The influence of hunger and breeding temperature on the venom production of the spider Cupiennius salei (Araneae, Ctenidae).

The venom production of the free hunting neotropic spider Cupiennius salei was tested under different breeding conditions. Three groups kept at different temperatures (17, 21 and 25 degrees C) showed that venom production remained stable within this temperature range, only at a temperature of 15 degrees C the spiders stopped feeding and venom synthesis. Hunger periods do not have a direct effect on the released venom quantity. Two groups of spiders--the first group after a four and the second after an eight weeks hunger period--were compared and no difference in venom production was found. Such long fasting periods are a natural situation for spiders. In this case Cupiennius salei reduces its body weight but not venom supply. This means that body weight is a parameter only of short-term fitness which changes with the actual living conditions (temperature, feeding intervals) of each individual. Long-term fitness is best described by the prosoma length, which was formed during the juvenile growth of each spider and is rather invariable in adulthood. It was shown that the quantity of released venom is better correlated with the length of the prosoma than with the weight of the animal. This means that venom production is mostly an indicator of long-term fitness.