.01c for neonates, juveniles and adults, respectively. Best parameters to quantifying ABW are LBW, NRL and TL for neonates; TL followed by LBW for juveniles and TL for adults. Neonates and juveniles will have better intelligence than adults, although their intelligence is generally less than average.

Key Words: African giant rat, brain, correlation, encephalisation quotient, regression analysi