The Cost of Burrowing by the Social Mole Rats (Bathyergidae) Cryptomys damarensis and Heterocephalus glaber: The Role of Soil Moisture

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Abstract
The cost of burrowing (oxygen consumption) was compared between two social mole rats, Cryptomys damarensis and Heterocephalus glaber, in damp and dry sand. Cryptomys damarensis had a digging metabolic rate (DMR) of 2.86 ± 0.31 cm³ • g⁻¹ • h⁻¹ in damp sand and of 2.58 ± 0.32 cm³ • g⁻¹ • h⁻¹ in dry sand. The DMR was 4.53-5.03 times the resting metabolic rate (RMR). Its burrowing speed was 3.53 ± 0.75m • h⁻¹ in damp sand and 0.92 ± 0.33m • h⁻¹ in dry sand. Body temperature increased by 1.3° C during burrowing in dry sand. Heterocephalus glaber had a DMR of 3.36 ± 0.25 cm³ • g⁻¹ • h⁻¹ in damp sand and of 2.78 ± 0.25 cm³ • g⁻¹ • h⁻¹ in dry sand. The DMR was 4.34-5.25 times RMR. Its burrowing speed was 0.75 ± 0.23 m • h⁻¹ in damp sand and 0.30 ± 0.02 m • h⁻¹ in dry sand. There was a 2.3° C drop in during burrowing in damp sand. For both species, the cost of burrowing was 1.5-3.7 times greater in dry sand than in damp sand. These data are compared with those of other subterranean mammals. Arguments are presented that suggest that the cost of burrowing may be an important factor selecting for body size, differentiation of labor, and polyethism in the bathyergids.