Allometric relationship of postmolt net ion uptake, ventilation, and circulation in the freshwater crayfish Procambarus clarkii: intraspecific scaling.

There are few intraspecific studies relating physiological parameters to body mass. This study relates scaling of ionic regulation and respiratory parameters with body mass in crayfish (Procambarus clarkii). These animals were chosen because of their direct development, spanning four orders of magnitude in body mass. Usually, these animals are hyperregulators and must maintain hemolymph electrolyte levels above those in the ambient freshwater. This is especially important in the postmolt, when ion imbalance can occur. Maintaining hemolymph ion levels above ambient involves active processes that are independently related to metabolic rate, ventilation, and circulation. Therefore, this study investigates relationships among size and ionic regulation, heart rate, and ventilation in crayfish, spanning a size range of 0.003-24 g. Postmolt net ion uptake of Ca, titratable base, Na, Cl, and NH4 increase with body mass (positive allometry) with slopes of 0.92, 0.79, 0.90, 0.84, and 0.87, respectively. Between 72% and 97% of variation in ionic regulation was related to body mass. The slopes differed from each other for Ca and titratable base but not for Na, Cl, and NH4. For heart rate and ventilation rate, different relationships were derived for animals smaller and larger than 0.01 g (between first and third instar). Animals larger than 0.01 g show a negative allometric relationship between heart rate and body size ([body mass](0.15)), while smaller animals show positive allometry with body size, but only 29% of variation in heart rate is explained by body size alone. For ventilation rates, the negative allometry with body size for animals larger than 0.01 g is present, but less than 15% of variation in ventilation rate is explained by size, while for smaller animals the size dependency disappears. Based on these results, predictions of physiological parameters such as ionic regulation based on body size are useful in crayfish, but estimates of respiratory parameters and body size should be used with caution.

Transport of tools and mental representation: is capuchin monkey tool behaviour a useful model of Plio-Pleistocene hominid technology?

Capuchin monkeys display greatly developed tool-using capacities, performing successfully a variety of tool-tasks. Impressed by their achievements in this respect, some investigators have suggested that capuchin tool-using behaviour could be used as a model of the tool behaviour of the first hominids. The transport of tools, a task requiring complex cognitive capabilities, is an essential ingredient in the technological behaviour of the first hominids. In this way, to qualify as another source for modelling hominid behavioural evolution, capuchins had to exhibit proficiency in the transport of tools. We investigated this problem through experiments designed to elicit the transport of objects. The results showed that the monkeys were able to transport food to be processed with the use of tools, but failed when the tools themselves had to be transported. Our hypothesis is that a limited capacity for abstract representation, together with the lack of a regulatory system ensuring that the food would not be lost and consumed by another individual during the search for and transport of the tools, were responsible for such a failure. We conclude that the tool-using behaviour of capuchins presents no functional analogy with the tool behaviour of the Plio-Pleistocene hominids, and that capuchin monkeys are a very inadequate source for modelling Plio-Pleistocene hominid's technological behaviour.