A water balance study was conducted on newly-emerged adults of seed beetle, Callosobruchus maculatus, to explore how South India strain survives longer than Brazil strain in laboratory cultures. No difference between strains was noted with regard to dehydration tolerance, and water conservation features confirm classification of this species as xerophilic. There was no evidence for critical transition temperature (CTT), thereby safeguarding against excessive water loss as the temperature rises, or for critical equilibrium humidity (CEH), indicating that water is imbibed as a liquid. In contrast to the Brazil strain, adults of the South India strain were distinguished by a larger body size, resulting in a lower net transpiration rate with suppressed activation energy (Ea, permeability constant) for water loss, and a lower percentage body water content due to a higher dry mass (fat). These modifications for water balance of the South India strain link enhancing time for reproduction and distribution spread in the adult with the higher seed consumption/respiratory rate trait that has been previously reported for larvae of this strain.
Net CO2 uptake rates (PN) were measured for the vine cacti Hylocereus undatus and Selenicereus megalanthus under relatively extreme climatic conditions in Israel. Withholding water decreased rates and the daily amount of CO2 uptake by about 10 % per day. Compared with more moderate climates within environmental chambers, the higher temperatures and lower relative humidity in the field led to a more rapid response to drought. The upper envelopes of scatter diagrams for PN versus temperature for these Crassulacean acid metabolism species, which indicate the maximal rates at a particular temperature, were determined for both night time CO2 uptake in Phase I (mediated by phosphoenolpyruvate carboxylase, PEPC) and early morning uptake in Phase II (mediated by ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO). As stem temperature increased above 13 °C, the maximal PN increased exponentially, reaching maxima near 27 °C of 12 and 8 μmol m-2 s-1 for Phases I and II, respectively, for H. undatus and 6 and 4 μmol m-2 s-1, respectively, for S. megalanthus. Based on the Arrhenius equation, the apparent activation energies of PEPC and RuBPCO were 103 and 86 kJ mol-1, respectively, for H. undatus and 77 and 49 kJ mol-1, respectively, for S. megalanthus, within the range determined for a diverse group of species using different methodologies. Above 28 °C, PN decreased an average of 58 % per °C in Phase I and 30 % per °C in Phase II for the two species; such steep declines with temperature indicate that irrigation then may lead to only small enhancements in net CO2 uptake ability. and J. Ben-Asher ... [et al.].