Participation of book lungs in evaporative water loss in Paraphysa parvula, a migalomorph spider from Chilean Andes

Small animals need efficient water conservation mechanisms for survival and reproduction, which is relevant for the spiders that have large book lungs with large respiratory surface. If lung evaporation is relevant to limit water loss, adjustments of the spiracle opening to metabolic demands should be expected. In this study, we measured the metabolic rate and total evaporative water loss mediated by the opening of the spiracles in the migalomorph spider Paraphysa parvula, a resident of fluctuating Mediterranean environments of the mountains of central Chile. We found that the metabolism of P. parvula was similar to other Theraphosidae and low compared to other arthropods. Carbon dioxide production and evaporative water loss increased with temperature, particularly at 40 °C. The total evaporative water loss at 40 °C increased dramatically to about 10 times that found with the lower temperatures. Thus, 40 °C will be the limit temperature for this species after which evaporative water loss starts to become damaging, so it has to avoid it. The exposition to hypercapnic environments had as a consequence an increase in evaporative water loss and the involvement of the book lungs in this loss was about 60%. The possibility of losing water could condition this species to seek temperate and oxygenated shelters under rocks.