Metabolic Variation and Body Composition

The relationship between brain mass and body mass in strepsirrhine (n=15) and haplorhine species (n = 21) demonstrates that strepsirrhines have relatively smaller brains than haplorhine species (Figure 2). The scaling coefficient for strepsirrhine species is significantly lower than that of the haplorhines (0.75 versus 0.64; P<0.05). Additionally, the y-intercept of strepsirrhines is significantly lower than haplorhines (P < 0.001). The relative size difference in brain mass of strepsirrhines and haplorhines is also evident from the z-scores of the brain mass to body mass regression for the pooled sample. Mean z-scores are significantly lower in strepsirrhines than haplorhines (P <0.001).

When the relationship of brain size and RMR in strepsirrhines (n = 15) and haplorhines (n = 21) is examined, the scaling coefficients for the strepsirrhines and haplorhine regressions are comparable and both scale isometrically (1.02 versus 0.96; n.s.). This suggests that both groups spend similar proportions of RMR on brain metabolism and that species with different body sizes have similar relationships between brain size and RMR. The y-intercepts in strepsirrhines and haplorhines are not significantly different. Additionally, strepsirrhines do

4 One of these species, Eulemur fulvus, is more appropriately classified as "cathemeral," which reflects its activity period both during the day and night (Fleagle, 1999); it has been collapsed into the category "diurnal" to allow statistical treatment.

* Subfossil lemurs

Haplorhines ■ Strepsirrhines

Log body mass (kg)

Figure 2. Log10 plot of brain mass (kg) versus body mass (kg) for strepsirrhine species (n =15) and haplorhine species (n = 21; humans excluded). The scaling coefficient for strepsirrhine species is significantly lower than that of the haplorhines (0.75 versus 0.64; P < 0.05). Asterisks represent values for subfossil Malagasy lemurs based on reconstructions (Table 4).

* Subfossil lemurs

Haplorhines ■ Strepsirrhines

Log body mass (kg)

Figure 2. Log10 plot of brain mass (kg) versus body mass (kg) for strepsirrhine species (n =15) and haplorhine species (n = 21; humans excluded). The scaling coefficient for strepsirrhine species is significantly lower than that of the haplorhines (0.75 versus 0.64; P < 0.05). Asterisks represent values for subfossil Malagasy lemurs based on reconstructions (Table 4).

not significantly differ from haplorhines in mean z-scores of the brain mass to RMR regression for the pooled sample.

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