Scaling of the respiratory, cardio‐vascular and skeletal muscle systems of the freshwater/terrestrial mountain crab, Pseudothelphusa garmani garmani

Abstract

The freshwater/terrestrial mountain crab Pseudothelphusa garmani garmani (Rathbun, 1898) is structurally well adapted for aerial gas exchange. Pseudothelphusa possesses complex lungs and gills within the branchial chambers.The present investigation sets out primarily to compare how the respiratory system (whole animal oxygen uptake, gills, lungs), cardio‐vascular system (heart, blood volume) and skeletal muscle system (muscles of third walking leg merus) scale as a function of live weight (i.e. Y = aXb; here Y= variables listed above, X= live weight, a= constant, b= scaling exponent).Whole animal aerial oxygen uptake scales to the power 0·70. In contrast, the weight of the gas exchange organs (gills and lungs) scale to the power 0·87 and 0·88, respectively, whilst heart weight and blood volume scale to 1·01 and 0·85, respectively. Skeletal muscle (weight of muscles from third walking leg merus), however, has a scaling exponent of 0·72 which resembles that of whole animal oxygen uptake.Scaling exponents for skeletal length as a function of live weight are significantly lower than those listed above, i.e. length of third walking leg merus (b= 0·32); carapace width (b= 0·34).‘Excitement’ due to handling stress induces an average increase in aerial oxygen uptake of ×2·08. Aerobic expansibilities of ×3·65 ×5·30 are reported for Pseudothelphusa during locomotor activity. A discontinuous pattern of ventilation was recorded during air breathing in quiescent animals.Heart wet weight expressed as a percentage of live body weight is 0·135% for a mean 71·5 g live weight crab.In conclusion, the oxygen uptake of inactive Pseudothelphusa appears to be limited at the tissue level rather than at the gas exchange surface or cardio‐vascular system.