Ecological Correlates of Strepsirrhine Hypometabolism

Hypometabolism is often observed in species consuming a nutrient-poor (low quality) diet (Kurland and Pearson, 1986; McNab, 1986). In the present sample, relatively lower DQ is associated with depressed metabolic rates in both strepsirrhine (n = 12) and haplorhine primates (n = 20). However, while variation in DQ helps to explain within-group differences in RMR, the metabolic differences between strepsirrhines and haplorhines cannot be explained by dietary differences.

All strepsirrhines are primarily arboreal, including Lemur catta, which spends roughly 25% of its time on the ground (Martin, 1990). Across all primates, arboreal species (n = 30) have significantly lower metabolic rates than terrestrial species (n =11) (-24.1% versus 10.2%) (P < 0.001). However, even after controlling for habitat use, strepsirrhines (n =17) have significantly lower metabolic rates than arboreal haplorhines (n =13) (-38.6 ± 4.7% versus -5.2 ± 5.1%; P<0.001). Both arboreal haplorhines and terrestrial haplorhines (n = 11) significantly differ from strepsirrhines (P <0.001).

The relationship between activity cycle (i.e., nocturnal or diurnal) and body mass to deviation from predicted RMR among species demonstrates that the degree of hypometabolism is significantly greater among the larger species. The diurnal4 strepsirrhine species (n = 4), of which all are Malagasy lemurs, have the largest body sizes and have significantly lower metabolic rates than the nocturnal strepsirrhine species (n =13) (61.5% versus -31.5%; P <0.01).

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